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astro-ph0511489

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our central assumption in this paper is that when a halo that contains metal - free gas ( i.e. , a halo for which no star has previously formed in any of its merger - tree progenitors ) collapses , a single massive star forms at the halo center after a cooling time . the mass of this star is assumed to be constant for all halos with metal - free gas . as explained in detail later ( [ sstform ] ) , the star forms in our model if the cooling time of the gas at the center of the halo is shorter than the lifetime of the halo . we develop an algorithm to define the lifetime of halos from the merger tree framework based on the extended press - schechter model , which is fully described in the appendix . the cooling time depends on the central gas density and temperature , which depends at the same time on the initial entropy of the gas prior to the collapse of the halo ( e.g. , oh & haiman 2003 ) . we compute the initial central gas density ( prior to the onset of cooling ) in halos at each redshift self - consistently , assuming hydrostatic equilibrium in a halo with the navarro , frenk , & white ( 1997 ) density profile for the dark matter ( hereafter , nfw ) . we calculate the ionizing radiation emitted by the metal - free stars to infer the history of reionization ( taking into account an escape fraction of ionizing photons from halos determined by recombinations in the halo gas ) , as well as the feedback effects of x - ray heating ( and consequent entropy raise of the atomic medium , which affects the gas density profiles in halos ) and molecular photodissociation . we also include a component of ionizing radiation from a normal stellar population assumed to form in metal - enriched halos , which have had previous star formation and ionization . this section explains in detail how all these ingredients are implemented in our model . our goal will be to find the maximum contribution that these metal - free stars could plausibly make to an early reionization , and how this is limited by the minimal expected feedback effects . we use the halo mass function of sheth & tormen ( 2002 ) . we assume that a first - generation star forms when the halo age exceeds the cooling time at the halo center . we adopt for this purpose the definition of halo formation time of lacey & cole ( 1993 ) , which is the time when the halo mass was half the present one . the probability distribution of the age of a halo as a function of its mass and redshift is calculated following lacey & cole , which we then use to compute the probability that a halo contains a metal - free star as described in the appendix . to determine the cooling time at the halo center , we assume the gas is in hydrostatic equilibrium in the halo gravitational potential , and that the dark matter follows a nfw density profile with concentration parameter @xmath22 . in reality , @xmath23 depends on the halo mass and redshift ( bullock et al . 2001 ; eke et al . 2001 ) , but here we approximate it as constant and with the same value used by oh & haiman ( 2003 ) . under the assumption of hydrostatic equilibrium , the gas density profile depends on its temperature . shock - heating of the gas during the collapse heats the gas to a roughly constant temperature , about equal to the halo virial temperature . this results in a final gas density profile similar to the dark matter , although with a small , constant density core , with a size that is determined by the minimum entropy @xmath24 of the gas in the halo . the gas with the lowest entropy is generally the one that is shock - heated to the virial temperature only after reaching a high density , and ends up near the halo center . however , if the gas had already been heated prior to the collapse , acquiring a high initial entropy , the value of @xmath24 may be increased , resulting in a much more extended gas profile and reduced central gas density , and therefore a much longer central cooling time . to take this into account we follow the procedure explained in oh & haiman ( 2003 ) . we define the function @xmath25 as @xmath26 where @xmath27 is the adiabatic index ( equal to @xmath28 for monatomic gas ) , and @xmath29 and @xmath30 the gas temperature and number density . note that the entropy of a gas is actually the logarithm of @xmath25 , although in this paper we refer to the function @xmath25 as `` entropy '' for convenience . the entropy before the collapse is what we call the entropy floor , @xmath31 , which we calculate as a function of redshift as described in [ xr ] . as an example , we show in figure [ fprof ] the gas density profile in a halo with @xmath32 m@xmath14 formed at different redshifts . the initial entropy is fixed to the primordial value given in oh & haiman ( 2003 ) , determined by early compton heating by the cmb on the adiabatically cooling gas , with the residual ionized fraction left over from recombination . at @xmath33 , the entropy of the igm is practically constant and the entropy floor decreases in importance with decreasing redshift because of the decreasing gas density , hence the gas density profile becomes steeper at low redshift . we show also the effect of raising the igm temperature to @xmath34 k at @xmath35 , which leads to a large reduction in the central gas density . we define the cooling timescale as the ratio of the internal energy of the gas to the cooling rate per unit of volume , @xmath36 : @xmath37 where @xmath38 is the boltzmann constant . we include only molecular hydrogen cooling for metal - free gas . in practice , atomic cooling can be neglected because metal - free stars form very rarely in halos with virial temperature above @xmath39 k in our model . the reason is that these halos usually have some progenitor of lower virial temperature that has already formed a star previously ( this will be seen in fig . 2 ) . in this case , we consider that the gas is already enriched with metals and that the emissivity per unit mass is constant , as described in [ semis_met_rich ] . the cooling rate ( due to collisional excitation of molecular hydrogen roto - vibrational lines ) is @xmath40 , where @xmath41 is the molecular fraction . we use the cooling function @xmath42 of galli & palla ( 1998 ) . the molecular fraction @xmath41 is determined by the continuous formation of molecules in the gas from @xmath43 , which is at the same time made by the primordial concentration of electrons from the recombination epoch ( see tegmark et al . we use equation ( 16 ) of tegmark et al . , although simplified and modified to consider h@xmath44 dissociation in the following way : @xmath45 where @xmath46 is the dissociation rate ( which we discuss later in [ sdiss ] ) and @xmath47 is the electron fraction , given by equation ( [ xr : fe ] ) . the constant @xmath48 determines the formation rate of @xmath43 ( which determines the formation rate of molecules ) , and is given by @xmath49 @xmath50 s@xmath51 . the initial , primordial value of @xmath41 is taken as @xmath52 ( galli & palla 1998 ) . note that the fraction of hydrogen that forms molecules from @xmath43 within collapsed halos is much larger than this primordial value , and therefore the long - term evolution of the molecular hydrogen fraction does not strongly depend on its initial value . as mentioned earlier , the main assumption in this work is that only one metal - free star is formed in each halo that collapses from progenitors that have never formed a star previously . the mass of the star , @xmath53 , is much lower than the baryonic mass of the halo , and is in fact lower than the gas mass in the core of the gas distribution . consequently , we can evaluate the cooling time at the halo center and consider that the star will form when the age of the halo is equal to this cooling time . the star forms in a halo of mass @xmath54 with formation time @xmath55 at a time @xmath56 that obeys @xmath57 the star will then live up to a time @xmath58 where @xmath59 is the main - sequence lifetime of a metal - free star with mass @xmath60 . the probability that a halo of mass @xmath54 at time @xmath61 has already formed a star can be evaluated by computing first numerically the formation time @xmath62 that obeys equation ( [ cool_c1 ] ) with @xmath63 , and then calculating the probability @xmath64 that the halo formation time is earlier than @xmath62 ( see eq . [ 2.26 ] of lacey & cole 1993 ) . similarly , the probability that the halo contains a metal - free star on the main - sequence at time @xmath61 is evaluated as the probability @xmath65 , where @xmath66 is the solution of @xmath55 of equation ( [ cool_c2 ] ) when @xmath67 . this condition , however , would be valid only if the halo gas were always metal - free . in reality , if a star had already formed in one of the halo progenitors , the supernova explosion from that star would already have polluted the gas with metals and blown it away . later on , as the sequence of halo mergers continues , the final halo present at time @xmath61 will accrete this gas , but since the gas is metal enriched it will form metal - rich stars . the emission from metal - rich stars will be treated differently in our model , as we describe later in [ semis_met_rich ] . here , our main assumption is that the very massive stars we consider that are highly efficient at emitting ionizing radiation are formed only when the gas is totally free of heavy elements . to take this into account , we evaluate at each time @xmath61 the average number of metal - free stars that have formed in a halo of mass @xmath54 , as ( see the appendix ) @xmath68 where @xmath69 is the number of halos of mass between @xmath70 and @xmath71 at time @xmath72 that have been incorporated into a halo of mass @xmath54 at time @xmath61 ( see eq . [ 2.25 ] in lacey & cole 1993 ) , and @xmath73 is the probability per unit time that a star forms at @xmath72 in a halo of mass @xmath70 . the way the probability @xmath74 is calculated is described in the appendix . we then assume that there is a poisson distribution of the number of stars that have formed within any halo , so that the probability that none has formed is @xmath75 . therefore , the probability that a halo of mass @xmath54 harbours a main - sequence star at time @xmath61 is @xmath76 where @xmath77 is the differential probability that a halo at time @xmath61 was formed at time @xmath55 and is given by equation ( 2.19 ) in lacey & cole ( 1994 ) . in practice , the lifetime of the main - sequence star ( @xmath78 years ) is short enough that the above integral can be approximated as @xmath79 figure [ fnstarm ] shows the probability that a halo with mass @xmath54 harbours a metal - free main - sequence star . different plots correspond to different redshifts ( @xmath80 , 15 , 10 , and 6 ) , and different lines to different models that will be described later . the model a1 corresponds to no feedback effects on the formation of metal - free stars , and the other models incorporate feedback effects that are described in 2.5 . the probability to contain a star tends to peak at halo masses of several times @xmath81 . at lower masses the molecular cooling rate is too slow and stars have not yet formed , while in halos of higher mass a metal - free star has typically already formed in one of their lower - mass progenitors ( i.e. , the second term in eq.is very small ) . as a byproduct , we can also calculate the global formation rate of metal - free stars ( see the appendix ) as @xmath82}{{{\rm d}}t}\ , . \label{dndt}\ ] ] where @xmath83 is the metal - free star formation rate and @xmath84 is the sheth - tormen halo mass function . this last formula is useful to calculate the preheating due to x - rays ( see section [ xr ] ) . we consider three feedback processes that affect metal - free star formation . the first is halo photoevaporation due to the ionizing background ( section [ sevap ] ) . the second , photodissociation of molecules due to a soft ultraviolet background ( section [ sdiss ] ) . finally , the third is reheating of the igm caused by x - rays ( section [ xr ] ) . the ionizing background reheats the gas in halos and causes a large increase in the entropy floor . gas trapped in minihalos escapes ( e.g. , shapiro et al . 2004 ) , quenching star formation . cooling and star formation in reionized regions can only occur in halos that are massive enough for the gas to undergo dissipation by atomic cooling . we neglect any possible formation of metal - free stars in these halos . in practice , once these halos collapse they should almost always have a progenitor that already formed a metal - free star in the past , because the number of halo progenitors increases with halo mass ; moreover , even if one metal - free star may form in one of these more massive halos cooling mainly by atomic processes , their contribution to the total number of metal - free stars formed should be negligible because the abundance of high - mass halos is greatly reduced compared to halos of low mass . we therefore neglect any possible formation of metal - free stars in reionized regions . to take this into account , equation ( [ prob_sh_star ] ) is multiplied by a factor @xmath85 , equal to the fraction of the igm that is neutral at every redshift . the calculation of the ionized fraction of the igm as a function of time using the global rate of star formation that we compute is described below in 2.6 . actually , the factor @xmath86 represents a lower limit to the suppression of the star formation by reionization , because in practice halos are correlated , or biased relative to the mass , so that more halos should be present in the reionized regions where other high - mass halos have already formed . is easily photodissociated by soft ultra - violet photons ( haiman et al . the rate at which dissociation is produced can be approximated by ( abel et al . 1997 ) @xmath87 being @xmath88 the flux at frequency @xmath89 in units of @xmath90 and @xmath91 the self - shielding factor given by draine & bertoldi ( 1996 ) . the mean free path of dissociating photons in the igm is typically larger than the mean distance between minihalos . therefore , this flux can be approximated as homogeneous and isotropic . to calculate this background we apply equation ( 7 ) of haiman et al . the emissivity of dissociating photons ( @xmath92 in their formula ) is computed similarly to that of ionizing ones ( see [ semis_met_free ] ) , although we take into account only the emission by the metal - free stars . emission from the metal - rich stars has a small effect at the high redshifts of interest , which we have neglected . as proposed by oh & haiman ( 2003 ) , soft x - ray photons raise the entropy floor , greatly reducing cooling and star formation in low - mass halos . x - rays can have a long mean free path through the atomic igm and can therefore heat this medium in an approximately uniform way , whereas the more abundant ultraviolet ionizing photons heat the medium only near the boundaries of hii regions . the mean free path in the atomic igm is roughly @xmath93 when this mean free path is in the range that goes from the mean distance between neighboring halos containing first - generation stars ( which is about @xmath94 kpc at @xmath95 ; see yoshida et al . 2003 ) to the horizon radius ( @xmath96 mpc at @xmath95 ) , the photons are effective at heating the atomic igm . this corresponds to a range of frequencies from 200 ev to 2 kev , or the soft x - ray band . soft x - ray photons can be produced by metal - free stars during two phases . first , these stars have a high enough effective temperature during the main sequence lifetime to emit substantially in soft x - rays ( schaerer 2002 ) . second , x - rays can be emitted by the hot gas in a supernova remnant after the death of the star . for simplicity we consider that all the emission is produced at the end of the metal - free star lifetime ( a good approximation because of the short lifetime ) . therefore , the rate of increase of the entropy floor is @xmath97 where @xmath98 is the rate of energy increase per particle , @xmath99 and @xmath100 is the rate of sne per unit of volume , equal to the star formation rate @xmath101 ( eq . [ [ dndt ] ] ) at the time @xmath102 . the constant @xmath103 is the total energy per star that is used to reheat the medium . note that this is not the same as the total energy radiated in x - rays by the star since some of that energy goes into collisional ionizations or emission of recombination photons . we leave the value of @xmath103 as a free parameter in our model ( the range of possible values is discussed in [ sres_xr ] ) . even though the reheating by x - rays is roughly homogeneous , the increase of the entropy is of course lower in regions of high gas density . to compute the entropy floor for a specific halo with formation at @xmath55 , we follow the evolution of the gas density during the collapse assuming the spherical top - hat model , and we compute the entropy increase from the previous history of the intensity of the x - ray background generated by metal - free stars . the evolution of @xmath100 is computed self - consistently with the model from the star formation rate . heating by x - rays is no longer taken into account after virialization ( this would be negligible in any case once the gas has reached a high density ) . x - rays have yet another effect : owing to secondary ionizations , they can produce a higher ionized fraction than the residual value after recombination ( which is @xmath104 , see galli & palla 1998 ) . this increases the formation rate of molecular hydrogen , enhancing the cooling rate ( haiman , rees , & loeb 1996 ) . according to shull & van steenberg ( 1985 ) , around 30 % of the total energy in x - rays is used in ionizations when the neutral fraction is high . the rate of ionizations is then found by dividing expression ( [ e : reh ] ) by 13.6 ev ( the ionization energy of hydrogen ) . considering this effect , the evolution of @xmath105 is determined by @xmath106 where @xmath107 is the recombination rate , which can be approximated by @xmath108 s@xmath51 ( hutchins 1976 ) and @xmath30 is the gas number density in the halo center after collapse . before collapse , the first term is negligible because the density is very low . the initial value of @xmath105 is given by the residual ionized fraction after recombination . to summarize , for each halo mass at a fixed time , stars can form only when the formation time satisfies equation ( [ cool_c1 ] ) . when considering feedback effects , cooling is delayed and therefore halo formation has to take place earlier . consequently , the probability that a halo hosts a main sequence star in equation ( [ prob_sh_star ] ) decreases , reflecting the feedback effects . to calculate the reionization history of the igm we must first calculate the emissivity @xmath109 of ionizing photons per igm baryon . we consider two contributions to the emissivity , one from metal - free stars which we discuss in [ semis_met_free ] , and another from stars with metals , discussed in [ semis_met_rich ] . finally , we explain the procedure to calculate the reionization history in [ semis_met_free ] . metal - free stars emit a higher quantity of ionizing photons than enriched stars ( see schaerer ( 2002 ) ) . we use here the fitting formula in table 6 of schaerer ( 2002 ) to compute the ionizing luminosity of each star as a function of its mass , @xmath110 . for the values of @xmath53 we consider here , this yields @xmath111 s@xmath51 and @xmath112 s@xmath51 . in addition , we take into account that some of the stellar photons may be absorbed locally in the halo gas surrounding the star , and only a fraction @xmath113 of these photons will be able to escape and ionize the igm . we use the following simple model to compute @xmath113 ( see whalen et al . 2004 for a more complete discussion and several examples of the evolution of the regions formed around a metal - free star ) : we assume that the star is initially surrounded by a distribution of atomic gas following a singular isothermal profile . an region grows around the star , and the heated gas acquires a sound speed of @xmath114 and starts expanding . this speed is typically larger than the halo circular velocity , but still smaller than the speed of the ionization front as long as the escape fraction is not very small and the star is capable of ionizing the halo ( the stellar lifetime is @xmath115 3 million years , which is short compared to the crossing time of the halo at this sound speed . hence , the ionization front advances supersonically . we use the simple approximation where all the gas moves out by the same distance @xmath116 . the gas distribution then has a central hole of radius @xmath117 , and at @xmath118 the density is @xmath119\frac{[r - r{_{\rm c}}(t)]^2}{r^2},\ ] ] where @xmath120 is the initial gas number density profile of the halo . the total rate of recombinations is computed from this density profile assuming the halo gas has been fully ionized by the star , and is subtracted from the photon emission rate of the star . the escape fraction of ionizing photons as a function of halo mass ( @xmath121 ) is plotted for different redshifts in figure [ ffesc ] . we consider two possible masses of metal - free stars , @xmath34 m@xmath14 ( left panel ) and @xmath122 m@xmath14 ( right panel ) . naturally , the escape fraction increases with stellar mass and decreases with halo mass , because the number of recombinations in a halo with the gas fully ionized increases with halo mass and does not depend on the luminosity of the ionizing star . these results agree with the numerical simulations of kitayama et al . ( 2004 ) , suggesting that our simple model is able to capture the main physics of the problem . the escape fraction increases when reheating is considered , being more significant in low mass halos , which have their density profiles flattened . note that there is a halo mass at which the escape fraction falls to zero ; for halos above this mass , the single central star is not able to ionize all the halo gas and the region reaches a strmgren radius ( the assumption that all the halo gas is ionized is then obviously incorrect , but this affects the calculation of @xmath113 only when @xmath113 is already very small in any case ) . the global emissivity from metal - free stars , @xmath123 , is finally calculated by integrating over all halo masses the number of photons emitted per igm particle corrected by absorption , i.e. , @xmath124 where @xmath125 is the baryonic number density of the igm at @xmath61 , and @xmath126 is the probability that a halo harbors a main sequence metal - free star ( see eq . [ prob_sh_star ] ) . for the emissivity of dissociating photons , we also use equation ( [ eq : emis : mf ] ) with @xmath127 . the emission of dissociating photons from metal - free stars , @xmath128 , is also computed from the fit given in table 6 in schaerer ( 2002 ) which yields @xmath129 s@xmath51 and @xmath130 s@xmath51 . after the formation of the first metal - free star in any halo , the surrounding gas is polluted with the metals released by this star . the metal - enriched gas can recombine and fall back into the halo . we assume the metallicity of this infalling gas is then sufficiently high to cool by the usual mechanisms that are prevalent in present galaxies ( bromm et al . however , halos with metal - enriched gas below a critical virial temperature may still not form stars because the cooling rates are too small ( e.g. , dijkstra et al . 2004b ) , and gas may remain close to @xmath131 k in a spherical or thick disk distribution where the gas is unable to cool further and fragment . in this paper , we adopt the simple assumption that in halos were metal - rich star formation takes place , the emissivity per unit baryonic mass is constant at all redshifts . then , the global emissivity due to enriched stars , @xmath132 , is calibrated to the observations of the ionizing background intensity and mean free path of ionizing photons at redshift @xmath0 ( see onken & miralda - escud 2004 ) : @xmath133 where @xmath134 is the emissivity at redshift 4 in units of ionising photons per particle and per hubble time , @xmath135 is the fraction of mass in halos where metal - rich star formation takes place , and @xmath136 is the same fraction of mass at @xmath0 . we assume that halos with circular velocity above @xmath137 km / s are the ones forming stars at @xmath0 ( as in onken & miralda - escud 2004 ; this affects only the normalization of the emissivity ) , but consider different possibilities for the emissivity at higher redshift , as explained below . in order to study the effect of varying the emission from normal , metal - rich galaxies , we consider several models listed in table [ tcases ] . these models are labeled by a number , and in general any model will be referred to by the letter specifying the feedback processes assumed ( see table 1 ) and this number . in models 1 and 2 , we compute @xmath135 as the fraction of mass in metal - enriched halos with a circular velocity greater than @xmath138 km / s , and in models 3 to 6 we assume that all halos that have been polluted by metals form enriched stars , with no minimum halo circular velocity . note that even by assuming a minimum halo circular velocity that is lower than at the calibration redshift @xmath0 , we are maximizing the emission at high redshift under the constraint that the emission per unit mass is not greater than in halos at @xmath0 . the value of the normalization constant @xmath134 is also subject to uncertainties arising from the process by which the intensity of the ionizing background is inferred from modelling the ly@xmath5 forest transmitted flux , and the measurement of the photon mean free path from the abundance of lyman limit systems . we adopt the values @xmath139 for models 1 to 4 ( as in miralda - escud 2003 ) , and twice this value , @xmath140 ( which would be favored by the measurement of the ionizing background intensity by bolton et al . 2005 ) , in models 5 and 6 . finally , the emissivity from the metal - free stars is varied by considering all stars to have a mass @xmath141 in models with odd number , and @xmath142 in models with even number . the evolution of the ionized fraction @xmath143 is calculated according to @xmath144 where @xmath145 is the total emissivity of ionizing photons , and @xmath146 is the recombination rate which we evaluate at @xmath147 k. the cosmic history of @xmath143 then yields the electron scattering optical depth @xmath148 .

we examine the impact of molecular hydrogen photodissociation ( which tends to reduce cooling when a photodissociating background is produced by the first stars ) and x - ray photoheating ( which heats the atomic medium , raising the entropy of the gas before it collapses into halos ) . we find that in the cdm model supported by present observations , and even assuming no negative feedbacks for the formation of metal - free stars , a reionized mass fraction of 50% is not reached until redshift .

we estimate the maximum contribution to reionization from the first generation of massive stars , with zero metallicity , under the assumption that one of these stars forms with a fixed mass in every collapsed halo in which metal - free gas is able to cool . we assume that any halo that has already had stars previously formed in one of their halo progenitors will form only stars with metals , which are assigned an emissivity of ionizing radiation equal to that determined at from the measured intensity of the ionizing background . we examine the impact of molecular hydrogen photodissociation ( which tends to reduce cooling when a photodissociating background is produced by the first stars ) and x - ray photoheating ( which heats the atomic medium , raising the entropy of the gas before it collapses into halos ) . we find that in the cdm model supported by present observations , and even assuming no negative feedbacks for the formation of metal - free stars , a reionized mass fraction of 50% is not reached until redshift . the combination of ordinary metal - enriched stars and early metal - free stars can yield a cmb optical depth to electron scattering of at most . the contribution of metal - free stars to the present cosmic infrared background is negligibly small .

astro-ph0511489

c

we have considered in this paper the maximum emissivity and the contribution to reionization that metal - free stars could make . our central assumption is that only one metal - free star is made in every halo where pristine gas is able to cool via molecular hydrogen rotovibrational lines . this is a reasonable assumption in view of the simulations that have been made of the formation of the first star and the effects of the subsequent ionizing radiation emitted and supernova explosion : the gas cools hydrostatically towards the center , avoiding fragmentation and forming a central star which can then ionize and heat all the gas in its host halo , and probably expel it in the supernova explosion ( e.g. , abel et al . 2002 ; bromm et al . 2002 , 2003 ) . once a star has exploded , it pollutes its host halo as well as every larger halo into which its host halo merges in the future . any halo that has already formed a metal - free star in any of its halo progenitors in the past is assumed to form a metal - enriched population of stars that has an emissivity of ionizing photons similar to the emissivity that is observationally determined at @xmath176 . under this basic assumption , the contribution of the metal - free stars to reionization is relatively modest . metal - free stars may dominate the emissivity at very high redshifts ( @xmath177 ) , but before they can manage to ionize much of the universe , the metal pollution of halos rapidly reduces their formation rate . moreover , the effects of the ionization itself prevent cooling in the remaining low - mass halos with pristine gas , delaying the formation of a central metal - free star to the time of formation of more massive halos that collapse later , and thereby reducing the number of metal - free stars that are formed per unit of mass in the universe . reionization was likely completed by a population of stars and quasars in galaxies forming from pre - enriched gas . we have analyzed the effects of molecular photodissociation and of increasing the entropy floor by x - ray heating . these can further reduce the amount of ionizing radiation that is emitted by the population of metal - free stars . in agreement with oh & haiman ( 2003 ) , we have found that the negative feedback induced by x - ray heating can in principle be very large . however , as pointed out by kuhlen & madau ( 2005 ) , this negative feedback might be much less important than suggested by the simple calculation of oh & haiman ( 2003 ) and the one we have presented here . in our calculation , we consider only the cooling time of the gas at the halo center in the hydrostatic equilibrium configuration obtained at the end , by assuming an increased initial entropy produced by the x - ray heating . in reality , the gas should be able to gradually cool and lose entropy as it collapses in dense regions of halos , and these halos later merge to form the final one where a star is formed . the same x - rays that heat the gas would also increase the ionization , allowing faster molecular cooling as the gas density increases , which might greatly reduce the x - ray negative feedback effect . nevertheless , our main conclusion is that even without feedback effects the emission from metal - free stars is strongly limited by the metal - pollution and the ionization itself . our models are generally in agreement with previous work . the value of @xmath148 we infer is always lower than @xmath3 , even when we increase the emissivity of the enriched stellar population and we minimize any negative feedback effects on the metal - free population . for a smaller contribution from metal - free stars , values of @xmath148 are closer to @xmath178 ( see table [ ttaue ] ) , in agreement with the results of ricotti & ostriker ( 2004 ) . our results are also compatible with those of sokasian et al . ( 2004 ) , who find that high cmb optical depths to electron scattering can be achieved only when many stars are assumed to be formed within halos that cool by molecular hydrogen . the model m9 of sokasian et al . is the only one that assumes that only one star is formed per halo , and in this case their results for the maximum optical depth are in good agreement with ours . similarly , wise & abel ( 2005 ) can also produce high optical depths only by assuming that many metal - free stars form in each halo with a total mass much larger than in our model . naturally , if one is willing to assume a mass for metal - free stars even larger than @xmath179 , their contribution to the cmb optical depth , @xmath148 , can be further increased , but their total emission increases by a factor smaller than the increase in the mass because of the enhanced negative feedbacks . at the same time , if miniquasars emitting copious amounts of ionizing radiation where produced by the black holes created by the metal - free stars ( which could occur when a halo containing a central clump of cooling gas merges with another halo that has already formed a star and contains a black hole in its center ) , much more ionizing radiation could be produced , although the x - rays emitted by these mini - quasars might then be in conflict with limits on any unresolved component of the present soft x - ray background ( dijkstra et al . 2004a ) . our work can also be used to estimate the contribution of metal - free stars to the cosmic infrared background , which might include the ultraviolet light of these stars from high redshift . the total number of ionizing photons that are ever emitted by metal - free stars can be computed straightforwardly by integrating the curves shown in figure 4 . the results are shown in table [ temis ] for each one of our models . even in the absence of negative feedbacks , and for stellar masses @xmath180 , metal - free stars do not emit more than @xmath115 one photon per baryon in the universe . this conclusion is not surprising , since in the absence of many recombinations one does not need a large number of ionizing photons to be emitted per baryon to complete the reionization . because of the very high effective temperatures of metal - free stars ( @xmath181 k ) , the number of photons emitted in ultraviolet light at wavelengths longer than the lyman limit is similar . hence , the contribution of metal - free stars to the present cosmic infrared background is not more than @xmath115 one photon per baryon under the assumptions we have made . recently , kashlinsky et al . ( 2005 ) detected brightness fluctuations in the cosmic infrared background after subtracting all contributions from known galaxies . the measured fluctuations are at a level of @xmath182 . this background intensity at a wavelength of @xmath183 corresponds to @xmath184 photons per baryon in the universe ; as discussed by kashlinsky et al . , in order to account for the observed fluctuations the absolute brightness of the infrared background contributed by metal - free stars would have to be as high as @xmath185 ( or @xmath115 5000 photons emitted per baryon ) , after taking into account the expected high bias in the spatial distribution of these stars . it is clear that very extreme assumptions about the number of metal - free stars that were formed need to be made if the unaccounted fluctuations in the cosmic infrared background are related in any way to these metal - free stars . as discussed by santos et al . ( 2002 ) , if metal - free stars are to make an important contribution to the cosmic infrared background , one needs to assume that a large fraction of all the gas in each halo where pristine gas cools by molecular hydrogen ( typically more than @xmath81 ) forms metal - free stars , and that most of the radiation from the stars is somehow internally absorbed in the halos in order to prevent an excessively early reionization of the igm . both of these requirements are not realistic : once a central star is formed in a @xmath186 halo , its ionizing radiation will ionize and push all the halo gas out over the short main - sequence lifetime of the star , and the escape fraction of the ionizing photons is high except in rare cases where a single star forms in a very massive halo ( see figure [ ffesc ] ) . the detected cosmic infrared background fluctuations have other more likely possible sources , such as an incomplete accounting of the faint - end of the galaxy luminosity function , or a normal population of low - luminosity galaxies with metal - enriched gas and stars at high redshift . jm acknowledges helpful conversations with mark kuhnen , piero madau , and daniel wang . jm would also like to thank the institute for advanced study for their hospitality , where part of this work was completed . this work was supported in part by the direccin general de investigacin cientfica y tcnica of spain , under contract aya2003 - 07468-c03 - 01 . jmr was supported by a fellowship of the ministerio de educacin , cultura y deporte of spain . abel , t. , anninos , p. , zhang , y. , & norman , m. l. 1997 , new astronomy , 2 , 181 abel , t. , bryan , g. l. , & norman , m. l. 2002 , science , 295 , 93 becker , r. h. , et al . 2001 , , 122 , 2850 bennett , c. l. , et al . 2003 , , 148 , 1 bolton , j. s. , haehnelt , m. g. , viel , m. , & springel , v. 2005 , , 357 , 1178 bromm , v. , coppi , p. s. , & larson , r. b. 2002 , , 564 , 23 bromm , v. , ferrara , a. , coppi , p. s. , & larson , r. b. 2001 , , 328 , 969 bromm , v. , yoshida , n. , & hernquist , l. 2003 , , 596 , l135 bullock , j. s. , kolatt , t. s. , sigad , y. , somerville , r. s. , kravtsov , a. v. , klypin , a. a. , primack , j. r. , & dekel , a. 2001 , , 321 , 559 chiu , w. a. , fan , x. , & ostriker , j. p. 2003 , , 599 , 759 cuby , j .- , le f ` evre , o. , mccracken , h. , cuillandre , j .- c . , magnier , e. , & meneux , b. 2003 , , 405 , l19 dijkstra , m. , haiman , z. , & loeb , a. 2004a , , 613 , 646 dijkstra , m. , haiman , z. , rees , m. j. , & weinberg , d. h. 2004b , , 601 , 666 draine , b. t. & bertoldi , f. 1996 , , 468 , 269 eke , v. r. , navarro , j. f. , & steinmetz , m. 2001 , , 554 , 114 fan , x. , narayanan , v. k. , strauss , m. a. , white , r. l. , becker , r. h. , pentericci , l. , & rix , h. 2002 , , 123 , 1247 galli , d. & palla , f. 1998 , , 335 , 403 gnedin , n. y. 2000 , , 535 , 530 haiman , z. , abel , t. , & rees , m. j. 2000 , , 534 , 11 haiman , z. , & holder , g. p. 2003 , , 595 , 1 haiman , z. , rees , m. j. , & loeb , a. 1996 , , 467 , 522 hu , e. m. , cowie , l. l. , mcmahon , r. g. , capak , p. , iwamuro , f. , kneib , j .- p . , maihara , t. , & motohara , k. 2002 , , 568 , l75 hutchins , j. b. 1976 , , 205 , 103 kashlinsky , a. , arendt , r. g. , mather , j. , & moseley , s. h. 2005 , , 438 , 45 kitayama , t. , yoshida , n. , susa , h. , & umemura , m. 2004 , , 613 , 631 kneib , j. , ellis , r. s. , santos , m. r. , & richard , j. 2004 , , 607 , 697 kodaira , k. , et al . 2003 , , 55 , l17 kogut , a. , et al . 2003 , , 148 , 161 kuhlen , m. , & madau , p. 2005 , , 860 lacey , c. & cole , s. 1993 , , 262 , 627 lacey , c. & cole , s. 1993 , , 271 , 676 madau , p. , & rees , m. j. 2000 , , 542 , l69 miralda - escud ' e , j. 2003 , , 597 , 66 miralda - escude , j. , & rees , m. j. 1998 , , 497 , 21 navarro , j. f. , frenk , c. s. , & white , s. d. m. 1997 , , 490 , 493 oh , s. p. & haiman , z. 2003 , , 346 , 456 onken , c. a. & miralda - escud ' e , j. 2004 , , 610 , 1 oh , s. p. , nollett , k. m. , madau , p. , & wasserburg , g. j. 2001 , apj , 562 , l10 raig , a. , gonzlez - casado , g. , & salvador - sol , e. 2001 , , 327 , 939 rhoads , j. e. , et al . 2004 , , 611 , 59 ricotti , m. , & ostriker , j. p. 2004 , , 350 , 539 santos , m. r. , bromm , v. , & kamionkowski , m. 2002 , , 336 , 1082 schaerer , d. 2002 , , 382 , 28 shapiro , p. r. , iliev , i. t. , & raga , a. c. 2004 , , 348 , 753 sheth , r. k. & tormen , g. 2002 , , 329 , 61 shull , j. m. , & van steenberg , m. e. 1985 , , 298 , 268 sokasian , a. , yoshida , n. , abel , t. , hernquist , l. , & springel , v. 2004 , , 350 , 47 spergel , d. n. , et al . 2003 , , 148 , 175 tegmark , m. , silk , j. , rees , m. j. , blanchard , a. , abel , t. , & palla , f. 1997 , , 474 , 1 whalen , d. , abel , t. , & norman , m. l. 2004 , apj , 610 , 14 white , r. l. , becker , r. h. , fan , x. , & strauss , m. a. 2003 , , 126 , 1 wise , j. h. , & abel , t. 2005 , , 629 , 615 yoshida , n. , abel , t. , hernquist , l. , & sugiyama , n. 2003 , , 592 , 645

we assume that any halo that has already had stars previously formed in one of their halo progenitors will form only stars with metals , which are assigned an emissivity of ionizing radiation equal to that determined at from the measured intensity of the ionizing background . the contribution of metal - free stars to the present cosmic infrared background is negligibly small .

we estimate the maximum contribution to reionization from the first generation of massive stars , with zero metallicity , under the assumption that one of these stars forms with a fixed mass in every collapsed halo in which metal - free gas is able to cool . we assume that any halo that has already had stars previously formed in one of their halo progenitors will form only stars with metals , which are assigned an emissivity of ionizing radiation equal to that determined at from the measured intensity of the ionizing background . we examine the impact of molecular hydrogen photodissociation ( which tends to reduce cooling when a photodissociating background is produced by the first stars ) and x - ray photoheating ( which heats the atomic medium , raising the entropy of the gas before it collapses into halos ) . we find that in the cdm model supported by present observations , and even assuming no negative feedbacks for the formation of metal - free stars , a reionized mass fraction of 50% is not reached until redshift . the combination of ordinary metal - enriched stars and early metal - free stars can yield a cmb optical depth to electron scattering of at most . the contribution of metal - free stars to the present cosmic infrared background is negligibly small .

0707.3046

i

in @xcite c. geiss , b. leclerc , and j. schrer initiated the study of the ( generalized ) tilting theory for preprojective algebras of dynkin type @xmath4 vis vie the cluster algebra structure of the coordinate ring of the maximal unipotent group @xmath5 attached to @xmath4 under the cartan - killing classification ; see @xcite , @xcite , and @xcite regarding _ cluster algebras_. specifically they construct an explicit map @xmath0 from the module category of the preprojective algebra to the coordinate ring of the corresponding maximal unipotent group which transforms exceptional objects into cluster variables and maximal rigid modules into clusters . the @xmath0-map can be interpreted ( and this is the view initially taken here ) as type of partition function which records the euler characteristics of _ generalized flag varieties _ attached to the module . recently both @xcite and @xcite have independently made the new step of examining the gls @xmath0-map in the affine setting . in particular @xcite studied examples of unipotent cells of the loop group @xmath3 and proved that their coordinate rings in accordance with the predictions made in @xcite are cluster algebras of geometric type . this was accomplished in part by evaluating the type @xmath2 gls @xmath0-map for a fixed family of nilpotent finite dimensional modules over the preprojective algebra of type @xmath2 . for each unipotent cell in @xmath3 the authors of @xcite conjecture an explicit list of nilpotent @xmath1-modules whose images under the type @xmath2 gls @xmath0-map form the initial seed generating the cluster algebra structure of the coordinate ring of the unipotent cell . moreover conjecture ( 4.3 ) of @xcite predicts determinantal expressions for these initial cluster variables . this paper evaluates the type @xmath2 gls @xmath0-map over a class of nilpotent @xmath1-modules called _ shape modules _ indeed a class which properly contains those modules stipulated in conjectures ( 4.1)-(4.3 ) of @xcite and expresses the result determinantally in order to settle ( 4.3 ) of @xcite . the proof entails computing the euler characteristic of any generalized flag variety attached to a shape module ; this is accomplished combinatorially by counting standard tableaux of requisite shape and parity . we now go into more detail : recall that the preprojective algebra @xmath1 of type @xmath2 is defined as the quotient of the _ path algebra _ associated to the quiver @xmath6 @xmath7^{\alpha } \ar@/_2.5pc/[r]_{\ \beta^ * } & 1 \ar@/^1.1pc/[l]^{\beta } \ar@/_2.5pc/[l]_{\ \alpha^ * } } \ ] ] by the ideal @xmath8 generated by @xmath9 and @xmath10 . let @xmath11 and @xmath12 denote the idempotents of @xmath1 . for a finite dimensional left @xmath1-module @xmath13 of dimension @xmath14 together with a choice of bit string @xmath15 in @xmath16 the _ generalized flag variety _ @xmath17 is the variety of all @xmath1-composition series @xmath18 with @xmath19 and @xmath20 such that @xmath21 whenever @xmath22 . here @xmath23 and @xmath24 are the simple left @xmath1-modules associated to the vertices labeled @xmath25 and @xmath26 in the quiver @xmath6 . let @xmath27 be an alternating bit string in @xmath28 and let @xmath29 denote for the moment formal variables . if @xmath13 is a finite dimensional left @xmath1-module then @xmath30 where @xmath31 is the bit string in @xmath16 given by @xmath32 with @xmath33 and where @xmath34 whenever @xmath22 . the symbol @xmath35 denotes euler characteristic ( for cohomology with compact support ; see @xcite ) . section ( 1 ) of this paper begins with a quick survey of partition and tableau combinatorics . the notion of @xmath36-_parity _ of a standard tableau is defined together with the auxiliary notion of a _ chess tableau_. proposition ( 1 ) proves that the number of standard tableaux of shape @xmath37 and @xmath36-parity @xmath31 equals @xmath38 times the number of chess tableaux of shape @xmath37 and content @xmath39 where @xmath40 is an alternating bit string in @xmath28 and @xmath41 . in section ( 2 ) we give a construction which associates to a pair @xmath42 of ordered partitions and choice of parity @xmath43 a nilpotent left @xmath1-module called the _ skew - shape module_. the modules considered in chapter ( 4 ) of @xcite are particular examples . _ shape modules _ are defined as skew - modules where the smaller partition @xmath44 is empty . following this section ( 3 ) details a proof of our first theorem : let @xmath13 be a shape module of shape @xmath37 , parity @xmath36 , and dimension @xmath45 . if @xmath46 is a bit string in @xmath16 then the euler characteristic @xmath47 equals the number of standard tableaux @xmath48 of shape @xmath37 whose @xmath36-parity equals @xmath49 . conjecture ( 1 ) of section ( 3 ) refines theorem ( 1 ) and tallies the number of @xmath50-rational points of @xmath51 when @xmath1 is viewed as an algebra over a finite field @xmath50 with @xmath52 elements . the _ algebraic loop group _ @xmath3 is the group consisting of all @xmath53-valued @xmath54 matrices @xmath55 with determinant @xmath26 where @xmath53 is the laurent polynomial ring @xmath56 $ ] . an element @xmath57 is viewed as encoding a regular map @xmath58 given by @xmath59 ; a closed contour or `` loop '' in @xmath60 is obtained upon restricting the map to the circle group @xmath61 in @xmath62 and taking its image hence the name . the _ maximal unipotent subgroup _ @xmath5 is the subgroup of @xmath3 containing all loops @xmath63 which extend to @xmath25 and for which @xmath64 is an upper triangular unipotent matrix . as @xmath53-valued matrices @xmath65 & \bbb{c}[t ] \\ \\ t\bbb{c}[t ] & 1 + t\bbb{c}[t ] \end{pmatrix } \ \bigg| \ \text{with $ \det(g ) = 1 $ } \ \bigg\}.\ ] ] for @xmath66 and @xmath67 let @xmath68 denote the 1-parameter subgroups defined by @xmath69 the set of elements @xmath70 which factorize as @xmath71 for some alternating bit string @xmath27 in @xmath28 , for some choice of parameters @xmath29 in @xmath62 , and for some @xmath72 is a zariski open subset within @xmath5 . consequently a regular function over @xmath5 is uniquely determined by its values over @xmath70 . in section ( 4 ) we define regular functions @xmath73 indexed by a choice of parity @xmath74 together with a pair of partitions @xmath44 and @xmath37 . these functions are expressed as minors of the infinite block - toeplitz matrix @xmath75 associated to the argument @xmath57 . in particular the minors consider in @xcite are of the form @xmath76 . these minors are shown to satisfy an @xmath36-pieri rule reminiscent of the generalized pieri identities considered by @xcite and as such behave like schur polynomials which carry a parity . this view is reinforced by remark ( 7 ) in section ( 5 ) which expresses @xmath77 as a generating function for chess tableaux of shape @xmath37 and parity @xmath36 . section ( 4 ) ends with conjecture ( 2 ) which claims that the type @xmath2-_generalized minors _ of fomin - zelevinsky ( see @xcite ) are among these block - toeplitz matrix minors . in section ( 5 ) the restriction of the minors @xmath78 to the maximal unipotent subgroup @xmath5 of the loop group are studied combinatorially by means of pairwise non - crossing families of paths in a weighted planar network @xmath79 . proposition ( 3 ) sets up a weight and content preserving bijection between families of non - crossing paths and chess tableaux which is then used to prove the main result of this paper : let @xmath13 be a shape module of shape @xmath37 , parity @xmath36 , and dimension @xmath45 . let @xmath27 be an alternating bit string in @xmath28 and let @xmath29 be parameters in @xmath62 then @xmath80

we evaluate the geiss - leclerc - schrer-map for _ shape modules _ over the preprojective algebra of type in terms of matrix minors arising from the block - toeplitz representation of the loop group . conjecturally these minors are among the cluster variables for coordinate rings of unipotent cells within . in so doing we compute the euler characteristic of any _ generalized flag variety _ attached to a shape module by counting standard tableaux of requisite shape and _ parity _ ; alternatively by counting _ chess tableaux _ of requisite shape and content .

we evaluate the geiss - leclerc - schrer-map for _ shape modules _ over the preprojective algebra of type in terms of matrix minors arising from the block - toeplitz representation of the loop group . conjecturally these minors are among the cluster variables for coordinate rings of unipotent cells within . in so doing we compute the euler characteristic of any _ generalized flag variety _ attached to a shape module by counting standard tableaux of requisite shape and _ parity _ ; alternatively by counting _ chess tableaux _ of requisite shape and content .

0811.3255

i

it is now generally believed that the power of active galactic nuclei ( agns ) is extracted through the accretion of gas onto a central supermassive black hole ( smbh ) . such energy mechanism means that agns are characterized by their strong hard x - ray emission ( @xmath3kev ) , which is widely used as direct evidence suggesting the existence of a nuclear accretion activity ( @xmath4 , e.g. , silverman et al . 2005 ; brusa et al . 2007 ; hasinger et al . the commonly accepted model is that the hard x - ray emission from agns is primarily produced by the inverse compton scattering of the uv / soft x - ray photons emitted from the accretion disk ( e.g , zdziarski et al . 1995 , 2000 ; haardt & maraschi 1991 ; kawaguchi et al . the absorption - corrected x - ray photon spectra within the energy band 2 - 10kev could be best described as a cut - off powerlaw with index @xmath5 ( e.g. , zdziarski et al . 1995 ; reeves & turner 2000 ; piconcelli et al . 2005 ; dadina 2008 ; panessa et al . the synthesis spectra become flat beyond 10kev because of the compton reflection caused by the ionized surface of the accretion disk ( e.g. , george & fabian 1991 ) . because the hard x - ray emission from central engine can penetrate the obscuration material much more easily than lower energy emission , it possesses particular importance in testing the traditional unified model ( antonucci 1993 ) in seyfert 2 galaxies ( e.g. , moran et al . 2002 ; cardamone et al . the studies of the _ chandra and _ xmm - newton observatories showed that the cosmic x - ray background ( cxrb ) at 2 - 30kev might be contributed by many unknown obscured agns which are predicted by the cxrb models ( e.g. , comastri et al . 1995 ; de luca & molendi 2004 ; worsley et al . 2005 ; gilli et al . 2007 ; severgnini et al . 2003 ; levenson et al . taking into account of the issue of co - evolution of agn and bulge of its host galaxy ( e.g. , heckman et al . 2004 ; kauffmann et al . 2003 ; wang et al . 2006 ; wang & wei 2008 and references therein ) , the hard x - ray emission from agns is also an important tool in detecting and separating agn s contribution from circumnuclear star formation activity . the x - ray luminosities of known most x - ray luminous starforming and elliptical galaxies are not higher than @xmath6 ( zezas et al . 2003 ; lira et al . 2002a , 2002b ; osullivan et al . _ heckman et al . ( 2005 ) identified a very tight correlation between the hard x - ray ( 3 - 20kev ) and [ ] luminosities in a sample of hard x - ray selected agns when they performed a comparison between the hard x - ray selected and [ ] emission - line selected agns . in 2 - 10kev bandpass , similar correlations were identified in the palomar optically selected agns by panessa et al . ( 2006 ) . on the contrary , a very weak @xmath7}}$]-@xmath8 correlation was identified in the agns selected by their bright [ ] emission lines ( heckman et al . 2005 ) . the result suggests that many agns might be missed in the hard x - ray survey . moreover , netzer et al . ( 2006 ) claimed that the @xmath7}}$]/@xmath8 ratio depends on the x - ray luminosity . the questions are therefore naturally raised : why is the @xmath7}}$]-@xmath8 correlation broken in some kind of agns ? which parameters ( or what are the physical reasons that ) determine the correlation ? are the hard x - ray selected agns particular in some parameters ? both black hole mass ( @xmath9 ) and eddington ratio ( @xmath10 ) are two key parameters determining the observed properties of agns . in addition , with the development of the technology in hard x - ray detection , a major advance in studying agn hard x - ray emission will be achieved in the next a few years due to the launch of new missions with enhanced hard x - ray capability ( in sensitivity and imaging ) , such as nustar , simbol - x , and next ( e.g. , takahashi et al . 2008 ; ferrando et al . the study on the existent surveys certainly prepares the ground for the future surveys . in this paper , we examine the optical spectral properties of a sample of 42 hard x - ray selected broad - line agns , which allows us to investigate the properties of @xmath9 and @xmath10 in these hard x - ray agns . the sample is mainly compiled from the agn catalog of the rxte 3 - 20kev all sky survey ( xss , sazonov & revnivtsev 2004 ) , and complemented by the agn catalog released by the _ integral all - sky hard x - ray survey ( bassani et al . 2006a and references therein ) . note that the energy range used in this work is extended to the compton reflection region , and is harder than the range ( i.e. , 0.5 - 10 kev ) usually used in the similar previous studies . the paper is organized as follows . section 2 and 3 shows the sample selection and spectroscopic observations , respectively . the data reduction is described in the next section . section 5 presents the results and discussions . the cosmology with @xmath11 , @xmath12 , and @xmath13 ( bennett et al . 2003 ) is adopted in our calculations throughout the paper . _

we examine the accretion properties in a sample of 42 hard ( 3 - 60kev ) x - ray selected nearby broad - line agns . the energy range in the sample is harder than that usually used in the similar previous studies . we believe the sample completeness will be improved in the next few years by the ongoing _ swift and _ integral missions , and by the next advanced missions , such as nustar , simbol - x , and next .

we examine the accretion properties in a sample of 42 hard ( 3 - 60kev ) x - ray selected nearby broad - line agns . the energy range in the sample is harder than that usually used in the similar previous studies . these agns are mainly complied from the rxte all sky survey ( xss ) , and complemented by the released _ integral agn catalog . the black hole masses , bolometric luminosities of agn , and eddington ratios are derived from their optical spectra in terms of the broad h emission line . the tight correlation between the hard x - ray ( 3 - 20kev ) and bolometric / line luminosity is well identified in our sample . also identified is a strong inverse baldwin relationship of the h emission line . in addition , all these hard x - ray agns are biased toward luminous objects with high eddington ratio ( mostly between 0.01 to 0.1 ) and low column density ( ) , which is most likely due to the selection effect of the surveys . the hard x - ray luminosity is consequently found to be strongly correlated with the black hole mass . we believe the sample completeness will be improved in the next few years by the ongoing _ swift and _ integral missions , and by the next advanced missions , such as nustar , simbol - x , and next . finally , the correlation between rfe ( = optical /h ) and disk temperature as assessed by leads us to suggest that the strength of the emission is mainly determined by the shape of the ionizing spectrum . _ _ _

0811.3255

r

table 2 lists the following items measured from the spectra . column ( 2 ) and ( 3 ) lists the equivalent widths ( ews ) of h@xmath38 and h@xmath39 , respectively . all the ews refer to the continuum level determined from the continuum fitting at the position of wavelength @xmath404861 . the line ratio rfe ( = /h@xmath41 ) is shown in column ( 4 ) . column ( 5 ) lists the luminosity of the h@xmath0 broad component , and column ( 6 ) the fwhm of the broad h@xmath0 in units of @xmath42 . all quoted widths are not corrected for the intrinsic resolution , since the widths are much broader than the resolution . column ( 7 ) shows the luminosity of the [ ] emission line . both [ ] and h@xmath41 luminosities are calculated from the cosmology - corrected luminosity distance given by ned . the next two columns show the absorption - corrected hard x - ray luminosities in the bandpass 3 - 20 kev ( xss ) and in 17 - 60 kev ( _ integral ) . _ six out of the 42 agns are detected by _ integral only . in order to estimate their x - ray luminosities in the bandpass 3 - 20 kev from the luminosities in 17 - 60 kev , a transformation is derived in terms of the 18 objects detected by both surveys . the left panel of figure 3 shows the relationship between the two sets of luminosity . a unweighted fitting yields a relationship @xmath43 with a standard deviation of 0.25 . after transform the luminosities in the bandpass 17 - 60 kev to 3 - 20 kev for the six objects , the strong correlation between the [ ] and 3 - 20 kev luminosity is shown in the right panel of figure 3 for the total 42 objects . the correlation is highly consistent with that derived in heckman et al . ( 2005 ) , which firmly demonstrates the accuracy of our observations and calibrations . _ the detection of hard x - ray emission from a nucleus is regarded as strong evidence of accretion activity occurring around the central smbh . the correlations between x - ray luminosity and luminosities of optical emission lines ( e.g. , h@xmath25 , h@xmath0 , [ ] ) have been extensively established in the previous studies ( e.g. , elvis et al . 1984 ; ward et al . 1988 ; mulchaey et al . 1994 ; heckman et al . 2005 ; panessa et al . however , the correlations seem to depend on sample selection ( heckman et al . 2005 ) and on x - ray luminosity itself ( netzer et al . 2006 ) . in this paper , we estimate the luminosity of agn at rest wavelength 5100 from the h@xmath41 component according to the calibration given by greene & ho ( 2005 ) : @xmath44 the bolometric luminosity is then derived by adopting the usually used bolometric correction @xmath45 ( e.g. , kaspi et al . the significant correlation between @xmath46 and @xmath47 is shown in the left panel in figure 4 . a unweighted least square fitting gives a relationship : @xmath48 or @xmath49 for simplification . the correlation strongly indicates a close link between the hard x - ray emission and ionizing radiation emitted from the accretion disk . note that the bolometric luminosity spans four orders of magnitude , down to @xmath50 , which is close to the formal definition of low luminous agns ( i.e. , @xmath51 , ho 2003 ) . these faint galaxies generally radiate at low state with eddington ratio marginally exceeds 0.01 . it is now generally believed that black hole mass ( @xmath9 ) and specific accretion rate ( @xmath10 ) are two basic parameters determining the properties of agns . the role of @xmath10 in driving the eigenvector i ( ei ) space , the ei space has been subsequently extended to ultraviolet and soft x - ray bands ( i.e. , fwhm ( ) and @xmath52 , e.g. , wang et al . 1996 ; xu et al . 2003 ; grupe 2004 ; sulentic et al . 2007 ; see sulentic et al . 2000a for a review ) . ] has been extensively investigated in numerous previous studies ( e.g. , boroson 2002 ; sulentic et al . 2006 ; xu et al . 2003 ; grupe 2004 ; zamanov & marziani 2002 ; marziani et al . 2001 ) , because of the great progress in the calibration of the @xmath53 relationship ( e.g , kaspi et al . 2000 , 2005 , 2007 ; mclure & jarvis 2004 ; vestergaard & peterson 2006 ; peterson et al . 2004 ; bentz et al . 2006 ) due to the recent great advance in the reverberation mapping ( e.g. , kapsi et al . 2000 ; peterson & bentz 2006 ) . we refer the reads to mcgill et al . ( 2008 , and references therein ) for a summary of the existing formula used to calculate @xmath9 basing upon `` single - epoch '' observation . in this work , the black hole mass is estimated by the width and luminosity of h@xmath41 in individual object , according to the scaling law obtained by greene & ho ( 2005 ) . @xmath54 for each object , the estimated @xmath9 and @xmath10 is listed in column ( 10 ) and ( 11 ) in table 2 , respectively . the bolometric luminosity @xmath46 is estimated from the h@xmath41 component as described above . the calculations of both @xmath46 and @xmath10 allow us to find that the current sample is strongly biased against sub - luminous agns usually with low @xmath10 . in fact , the left panel of figure 4 shows the lack of agns with @xmath51 . figure 5 displays the distributions of the @xmath10 ( _ left panel ) and @xmath9 ( _ middle panel ) for the total 42 agns . as shown in the middle panel , the @xmath9 is sampled within a wide range ( @xmath55 dex ) from @xmath56 to @xmath57 with a peak at @xmath58 . in contrast , the left panel shows that @xmath10 distributes in a relatively narrow range as compared with the previous studies . the total range of our @xmath10 spans from 0.01 to 1 . in particular , about @xmath59% objects listed in the sample have @xmath10 between 0.01 and 0.1 . however , the @xmath10 of bright local agns usually spans at least three orders of magnitude from 1 to 0.001 ( e.g. , woo & urry 2002 ; boroson 2002 ) . basing upon the 2 - 10kev x - ray luminosity , panessa et al . ( 2006 ) indicated that the @xmath10 of the palomar optically selected agns ranges from @xmath60 to 0.1 . as an additional test , the right panel of figure 4 shows the @xmath9 vs. @xmath47 plot . @xmath47 as a function of @xmath9 is over - plotted as dashed lines for three different @xmath10 ( i.e. , 1 , 0.1 , and 0.01 ) . as shown in the plot , a majority of our objects are located below the line with @xmath61 and above the line with @xmath62 . _ _ in summary , the hard x - ray selected agns listed in our sample are luminous agns with a wide range of @xmath9 but a nearly constant accretion activity ( i.e. , @xmath10 ) , which is likely due to the selection effect of the survey that is biased toward x - ray luminous objects . in active ( or luminous ) agn , the optical / uv ionizing radiation is believed to be emitted from a standard geometric thin disk ( e.g. , shakura & sunyaev 1973 ) . the low energy photon is comptonized by a hot corona to produce the hard x - ray emission below 10kev ( haardt & maraschi 1991 ) . a compton recoil of the soft photon is required to occur on the ionized surface of the accretion disk to produce the emission spectrum beyond 10kev . the main observation feature of the reflection is a bump peaked at about 30kev ( e.g. , george & fabian 1991 ; zycki et al . 1994 ; ross & fabian 2002 , 2005 ) . the bias towards active agns could be possibly caused by the fact that either intensive compton reflection takes place only in agns at high state with large @xmath10 or the surveys are biased against the compton - thick objects . in the first case , the theory of the compton reflection predicts that the x - ray emission contributed by the reflection depends primarily on the x - ray ionizing parameter , and secondarily on the uv radiation produced by the dissipation inside the accretion disk . in the second case , our analysis implies a possible connection between the less x - ray absorption and high @xmath10 in broad - line agns . in fact , we selected the objects with regardless of their x - ray spectral properties . figure 1 shows the lack of objects with large column density in the sample . we believe that the sample completeness would be improved by including the ongoing _ swift / bat survey with large effective collecting area and harder energy bandpass ( 14 - 195 kev ) in the future studies . _ figure 4 shows that the hard x - ray luminosity is strongly correlated with the @xmath9 in our sample . in fact , the correlation is naturally expected given the tight @xmath47 vs. @xmath46 correlation and nearly constant @xmath10 . the @xmath63 vs. @xmath9 correlation provides us a potential estimate of black hole mass for luminous agns within @xmath64 . the following relationship is obtained by us through a least square fitting : @xmath65 . our results conflicts with panessa et al . ( 2006 ) and pellegrini ( 2005 ) who did not find the correlation , but is in agreement with kiuchi et al . panessa et al . ( 2006 ) investigated a sample of 47 nearby seyfert galaxies selected from the palomar spectroscopy ( ho et al . the luminosity obtained by different x - ray instruments is down to @xmath66 . the studies in pellegrini ( 2005 ) are based on the _ chandra observations down to a luminosity @xmath66 . kiuchi et al . ( 2006 ) used the broad - line agn sample detected by the _ asca large sky survey ( alss ) and _ asca medium sensitivity survey in the northern sky ( amssn ) with a detection limit of a few @xmath67 in 2 - 10kev bandpass . as discussed above , it is worthy noting that the correlation most likely does not reflect the physics but a selection effect of the surveys . _ _ _ as a key parameter in the ei space , the ratio ( rfe ) is defined as the ratio of the optical complex to h@xmath0 . although the total emission increases by fourfold with reasonable ionization parameter in agn ( korista et al . 1997 ) , traditional photoionization models can not explain the strong emission in optical and uv bands ( e.g , netzer & wills 1983 ; joly 1987 ; collin - souffrin et al . 1988 ) . at present , the problem is only slightly alleviated by the major improvements in the atomic data and by the improved treatment of the line excitation process ( sigut & pradhan 2003 ; baldwin et al . we refer the reads to collin & joly ( 2000 ) for a summary of the mechanisms that can enhance the emission . bg92 put forward a picture in which the rfe is determined by the vertical structure of the accretion disk . the vertical structure is governed by @xmath10 . a large @xmath10 leads to a large x - ray heated volume that could generate large emission . sulentic et al . ( 2000b ) developed a semi - analysis model in which the rfe depends on @xmath10 as @xmath68 . although the rfe is found to generally increase with @xmath10 in optical bright quasars , netzer et al . ( 2004 ) found that a number of high - z quasars deviate the trend , i.e. , with very small rfe but large @xmath10 ( see also in netzer & trakhtenbrot 2007 ) . using the large database provided by the sloan digital sky survey , netzer & trakhtenbrot ( 2007 ) recently suggested that the enhanced rfe is mainly caused by increased metal abundance . in the current sample , the distribution of rfe is shown in the right panel of figure 5 . rfe uniformly ranges from @xmath69 to 1 . on the contrary , @xmath10 distributes in a quite narrow range as describe above . in fact , no correlation between rfe and @xmath10 is found in our sample ( see the upper panel in figure 6 ) , which motivates us to suspect that rfe does not depend on @xmath10 only . rfe is plotted against the characteristic disk temperature @xmath70 in the bottom panel in figure 6 . the temperature scales with @xmath10 and @xmath9 as predicted by the standard geometric thin disk model ( e.g. , shakura & sunyaev 1973 ) . the exact formula of disk temperature depends on various accretion disk models . for a rapidly rotating kerr hole , with a spin parameter @xmath71 and efficiency of 0.31 , we have @xmath72 . the diagram indicates an obvious correlation between the two parameters . a spearman rank - order test calculated by survival analysis yields a formal correlation coefficient @xmath73 ( @xmath74 , where @xmath75 is the probability of null correlation ) . the correlation is not highly significant probably because of the small sample size . the estimated temperature spans about one order of magnitude ( @xmath76 ) , corresponding to a factor of @xmath77 . the correlation then suggests a trend of more intensive emission for higher disk temperature . a marginal dependence of the continuum shape of qsos on @xmath70 was recently identified by bonning et al . ( 2007 ) who compared the observations of sdss with the nlte models of accretion disk . the current result means that the strength of the emission is likely controlled by the spectral shape of the ionizing continuum . the physical reason of the absence of the baldwin relationship ( baldwin 1977 ) for low ionization emission lines is still an open question . in fact , a weak inverse baldwin relationship for h@xmath0 has been demonstrated by recent studies basing upon large agn samples ( e.g. , croom et al . 2002 ; greene & ho 2005 ) . we identify a tight , positive correlation between @xmath63 and ew(h@xmath41 ) in our hard x - ray selected agns ( i.e. , an inverse baldwin relationship ) . figure 7 presents the correlation with correlation coefficient @xmath78 ( @xmath79 ) estimated by the spearman rank - order analysis . ew(h@xmath41 ) roughly scales with hard x - ray luminosity as @xmath80 . wilkes et al . ( 1999 ) identified a marginal baldwin effect in h@xmath0 line . noted that they examined only the luminous local quasars with @xmath81 although many models are developed to explain the baldwin effect for high ionization emission lines ( e.g. , , wandel 1999 ; korista et al . 1998 ; shields et al . 1995 ; wills et al . 1999 ; baskin & loar 2004 ; bachev et al . 2004 ) , these models can not explain the difference between and h@xmath0 . croom et al . ( 2002 ) suggested that the inverse baldwin relationship could be explained if the longer wavelength continuum contains emission from other components ( e.g. , thermal dust emission , non - thermal radio emission , starlight ) . we estimate the possible contribution of the unknown sources as follows . we start from the relationship @xmath82 , and re - write @xmath83 , where @xmath84 and @xmath85 is the agn luminosity and luminosity of other unknown sources at the h@xmath0 wavelength , respectively . the x - ray luminosity could be replaced by @xmath84 given eq . ( 2 ) and the bolometric correction factor of 9 . replacing @xmath86 as @xmath84 given eq.(1 ) finally yields a relationship @xmath87 . considering the typical case with @xmath88 , about 40% of the observed continuum at h@xmath0 wavelength is estimated to be contributed by the unknown sources .

in addition , all these hard x - ray agns are biased toward luminous objects with high eddington ratio ( mostly between 0.01 to 0.1 ) and low column density ( ) , which is most likely due to the selection effect of the surveys . the hard x - ray luminosity is consequently found to be strongly correlated with the black hole mass .

we examine the accretion properties in a sample of 42 hard ( 3 - 60kev ) x - ray selected nearby broad - line agns . the energy range in the sample is harder than that usually used in the similar previous studies . these agns are mainly complied from the rxte all sky survey ( xss ) , and complemented by the released _ integral agn catalog . the black hole masses , bolometric luminosities of agn , and eddington ratios are derived from their optical spectra in terms of the broad h emission line . the tight correlation between the hard x - ray ( 3 - 20kev ) and bolometric / line luminosity is well identified in our sample . also identified is a strong inverse baldwin relationship of the h emission line . in addition , all these hard x - ray agns are biased toward luminous objects with high eddington ratio ( mostly between 0.01 to 0.1 ) and low column density ( ) , which is most likely due to the selection effect of the surveys . the hard x - ray luminosity is consequently found to be strongly correlated with the black hole mass . we believe the sample completeness will be improved in the next few years by the ongoing _ swift and _ integral missions , and by the next advanced missions , such as nustar , simbol - x , and next . finally , the correlation between rfe ( = optical /h ) and disk temperature as assessed by leads us to suggest that the strength of the emission is mainly determined by the shape of the ionizing spectrum . _ _ _

0811.3255

c

the properties ( @xmath10 and @xmath9 ) of accretion onto smbh are examined in a sample of 42 hard x - ray selected ( 3 - 60kev ) broad - line agns in terms of their optical spectra taken by us . the energy range is harder than that usually used in the similar previous studies . these agns are mainly compiled from the rxte all sky survey ( sazonov & revnivtsev 2004 ) , and are complemented by the released _ integral agn sample ( bassani et al . the statistical analysis allows us to draw the following conclusions : _ 1 . we confirm the tight correlation between the hard x - ray and optical emission line luminosities ( and bolometric luminosity ) in our sample , which suggests a close link between the hard x - ray emission reflected by the ionized surface of the accretion disk and uv / optical radiation . using the hard x - ray luminosity , a strong inverse baldwin relationship of the h@xmath0 emission line is identified in the sample . 2 . the hard x - ray selected broad - line agns listed in the sample are found to be strongly biased toward luminous agns with high @xmath10 and low column density . since @xmath10 is constant ( mostly between 0.01 and 0.1 ) in a first order approximation , the hard x - ray luminosity is strongly correlated with the black hole mass in our sample , which is most likely due to the selection effect of the surveys . although the rfe parameter is independent on @xmath10 in our sample , it is found to be correlated with the accretion disk temperature as assessed by @xmath89 . this result implies that the strength of the emission is determined by the shape of the ionizing spectrum . finally , it should be mentioned that a new era in agn hard x - ray study will be opened in next a few years due to the launch of new missions with enhanced hard x - ray detection capability in not only sensitivity , but also imaging , such as simbol - x , next and nustar . these missions will provide larger , and more complete samples to study the present open issues . we would like to thank the anonymous referee for his / her valuable comments that help to improve the paper . the authors are grateful to todd a. boroson and richard f. green for providing us the template . special thanks go to the staff at xinglong observatory as a part of national astronomical observatories , china academy of science for their instrumental and observational help . this search is supported by the nfs of china under grant 10503005 . antonucci , r. , 1993 , , 31 , 473 bachev , r. , et al . , 2004 , , 617 , 171 baldwin , j. a. , 1977 , , 214 , 679 baldwin , j. a. , ferland , g. j. , korista , k. t. , et al . , 2004 , , 615 , 610 barthelmy , s. d. , barbier , l. m. , cummings , j. r. , et al . , 2005 , ssrv , 120 , 143 baskin , a. , & loar , a. , 2004 , , 350 , l31 bassani , l. , malizia , a. , stephen , j. b. , et al . , 2006b , arxiv : astro - 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012 & 00 36 21.0 & 45 39 54 & 0.048 & 2400 & 2006 aug 15 & 15.45 & s1 + qso0241 + 622 & & 02 44 57.7 & 62 28 07 & 0.044 & 3600 & 2006 dec 17 & 16.1 & s1 + 3c111 & & 04 18 21.3 & 38 01 36 & 0.0485 & 3600 & 2007 nov 03 & 18.0 & s1 + xssj04331 + 0520 & 3c120 & 04 33 11.1 & 05 21 16 & 0.033 & 1800 & 2007 feb 16 & 14.2 & blrg + xssj05103 + 1640 & iras05078 + 1626 & 05 10 45.5 & 16 29 56 & 0.018 & 1800 & 2007 feb 16 & 15.6 & s1 + xssj05162 - 0008 & akn120 & 05 16 11.4 & -00 08 59 & 0.033 & 1200 & 2006 nov 18 & 14.1 & s1 + xssj05552 + 4617 & mcg+8 - 11 - 11 & 05 54 53.6 & 46 26 22 & 0.02 & 1800 & 2007 feb 17 & 15.0 & s1 + mark6 & & 06 52 12.2 & 74 25 37 & 0.01881 & 3600 & 2007 feb 16 & 15.0 & s1.5 + xssj07434 + 4945 & mrk79 & 07 42 32.8 & 49 48 35 & 0.022 & 1800 & 2005 nov 29 & 14.9 & s1 + xssj08117 + 7600 & pg0804 + 761 & 08 10 58.6 & 76 02 42 & 0.1 & 2400 & 2007 nov 16 & 15.15 & s1 + xssj09204 + 1608 & mrk704 & 09 18 26.0 & 16 18 19 & 0.029 & 1800 & 2006 nov 17 & 15.38 & s1 + xssj09261 + 5204 & mrk110 & 09 25 12.9 & 52 17 11 & 0.036 & 1800 & 2005 nov 30 & 15.6 & nls1 + xssj10231 + 1950 & ngc3227 & 10 23 30.6 & 19 51 54 & 0.0038 & 1800 & 2006 jan 31 & 11.1 & s1 + xssj11067 + 7234 & ngc3516 & 11 06 47.5 & 72 34 07 & 0.008836 & 900 & 2006 dec 18 & 12.5 & s1 + xssj11417 + 5910 & sbs1136 + 594 & 11 39 08.9 & 59 11 55 & 0.06 & 2400 & 2007 jan 26 & 15.5 & s1 + xssj12032 + 4424 & ngc4051 & 12 03 09.6 & 44 31 53 & 0.0023 & 1200 & 2006 nov 16 & 10.83 & nls1 + xssj12106 + 3927 & ngc4151 & 12 10 32.6 & 39 24 21 & 0.0033 & 1800 & 2006 jan 29 & 11.5 & s1 + xssj12164 + 1427 & pg1211 + 143 & 12 14 17.7 & 14 03 13 & 0.081 & 3600 & 2006 feb 04 & 14.63 & nls1 + ngc4253 & & 12 18 26.5 & 29 48 46 & 0.01293 & 1200 & 2006 dec 21 & 13.7 & s1.5 + xssj12206 + 7509 & mrk205 & 12 21 44.0 & 75 18 38 & 0.07 & 2400 & 2007 jan 27 & 14.5 & s1 + xssj12288 + 0200 & 3c273 & 12 29 06.7 & 02 03 08 & 0.15834 & 900 & 2006 dec 21 & 12.86 & rlq + xssj12408 - 0516 & ngc4593 & 12 39 39.4 & -05 20 39 & 0.009 & 1200 & 2007 jan 26 & 14.67 & s1 + xssj13420 - 1432 & npm1g-14.0512 & 13 41 12.9 & -14 38 41 & 0.042 & 2400 & 2008 mar 13 & 15.50 & nls1 + xssj13530 + 6916 & mrk279 & 13 53 03.4 & 69 18 30 & 0.031 & 1200 & 2007 feb 16 & 14.57 & s1 + xssj14181 + 2514 & ngc5548 & 14 17 59.5 & 25 08 12 & 0.017 & 1800 & 2008 mar 03 & 13.3 & s1 + xssj15042 + 1046 & mrk841 & 15 04 01.2 & 10 26 16 & 0.036 & 1200 & 2007 feb 16 & 14.0 & s1 + xssj15348 + 5750 & mrk290 & 15 35 52.3 & 57 54 09 & 0.030 & 2400 & 2008 mar 13 & 15.1 & s1 + xssj17276 - 1359 & pds456 & 17 28 19.8 & -14 15 56 & 0.184 & 1800 & 2007 sep 07 & 14.69 & rqq + xssj17413 + 1851 & 4c+18.51 & 17 42 07.0 & 18 27 21 & 0.19 & 2400 & 2007 sep 07 & 16.43 & rlq + xssj18196 + 6454 & h1821 + 643 & 18 21 57.3 & 64 20 36 & 0.297 & 1800 & 2006 aug 16 & 14.1 & rqq + xssj18348 + 3238 & 3c382 & 18 35 02.1 & 32 41 50 & 0.059 & 1800 & 2006 aug 16 & 15.5 & blrg + xssj18408 + 7947 & 3c390.3 & 18 42 09.0 & 79 46 17 & 0.056 & 1800 & 2006 aug 15 & 14.37 & blrg + 1h1934 - 063a & & 19 37 33.0 & -06 13 05 & 0.01059 & 1800 & 2006 aug 16 & 14.09 & s1 + ngc6814 & & 19 42 40.6 & -10 19 25 & 0.00521 & 1800 & 2007 nov 04 & 12.06 & s1.5 + xssj20404 + 7521 & 4c+74.26 & 20 42 37.3 & 75 08 02 & 0.1 & 1800 & 2006 sep 15 & 15.13 & rlq + xssj20441 - 1042 & mrk509 & 20 44 09.7 & -10 43 25 & 0.034 & 1800 & 2006 sep 15 & 13.0 & s1 + xssj21128 + 8216 & s52116 + 81 & 21 14 01.2 & 82 04 48 & 0.084 & 2400 & 2006 aug 15 & 15.7 & blrg + xssj22423 + 2958 & akn564 & 22 42 39.3 & 29 43 31 & 0.025 & 1800 & 2006 nov 15 & 14.55 & nls1 + xssj22539 - 1735 & mr2251 - 178 & 22 54 05.8 & -17 34 55 & 0.064 & 1800 & 2006 nov 15 & 14.36 & rqq + xssj23033 + 0858 & ngc7469 & 23 03 15.6 & 08 52 26 & 0.016 & 1800 & 2006 aug 15 & 13.0 & s1 + xssj23040 - 0834 & mrk926 & 23 04 43.5 & -08 41 09 & 0.047 & 1800 & 2007 nov 03 & 14.6 & s1 + xssj23073 + 0447 & pg2304 + 042 & 23 07 02.9 & 04 32 57 & 0.042 & 2400 & 2007 nov 02 & 15.44 & s1 + ccccccccccc xssj00368 + 4557 & & 82.6 & 0.35 & 42.1 & 2555 & 41.3 & 43.48 & & 7.42 & 0.23 + qso0241 + 622 & & 43.6 & 0.26 & 42.1 & 9401 & 41.8 & 44.34 & 44.28 & 8.54 & 0.02 + 3c111 & & 119.9 & 0.00 & 43.3 & 3445 & 42.8 & 44.53 & 44.59 & 8.33 & 0.30 + xssj04331 + 0520 & 10.5 & 82.7 & 0.24 & 42.2 & 5367 & 42.1 & 44.16 & & 8.11 & 0.06 + xssj05103 + 1640 & 9.0 & 74.5 & @xmath91 & 41.3 & 4855 & 41.5 & 43.47 & 43.58 & 7.55 & 0.04 + xssj05162 - 0008 & 2.3 & 72.7 & 0.55 & 42.5 & 6595 & 41.5 & 44 . & 44.26 & 8.48 & 0.05 + xssj05552 + 4617 & 53.5 & 103.2 & 0.30 & 41.2 & 5761 & 41.7 & 43.56 & 43.67 & 7.60 & 0.02 + mark6 & 6.0 & 37.4 & 0.42 & 41.4 & 5627 & 41.7 & 43.32 & 43.41 & 7.74 & 0.03 + xssj07434 + 4945 & 8.6 & 65.8 & 0.40 & 41.6 & 3815 & 41.7 & 43.45 & & 7.47 & 0.07 + xssj08117 + 7600 & & 74.7 & 0.52 & 43.4 & 3146 & 42.3 & 44.47 & 44.43 & 8.32 & 0.39 + xssj09204 + 1608 & 6.9 & 91.8 & 0.29 & 41.9 & 6421 & 41.6 & 43.65 & & 8.11 & 0.03 + xssj09261 + 5204 & & 118.6 & 0.08 & 42.1 & 1798 & 41.8 & 43.81 & 44.17 & 7.12 & 0.47 + xssj10231 + 1950 & 5.1 & 39.3 & 0.007 & 40.5 & 4556 & 40.6 & 42.4 & 42.67 & 7.01 & 0.02 + xssj11067 + 7234 & & 31.9 & & 41.1 & 5020 & 40.7 & 43.04 & & 7.46 & 0.03 + xssj11417 + 5910 & 7.3 & 73.8 & 0.13 & 42.0 & 4608 & 41.9 & 43.82 & & 7.91 & 0.07 + xssj12032 + 4424 & & 21.5 & 0.61 & 39.9 & 1202 & 40.0 & 42.04 & 41.87 & 5.53 & 0.20 + xssj12106 + 3927 & 37.2 & 100.0 & 0.12 & 40.8 & 6354 & 41.3 & 43.17 & 43.37 & 7.49 & 0.01 + xssj12164 + 1427 & & 120.3 & 0.40 & 42.5 & 1804 & 41.7 & 44.22 & & 7.32 & 0.60 + ngc4253 & 11.3 & 32.1 & 0.72 & 40.8 & 2153 & 41.3 & 42.59 & 42.7 & 6.57 & 0.13 + xssj12206 + 7509 & & 95.6 & 0.21 & 42.5 & 3037 & 41.8 & 43.88 & & 7.83 & 0.23 + xssj12288 + 0200 & & 71.3 & 0.51 & 44.1 & 2970 & 43.2 & 45.91 & 45.92 & 8.66 & 0.74 + xssj12408 - 0516 & & 49.8 & 0.54 & 41.0 & 3654 & 40.4 & 42.57 & 43.04 & 7.12 & 0.05 + xssj13420 - 1432 & 15.3 & 64.6 & 0.66 & 41.8 & 4112 & 41.8 & 43.57 & & 7.67 & 0.07 + xssj13530 + 6916 & 5.7 & 59.6 & 0.44 & 42.2 & 5147 & 41.8 & 43.94 & & 8.07 & 0.06 + xssj14181 + 2514 & 7.8 & 62.7 & 0.04 & 41.3 & 10312 & 41.5 & 43.66 & 43.08 & 8.20 & 0.008 + xssj15042 + 1046 & 9.4 & 129.6 & 0.33 & 42.5 & 5709 & 42.2 & 43.67 & & 8.33 & 0.061 + xssj15348 + 5750 & 4.2 & 23.5 & 0.71 & 41.1 & 4740 & 41.6 & 43.43 & & 7.41 & 0.03 + xssj17276 - 1359 & & 74.6 & 3.58 & 44.1 & 2957 & @xmath92 & 44.93 & & 8.66 & 0.75 + xssj17413 + 1851 & 1.8 & 115.5 & 0.04 & 43.0 & 13506 & 42.2 & 45.45 & & 9.35 & 0.02 + xssj18196 + 6454 & 2.9 & 65.4 & 0.18 & 44.3 & 5797 & 43.7 & 45.61 & & 9.36 & 0.23 + xssj18348 + 3238 & & 111.4 & 0.19 & 42.8 & 8340 & 41.8 & 44.58 & 44.45 & 8.84 & 0.04 + xssj18408 + 7947 & 3.2 & 118.8 & 0.15 & 42.5 & 13799 & 42.0 & 44.39 & 44.61 & 9.13 & 0.01 + 1h1934 - 063a & & 55.2 & 0.94 & 41.1 & 1354 & 41.0 & 42.48 & 42.59 & 6.29 & 0.38 + ngc6814 & & 38.8 & 0.75 & 40.2 & 5182 & 40.2 & 42.35 & 42.47 & 6.95 & 0.01 + xssj20404 + 7521 & & 85.4 & @xmath91 & 43.6 & 9418 & 42.5 & 44.73 & 44.98 & 9.37 & 0.05 + xssj20441 - 1042 & 10.7 & 111.8 & 0.21 & 42.4 & 2261 & 42.1 & 44.2 & 44.13 & 7.47 & 0.36 + xssj21128 + 8216 & 6.3 & 150.0 & 0.14 & 42.6 & 4123 & 42.3 & 44.25 & 44.65 & 8.12 & 0.13 + xssj22423 + 2958 & & 56.6 & 0.74 & 41.7 & 3649 & 41.7 & 43.42 & & 7.52 & 0.09 + xssj22539 - 1735 & 5.7 & 132.5 & 0.02 & 42.9 & 4093 & 42.6 & 44.63 & 44.62 & 8.28 & 0.16 + xssj23033 + 0858 & 13.7 & 45.3 & 0.30 & 41.5 & 2819 & 41.6 & 43.27 & 43.40 & 7.17 & 0.12 + xssj23040 - 0834 & 3.4 & 65.1 & @xmath91 & 42.5 & 7083 & 42.2 & 44.23 & 44.21 & 8.51 & 0.04 + xssj23073 + 0447 & 2.7 & 42.0 & @xmath91 & 41.2 & 7322 & 41.2 & 43.67 & & 7.85 & 0.01 +

these agns are mainly complied from the rxte all sky survey ( xss ) , and complemented by the released _ integral agn catalog . the black hole masses , the tight correlation between the hard x - ray ( 3 - 20kev ) and bolometric / line luminosity is well identified in our sample . also identified is a strong inverse baldwin relationship of the h emission line . finally , the correlation between rfe ( = optical /h ) and disk temperature as assessed by leads us to suggest that the strength of the emission is mainly determined by the shape of the ionizing spectrum . _ _ _

we examine the accretion properties in a sample of 42 hard ( 3 - 60kev ) x - ray selected nearby broad - line agns . the energy range in the sample is harder than that usually used in the similar previous studies . these agns are mainly complied from the rxte all sky survey ( xss ) , and complemented by the released _ integral agn catalog . the black hole masses , bolometric luminosities of agn , and eddington ratios are derived from their optical spectra in terms of the broad h emission line . the tight correlation between the hard x - ray ( 3 - 20kev ) and bolometric / line luminosity is well identified in our sample . also identified is a strong inverse baldwin relationship of the h emission line . in addition , all these hard x - ray agns are biased toward luminous objects with high eddington ratio ( mostly between 0.01 to 0.1 ) and low column density ( ) , which is most likely due to the selection effect of the surveys . the hard x - ray luminosity is consequently found to be strongly correlated with the black hole mass . we believe the sample completeness will be improved in the next few years by the ongoing _ swift and _ integral missions , and by the next advanced missions , such as nustar , simbol - x , and next . finally , the correlation between rfe ( = optical /h ) and disk temperature as assessed by leads us to suggest that the strength of the emission is mainly determined by the shape of the ionizing spectrum . _ _ _

astro-ph0412613

c

we believe that this analysis is the most thorough investigation of the detectability of a trans - planckian modulation to the primordial power spectrum that has been performed to date . we consider three complementary approaches a simple grid search , a fisher matrix evaluation of the likely error ellipses , and a monte carlo markov chain fit to a simulated cmb spectrum , and find that they are all in broad agreement . moreover , we also explain the `` islands '' seen in the likelihood space in previous papers on this topic @xcite , and show that their distribution and properties can be understood and reproduced via a simple analytic argument . the approach we have taken here is analyze a _ specific _ ansatz for introducing a minimum length into the calculation of the perturbation spectrum in a general model of slow - roll inflation @xcite . we do not claim that this model is a correct description of the trans - planckian contribution to the perturbation spectrum , but intend it as a case study of what might be possible if one has a specific and well - motivated correction to the spectrum that leads to a @xmath18 dependent modulation . there is considerable theoretical uncertainty surrounding this point , and it is entirely possible that a future rigorous calculation of the perturbation spectrum within string theory or some other model of ultra high energy physics will predict that there is _ no _ modulation to be observed , and the bound calculated here will not apply . we believe that the constraint obtained here is applicable to a general class of modulated spectra . in practice , one can imagine adding an arbitrary modulation to the primordial spectrum , as considered by okamoto and lim @xcite , in which case one has parameters which describe the amplitude , wavelength , and phase of the modulation as a function of @xmath18 . in our model there are only two free parameters the phase of the modulation , and @xmath6 which determines the amplitude . the phase will always be arbitrary in the absence of detailed theory that matches specific scales in the present universe to those during inflation , which would require a full understanding of the post - inflationary expansion history and the physics of reheating , while the amplitude is directly related to the scale of new physics , which is what we are trying to measure . however , the wavelength of the oscillation turns out to be given in terms of the slow - roll parameter @xmath38 , which is itself directly related to the tensor / scalar ratio @xmath5 . this dependence is easy to understand , since the form of the modulation is not determined by the ( fixed ) boundary condition , but by the slow variation in the horizon size @xmath199 with time . the precise functional form of the connection between @xmath38 and the modulated spectrum may vary in other specific models . however , it is very likely that the modulation can always be expressed in terms of @xmath6 and the scale dependence of @xmath1 or thus @xmath38 , and perhaps the higher order slow - roll parameters , which are also reachable through their contribution to the scalar spectral index . consequently , we believe that the results we have seen here will generalize to other modulated spectra , even though we have reduced the number of trans - planckian parameters relative to those considered by okamoto and lim . the second general conclusion we draw is that the detectability of any modulated spectrum depends on the value of @xmath1 . since the wavelength of the modulation depends on @xmath38 , detecting the primordial tensors provides an orthogonal constraint on the value of this parameter , and thus constrains the trans - planckian corrections . since @xmath1 fixes the energy scale at which inflation occurs , it is arguably the single most interesting cosmological parameter that is not currently fixed by observations . the analysis here simply adds to the importance of this parameter , since we have shown that measuring @xmath1 will put tighter bounds on any trans - planckian corrections to the spectrum . since the theoretical uncertainty about the form and existence of these corrections is yet to be resolved , we can not advocate mounting an observational campaign solely to look for this kind of signal . however , there is already good and sufficient reason to make an all out effort to measure @xmath1 during inflation , via high precision measurements of the cmb and particularly its polarization . we believe that mission planners will want to be aware of the possibility that precision cmb measurements may potentially probe physics at the string scale , since this will not add to the cost of any mission but represents an exciting and additional use of the data they can be expected to return . in quantitative terms , we see that the with a large ( @xmath200 ) value of the tensor to scalar ratio , a `` perfect '' map of the primordial temperature and polarization anisotropies to the cmb could rule out a trans - planckian modulation to the spectrum at the @xmath201 level for @xmath202 . this is roughly the same as the result reported by okamoto and lim . we vary a larger set of cosmological parameters than they do , which reduces the level of precision we can hope for . however by adding the tensor contribution to the analysis and removing a free parameter from the specification of modulation we can tighten the bound . like okamoto and lim , we consider a perfect measurement of the cmb and any real experiment will be contaminated by imperfectly removed foregrounds . consequently , we believe that a value of @xmath6 on the order of 0.01 represents a reasonable lower bound on what can be detected in practice , provided the amplitude of the tensor contribution is significant . on the other hand , adding other orthogonal datasets , such as a measurement of @xmath179 and the late time expansion history of the universe from a snap - like mission , or constraints on the primordial spectrum from future large scale structure surveys will further constrain the error ellipses relative to those which can be achieved via the cmb alone . at this point , the theoretical uncertainty surrounding this calculation makes it unwise to push this analysis significantly further . however , we believe that considerable progress has been made in understanding the physical issues surrounding the trans - planckian corrections to the primordial spectrum over the last few years . consequently , it is not excessively optimistic to hope that the remaining issues can be resolved on a shorter timescale than it will take to perform a measurement of the cmb that even approaches the precision we have assumed in our analysis . in this light , we are particularly interested in the effective field theory approach taken in @xcite , and extended in the more recent preprint @xcite . in this case , the operators which can contribute to a modification to the spectrum can be cataloged within effective field theory . from the observational perspective , an analogous calculation to the one presented here will constrain the values of the prefactors in front of these operators , and we intend to pursue this in future work .

we focus on models of trans - planckian physics which lead to a modulated primordial spectrum . rather than looking at a generic modulated spectrum , our calculations are based on a specific model , and are intended as a case study for the sort of constraints one could hope to apply on a well - motivated model of trans - planckian physics . we present results for three different approaches a grid search in a subset of the overall parameter space , a fisher matrix estimate of the likely error ellipses , and a monte carlo markov chain fit to a simulated cmb sky . as was seen in previous analyses , the likelihood space has multiple peaks , and we show that their distribution can be reproduced via a simple semi - analytic argument . we vary 10 cosmological parameters ( including two related to the trans - planckian terms ) and show that the amplitude of the tensor perturbations is directly correlated with the detectability of any trans - planckian modulation . we conclude that if the tensor to scalar ratio , , the ratio between the inflationary hubble scale , and the scale of new physics has to be on the order of if the modulation is detectable at the 2 level . for a lower value of , the bound on becomes looser .

we examine the constraints cosmological observations can place on any trans - planckian corrections to the primordial spectrum of perturbations underlying the anisotropies in the cosmic microwave background . we focus on models of trans - planckian physics which lead to a modulated primordial spectrum . rather than looking at a generic modulated spectrum , our calculations are based on a specific model , and are intended as a case study for the sort of constraints one could hope to apply on a well - motivated model of trans - planckian physics . we present results for three different approaches a grid search in a subset of the overall parameter space , a fisher matrix estimate of the likely error ellipses , and a monte carlo markov chain fit to a simulated cmb sky . as was seen in previous analyses , the likelihood space has multiple peaks , and we show that their distribution can be reproduced via a simple semi - analytic argument . all three methods lead to broadly similar results . we vary 10 cosmological parameters ( including two related to the trans - planckian terms ) and show that the amplitude of the tensor perturbations is directly correlated with the detectability of any trans - planckian modulation . we argue that this is likely to be true for any trans - planckian modulation in the paradigm of slow - roll inflation . for the specific case we consider , we conclude that if the tensor to scalar ratio , , the ratio between the inflationary hubble scale , and the scale of new physics has to be on the order of if the modulation is detectable at the 2 level . for a lower value of , the bound on becomes looser .

0710.4371

c

we have examined whether the effective low - energy hamiltonian derived from the downfolding procedure is able to describe dynamics and excitation spectra in a proper way . the calculation is performed in the three - stage scheme . in the first stage , we calculate the global electronic structure from the density functional theory supplemented by the generalized gradient approximation . the high - energy degrees of the freedom in the global electronic band structure are , in the second stage , eliminated by the downfolding scheme , which leaves only the low - energy bands near the fermi level . in the present example of gaas , we retain up to 25 ry for the calculation of the global electronic bands , while the downfolded hamiltonian keeps only eight bands near the fermi level up to 15 ev ( @xmath183 1 ry ) . by the downfolding , kinetic and interaction energies are separately renormalized into the low - energy eight bands and the effective hamiltonian , where we employ the cndo model neglecting the offdiagonal part of the coulomb interaction , is constructed from first principles , with the help of the maximally localized wannier functions . this procedure , though several simplified treatments are employed , in principle , does not contain any _ ad hoc _ parameters . in the third stage , the hartree - fock method for the ground state supplemented by the single - excitation configuration - interaction treatment for considering the electron - hole interactions has been applied to obtain electronic excitation spectra of semiconductor gaas . the spectra thus obtained have quite well reproduced the experimental results ; the intensity and position for the excitonic peak are well reproduced at a quantitative level . we believe that the present model construction based on the downfolding offers a reliable _ ab initio _ scheme , where the downfolded effective hamiltonian is capable of not only the ground state properties but also the excitation spectra . the present result opens a way of treating excitations such as the optical spectra by the hybrid method combining the density functional approach and the accurate low - energy solver for the low - energy effective models . beyond the present application to semiconductors , it would be interesting to apply this approach to excitations in strongly correlated electron systems such as transition metal oxides including the cuprates . in the present paper , we have used the hartree - fock approximation for the ground state and the single - excitation configuration - interaction treatment for the excitations . optical excitation spectra of gaas have satisfactorily been treated by these approximations and the experimental results have been well reproduced . however , stronger electron correlation effects require more sophisticated low - energy solver than the hartree fock / single excitation configuration interaction treatment . for more different and challenging issues of the electron correlation , the low - energy effective hamiltonian may indeed be treated by much more reliable low - energy solver for electrons in solids , such as quantum monte carlo methods for lattice fermions,@xcite path - integral renormalization group method,@xcite and cluster extensions of the dynamical mean field theory.@xcite as is well known , there are many direct _ ab initio _ schemes aiming at considering correlation effects ; for example , the gw,@xcite transcorrelated , @xcite and quantum monte carlo methods.@xcite they are straightforward ways for approaching the problem compared to the present approach . however , the straightforward methods are faced with two serious problems : one is that the computational load becomes extremely heavy when all the electrons or even all the valence electrons are treated equally . the other problem is that the so far developed straightforward methods do not offer a sufficiently accurate framework if the electron correlation becomes strong such as in the genuine mott insulator . the crucial point is that we need to treat dynamical as well as spatial correlations and fluctuations near the fermi level in a controllable way . in the present stage of the computer power , such sufficient accuracies are undertaken only within simple models , which can be achieved in the low - energy effective model after downfolding . in fact , the high accuracy required from the temporal and spatial quantum fluctuations is important only in the low - energy region near the fermi level , which justifies to restrict the high - accuracy treatment only in the region of low - energy excitations and thus only within the downfolded hamiltonian . within the present computer power , this downfolding procedure opens an avenue of studying highly correlated electron systems as well as excitations without relying on _ ad hoc _ parameters . by explicitly considering the energy hierarchy in the electronic structure , the first principles calculations become tractable even when the electron correlation is essential . we would like to thank takashi miyake , atsushi yamasaki , youhei yamaji , takahiro misawa , and taichi kosugi for helpful discussions and comments . this work was supported by a grant - in - aid for scientific research in priority areas , `` development of new quantum simulators and quantum design '' ( no . 17064004 ) of the ministry of education , culture , sports , science and technology , japan . one of us ( k.n . ) acknowledges research fellowships of the japan society for the promotion of science for young scientists . all the calculations were performed on hitachi sr11000 system of the super computer center at the institute for solid state physics , the university of tokyo .

we examine whether essence and quantitative aspects of electronic excitation spectra are correctly captured by an effective low - energy model constructed from an _ ab initio _ downfolding scheme . a global electronic structure is first calculated by _ ab initio _ density - functional calculations with the generalized gradient approximation . with the help of constrained density functional theory , the low - energy effective hamiltonian for bands near the fermi level is constructed by the downfolding procedure in the basis of maximally localized wannier functions . the excited states of this low - energy effective hamiltonian ascribed to an extended hubbard model are calculated by using a low - energy solver . as the solver , we employ the hartree - fock approximation supplemented by the single - excitation configuration - interaction method considering electron - hole interactions . the present three - stage method is applied to gaas , where eight bands are retained in the effective model after the downfolding . the resulting spectra well reproduce the experimental results , indicating that our downfolding scheme offers a satisfactory framework of the electronic structure calculation , particularly for the excitations and dynamics as well as for the ground state .

we examine whether essence and quantitative aspects of electronic excitation spectra are correctly captured by an effective low - energy model constructed from an _ ab initio _ downfolding scheme . a global electronic structure is first calculated by _ ab initio _ density - functional calculations with the generalized gradient approximation . with the help of constrained density functional theory , the low - energy effective hamiltonian for bands near the fermi level is constructed by the downfolding procedure in the basis of maximally localized wannier functions . the excited states of this low - energy effective hamiltonian ascribed to an extended hubbard model are calculated by using a low - energy solver . as the solver , we employ the hartree - fock approximation supplemented by the single - excitation configuration - interaction method considering electron - hole interactions . the present three - stage method is applied to gaas , where eight bands are retained in the effective model after the downfolding . the resulting spectra well reproduce the experimental results , indicating that our downfolding scheme offers a satisfactory framework of the electronic structure calculation , particularly for the excitations and dynamics as well as for the ground state .

1304.4992

i

we analyzed the anisotropic psf of suprime - cam data utilizing the dense star field data . we decomposed the psf ellipticities into three components ( the optical aberration , atmospheric turbulence , and the chip - misalignment ) in an empirical manner , and assessed the amplitude of each component . we then tested a standard method for correcting the psf ellipticities against a mock simulation based on models of the psf ellipticities obtained from the dense star field data analysis . finally we examined the impact of the residual psf ellipticities on the cosmic shear measurement . we found that the optical aberration has the largest contribution to the psf ellipticities of long - exposure ( say , longer than 10 minutes ) data . we also found that the spatial variation of the optical psfs can be modeled by a simple three - component model , which is based on the lowest - order aberration theory described in appendix [ appendix : aberration ] . it was also found that the optical psf ellipticities vary smoothly on the focal plane , and thus are well corrected by the standard correction method in which the spatial variation is modeled by a polynomial function . the psf ellipticities after subtracting the optical psf model ellipticities show discontinuities between ccd chips , which indicates that the misalignment of chips on the focal plane induces an additional psf ellipticity . in order to make a crude estimation of the amplitude of the chip - misalignment psf ellipticities , we fitted the residual psf ellipticities to the 2nd order bi - polynomial function on a chip - by - chip basis . it turns out that the amplitude of the chip - misalignment psf ellipticities is lower than the optical component , though it is not negligible . it was found from the mock simulation that the chip - misalignment component combined with the optical component puts a lower limit on the capability of the psf correction , which can be , in principle , avoided by employing a chip - basis correction scheme . we investigated the properties of psf ellipticities resulting from the atmospheric turbulence using a numerical simulation of wave propagation through atmospheric turbulence under a typical weather condition of the subaru telescope at mauna - kea ( appendix [ appendix : atmos ] ) . from the simulation results , we evaluated the power spectrum and aperture mass variance of the atmospheric psf ellipticities , and derived power - law fitting functions of them . as was already pointed out in literature ( wittman 2005 ; de vries et al 2007 ; jee & tyson 20011 ; chang et al . 2012 ; 2013 heymans et al . 2012 ) , the rms amplitude of the atmospheric psf ellipticities decreases as @xmath100 . we computed the aperture mass variance of the dense star field data for various exposure time ( from 30-second to @xmath76-second ) . the amplitude of the atmospheric psf ellipticities was evaluated by assuming that the deepest data represents the amplitude of ( quasi-)static psf components , and the difference from that is due to the atmospheric psfs ellipticities . the results are found to be in reasonable agreement with the simulation results . therefore , we may conclude that the aperture mass variance of the atmospheric psf ellipticies for a long - exposure data ( say , longer than 10 minutes ) , is at least one order of magnitude smaller than that of the optical psf ellipticities . since the atmospheric psfs are not smoothly varying component , its correction is affected by the common limitation that the psf correction on scales smaller than the mean star separation works very poorly because of the poor sampling of the spatial variation of psfs on those scales . the above findings provide us a clue to develop an optimal psf interpolation scheme , it is found that the spatial variation of psf ellipticities consists of two components : one is a smooth and parameterizable component arising from the optical aberration and chip - misalignment ; the other is a non - smooth and stochastic component arising from the atmospheric psfs . the former can be modeled with a parametric model , as shown in this paper . also it has been argued that an interpolation scheme based on the principle - component analysis is effective for such a case ( jarvis & jain 2004 ; jee & tyson 2011 ; see also miyatake et al 2013 and lupton et al 2001 for an actual implementation for suprime - cam data reduction pipeline ) . on the other hand , it is shown in berg , et al ( 2012 ) and gentile et al . ( 2013 ) that local - type correction schemes , such like the radial basis functions and kriging work well for atmospheric psfs . apparently , a hybrid interpolation scheme , in which the above two types of interpolation schemes are optimally incorporated , is a strong candidate for achieving a better psf correction . we examined the effects of the residual psf anisotropies on suprime - cam cosmic shear data . we also compared the b - mode shear variance measured from 5.6-degree@xmath0 @xmath1-band data with the residual psf ellipticities ( but being properly transformed into shear ) measured from the dense star field data , which can be considered as the `` best performance '' of our psf ellipticity correction scheme . it is found that the shape and amplitude of the b - mode shear variance are broadly consistent with those of the residual psf ellipticities . this indicates that most of the sources of residual systematic are understood , which is an important step for cosmic shear statistics to be a practical tool of precision cosmology . however , it is also found that the b - mode shear amplitude at scales @xmath101 arcmin are systematically larger than the residual psf . the reason for this excess is unclear ; one possible reason is thestacking of dithered multiple exposures , which is not involved in the dense star field analysis . such stacking - related issues may be avoided by employing a weak - lensing shape measurement scheme on the basis of individual exposures ( e.g. , miller et al . 2007 ; 2013 ; and miyatake et al . 2013 ) , which combined with a hybrid interpolation scheme will be addressed in a future work . we thank m. takada , m. oguri and h. miyatake for useful discussions . we thank y. utsumi for help with the photometric calibration of suprime - cam data . we also thank l. van waerbeke , h. hoekstra j. d. rhodes and r. mandelbaum for valuable comments on an earlier manuscript , which improved the paper . th greatly thanks y. mellier for many fruitful discussions on various aspects of this work . we would like to thank m. britton for making the arroyo software available . numerical computations in this paper were in part carried out on the general - purpose pc farm at center for computational astrophysics , cfca , of national astronomical observatory of japan . this work is based in part on data collected at subaru telescope and obtained from the smoka , which is operated by the astronomy data center , national astronomical observatory of japan . this work is supported in part by grant - in - aid for scientific research from the jsps promotion of science ( 23540324 ) .

we examined the anisotropic point spread function ( psf ) of suprime - cam data utilizing the dense star field data . we decompose the psf ellipticities into three components , the optical aberration , atmospheric turbulence and chip - misalignment in an empirical manner , and evaluate the amplitude of each component . we then tested a standard method for correcting the psf ellipticities used in weak lensing analysis against mock simulation . we found that , for long - exposure data , the optical aberration has the largest contribution to the psf ellipticities , which could be modeled well by a simple analytic function based on the lowest - order aberration theory . the statistical properties of psf ellipticities resulting from the atmospheric turbulence are investigated by using the numerical simulation . the simulation results are in a reasonable agreement with the observed data . it follows from those findings that the spatial variation of psf ellipticities consists of two components ; one is a smooth and parameterizable component arising from the optical psf , and the other is a non - smooth and stochastic component resulting from the atmospheric psf . the former can be well corrected by the standard correction method with polynomial fitting function . however , for the later , its correction is affected by the common limitation caused by sparse sampling of psfs due to a limited number of stars . we found that the shape and amplitude of b - mode shear variance are broadly consistent with those of the residual psf ellipticities measured from the dense star field data . this indicates that most of the sources of residual systematic are understood , which is an important step for cosmic shear statistics to be a practical tool of the precision cosmology .

we examined the anisotropic point spread function ( psf ) of suprime - cam data utilizing the dense star field data . we decompose the psf ellipticities into three components , the optical aberration , atmospheric turbulence and chip - misalignment in an empirical manner , and evaluate the amplitude of each component . we then tested a standard method for correcting the psf ellipticities used in weak lensing analysis against mock simulation . we found that , for long - exposure data , the optical aberration has the largest contribution to the psf ellipticities , which could be modeled well by a simple analytic function based on the lowest - order aberration theory . the statistical properties of psf ellipticities resulting from the atmospheric turbulence are investigated by using the numerical simulation . the simulation results are in a reasonable agreement with the observed data . it follows from those findings that the spatial variation of psf ellipticities consists of two components ; one is a smooth and parameterizable component arising from the optical psf , and the other is a non - smooth and stochastic component resulting from the atmospheric psf . the former can be well corrected by the standard correction method with polynomial fitting function . however , for the later , its correction is affected by the common limitation caused by sparse sampling of psfs due to a limited number of stars . we also examine effects of the residual psf anisotropies on suprime - cam cosmic shear data ( 5.6-degree of-band data ) . we found that the shape and amplitude of b - mode shear variance are broadly consistent with those of the residual psf ellipticities measured from the dense star field data . this indicates that most of the sources of residual systematic are understood , which is an important step for cosmic shear statistics to be a practical tool of the precision cosmology .

1009.0125

i

this paper is concerned with a concrete characterization of continuous functions that are nonnegative on a closed set @xmath1 and its application for optimization purposes . by concrete we mean a systematic procedure , e.g. a numerical test that can be implemented by an algorithm , at least in some interesting cases . for polynomials , stengle s nichtnegativstellensatz @xcite provides a certificate of nonnegativity ( or absence of nonnegativity ) on a semi - algebraic set . moreover , in principle , this certificate can be obtained by solving a single semidefinite program ( although the size of this semidefinite program is far beyond the capabilities of today s computers ) . similarly , for compact basic semi - algebraic sets , schmdgen s and putinar s positivstellenstze @xcite provide certificates of strict positivity that can be obtained by solving finitely many semidefinite programs ( of increasing size ) . extensions of those certificates to some algebras of non - polynomial functions have been recently proposed in lasserre and putinar @xcite and in marshall and netzer @xcite . however , and to the best of our knowledge , there is still no hierarchy of explicit ( outer or inner ) semidefinite approximations ( with or without lifting ) of the cone of polynomials nonnegative on a closed set @xmath4 , except if @xmath4 is compact and basic semi - algebraic ( in which case outer approximations exist ) . another exception is the convex cone of quadratic forms nonnegative on @xmath8 for which inner and outer approximations are available ; see e.g. anstreicher and burer @xcite , and dr @xcite . + * contribution : * in this paper , we present a different approach based on a new ( at least to the best of our knowledge ) and simple characterization of continuous functions that are nonnegative on a closed set @xmath1 . this characterization involves a _ single _ ( but known ) measure @xmath5 with @xmath3 , and sums of squares of polynomials . namely , our contribution is twofold : \(a ) we first show that a continuous function @xmath0 is nonnegative on a closed set @xmath1 if and only if @xmath9 is nonnegative for all polynomials @xmath10 $ ] , where @xmath5 is a finite borel measure on @xmath7 is a nonnegative set function defined on the borel @xmath11-algebra of @xmath7 ( i.e. , the @xmath11-algebra generated by the open sets ) , such that @xmath12 , @xmath13 , and @xmath14 for any collection of disjoint measurable sets @xmath15 . its support ( denoted @xmath16 ) is the smallest closed set @xmath4 such that @xmath17 ; see e.g. royden @xcite . ] with @xmath3 . the measure @xmath5 is arbitrary if @xmath4 is compact . if @xmath4 is not compact then one may choose for @xmath5 the finite borel measure : - @xmath18 if @xmath0 is a polynomial , and - @xmath19 , if @xmath0 is not a polynomial , where @xmath20 is any finite borel measure with support exactly @xmath4 . but many other choices are possible . equivalently , @xmath0 is nonnegative on @xmath4 if and only if every element of the countable family @xmath21 of moment matrices associated with the signed borel measure @xmath22 , is positive semidefinite . the absence of nonnegativity on @xmath4 can be _ certified _ by exhibiting a polynomial @xmath10 $ ] such that @xmath23 , or equivalently , when some moment matrix in the family @xmath21 is not positive semidefinite . and so , interestingly , as for nonnegativity or positivity , our certificate for absence of nonnegativity is also in terms of sums of squares . when @xmath0 is a polynomial , these moment matrices are easily obtained from the moments of @xmath5 and this criterion for absence of nonnegativity complements stengle s nichtnegativstellensatz @xcite ( which provides a certificate of nonnegativity on a semi - algebraic set @xmath4 ) or schmdgen and putinar s positivstellenstze @xcite ( for certificates of strict positivity on compact basic semi - algebraic sets ) . at last but not least , we obtain a convergent _ explicit _ hierarchy of semidefinite ( outer ) approximations with _ no _ lifting , of the cone @xmath24 of nonnegative polynomials of degree at most @xmath25 . that is , we obtain a nested sequence @xmath26 such that each @xmath27 is a spectrahedron defined solely in terms of the vector of coefficients of the polynomial , with no additional variable ( i.e. , no projection is needed ) . similar explicit hierarchies can be obtained for the cone of polynomials nonnegative on a closed set @xmath4 ( neither necessarily basic semi - algebraic nor compact ) , provided that all moments of an appropriate measure @xmath5 ( with support exactly @xmath4 ) can be obtained . to the best of our knowledge , this is first result of this kind . \(b ) as a potential application , we consider the problem of computing the _ global _ minimum @xmath28 of a polynomial @xmath0 on a closed set @xmath4 , a notoriously difficult problem . in nonlinear programming , a sequence of upper bounds on @xmath28 is usually obtained from a sequence of feasible points @xmath29 , e.g. , via some ( local ) minimization algorithm . but it is important to emphasize that for non convex problems , providing a sequence of upper bounds @xmath30 , @xmath31 , that converges to @xmath28 is in general impossible , unless one computes points on a grid whose mesh size tends to zero . we consider the case where @xmath1 is a closed set for which one may compute all moments of a measure @xmath5 with @xmath3 . typical examples of such sets are e.g. @xmath32 or @xmath8 in the non compact case and a box , a ball , an ellipsoid , a simplex , or the vertices of an hypercube ( or hyper rectangle ) in the compact case . we then provide a hierarchy of semidefinite programs ( with only one variable ! ) whose optimal values form a monotone nonincreasing sequence of _ upper _ bounds which converges to the global minimum @xmath28 . in fact , each semidefinite program is a very specific one as it reduces to solving a _ generalized eigenvalue _ problem for a pair of real symmetric matrices .. ( therefore , for efficiency one may use specialized software packages instead of a sdp solver . ) however , the convergence to @xmath28 is in general only asymptotic and not finite ( except when @xmath4 is a discrete set in which case finite convergence takes place ) . this is in contrast with the hierarchy of semidefinite relaxations defined in lasserre @xcite which provide a nondecreasing sequence of _ lower _ bounds that also converges to @xmath28 , and very often in finitely many steps . hence , for compact basic semi - algebraic sets these two convergent hierarchies of upper and lower bounds complement each other and permit to locate the global minimum @xmath28 in smaller and smaller intervals . notice that convergence of the hierarchy of convex relaxations in @xcite is guaranteed only for compact basic semi - algebraic sets , whereas for the new hierarchy of upper bounds , the only requirement on @xmath4 is to know all moments of a measure @xmath5 with @xmath3 . on the other hand , in general computing such moments is possible only for relatively simple ( but not necessarily compact nor semi - algebraic ) sets . at last but not least , the nonincreasing sequence of upper bounds converges to @xmath28 even if @xmath28 is not attained , which when @xmath32 , could provide an alternative and/or a complement to the hierarchy of convex relaxations provided in schweighofer @xcite ( based on gradient tentacles ) and in h and pham @xcite ( based on the truncated tangency variety ) , which both provide again a monotone sequence of lower bounds . finally , we also give a very simple interpretation of the hierarchy of dual semidefinite programs , which provides some information on the location of global minimizers .

we first show that a continuous function is nonnegative on a closed set if and only if ( countably many ) moment matrices of some signed measure with , are all positive semidefinite ( if is compact is an arbitrary finite borel measure with ) . in particular , we obtain a convergent explicit hierarchy of semidefinite ( outer ) approximations with _ no _ lifting , of the cone of nonnegative polynomials of degree at most .

we first show that a continuous function is nonnegative on a closed set if and only if ( countably many ) moment matrices of some signed measure with , are all positive semidefinite ( if is compact is an arbitrary finite borel measure with ) . in particular , we obtain a convergent explicit hierarchy of semidefinite ( outer ) approximations with _ no _ lifting , of the cone of nonnegative polynomials of degree at most . wen used in polynomial optimization on certain simple closed sets ( like e.g. , the whole space , the positive orthant , a box , a simplex , or the vertices of the hypercube ) , it provides a nonincreasing sequence of upper bounds which converges to the global minimum by solving a hierarchy of semidefinite programs with only one variable ( in fact , a generalized eigenvalue problem ) . in the compact case , this convergent sequence of upper bounds complements the convergent sequence of lower bounds obtained by solving a hierarchy of semidefinite relaxations as in e.g. . [ section ] [ thm]corollary [ thm]lemma [ thm]proposition [ thm]definition [ thm]assumption [ thm]remark c v u !

1009.0125

c

in this paper we have presented a new characterization of nonnegativity on a closed set @xmath4 which is based on the knowledge of a single finite borel measure @xmath5 with @xmath3 . it permits to obtain a hierarchy of spectrahedra which provides a nested sequence of outer approximations of the convex cone of polynomials of degree at most @xmath6 , nonnegative on @xmath4 . when used in polynomial optimization for certain simple sets " @xmath4 , one obtains a hierarchy of semidefinite approximations ( with only one variable ) which provides a nonincreasing sequence of upper bounds converging to the global optimum , hence a complement to the sequence of upper bounds provided by the hierarchy of semidefinite relaxations defined in e.g. @xcite when @xmath4 is compact and basic semi - algebraic . a topic of further investigation is to analyze the efficiency of such an approach on a sample of optimization problems on simple closed sets like the whole space @xmath7 , the positive orthant @xmath175 , a box , a simplex , or an ellipsoid , as well as for some inverse problems from moments .

wen used in polynomial optimization on certain simple closed sets ( like e.g. , the whole space , the positive orthant , a box , a simplex , or the vertices of the hypercube ) , it provides a nonincreasing sequence of upper bounds which converges to the global minimum by solving a hierarchy of semidefinite programs with only one variable ( in fact , a generalized eigenvalue problem ) . in the compact case , this convergent sequence of upper bounds complements the convergent sequence of lower bounds obtained by solving a hierarchy of semidefinite relaxations as in e.g. .

we first show that a continuous function is nonnegative on a closed set if and only if ( countably many ) moment matrices of some signed measure with , are all positive semidefinite ( if is compact is an arbitrary finite borel measure with ) . in particular , we obtain a convergent explicit hierarchy of semidefinite ( outer ) approximations with _ no _ lifting , of the cone of nonnegative polynomials of degree at most . wen used in polynomial optimization on certain simple closed sets ( like e.g. , the whole space , the positive orthant , a box , a simplex , or the vertices of the hypercube ) , it provides a nonincreasing sequence of upper bounds which converges to the global minimum by solving a hierarchy of semidefinite programs with only one variable ( in fact , a generalized eigenvalue problem ) . in the compact case , this convergent sequence of upper bounds complements the convergent sequence of lower bounds obtained by solving a hierarchy of semidefinite relaxations as in e.g. . [ section ] [ thm]corollary [ thm]lemma [ thm]proposition [ thm]definition [ thm]assumption [ thm]remark c v u !

1203.6127

i

we consider the list decoding of one - point algebraic geometry ( ag ) codes . @xcite proposed the well - known list decoding algorithm for one - point ag codes , which consists of the interpolation step and the factorization step . the interpolation step has large computational complexity and many researchers have proposed faster interpolation steps , see ( * ? ? ? * figure 1 ) . by modifying the unique decoding algorithm @xcite for primal one - point ag codes , we propose another list decoding algorithm based on voting in grbner bases whose error correcting capability is higher than @xcite and whose computational complexity is smaller than @xcite in many cases . a decoding algorithm for primal one - point ag codes was proposed in @xcite , which was a straightforward adaptation of the original feng - rao majority voting for the dual ag codes @xcite to the primal ones . the feng - rao majority voting in @xcite for one - point primal codes was generalized to multi - point primal codes in ( * ? ? ? * section 2.5 ) . the one - point primal codes can also be decoded as multi - point dual codes with majority voting @xcite , whose faster version was proposed in @xcite for the multi - point hermitian codes . @xcite proposed another unique decoding ( not list decoding ) algorithm for primal codes based on the majority voting inside grbner bases . the module used by them @xcite is a curve theoretic generalization of one used for reed - solomon codes in @xcite that is a special case of the module used in @xcite . an interesting feature in @xcite is that it did not use differentials and residues on curves for its majority voting , while they were used in @xcite . the above studies @xcite dealt with the primal codes . we recently proved in @xcite that the error - correcting capabilities of @xcite are the same . the earlier papers @xcite suggest that central observations in @xcite were known to the dutch group , which is actually the case @xcite . @xcite , @xcite and @xcite studied the error - correcting capability of the feng - rao @xcite or the bms algorithm @xcite with majority voting beyond half the designed distance that are applicable to the dual one - point codes . there was room for improvements in the original result @xcite , namely , ( a ) they have not clarified the relation between its error - correcting capability and existing minimum distance lower bounds except for the one - point hermitian codes , ( b ) they have not analyzed the computational complexity , ( c ) they assumed that the maximum pole order used for code construction is less than the code length , and ( d ) they have not shown how to use the method with the feng - rao improved code construction @xcite . we shall ( 1 ) prove that the error - correcting capability of the original proposal is always equal to half of the bound in @xcite for the minimum distance of one - point primal codes ( proposition [ prop : ag ] ) , ( 2 ) generalize their algorithm to work with any one - point ag codes , ( 3 ) modify their algorithm to a list decoding algorithm , ( 4 ) remove the assumptions ( c ) and ( d ) above , ( 5 ) remove unnecessary computational steps from the original proposal , ( 6 ) analyze the computational complexity in terms of the number of multiplications and divisions in the finite field . the proposed algorithm is implemented on the singular computer algebra system @xcite , and we verified that the proposed algorithm can correct more errors than @xcite with manageable computational complexity . this paper is organized as follows : section [ sec2 ] introduces notations and relevant facts . section [ sec3 ] improves @xcite in various ways , and the differences to the original @xcite are summarized in section [ sec : diff ] . section [ sec4 ] shows that the proposed modification to @xcite works as claimed . section [ sec : experiment ] compares its computational complexity with the conventional methods . section [ sec6 ] concludes the paper . part of this paper was presented at 2012 ieee international symposium on information theory , cambridge , ma , usa , july 2012 @xcite .

we also extend their unique decoding algorithm to list decoding , modify it so that it can be used with the feng - rao improved code construction , prove equality between its error correcting capability and half the minimum distance lower bound by that has not been done in the original proposal except for one - point hermitian codes , remove the unnecessary computational steps so that it can run faster , and analyze its computational complexity in terms of multiplications and divisions in the finite field . as a unique decoding algorithm , + * keywords : * algebraic geometry code , grbner basis , list decoding + * msc 2010 : * primary : 94b35 ; secondary : 13p10 , 94b27 , 14g50

we generalize the unique decoding algorithm for one - point ag codes over the miura - kamiya curves proposed by to general one - point ag codes , without any assumption . we also extend their unique decoding algorithm to list decoding , modify it so that it can be used with the feng - rao improved code construction , prove equality between its error correcting capability and half the minimum distance lower bound by that has not been done in the original proposal except for one - point hermitian codes , remove the unnecessary computational steps so that it can run faster , and analyze its computational complexity in terms of multiplications and divisions in the finite field . as a unique decoding algorithm , the proposed one is as fast as the bms algorithm for one - point hermitian codes , and as a list decoding algorithm it is much faster than the algorithm by . + * keywords : * algebraic geometry code , grbner basis , list decoding + * msc 2010 : * primary : 94b35 ; secondary : 13p10 , 94b27 , 14g50

1203.6127

c

in this paper , we modified the unique decoding algorithm for plane ag codes in @xcite so that it can support one - point ag codes on _ any _ curve , and so that it can do the list decoding . the error correction capability of the original @xcite and our modified algorithms are also expressed in terms of the minimum distance lower bound in @xcite . we also proposed procedures to compute products and quotients in coordinate ring of affine algebraic curves , and by using those procedures we demonstrated that the modified decoding algorithm can be executed quickly . specifically , its computational complexity is comparable to the bms algorithm @xcite for one - point hermitian codes , and much faster than the standard list decoding algorithms @xcite for several cases . the original decoding algorithm @xcite allows parallel implementation on circuits like the ktter architecture @xcite . our modified algorithm retains this advantage . moreover , if one can afford large circuit size , the proposed list decoding algorithm can be executed as quickly as the unique decoding algorithm by parallel implementation on a circuit .

we generalize the unique decoding algorithm for one - point ag codes over the miura - kamiya curves proposed by to general one - point ag codes , without any assumption . the proposed one is as fast as the bms algorithm for one - point hermitian codes , and as a list decoding algorithm it is much faster than the algorithm by .

we generalize the unique decoding algorithm for one - point ag codes over the miura - kamiya curves proposed by to general one - point ag codes , without any assumption . we also extend their unique decoding algorithm to list decoding , modify it so that it can be used with the feng - rao improved code construction , prove equality between its error correcting capability and half the minimum distance lower bound by that has not been done in the original proposal except for one - point hermitian codes , remove the unnecessary computational steps so that it can run faster , and analyze its computational complexity in terms of multiplications and divisions in the finite field . as a unique decoding algorithm , the proposed one is as fast as the bms algorithm for one - point hermitian codes , and as a list decoding algorithm it is much faster than the algorithm by . + * keywords : * algebraic geometry code , grbner basis , list decoding + * msc 2010 : * primary : 94b35 ; secondary : 13p10 , 94b27 , 14g50

math0602195

i

let @xmath2 be a graph on @xmath3 $ ] ; unless otherwise stated , we allow multiple edges and isolated vertices , but no loops . two edges @xmath4 and @xmath5 are a _ crossing _ if @xmath6 and they are a _ nesting _ if @xmath7 . if we draw the vertices of @xmath2 on a line and represent the corresponding edges by arcs above the line , crossings and nestings have the obvious geometric meaning . a graph without crossings ( respectively , nestings ) is called _ noncrossing _ ( resp . , _ nonnesting _ ) . klazar @xcite proves the equality between the numbers of noncrossing and nonnesting simple graphs , counted by order , and also between the numbers of noncrossing and nonnesting graphs without isolated vertices , counted by size . the purpose of this paper is to study analogous results for sets of @xmath0 pairwise crossing and @xmath0 pairwise nested edges . a _ @xmath0-crossing _ is a set of @xmath0 edges every two of them being a crossing , that is , edges @xmath8 @xmath9 such that @xmath10 . @xmath0-nesting _ is a set of @xmath0 edges pairwise nested , that is , @xmath8 @xmath9 such that @xmath11 . a graph with no @xmath0-crossing is called _ @xmath0-noncrossing _ and a graph with no @xmath0-nesting is called _ @xmath0-nonnesting_. the largest @xmath0 for which a graph @xmath2 has a @xmath0-crossing ( respectively , a @xmath0-nesting ) is denoted @xmath12 ( resp . , @xmath13 ) . the aim of this paper is to show that the number of @xmath0-noncrossing graphs equals the number of @xmath0-nonnesting graphs , counted by order , size , and degree sequences . this problem was originally posed by martin klazar and we learned of it at the homonolo 2005 workshop @xcite ; the case where the number of vertices of the graph is @xmath14 was proved by a. pr ( unpublished ) . our main result ( theorem [ thm : kcrossknest ] ) states that the numbers of @xmath0-noncrossing and @xmath0-nonnesting graphs with a given degree sequence are the same . chen et al . @xcite prove the equality of the numbers of @xmath0-noncrossing and @xmath0-nonnesting graphs for two subclasses of graphs , namely for perfect matchings and for partition graphs , also counted by degree sequences ( under a different but equivalent terminology ) . a perfect matching is a graph where each vertex has degree one , and a partition graph is a graph that is a disjoint union of monotone paths , that is , where each vertex has at most one edge to its right and at most one to its left . the latter correspond in a natural way to set partitions , hence the result can be stated in terms of these . the paper @xcite also contains other identities and enumerative results on @xmath0-noncrossing and @xmath0-nonnesting matchings and partitions . krattenthaler @xcite deduces most of these from his more general results on fillings of ferrers diagrams . in this paper we also use fillings of diagrams to prove results about graphs . the difference is that whereas in @xcite , and also in @xcite , the results about graphs follow from general theorems by restricting the shape of the diagram , here we show that the results about graphs are in fact equivalent to those about fillings with arbitrary shapes . the main idea is to encode graphs by fillings of ferrers diagrams in such a way that @xmath0-crossings and @xmath0-nestings are easy to recognize . a @xmath0-noncrossing ( @xmath0-nonnesting ) graph becomes a filling of a diagram that avoids the identity ( antiidentity ) matrix of order @xmath0 , and the degree sequence of the graph can be recovered from the shape of the diagram and the row and column sums of the filling . then proving that there are as many @xmath0-noncrossing as @xmath0-nonnesting graphs is equivalent to showing that the numbers of fillings avoiding these two matrices are the same . this idea generalizes easily to other subgraphs in addition to crossing and nestings , and allows us to show that the study of fillings of ferrers diagrams with forbidden configurations is equivalent to the study of graphs avoiding certain subgraphs , in the sense defined in section [ sec : degree ] . the structure of the paper is as follows . in section [ sec : general ] we show that the equality of the numbers of @xmath0-noncrossing and @xmath0-nonnesting graphs counted by size and order is already in the literature , although not explicitly stated in this form . we introduce some notation on pattern avoiding fillings of ferrers diagrams and we rephrase results of krattenthaler @xcite and jonsson and welker @xcite in terms of @xmath0-noncrossing and @xmath0-nonnesting graphs . section [ sec : degree ] introduces a new correspondence between graphs and fillings of diagrams that keeps track of degree sequences . then we discuss why , from the perspective of pattern avoiding , graphs and fillings of diagrams are equivalent objects . in particular , showing that the number of @xmath0-noncrossing graphs with a fixed degree sequence equals the number of such @xmath0-nonnesting graphs is equivalent to proving a result on fillings of diagrams with restrictions on the row and column sums . our proof is an adaptation of the one in @xcite to allow arbitrary entries in the filling , and this is the content of section [ sec : proof ] . we conclude with some remarks and open questions .

we give a correspondence between graphs with a given degree sequence and fillings of ferrers diagrams by nonnegative integers with prescribed row and column sums . in this setting ,-crossings and-nestings of the graph become occurrences of the identity and the antiidentity matrices in the filling . we use this to show the equality of the numbers of-noncrossing and-nonnesting graphs with a given degree sequence . this generalizes the analogous result for matchings and partition graphs of chen , deng , du , stanley , and yan , and extends results of klazar to .

we give a correspondence between graphs with a given degree sequence and fillings of ferrers diagrams by nonnegative integers with prescribed row and column sums . in this setting ,-crossings and-nestings of the graph become occurrences of the identity and the antiidentity matrices in the filling . we use this to show the equality of the numbers of-noncrossing and-nonnesting graphs with a given degree sequence . this generalizes the analogous result for matchings and partition graphs of chen , deng , du , stanley , and yan , and extends results of klazar to . moreover , this correspondence reinforces the links recently discovered by krattenthaler between fillings of diagrams and the results of chen et al .

astro-ph0604144

i

astrophysical and laboratory plasmas which are not in ( local ) thermodynamic equilibrium require a detailed modelling of their atomic and , sometimes , molecular reactions so as to determine the level populations and ionization balance of their constituents . these in turn are basic ingredients for the physical and spectral diagnostic modelling of stellar coronae , gaseous nebulae , supernova remnants , fusion plasmas , etc . at low particle densities , e.g. the ` coronal approximation ' , ionization balance is between total groundstate dielectronic - plus - radiative recombination and groundstate ionization by electrons and/or photons , while level populations are determined by collisional excitation from the groundstate and radiation to all possible lower states . as the particle density increases , a separation between the two is no longer possible and level populations , effective recombination & ionization rate coefficients and ionization balance are determined by solving the collisional radiative population rate equations @xcite . furthermore , even at the low densities found in gaseous nebulae , for example , the populations of ions of c , n , o which have fine - structure levels in their ground term are not concentrated in the ground level . recombination from excited levels within the ground term is quite different ( smaller ) compared to that for the ground level , due to the presence of additional autoionization pathways . furthermore , transient plasmas such as solar flares do not have time to establish quasi - static equilibrium with the ground level and so require metastable levels ( and the excited - state populations built upon them ) to be treated on an equal footing as the ground level when it comes to collisional radiative modelling @xcite . however , historically , total ( zero - density ) ground state recombination rate coefficients have dominated the literature see , for example , those used by @xcite . a systematic attempt to move beyond this picture has been described by @xcite , who focussed on dielectronic recombination but much of the discussion there is applicable to radiative recombination deliberately so . now , using autostructure @xcite , we have calculated partial final - state resolved radiative recombination ( rr ) rate coefficients from the initial ground and metastable levels of all elements up to and including zn , plus kr , mo and xe , for all isoelectronic sequences up to na - like forming mg - like . the data are archived according to the atomic data and analysis structure ( adas ) data class _ adf48 _ @xcite . fits to total rr rate coefficients have been determined , for both the ground and metastable levels , and those for the ground are presented here . all of the data are available online @xcite , along with corresponding data for dr @xcite . previous work on rr has been summarized by @xcite . since then , @xcite has presented rr rate coefficients obtained using his flexible atomic code fac for mg , si , s , ar , ca , fe , and ni , for all isoelectronic sequences through to f - like forming ne - like . the time reversed process of rr ( plus dr ) is photoionization ( pi ) , indeed , our rr is determined from our direct photoionization cross sections on using the principle of detailed balance . we make comparison of our groundstate - to - groundstate photoionization cross sections of neutral atoms with those obtained from various @xmath2-matrix calculations , by others , as the most severe test of our results . similar @xmath2-matrix data has been used by nahar and co - workers ( e.g. , * ? ? ? * ) to form total ( dr+rr ) rate coefficients , and we make a comparison with it by combining our rr data with complementary dr data @xcite . the remainder of the paper is organized as follows : in section 2 we describe our methodology , in section 3 we present our results and make comparisons with the results of earlier works , and then make some concluding remarks .

we have calculated partial final - state resolved radiative recombination ( rr ) rate coefficients from the initial ground and metastable levels of all elements up to and including zn , plus kr , mo , and xe , for all isoelectronic sequences up to na - like forming mg - like . the data are archived according to the atomic data and analysis structure ( adas ) data class _ adf48 _ , which spans a temperature range of k , where is the initial ion charge . fits to total rate coefficients have been determined , for both the ground and metastable levels , and those for the ground are presented here . comparison is made both with previous rr rate coefficients and with ( background )-matrix photoionization cross sections .

we have calculated partial final - state resolved radiative recombination ( rr ) rate coefficients from the initial ground and metastable levels of all elements up to and including zn , plus kr , mo , and xe , for all isoelectronic sequences up to na - like forming mg - like . the data are archived according to the atomic data and analysis structure ( adas ) data class _ adf48 _ , which spans a temperature range of k , where is the initial ion charge . fits to total rate coefficients have been determined , for both the ground and metastable levels , and those for the ground are presented here . comparison is made both with previous rr rate coefficients and with ( background )-matrix photoionization cross sections . this rr database complements a dr database already produced and both are being used to produce updated ionization balances for both ( electron ) collisionally ionized and photoionized plasmas .

1108.4214

i

when performing molecular dynamics simulations , we distinguish between bonded and non - bonded interactions.@xcite effectively , this means that the interactions have been coarse - grained on the energy scale of the simulation . certain degrees of freedom are frozen , and we describe them as being permanent bonded . other degrees of freedom remain dynamic , and we describe them with relatively weak non - bonded interactions . however , this situation is less clear when simulating systems undergoing chemical reactions where bonds are created or broken . another example is dna molecules where hybridization bonds are broken at high temperatures and reformed when cooling the system . for such systems , it can be computationally more efficient to model these degrees of freedom as being dynamically bonded . the problem of bond dynamics is closely related to the question of how to represent chemical reactions in a molecular dynamics simulation . reactive force fields such as reaxff and empirical valence bond ( evb ) can be used to model chemical reactions.@xcite bond order potentials are interesting since they allow three body interactions in the neighborhood of a bond to modify the strength of the bond.@xcite when coarse - graining systems capable of chemical reactions , it is important to note that the reaction radius and probability also has to be appropriately coarse - grained.@xcite when the bonds become dynamic , this also induces a dynamic for the angular and dihedral interactions . when breaking a bond , all angular and dihedral interactions involving that bond become invalid , and should be removed . similarly , when creating a bond , we have to identify which angular and dihedral interactions to create in the bond neighborhood . this ensures that after melting and renaturing of a system , it is again governed by the same set of interactions and return to the same equilibrium structure . dna molecules are comprised of the four bases adenine ( a ) , cytosine ( c ) , guanine ( g ) , and thymine ( t ) . the bases are attached to a 2-deoxyribose sugar ring . for naturally occurring dna , sugar rings are linked to each other through phosphodiester bonds , that connect the 3 to 5 carbons in consecutive sugar rings . this builds a molecular directionality into the back bone of a dna strand , which will have a 3 and a 5 end . the strand is also characterized by a specific sequence of bases . together the phosphate backbone , the sugar and the base is denoted a nucleotide , which is the repeat unit of a single dna strand . a - t and c - g are watson - crick pairs and can form hydrogen bonds with each other . the energetically favorable stacking interactions allow two complementary single strands to form 3-5/ 5-3 anti - parallel aligned double strands . double stranded dna can be melted and renatured by repeated cycling the temperature around the melting point or by varying solvent conditions . dna is a very complex molecule and numerous models exists to describe behavior from atomistic properties to mesoscopic mechanical properties . the molecular structural details of short dna oligomers can be studied with atomistic molecular dynamics simulations such as amber@xcite and charmm@xcite . however , when we want to understand the large scale properties of dna molecules or materials in which dna molecules are a component , coarse - grained dna models are essential . coarse - graining is the statistical mechanical process by which uninteresting microscopic details are systematically removed , leaving a coarse - grained , effective model that is described by an effective free energy functional.@xcite a major advantage of coarse - grain models are that we can use them to simulate the interesting large scale dynamics of a system directly without wasting time on uninteresting details . this allows larger systems to be studied for longer times which paves the way for studying e.g. the properties materials rather than single molecules . a number of coarse - grain dna molecular dynamics models exists . in the `` three site per nucleotide '' model of de pablo and co - workers , a single nucleotide is represented by a phosphate backbone site , a sugar group site , and a base site , respectively@xcite . the model uses an implicit representation of counter ions at the level of debye - hckel theory , but has recently been generalized to explicit counter ions.@xcite a version of this model has also been generalized to include non - watson - crick base pairing such as hoogsteen pairing.@xcite there is also a number of `` two site per nucleotide '' models where one site represents the back bone and the sugar ring . the other site represents the base.@xcite one challenge to `` one site per nucleotide '' models are to represent the dna double helix . savelyev and papoian@xcite does this by special `` fan '' shaped pair - interactions between a bead and a large number of beads on the opposite strand . this model does not allow for dna melting . trovato and tozzini@xcite produce a helical structure using angular and dihedral interactions along the double strand . in the case where the large scale dna mechanical properties are of interest , it can be advantageous to coarse - grain a whole base - pair to a single rigid ellipsoidal or plate - shaped object and regard dna as a latter - like chain of such objects.@xcite here the coarse - graining has eliminated the melting and renaturation dynamics all together . other types of coarse - grain dna models are applied to study behavior of dna functionalized nano - particles . the dna molecules can e.g. be modeled as rigid rods with a single sticky site on one end and tethered to the surface of the nano - structure by the other end@xcite , as semi - flexible polymers with attractive sites on the monomers@xcite , or the whole dna molecule can be modeled as a single sticky site that can be hybridized to complementary free sticky sites.@xcite here the coarse - graining has completely eliminated the chemical structure , while the melting , renaturing , and sequence specificity has been retained in the dynamics . the two most prevalent statistical mechanical models of rna and dna melting are the poland - scheraga@xcite ( ps ) and the dauxois - peyrard - bishop@xcite ( dpb ) models . the poland - scheraga model describes dna as a 1d lattice model where a base - pair can either be hybridized or open . the free energy expression for the ps model contains empirical stacking free energies each stack of hybridized base - pairs as well as contributions from the strand configuration entropy due to internal bubbles , frayed ends and empirical initiation terms . the dpb model also describes dna as a 1d lattice model , but where each base - pair is characterized by a continuous base - pair distance . contrary to the ps model , the dpb model has a hamiltonian where the base - base potential is described by an anharmonic potential representing hydrogen bonding , and deviations between nearest neighbor base - pair extensions are penalized by a harmonic term . a generalization of the ps model exists , where the strand conformations are represented explicitly as lattice polymers . this provides a conceptual simplification since the conformational entropy of bubbles and frayed ends emerges naturally from the polymer model . this real space lattice ps model has been studied using exact enumeration techniques@xcite , a version of the model has also been applied to study rna folding using monte carlo simulations.@xcite the dynamic bonding framework allows us to study classes of dna models where hybridization bonds , angular bonds , and dihedral bonds are created and broken dynamically . these dynamic bonding dna models are intermediates between the real space lattice ps models , the coarse - grained molecular dynamics models , and the sticky dna models described above . in the ps model , base pairs can either be hybridized or open and are characterized by a corresponding free energy . in a dynamic bonding model , base pairs will be either hybridized or open and a free energy will also characterize this transition . in the coarse - grained molecular dynamics models and the dpb model , base pairs are represented by a continuous non - bonded pair - potential . in the dynamic bonding dna models , base pairs are characterized by a continuous bond potential . the dynamic bond dna models can also be regarded as being off - lattice generalizations of the real space lattice ps model , where a single strand is described as a semi - flexible bead - spring polymer where complementary monomers will form hybridization bonds when they are close . the dynamic bonded dna models are `` one site per nucleotide '' models , but we can also lump sequence of nucleotides into a single coarse - grained bead . in this case , we can as a first approximation assume that only beads representing complementary sequences can hybridize , and that the breaking of a hybridization bond corresponds to the creation of a dna bubble . this would be a `` many nucleotides per site '' dynamic bonding dna model more akin to the sticky site dna models used to study dna functionalized nano - particles . the dynamic bonded dna models ensure anti - parallel strand alignment in the double strand state , through the interplay between the dihedral interactions and the directional bonds . such degrees of freedom are absent from both the ps and dpb 1d lattice models . the coarse - grained models use angular and dihedral interactions to ensure a structure resembling the real chemical structure of dna molecules . in dynamic bonded dna models , the angular and dihedral interactions are dynamically introduced when hybridization bonds are formed to promote a zipper - like closing dynamic . similarly angular and dihedral interactions are dynamically removed as hybridization bonds are broken to promote zipper - like opening dynamic . hence in dynamic bond dna model , we utilize the interplay between dynamic bonded , angular , and dihedral interactions to model cooperative effects in the dna bubble and zippering dynamics , rather than to model chemical structure . the simplicity and success of the ps model in predicting sequence specific dna melting temperatures suggests that the essential physics of dna hybridization , melting and renaturing can , in fact , be accurately captured in a model without chemical details , and where the key property is the dynamics of hybridization . this is our motivation for developing the dynamic bonding framework . we will use it to develop and apply models to study the properties of hybrid materials containing both dna molecules and soft - condensed matter . we have implemented directional bonds and dynamic bonding in the large - scale atomic / molecular massively parallel simulator@xcite ( lammps ) . lammps is a versatile , parallel , highly optimized , open source code for performing molecular dynamics ( md ) and dissipative particle dynamics ( dpd ) simulations of coarse - grained models . due to the modular design , lammps is easy to extend with new interactions and functionality . the dynamic bonding implementation is also modular and easy to extend with new functionality . our extension is by no means limited to modeling dna , but could equally well be used for simulations of chemical reactions such as living polymerization , cross - linking of stiff polymers , coarse - grained dynamics of worm - like micelles and active driven materials . a snapshot of the lammps code with the directional bonds and dynamic bonding implementation can be obtained from the cpc program library . included with the code is also the documentation necessary for porting the directional and dynamic bonding framework to future lammps versions . [ sec : implementation1 ] is a summary of the implementation of directional bonds and the dynamic bonding framework . we present a simplified dna model based on the dynamic bonding framework in sect . [ sec : dna - model ] , which is provides the examples of dna dynamics shown in sect . [ sec : illustrations ] . we conclude with our conclusions in sect . [ sec : conclusions ] , and present the details of the directional bonds and dynamic bonding implementation in an appendix .

bond formation can be controlled to limit the maximal functionality of a bead with respect to various bond types . concomitant with the bond dynamics , angular and dihedral interactions are dynamically introduced between newly connected triplets and quartets of beads , where the interaction type is determined from the local pattern of bead and bond types . when breaking bonds , all angular and dihedral interactions involving broken bonds are removed . the framework allows chemical reactions to be modeled , and use it to simulate a simplistic , coarse - grained dna model .

we have extended the large - scale atomic / molecular massively parallel simulator ( lammps ) to support directional bonds and dynamic bonding . the framework supports stochastic formation of new bonds , breakage of existing bonds , and conversion between bond types . bond formation can be controlled to limit the maximal functionality of a bead with respect to various bond types . concomitant with the bond dynamics , angular and dihedral interactions are dynamically introduced between newly connected triplets and quartets of beads , where the interaction type is determined from the local pattern of bead and bond types . when breaking bonds , all angular and dihedral interactions involving broken bonds are removed . the framework allows chemical reactions to be modeled , and use it to simulate a simplistic , coarse - grained dna model . the resulting dna dynamics illustrate the power of the present framework . dynamic directional bonds , coarse - grain dna models , chemical reactions , molecular and dissipative particle dynamics

1509.03849

i

investigations of two - dimensional systems ( 2dss ) on si surfaces began with metal - oxide - semiconductor field - effect transistors ( mosfets ) @xcite . however , the amorphous sio@xmath10/si interface severely limits the quality of the 2dss . the development @xcite of hydrogen - terminated silicon ( 111 ) [ h - si(111 ) ] vacuum field effect transistors ( fets ) is based on a simple but extraordinary fact : a wet chemical treatment of a si(111 ) surface with an ammonium fluoride ( nh@xmath11f ) solution can produce an ideal h - passivated si surface , which is both atomically flat and possesses a very low surface state density ( @xmath12 @xmath2 ) @xcite , leading to much higher carrier mobilities . in recent years , both a high quality two - dimensional electron system ( 2des ) with electron mobility of 325,000 @xmath13/vs @xcite and a high quality two - dimensional hole system ( 2dhs ) with hole mobility of 10,000 @xmath13/vs @xcite have been realized in this system . they are comparable to the best si / sige heterostructures @xcite , which are limited to the ( 100 ) oriented surfaces because of much higher threading dislocation densities on the other surface orientations @xcite . in this work we have fabricated ambipolar hexagonal devices , which can switch between a 2des and a 2dhs in the same device by changing a gate voltage . compared to other ambipolar devices @xcite , the 2des on the si(111 ) surface has a sixfold valley degeneracy , while the valley degeneracy of holes is one . the ambipolar devices provide a direct comparison between electrons and holes with very different valley degeneracies in the same conduction channel , which allows a new perspective to the fundamental research , such as the properties of 2d metals @xcite . in addition , the hexagonal devices enable the exploration of the sixfold valley - degenerate electron system . in the h - si(111 ) vacuum fet device , a global si / sio@xmath10 gate piece is used to induce a 2ds , which is further confined into a well - defined 2d region by pn junction isolation and trench isolation . similarly , future nanoelectronic devices , like quantum point contacts ( qpcs ) and quantum dots ( qds ) , may be realized on the si(111 ) surfaces using the in - plane depleting gates based on pn junctions . moreover , because of the sixfold valley degeneracy of the 2des , the valley degree of freedom can provide extra resources for practical applications in the same way as spintronic devices utilize the spin degree of freedom . this will open up new opportunities for another class of devices valleytronic devices @xcite . the remainder of this paper is organized as follows . in sec . [ sec : fab ] , we describe the device structure and operation principles , followed by detailed fabrication processes . in sec . [ sec : characterization ] , we characterize the devices to make sure that they work as intended , including surface topography measurement , a gate leakage check , pn junction isolation and leakage tests , and contact resistance measurements . in sec . [ sec : transport ] , we discuss the transport measurement results on these devices . we determined the 2d carrier mobilities in the experimentally accessible range of densities , which show that electron and hole mobilities are very different . magnetotransport measurements show rich phenomena , including shubnikov - de haas ( sdh ) oscillations , integer quantum hall effect ( iqhe ) , fractional quantum hall effects ( fqhe ) and large anisotropy in three magnetoresistance measurements at @xmath9 . in sec . [ sec : degradation ] , we discuss the device degradation with time and with exposure to ambient air , including the mobility deterioration and the increase of contact resistance . we conclude in sec . [ sec : conclusion ] with a discussion of further improvements and future directions .

we have fabricated ambipolar transistors on chemically prepared hydrogen - terminated si(111 ) surfaces , in which a two - dimensional electron system ( 2des ) or a two - dimensional hole system ( 2dhs ) can be populated in the same conduction channel by changing the gate voltage of a global gate applied through a vacuum gap . depending on the gate bias , ion implanted n and p regions function either as ohmic contacts or as in - plane gates , which laterally confine the carriers induced by the global gate . on one device , electron and hole densities of up to and respectively are obtained .

we have fabricated ambipolar transistors on chemically prepared hydrogen - terminated si(111 ) surfaces , in which a two - dimensional electron system ( 2des ) or a two - dimensional hole system ( 2dhs ) can be populated in the same conduction channel by changing the gate voltage of a global gate applied through a vacuum gap . depending on the gate bias , ion implanted n and p regions function either as ohmic contacts or as in - plane gates , which laterally confine the carriers induced by the global gate . on one device , electron and hole densities of up to and respectively are obtained . the peak electron mobility is/vs , and the peak hole mobility is/vs at 300 mk ; the ratio of about 20 is mainly due to the very different valley degeneracies ( 6:1 ) of electrons and holes on the si(111 ) surface . on another device , the peak electron mobility of/vs is reached at 300 mk . these devices are hexagonal in order to investigate the underlying symmetry of the 2dess , which have a sixfold valley degeneracy at zero magnetic field . three magnetoresistance measurements with threefold rotational symmetry are used to determine the symmetry of the 2dess at different magnetic field . at filling factor , the observed anisotropy can be explained by a single valley pair occupancy of composite fermions ( cfs ) . qualitatively the cfs preserve the valley anisotropy , in addition to the twofold valley degeneracy . at magnetic field up to 35 t , the 2/3 fractional quantum hall state is observed with a well developed hall plateau ; at , the three magnetoresistances show a large anisotropy ( 50:1 ) . we also show that device degradation is not a serious issue for our measurements , if the device is kept in vacuum or a nitrogen gas environment and its time in air is minimized .

1104.0549

r

figure 2 shows the time evolution of a density isosurface for constant helical pitch with @xmath51 and @xmath74 ( cps2a ) where the time , @xmath75 , is in units of @xmath76 ( light travel time across the largest velocity shear surface radius , @xmath77 , considered in this study ) . displacement of the initial force - free helical magnetic field by growth of the cd kink instability leads to a helically twisted magnetic filament wound around the density isosurface . in the nonlinear phase , helically distorted density structure shows continuous transverse growth and propagates in the flow direction . this propagation of the helical kink structure does not occur for a static plasma column ( mizuno et al . 2009a ) . in order to investigate the dependence of kink growth and propagation on the location of the velocity shear surface , we consider four velocity shear radii from @xmath78 to @xmath59 ( see table 1 ) . the effect of different radii on the growth of the cd kink for constant magnetic pitch and @xmath51 is shown in figure 3 . in figure 3 we show the time evolution of the volume - averaged kinetic , @xmath79 , and magnetic , @xmath80 , energy transverse to the @xmath81-axis determined within a cylinder of radius @xmath82 as an indicator of the growth of the cd kink instability . the wavelength of the kink is @xmath83 . note that according to the kruskal - shafranov criterion , the instability develops at @xmath84 . the instability growth rate reaches a maximum at @xmath85 , the exact coefficient being dependent on the transverse distribution of the density and magnetic pitch , and also possibly the location and magnitude of the velocity shear . for the case of constant pitch and uniform density appl et al . ( 2000 ) found @xmath86 and a corresponding growth rate of @xmath87 . in general , one can use the estimate @xmath88 in the rest frame of the kink . for a moving kink we might expect the temporal growth rate in the lab frame to be reduced with @xmath89 where @xmath90 is the moving kink lorentz factor , e.g. , narayan et al . change in the evolution of @xmath79 and @xmath80 indicate an initial linear growth phase at @xmath91 with duration depending on the velocity shear radius , and followed by a nonlinear evolution phase . in all cases , the initial growth phase is characterized by an exponential increase in @xmath79 by about 3 orders of magnitude to a maximum amplitude followed by a slow decline in the nonlinear phase . by fitting the linear portion of the slope in @xmath79 between the amplitudes of @xmath92 and @xmath93 we can determine an e - folding time where @xmath94 and @xmath95 is the time interval . the e - folding times can be found in table 2 in 4 . in general , the e - folding time increases as the velocity shear radius increases for @xmath96 . the e - folding time at @xmath97 decreases but is still significantly longer than for the static plasma column . the time evolution trend of @xmath80 is opposite to the time evolution of @xmath79 . @xmath80 gradually decreases in the early linear growth phase , then exhibits an initial rapid decrease into the nonlinear phase to a minimum followed by a slight increase at later times . at the smallest velocity shear radius the behavior of @xmath79 and @xmath80 are very similar to that of a static plasma column . increased difference in behavior from that of a static plasma column appears as the velocity shear radius increases to @xmath98 and @xmath57 . for these cases as the velocity shear radius increases the growth rate of the cd kink slows , and @xmath79 achieves a somewhat higher maximum amplitude with a later transition to the nonlinear stage . as the shear radius increases @xmath80 exhibits a more gradual decline in the transition to the nonlinear stage than for the static plasma column . however , for the largest velocity shear radius , @xmath64 , the difference relative to the static plasma column in the linear and early non - linear phase is reduced , and the growth rate of the cd kink instability is faster and with lower maximum @xmath79 than for the cases with velocity shear radius @xmath98 and @xmath74 . but note that @xmath79 becomes slightly larger than the static case at the longest comparable simulation times . when the velocity shear radius is much larger than the characteristic radius of the helical magnetic field , we would expect the growth of cd kink instability to approach that of a static plasma column moving with respect to the observer . however , in the flow reference frame the alfvn speed for the sub - alfvnic jet is not the same as that for a static plasma column in addition to a small relativistic clock effect . thus , we do not expect the initial growth rate of largest jet radius case to perfectly match that of the static plasma column as determined in the observer ( simulation ) rest frame . the effect of the velocity shear is greatest for the case with velocity shear radius @xmath74 but also significant when @xmath98 and @xmath59 . figure 4 shows a density isosurface at @xmath99 for the constant pitch cases with @xmath51 at different velocity shear radii . in the linear growth phase , the behavior of the growing kink is almost the same for different velocity shear radius . however , in the nonlinear phase , the behavior of the kink is different for different velocity shear radius . for the smallest radius , @xmath78 , the kink does not propagate along the z - axis significantly . transverse amplitude growth dominates this case and is very similar to that of a static plasma column . in general the flow appears to follow the helical twist indicated by the density isosurface . flow velocities in the transverse x - y plane are larger than flow along the z - axis . when @xmath98 flow in the x - y plane is reduced somewhat relative to flow along the z - axis and the kink propagates slowly along the z - axis . as the radius increases the kink propagates along the z - axis more rapidly ( see more detail in figure 5 ) while continuing transverse growth . flow is less twisted helically as the velocity shear radius increases and at @xmath100 we see a helical kink embedded within and moving with the flow . recall that the time evolution of the volume averaged transverse kinetic energy , i.e. , fig . 3 , were the most similar to a static plasma column for smallest and largest shear radius . the principal difference between the smallest and largest velocity shear radius cases lies in the flow morphology relative to the kink morphology indicated by the density isosurface . in figure 5 we follow the time evolution of the @xmath101 and @xmath102position of the maximum density in the @xmath103 plane at @xmath104 . transverse growth of the kink is revealed by displacement of this maximum away from zero in the @xmath103 plane . in all cases significant displacement of the density maximum begins at @xmath105 , when growth is still within the linear regime . an oscillation of the maximum indicates rotation around the z - axis in the @xmath103 plane and is related to the propagation speed of the kink . since the kink wavelength is @xmath106 in all simulations , the kink propagation speed is @xmath107c = ( 3/\delta t)c$ ] where @xmath95 is the length of time for one rotation in simulation time units . at the smallest shear radius ( red solid lines ) , no oscillation is evident and transverse growth is very similar to that of the static plasma column ( black dash double dotted lines ) . the lack of measurable propagation implies that the flow moves through the growing helical twist at nearly the flow speed , as suggested by the velocity vectors in panel ( a ) of figure 4 . when the shear radius is @xmath98 ( orange dashed lines ) , only a partial oscillation occurs by the end of the simulation . our best estimate of @xmath108 comes from panel ( b ) in figure 5 with a maximum and minimum displacement of @xmath109 occurring at @xmath110 and @xmath111 , respectively . this implies a kink propagation speed of @xmath112 . the kink is propagating along jet axis while transverse growth continues but the propagation speed is slow . in this case the flow is still helically twisted but with less than the apparent helical twist of the density isosurface shown in panel ( b ) of figure 4 . more than one complete oscillation is evident for a shear radius @xmath74 ( see the green dotted lines ) and visual inspection suggests that the oscillation period becomes longer with time . at @xmath113 three measurements indicate @xmath114 , where @xmath115 " indicates the range of the measurements . this implies a kink propagation speed @xmath116 . at @xmath117 three measurements indicate @xmath118 . this implies a kink propagation speed @xmath119 . the kink is propagating rapidly along the axis but as transverse growth continues the kink slows . in this case the flow is only modestly helically twisted and with much less than the apparent helical twist of the density isosurface shown in panel ( c ) of figure 4 . multiple oscillations are evident for a shear radius @xmath64 ( see blue dash - dotted lines ) and again the oscillation period becomes longer with time . five measurements at @xmath113 provide @xmath120 , and five measurements at @xmath121 provide @xmath122 . here the initial kink speed @xmath123 is approximately equal to the flow speed . at later times the kink speed @xmath124 has slowed significantly . at early time the smaller transverse amplitude of the kink is embedded within the flow and the flow exhibits little helical twist . the oscillation amplitude , indicative of the transverse amplitude of the kink , increases up to about @xmath125 and then declines slightly with time . this suggests a decrease in transverse amplitude growth as the growing kink encounters the velocity shear surface and slows . we see from these results that kink propagation and flow morphology are strongly dependent on the velocity shear radius relative to the characteristic radius of the force - free plasma column . at one extreme the fluid flows through the kink with helicity comparable to that of the kink and at the other extreme the kink is embedded within a more uniform flow . the kink propagation speeds are listed in table 2 in 4 . in figure 6 we show the time evolution of the volume - averaged kinetic , @xmath79 , and magnetic , @xmath80 , energy transverse to the @xmath81-axis determined within a cylinder of radius @xmath82 , e.g. , figure 3 . here we see an initial linear growth phase , @xmath126 , and subsequent nonlinear evolution phase . the exponential increase in @xmath79 by about 3 orders of magnitude to a maximum amplitude followed by a slow decline in the nonlinear phase and behavior of @xmath80 is similar to what was found for the constant pitch cases . by fitting the linear portion of the slope in @xmath79 between the amplitudes of @xmath92 and @xmath93 we can determine an e - folding time where @xmath94 and @xmath95 is the time interval . the e - folding times can be found in table 2 in 4 . in this case , the e - folding time is increased relative to the static plasma column by about the same amount only for velocity shear radii @xmath127 . however , the decreasing helical pitch results in more rapid growth in the linear phase , and makes a transition to the nonlinear phase in about 60% of the time for the constant pitch cases shown in figure 3 . this more rapid growth is similar to results for a static plasma column ( mizuno et al . thus , the growth rate trends found for the static plasma column are maintained in the presence of sub - alfvnic flow . the maximum amplitude of @xmath79 is comparable to that found for constant helical pitch . however , the amplitude of @xmath79 declines less in the non - linear phase relative to the static case than was found for the constant pitch cases . we note however that the constant pitch cases might have exhibited similar behavior at longer timescales . here the decline in @xmath79 is clearly the least when @xmath74 with decline increasing for @xmath128 , @xmath15 and @xmath54 , respectively . the same trend is evident in figure 3 for constant helical pitch . in this set of simulations we follow the development of the kink to a much longer time relative to the transition time from the linear growth phase to the non - linear phase . again we find that the largest effects occur for velocity shear radius @xmath74 but now confirm relatively large effects for @xmath98 and @xmath100 . however , even for @xmath78 we clearly see the influence of velocity shear when compared with the results for constant pitch . we conclude that non - linear development is more influenced by a velocity shear surface in the case of decreasing helical pitch . figure 7 shows a density isosurface for the decreasing pitch cases with @xmath51 for different velocity shear radius at @xmath99 . the decreasing pitch cases shown here all appear similar to results shown for static plasma columns ( mizuno et al . 2009a ) . in the linear growth phase the properties are almost same for different shear radius but after transition to the nonlinear phase the behavior of the kink is different for different shear radius . in general , the behavior is similar to what was found for constant helical pitch . for the smallest radius , @xmath78 , the kink does not propagate along the z - axis significantly . in general the flow appears to follow the helical twist indicated by the density isosurface . flow velocities in the transverse x - y plane are larger than flow along the z - axis . when @xmath98 flow in the x - y plane is reduced somewhat relative to flow along the z - axis and the kink propagates slowly along the z - axis . as the radius increases the kink propagates along the z - axis more rapidly ( see more detail in figure 8) while continuing transverse growth . flow is less twisted helically as the velocity shear radius increases . however , we note that when @xmath100 we see considerably more indication of flow helicity than for the constant pitch case . in figure 8 we follow the time evolution of the @xmath101 and @xmath102position of the maximum density in the @xmath103 plane at @xmath104 , e.g. , figure 5 for constant pitch cases . in all the decreasing pitch cases significant displacement of the density maximum begins at @xmath129 , when growth is still within the linear regime , and significant displacement occurs earlier than for the constant pitch cases . at the smallest shear radius ( red solid lines ) , no oscillation is evident and transverse growth is very similar to that of the static plasma column ( black dash - double dotted lines ) . the lack of measurable propagation implies that the flow moves through the growing helical twist at nearly the flow speed , as suggested by the velocity vectors in panel ( a ) of figure 7 . when the shear radius is @xmath98 ( orange dashed lines ) , only a partial oscillation occurs by the end of the simulation . our best estimate of @xmath130 comes from panel ( a ) in figure 7 with a minimum and zero displacement of @xmath131 occurring at @xmath132 and @xmath133 , respectively . this implies a kink propagation speed of @xmath134 . comparison to the comparable constant pitch case suggests a reduction in the propagation speed but our level of accuracy does not make this a firm conclusion . the kink is propagating along jet axis while transverse growth continues but the propagation speed is slow . in this case the flow is still helically twisted but with less than the apparent helical twist of the density isosurface shown in panel ( b ) of figure 7 . more than one complete oscillation is evident for a shear radius @xmath74 ( see the green dotted lines ) and visual inspection suggests that the oscillation period becomes longer with time . at @xmath135 two measurements indicate @xmath136 , where @xmath115 " indicates the range of the measurements . this implies a kink propagation speed @xmath137 . at @xmath138 two measurements indicate @xmath139 . this implies a kink propagation speed @xmath140 . the kink is propagating along the axis but as transverse growth continues the kink slows . here the kink speed both at early and late times is significantly less than that found for the comparable constant pitch case . multiple oscillations are evident for a shear radius @xmath64 ( see blue dash - dotted lines ) and again the oscillation period becomes longer with time . four measurements at @xmath135 provide @xmath120 , and three measurements at @xmath138 provide @xmath141 . here the initial kink speed @xmath123 is approximately equal to the flow speed . at later times the kink speed @xmath142 has slowed significantly . at early time the smaller transverse amplitude of the kink is embedded within the flow and the flow exhibits little helical twist . the oscillation amplitude , indicative of the transverse amplitude of the kink , increases up to about @xmath133 . here we see transverse amplitude growth continuing to longer times and achieving larger amplitude than the comparable constant pitch case . the kink speed at later times is significantly less than that found for the comparable constant pitch case . we see from these results that kink propagation and flow morphology are again strongly dependent on the velocity shear radius relative to the characteristic radius of the force - free plasma column . in general , the presence of a velocity shear surface influences the propagation speed more than was found for the constant pitch cases . the slower kink propagation speeds found for the decreasing pitch cases are likely the result of the faster amplitude growth of the kink to a larger transverse amplitude . thus , at the larger velocity shear radii the growing kink approaches the velocity shear surface more rapidly and/or more closely . the kink propagation speeds are listed in table 2 in 4 . figure 9 shows the time evolution of the volume - averaged kinetic energy ( @xmath79 ) and magnetic energy ( @xmath80 ) transverse to the @xmath81-axis within a cylinder of radius @xmath144 for constant pitch with @xmath52 , similar to figures 3 and 6 . change in the evolution of @xmath79 and @xmath80 indicate an initial linear growth phase at @xmath145 with duration of the linear growth phase depending on the velocity shear radius . in all cases , the initial growth phase is characterized by an exponential increase in @xmath79 by about 3 orders of magnitude to a maximum amplitude followed by a slow decline in the nonlinear phase . by fitting the linear portion of the slope in @xmath79 between the amplitudes of @xmath92 and @xmath93 we can determine an e - folding time . the e - folding times are listed in table 2 in 4 . in general , the e - folding time increases as the velocity shear radius increases for @xmath96 . the e - folding time at @xmath97 decreases but is still significantly longer than for the static plasma column . evolution is qualitatively similar but quantitatively different from the constant pitch slower jet cases . in particular , the maximum value for @xmath79 is about a factor of two larger than found for the constant pitch cases with @xmath51 , and is likely the result of the initial flow kinetic energy being about a factor of two higher . as was found for the slower jet cases , the growth rate is slower and transition to the nonlinear phase occurs later as the shear radius increases from @xmath78 ( red lines ) to @xmath146 ( green dotted lines ) . as was found previously , the largest effects of velocity shear appear when @xmath146 with smaller but still significant effects when @xmath147 . the @xmath100 simulation terminated before the maximum amplitude in @xmath79 was achieved , but it is clear that the maximum amplitude in @xmath79 will occur at significantly later time than when @xmath147 . this result is different from the comparable slower flow case . this difference is likely the result of relativistic effects and will be considered further in 4 . the three - dimensional helical structure of these faster jet cases is qualitatively similar to that of slower jet cases with constant pitch . density isosurfaces , magnetic field lines and velocity vectors appear similar to those shown in figures 2 & 4 . in figure 10 we show the time evolution of the @xmath101 and @xmath102position of the maximum density in the @xmath103 plane at @xmath104 , e.g. , figure 5 for the slower flow constant pitch cases . here significant displacement of the density maximum begins at @xmath148 , when growth is still within the linear regime . this is similar to the slower flow constant pitch cases . at the smallest shear radius ( red solid lines ) , there is a suggestion of an oscillation in @xmath109 ( panel b ) with a maximum negative displacement at @xmath149 and @xmath150 , although no oscillation is evident in @xmath131 ( panel a ) . we can use this apparent oscillation to set an upper limit to the propagation speed of @xmath151 . thus , the flow moves through the growing helical twist at nearly the flow speed , as was found for the previous cases . when the shear radius is @xmath98 ( orange dashed lines ) , a full oscillation occurs and visual inspection suggests that the oscillation period increases with time . at @xmath135 two measurements indicate @xmath152 , where @xmath115 " indicates the range . this implies a kink propagation speed @xmath153 . at @xmath138 two measurements indicate @xmath154 . this implies a kink propagation speed @xmath155 . the kink is propagating along the axis but as transverse growth continues the kink slows . here the kink speed at late times is similar to that found for the comparable slower flow speed constant pitch case . multiple oscillations are evident for a shear radius @xmath74 ( see the green dotted lines ) and visual inspection suggests that the oscillation period becomes slightly longer with time . at @xmath113 measurements indicate @xmath156 , where @xmath115 " indicates the range . this implies a kink propagation speed @xmath157 . at @xmath121 measurements indicate @xmath158 . this implies a kink propagation speed @xmath159 . the kink is propagating relatively rapidly along the axis at early times but as transverse growth continues the kink slows . multiple oscillations are evident for a shear radius @xmath64 ( see blue dash - dotted lines ) but there is no evidence that the oscillation period becomes longer with time for @xmath160 when the simulation terminated . the multiple oscillations provide @xmath161 . here the kink speed @xmath162 is approximately equal to the flow speed . the oscillation amplitude , indicative of the transverse amplitude of the kink , increases up to the end of this simulation . this suggests that the kink remains embedded in the flow up to the end of this simulation . these results are similar to those found for the slower flow cases with constant pitch . when the shear radius is larger , the propagation speed of the helical kink becomes faster . quantitative comparison with individual slower jet cases ( fig . 5 ) , on average indicates a more rapid propagation speed for each shear radius . the kink propagation speeds are listed in table 2 in 4 .

displacement of the initial force - free helical magnetic field leads to the growth of cd kink instability . we find that helically distorted density structure propagates along the jet with speed and flow structure dependent on the radius of the velocity shear surface relative to the characteristic radius of the helically twisted force - free magnetic field . at simulations show continuous transverse growth in the nonlinear phase of the instability . the growth rate of the cd kink instability and the nonlinear behavior also depend on the velocity shear surface radius and flow speed , and the magnetic pitch radial profile . larger velocity shear radius leads to slower linear growth , makes a later transition to the nonlinear stage , and with larger maximum amplitude than occur for a static plasma column . however , when the velocity shear radius is much greater than the characteristic radius of the helical magnetic field , linear and non - linear development can be similar to the development of a static plasma column .

we have investigated the influence of a velocity shear surface on the linear and non - linear development of the cd kink instability of force - free helical magnetic equilibria in 3d . in this study we follow the temporal development within a periodic computational box and concentrate on flows that are sub - alfvnic on the cylindrical jet s axis . displacement of the initial force - free helical magnetic field leads to the growth of cd kink instability . we find that helically distorted density structure propagates along the jet with speed and flow structure dependent on the radius of the velocity shear surface relative to the characteristic radius of the helically twisted force - free magnetic field . at small velocity shear surface radius the plasma flows through the kink with minimal kink propagation speed . the kink propagation speed increases as the velocity shear radius increases and the kink becomes more embedded in the plasma flow . a decreasing magnetic pitch profile and faster flow enhance the influence of velocity shear . simulations show continuous transverse growth in the nonlinear phase of the instability . the growth rate of the cd kink instability and the nonlinear behavior also depend on the velocity shear surface radius and flow speed , and the magnetic pitch radial profile . larger velocity shear radius leads to slower linear growth , makes a later transition to the nonlinear stage , and with larger maximum amplitude than occur for a static plasma column . however , when the velocity shear radius is much greater than the characteristic radius of the helical magnetic field , linear and non - linear development can be similar to the development of a static plasma column .

1104.0549

i

we have investigated the development of the cd kink instability of a force - free helical magnetic field with a sub - alfvnic velocity shear surface located at various radii relative to the characteristic radius of the magnetic field . we restricted this study to sub - alfvnic shear as this regime is appropriate to the magnetically dominated flows thought to exist in the acceleration and collimation regions of relativistic jets . in this magnetically dominated parameter regime the flow is stable to the velocity shear driven kelvin - helmholtz instability so that we could focus solely on the effect of the shear flow on growth and propagation of the current driven kink and the velocity flow field accompanying the helically twisted kink . the growth of cd kink instability in the initial exponential growth phase is slower than found for a static plasma column . in general , the reduction in the growth rate is larger for constant magnetic pitch than for decreasing magnetic pitch , and is larger if the velocity is larger . in all cases , effects resulting from the presence of a velocity shear surface are largest when the velocity shear surface lies at or not too far outside , @xmath163 , the characteristic radius , @xmath15 , of the force - free magnetic field . for the slower speed , @xmath73 , and constant pitch case it was clear that the initial growth was least affected when the velocity shear surface was inside , @xmath164 , or far outside , @xmath77 , the characteristic radius . for the higher speed , @xmath143 , and constant pitch case initial growth was again least affected when @xmath164 but relativistic effects slowed the initial growth when @xmath77 . transition to the nonlinear stage occurs at a later time but with larger maximum amplitude in the volume averaged transverse kinetic energy , @xmath79 , as the velocity shear radius is increased for @xmath165 , when compared to a static plasma column . however , when the velocity shear radius is far from the characteristic radius , @xmath166 , the maximum amplitude is comparable to that of the static plasma column although that maximum is reached after longer time . in the absence of relativistic effects which slow the observed rate of growth , it is clear that the presence of a velocity shear surface has the strongest influence on both the linear and non - linear behavior of the growing kink when the velocity shear surface is located at or not too far outside the characteristic radius . in general , decreasing the magnetic pitch or increasing the flow velocity enhances the influence of the velocity shear surface . the location of the velocity shear surface has profound consequences for kink propagation and the associated flow field . for the velocity shear surface well inside the characteristic radius , transverse growth is similar to the static plasma column . in this case the plasma flows through the growing helical kink . for the velocity shear surface well outside the characteristic radius , the kink is embedded within and moves with the flow until the kink amplitude becomes large and the kink approaches the velocity shear surface . in this case the initial transverse growth is similar to that of a static plasma column advected with the flow and with growth computed in the proper reference frame . as the growing helically twisted kink approaches the velocity shear surface the kink slows and the flow field becomes slightly helically twisted . for velocity shear radii on the order of the characteristic radius there is a more intimate interaction between the growing kink and the flow field . in general , the kink propagates more slowly than the flow and slows as the amplitude increases . thus , the flow field becomes more helically twisted as the kink amplitude increases . for these cases the flow helicity remains less than kink helicity . the lorentz factors for slower and faster flows are @xmath167 1.02 and 1.05 , respectively . the growth rate of the cd kink instability depends on the alfvn velocity ( e.g. , appl et al . 2000 ) and also depends on relativistic time dilation . in the flow reference frame , the toroidal and axial magnetic field components are reduced by the lorentz factor and the mass density is reduced by the lorentz factor squared . the alfvn velocity is decreased slightly in the flow reference frame because @xmath168 is slightly larger . therefore in faster flow cases , we would expect the growth rate to be reduced primarily by time dilation related to the lorentz factor of the moving kink , @xmath90 . our results for kink e - folding times in the linear growth phase are summarized in table 2 along with the kink propagation speeds for the various different simulations . lcccc [ table1 ] cp0 & 0.0 & 0.0 & 3.75 & 0.0 + cpsa/2 & 0.2 & 0.5 & 3.75 & @xmath169 0 + cpsa & 0.2 & 1.0 & 4.10 & 0.06 + cps2a & 0.2 & 2.0 & 4.35 & 0.15 - 0.10 + cps4a & 0.2 & 4.0 & 4.05 & 0.20 - 0.16 + dp0 & 0.0 & 0.0 & 2.45 & 0.0 + dpsa/2 & 0.2 & 0.5 & 2.40 & @xmath169 0 + dpsa & 0.2 & 1.0 & 2.45 & 0.04 + dps2a & 0.2 & 2.0 & 2.75 & 0.12 - 0.06 + dps4a & 0.2 & 4.0 & 2.70 & 0.20 - 0.10 + cp0 & 0.0 & 0.0 & 3.75 & 0.0 + cpfa/2 & 0.3 & 0.5 & 3.70 & @xmath170 0.05 + cpfa & 0.3 & 1.0 & 4.30 & 0.12 - 0.06 + cpf2a & 0.3 & 2.0 & 5.60 & 0.23 - 0.17 + cpf4a & 0.3 & 4.0 & 5.30 & 0.30 + quantitative comparison between our results and instability predictions is difficult because no sufficiently general stability analysis has been performed for magnetically dominated jets . the stability analysis performed by narayan et al . ( 2009 ) considers the case of a `` ... rigid impenetrable wall at the outer cylindrical radius , @xmath171 . '' , that unfortunately is not appropriate to our simulations . nevertheless , we can make some comparison with previous results for static plasma columns and consider the implications for the spatial development of the instability . in all cases , the initial axisymmetric structure is strongly distorted by the kink instability , even though not disrupted . in general , the addition of a sub - alfvnic velocity shear surface leads to slower temporal development of the instability than for the static case . comparison between the static and moving kink constant pitch cases shows that the e - folding times ( see table 2 ) are significantly longer , up to @xmath172 and @xmath173 longer for slow and fast velocity shear , when the shear surface is located at twice the characteristic radius of the plasma column . when the velocity shear surface is located far outside the characteristic radius of the plasma column the kink is advected at about the flow speed in the linear growth regime and the e - folding times are shortened somewhat to about @xmath174 and @xmath175 longer than for the comparable static case . with the kink moving with the flow frame we would expect the growth rate in the flow frame to be related to the growth rate in the lab frame by the lorentz factor of the flow . however , comparison between our static plasma column kink e - folding times and our moving kink e - folding times is complicated by length contraction in addition to time dilation . time dilation increases the e - folding times from fluid to lab frames by the lorentz factor . length contraction means that our simulation box imposes a wavelength that appears longer in the fluid frame than in the lab frame by the lorentz factor . in either frame the wavelength is longer than the fastest growing wavelength . examination of our previous static case numerical results for the growth of @xmath176 at wavelengths of @xmath83 and @xmath177 ( see figure 2 in mizuno et al . ( 2009a ) for constant pitch cases a and b ) indicates that the e - folding time increases about @xmath178 faster than proportional to the wavelength over this wavelength range . thus , length contraction means that our e - folding time observed for a static kink should convert approximately to our e - folding time observed for a moving kink by @xmath179 . the e - folding times for cases cps4a and cpf4a when compared to the comparable static case , cp0 , are significantly longer than the predicted 4% ( @xmath180 ) and 11% ( @xmath181 ) increase . we can only assume that a much larger velocity shear radius is required to further reduce the e - folding times for the propagating kinks to that predicted . on the other hand , this also means that temporal kink growth is significantly slowed even for a velocity shear surface at four times the characteristic radius . it is interesting to note that the fluid inertia increases by @xmath182 and if the growth time is also increased by the fluid inertia then the e - folding times in the lab frame should be increased by @xmath183 = 1.16 and 1.31 relative to the static case , and this increase comes much closer to the observed increase . we speculate that the large increase in e - folding times measured in the lab frame is partly a result of the increased inertia of the relativistically moving fluid . the characteristic time for the instability to affect strongly the initial structure varies from @xmath184 for the decreasing pitch case to @xmath185 for the constant pitch cases . for the constant pitch cases the characteristic time is roughly @xmath186 , with values for @xmath187 being dependent on the structure of the undisturbed state . in a jet context our perturbations remain static or can propagate with the flow frame depending on the location of the velocity shear surface . in order to check whether the instability would affect a jet flow , one has to compare @xmath188 with a propagation time . if we identify @xmath187 with the fastest growing wavelength , our present results suggest a scaling like @xmath189 with @xmath190 for a moving kink and with velocity shear surface a few times the characteristic radius . here @xmath60 would correspond to time dilation only and @xmath191 to time dilation plus inertial effects from the relativistically moving fluid . in this case the condition for the instability to affect the jet structure might be written as @xmath192 where we set @xmath193 and @xmath194 is a function of @xmath195 and is sensitively dependent on the location of the velocity shear surface provided @xmath196 . this result suggests that the characteristic scale for kink development could be longer or very much shorter than for a kink simply advected with a broad flow for which @xmath197 . in order to find a more general criteria one has to know how the characteristic radius , @xmath15 , and lorentz factor , @xmath90 , increase with distance . if the jet is narrow enough so that @xmath198 , where @xmath199 is the angular velocity at the base of the jet , one can use the scaling ( tchekhovskoy et al . 2008 ; komissarov et al . 2009 ; lyubarsky 2009 ) @xmath200 and assume that @xmath201 . in this case one finds that the criterion for the kink instability can be written as @xmath202^{1/2 } a~.\ ] ] the instability could affect the jet structure only if the jet expands slowly enough and/or the kink moves slowly enough . assuming the parabolic shape for the jet , @xmath203 , where @xmath204 and @xmath205 are dimensionless numbers , one finds that the instability develops only if @xmath206 . in this case the characteristic scale for the development of the instability can be written as @xmath207}[1 - ( \epsilon \xi \chi^k)^{-2}]^{1/2[1 - ( \alpha + 1)k]}~.\ ] ] for @xmath208 , @xmath209 and @xmath210 we recover the case for a kink advected with the flow field , eq.(9 ) in mizuno et al . ( 2009a ) , @xmath211 for a = 100 . here as @xmath212 , @xmath213 and @xmath214 so the characteristic scale for development of instability can be very short . for @xmath22 , i.e. , potential inertial effects , the characteristic time is lengthened and this has the potential for lengthening the characteristic scale for the development of the instability . this shows up in the constraint on @xmath215 , i.e. , only if the jet expands slowly enough . the 3d relativistic jet generation simulation performed by mckinney & blandford ( 2009 ) indicates relatively rapid , less than 100 gravitational radii , but non - disruptive kink development over 500 gravitational radii . our previous and present simulations for static and moving kinks suggest that the rapid but non - disruptive kink development in the jet generation simulation could be a result of a velocity shear surface located less or on order of the characteristic magnetic radius and a density increasing with radius . this combination would result in a slowly moving kink , hence rapid initial spatial development , but with non - linear growth slowed by the density increase and accompanying alfvn speed decline with radius , increasing the alfvn crossing time and slowing spatial development . a non - linearly stabilizing increasing density profile is what might be expected for a poynting flux jet core confined within a senser slowly moving sheath , as appears to be predicted by jet generation simulations . of course , a proper investigation of spatial growth requires stability simulations designed to study spatial kink development using more realistic flow , magnetic , and density profiles . in this paper , we considered sub - alfvnic jet flow and focused on the development of the cd kink instability . if the velocity shear is super - alfvnic , the flow can be kh unstable and cd unstable . baty & keppens ( 2002 ) have investigated the interaction between kh and cd driven instabilities of a magnetized force - free cylindrical configuration via 3d mhd simulations in the non - relativistic regime . they found that the cd unstable modes provided a stabilizing effect on kh instability driven vortical structure . however , they assumed a relatively weak magnetic field in their simulations and studied the super - alfvnic regime where the kh instability grows faster than the cd kink instability ( e.g. , appl et al . 2000 ; baty 2005 ) . if the magnetic field is strong but the velocity shear is weakly super - alfvnic , the growth rate of the kh instability can be less than or comparable to that of the cd instability . even in the super - alfvnic regime the kh instability can be suppressed if a jet is embedded in a slower moving magnetized sheath that reduces the velocity shear to being effectively sub - alfvnic ( hardee 2007 ; mizuno et al . 2007 ) . such a sheath may exist around jets in the acceleration and collimation region . thus , investigation of the weakly super - alfvnic parameter regime will be particularly important to understanding the development of the twisted structures that are observed on relativistic jets . in future work we will investigate the spatial development of cd instability and the coupling between cd instability and kh instability . thanks y. lyubarsky , k. shibata , b. zhang , m. a. aloy , and j. m. stone for helpful discussions . this work is supported by nsf awards ast-0506719 , ast-0506666 , ast-0908010 , and ast-0908040 , and nasa awards nng05gk73 g , nnx07aj88 g , and nnx08ag83 g , and us - israeli bsf award 2006170 . the simulations were performed on the columbia supercomputer at nas division at nasa ames research center , the sgi altix ( cobalt ) at the national center for supercomputing applications in teragrid project which is supported by the nsf and the altix3700 bx2 at yitp in kyoto university .

we have investigated the influence of a velocity shear surface on the linear and non - linear development of the cd kink instability of force - free helical magnetic equilibria in 3d . in this study we follow the temporal development within a periodic computational box and concentrate on flows that are sub - alfvnic on the cylindrical jet s axis . small velocity shear surface radius the plasma flows through the kink with minimal kink propagation speed .

we have investigated the influence of a velocity shear surface on the linear and non - linear development of the cd kink instability of force - free helical magnetic equilibria in 3d . in this study we follow the temporal development within a periodic computational box and concentrate on flows that are sub - alfvnic on the cylindrical jet s axis . displacement of the initial force - free helical magnetic field leads to the growth of cd kink instability . we find that helically distorted density structure propagates along the jet with speed and flow structure dependent on the radius of the velocity shear surface relative to the characteristic radius of the helically twisted force - free magnetic field . at small velocity shear surface radius the plasma flows through the kink with minimal kink propagation speed . the kink propagation speed increases as the velocity shear radius increases and the kink becomes more embedded in the plasma flow . a decreasing magnetic pitch profile and faster flow enhance the influence of velocity shear . simulations show continuous transverse growth in the nonlinear phase of the instability . the growth rate of the cd kink instability and the nonlinear behavior also depend on the velocity shear surface radius and flow speed , and the magnetic pitch radial profile . larger velocity shear radius leads to slower linear growth , makes a later transition to the nonlinear stage , and with larger maximum amplitude than occur for a static plasma column . however , when the velocity shear radius is much greater than the characteristic radius of the helical magnetic field , linear and non - linear development can be similar to the development of a static plasma column .

1611.08611

i

the dwarf - irregular galaxy ic 10 in cassiopeia presents one of the most active starbursts in the local group and a unique environment to study the immediate relics of the most massive stars : black holes and neutron stars in high mass x - ray binaries ( hmxbs ) . motivated by the discovery of the black hole hmxb ic 10 x-1 @xcite and the very large amplitude transient ic 10 x-2 @xcite we conducted a 7-shot monitoring campaign with _ chandra _ during 2009 - 10 . combined with deep observations taken in 2003 and 2006 , we were able to span timescales ranging up to 7 years reaching a limiting sensitivity of @xmath2erg s@xmath3 . this cadence and sensitivity , coupled with the angular resolution of _ chandra _ , enable light - curves to be constructed for individual point sources . ic 10 hosts a young ( @xmath56 @xmath6 yr ) stellar population @xcite accompanied by the highest known space - density of wolf rayet ( wr ) stars @xcite , which are the evolved helium cores of stars with initial stellar masses in excess of 20 @xmath7 . the star formation rate ( sfr ) is reported to be as high as 0.5 @xmath7@xmath8 @xcite , which when normalized by the mass of the galaxy ( 2 @xmath9 @xmath7 ; @xcite ) yields 2.5 @xmath10 @xmath7@xmath8 @xmath7@xmath3 which is among the highest specific sfrs in the local universe exceeding the values for the milky way ( mw ) , small magellanic cloud ( smc ) , and large magellanic cloud ( lmc ) . depending on the indicators and methods used , there is an order of magnitude dispersion among sfr values for ic 10 @xcite . the chaotic structure of ic 10 is probably part of the picture and indeed much of the galaxy resembles an ob association , but on a kiloparsec scale @xcite . ic 10 is replete with a complex structure of @xmath11-bright and radio - bright bubbles , filaments , and hii regions , all signaling its turbulent evolution under the influence of the kinetic energy being injected by winds and supernovae . the similarities between ic10 and the smc are striking ; both are gas - rich dwarf irregulars and both are thought to have undergone tidal disruption in the recent past @xcite leading to triggered star formation activity . however , two critical differences exist between these galaxies that make ic 10 an exciting new laboratory for stellar astrophysics . the first and most important contrast is the time since star formation began . this is @xmath56 @xmath6 yr for ic 10 compared to 40 - 200 @xmath6 yr for the various distinct age - segregated populations identified in the smc @xcite , where the hmxbs are found in the 40 - 70 myr sub - population @xcite . the second contrast is in metallicity which for ic 10 is @xmath12 @xcite , intermediate between the smc and the mw . complete censuses of x - ray binary populations in local group galaxies are a powerful approach to discover the underlying physics of stellar evolution , for example the effect of metallicity . the magellanic clouds have historically served this purpose , but gaining proper control of secular differences between galaxies requires new independent laboratories such as ic 10 to be added . important large samples have been constructed by mining the _ chandra _ archive , ( for example @xcite ) and by concerted multi - year efforts to intensively observe nearby galaxies ( e.g. , @xcite ) . an x - ray study of point sources in ic 10 was conducted by @xcite using single epoch data from _ xmm - newton _ and _ chandra_. among their important findings was a population of point sources significantly above the expected background density and spatially concentrated within the optical outline of the galaxy . the combined x - ray spectrum of these point - sources was consistent with an absorbed power - law with parameters characteristic of hmxbs . key physics goals to be addressed by ic 10 s x - ray binary ( xrb ) sample include : constructing the x - ray luminosity function ( xlf ) in order to compare it with the sfr history ; discovering what type of xrbs are formed at the earliest times ; and breaking the degeneracy between compact - object mass and accretion - mechanism that currently bedevils attempts to understand the nature of both ultraluminous x - ray ( ulx ) sources and the xlf - sfr relation . the relative proximity of ic10 is crucial because the individual xrbs can be studied in detail once they are identified . in the larger samples of galaxies , the questions are addressed on a purely statistical basis . identifying optical counterparts to x - ray sources at the 660 kpc distance of ic 10 is a daunting prospect since it lies at low galactic latitude and it is viewed by us through the outer portion of the galactic plane . since most xrbs are highly variable , a monitoring campaign offers an alternative path to discovering the nature of these individual sources . this paper begins with a uniform reduction / analysis of the _ chandra _ monitoring and archival observations and visualizations of the ccd data ( [ sect : obs ] ) followed by the construction of the source catalog ( [ sect : catalog ] ) and the generation of x - ray light curves ( [ sect : lc ] ) . we outline our spectral analysis using quantiles and ccd pulse - height spectra in [ sect : quantile ] , we briefly describe how optical counterparts were identified ( [ sect : optical ] ) , and then we proceed to [ sect : discussion ] , where we look at each variable source in turn in order to summarize the available information and to discuss its likely nature . finally , in [ sect : conclusions ] , we present an overview of the results and we lay out the direction of future progress .

we have monitored the cassiopeia dwarf galaxy ( ic 10 ) in a series of 10 _ chandra _ acis - s observations to capture its variable and transient x - ray source population , which is expected to be dominated by high mass x - ray binaries ( hmxbs ) . the observations span years 2003 - 2010 and reach a limiting luminosity oferg s , providing sensitivity to x - ray binaries in ic 10 as well as flare stars in the foreground milky way . the purpose of this study is to discover the composition of the x - ray binary population in a young starburst environment . ic 10 provides a sharp contrast in stellar population age ( my ) when compared to the magellanic clouds ( 40 - 200 my ) where most of the known hmxbs reside .

we have monitored the cassiopeia dwarf galaxy ( ic 10 ) in a series of 10 _ chandra _ acis - s observations to capture its variable and transient x - ray source population , which is expected to be dominated by high mass x - ray binaries ( hmxbs ) . we present a sample of 21 x - ray sources that are variable between observations at the 3 level , from a catalog of 110 unique point sources . we find 4 transients ( flux variability ratio greater than 10 ) and a further 8 objects with ratio 5 . the observations span years 2003 - 2010 and reach a limiting luminosity oferg s , providing sensitivity to x - ray binaries in ic 10 as well as flare stars in the foreground milky way . the nature of the variable sources is investigated from light - curves , x - ray spectra , energy quantiles , and optical counterparts . the purpose of this study is to discover the composition of the x - ray binary population in a young starburst environment . ic 10 provides a sharp contrast in stellar population age ( my ) when compared to the magellanic clouds ( 40 - 200 my ) where most of the known hmxbs reside . we find 10 strong hmxb candidates , 2 probable background active galactic nuclei , 4 foreground flare - stars or active binaries , and 5 not yet classifiable sources . complete classification of the sample requires optical spectroscopy for radial velocity analysis and deeper x - ray observations to obtain higher s / n spectra and search for pulsations . a catalog and supporting dataset are provided .

astro-ph9708104

r

we have constructed models using the cloudy program ( ferland 1993 ) in order to investigate the ionization of the observed species , the spectrum of the uv ionizing radiation field , and the molecular fraction of the damped ly@xmath0 absorption line system at z = 2.8115 . the column densities for the species observed in the a@xmath42 and a@xmath3 components ( z = 2.8108 , z = 2.8132 ) of the z = 2.81 damped ly@xmath0 system are shown in table 2 . because the resolution of the available spectra is insufficient to resolve the profiles of the lines listed in table 2 , we use a curve - of - growth analysis to infer column densities . we adopt the doppler parameter b = 60 km s@xmath12 for lines from the a@xmath42 component and b = 30 km s@xmath12 for lines from the a@xmath3 component which are obtained from the curve - of - growth of fe ii ( meyer _ et al . if the absorption lines from the a@xmath42 and a@xmath3 components are blended with each other , we adopt b = 100 km s@xmath12 obtained from fitting the lyman lines ( foltz _ et al . _ 1988 ) . however , the si iv and c iv doublets in the a@xmath42 component suggest that the doppler parameter b = 60 km s@xmath12 derived for fe ii lines does not apply . a higher doppler parameter b = 80 km s@xmath12 gives a better fit . therefore , we adopt b = 80 km s@xmath12 to calculate column densities of high ionization species , c iv , si iii , si iv , n v , o vi in the a@xmath42 component ( table 2 ) . the b - values indicate there are probably several velocity components blended with each other in each line . however , the uncertainties in the column densities from single b - value curve - of - growth analysis may be less than a factor of 2 ( jenkins 1986 ) . in fact , our derived column densities are consistent with the results given by songaila & cowie ( 1995 ) , and lu _ et al . _ ( 1996 ) based on higher resolution spectra . as the input to cloudy , we adopt a metallicity of 10% of the solar value for all the elements in both a@xmath42 and a@xmath3 components of the z = 2.8115 damped ly@xmath0 system . we also consider the relative depletions by dust grains to zn ( about 0.6 - 0.7 in the logarithm unit ) of heavily depleted elements such as al , si , ca , fe and ni ( meyer _ et al . _ 1989 ) . the dust - to - gas ratio is 10% of the milky way and the constituents of dust grains are assumed the same as the milky way . the total neutral hydrogen column density n(h i ) for the two components is @xmath50 @xmath5 ( mller & warren 1993 ) . it is obtained by fitting the profile of the damped ly@xmath0 absorption line including the ly@xmath0 emission of the quasar because the redshift of the damped ly@xmath0 system ( z = 2.8115 ) is about the same as that of the quasar ( z = 2.765 , morton _ et al . _ 1980 ; mller & warren 1993 ) . the neutral hydrogen column density for each of the two components in the z = 2.8115 damped ly@xmath0 system is uncertain . however , similar absorption of dominant ions of most species , such as o i , si ii , s ii , fe ii , ni ii , in these two components suggest that the total neutral hydrogen column density in each component is also similar ( cf . table 2 ) . we take the total column density as the approximate value for each of the components in the following discussion . there is therefore at least a factor of 2 uncertainty in the results from cloudy from the uncertainty in the neutral hydrogen column density in each velocity component . since the damped ly@xmath0 system is possibly near the quasar , the uv flux from the quasar can affect the ionization . we therefore have considered five types of spectral energy distributions ( sed ) . figure 3 shows these seds , along with the ionization potential of several ions . we use a power - law with index @xmath51 for @xmath52 , where @xmath53 , measured for pks 0528@xmath54250 by sargent _ et al . _ we extrapolate the power to longer wavelengths which has little affect on our results . the quasar energy distribution at wavelengths shorter than the lyman limit is uncertain . we therefore consider two different quasar seds : a(1 ) and a(2 ) ( figure 3 ) . in these two models , the upper limit to the x - ray flux from the einstein ipc at 1.0 kev is adopted for the wavelength longer than 0.2 kev ( wilkes _ et al . _ 1994 ) . in a(1 ) , we assume a power - law with index between the lyman limit and 0.2 kev of @xmath55 ; this is the hardest spectrum that seems reasonable . in a(2 ) , the sed between the lyman limit and 0.2 kev is a power law connecting these two points . we consider the models for the evolution of galactic sed s , as calculated by bruzual & charlot ( 1993 ) . the shape of the uv sed in the @xmath56 region does not change after about 0.1 gyr if the sfr is constant , so we consider the sed of 1 gyr old galaxy as representative . this is shown in the figure 3 as model b. for an age less than 0.1 gyr the sed is similar to the sed of an instantaneous starburst galaxy , which we consider in the next model . compared with a 1 gyr old constant sfr galaxy sed model , this model lacks hard uv photons because of the lack of agb stars . this is shown in figure 3 as model c. we adopt the parameterization of the milky way radiation field by black ( 1987 ) . this includes starlight , cosmic background radiation , thermal emission of dust , hot interstellar gas heated by supernova remnants , stellar winds , and uv radiation from extragalactic sources such as qsos and nearby active galaxies . the energy distribution between 13.6 ev and 54 ev is a power law extrapolated from other wavelengths . this is shown in figure 3 as model d. the sed is a single power - law from radio to x - ray wavelengths . the energy distribution between the lyman limit and 1100 is harder than the milky way sed , the constant sfr galaxy sed and the starburst galaxy sed , but is much softer than the quasar seds . this is shown in figure 3 as model e. figure 4 shows the cloudy results for low ionization species . the ordinate is the column density of the various species , and the abscissa is the ionization parameter , u = @xmath57(h)/n(h)c , where @xmath57(h ) is the surface flux of hydrogen - ionizing photons , n(h ) is the total hydrogen number density ( ionized , neutral , and molecular hydrogen ) , and c is the speed of light . cloudy shows that the column densities of o i , s ii , fe ii , si ii and ni ii , which are the dominant ions of those species in the h i dominant regions , are not sensitive to different sed models over a large range of ionization parameter . since all sed models give similar results for these ions , we only show the result from model e in figure 4 . the abundance of these ions from cloudy are consistent with the observed ones within about a factor of two indicating that we have a reasonable set of assumptions for the abundance and depletions . figure 5 shows the calculated and observed ratios of n(h@xmath3)/n(c i ) in the a@xmath42 component of z = 2.8115 damped system . the common trend in the figure of n(h@xmath3)/n(c i ) vs. n(c i ) can be explained by molecular hydrogen chemistry . the main destruction process of h@xmath3 , photodissociation through the process of spontaneous radiative dissociation by the lyman and werner bands , is initiated by discrete line absorptions . the lines are very narrow . thus , the lines rapidly become optically thick , and then h@xmath3 shields itself effectively , so that most of the hydrogen forms h@xmath3 ( e.g. van dishoeck 1990 ) . this is why we see a rapid increase of n(h@xmath3)/n(c i ) vs. n(c i ) when the uv flux drops below a certain threshold . after that , the abundance of c i still increases as the uv decreases , but the abundance of h@xmath3 increases slowly due to lack of formation material , hydrogen , which has already been changed into h@xmath3 . this is why the ratio of n(h@xmath3)/n(c i ) decreases after the rapid increase phase . the best fit to the observed ratios is the starburst model ( b ) and ( c ) . model ( d ) and ( e ) can fit the observed ratios within about 3@xmath22 . the quasar sed models ( model a(1 ) and a(2 ) ) can not explain the observed ratios . the observed ratios are best explained by the soft uv energy distribution models , which suggest stars contribute most of the ionizing radiation field in the a@xmath42 component of z = 2.8115 damped ly@xmath0 system . thus , the sed model where the uv flux is mainly contributed by pks 0528 - 250 can be ruled out , i.e. the distance between the a@xmath42 component and the quasar is probably large enough ( @xmath58 1 mpc ) that the uv flux from the quasar does not dominate the uv background radiation field in the a@xmath42 component . figure 6 shows the cloudy results for the high ionization species assuming the total neutral hydrogen column density used in figure 4 . none of the model seds can explain the c iv , n v , si iv , o vi and si iii column densities . hence the absorption lines for these high ionization species are not coming from the same material as the absorption for the low ionization species . however , assuming the equilibrium between collisional ionization and radiative and dielectronic recombination , we find that t @xmath59 k can explain the relative ratios of these species ( shull & van steenberg 1982 ) . the a@xmath42 component may be a combination of a disk - like system and a halo , or warm and cold h i clouds associated with a hot intercloud medium . using the cloudy model , we can further estimate the average value of the uv radiation field along the sightline to the quasar in the a@xmath42 component . in order to calculate this , we need to know the number density of neutral hydrogen . we estimate this density using the relative population ratio of the excited state si ii@xmath60 @xmath18 1533 to the ground state si ii @xmath18 1526 . in the h i dominant region with density less than @xmath61 @xmath2 , this population ratio can be expressed as @xmath62 where @xmath63 , @xmath64 , @xmath65 and @xmath66 are , respectively , the electron , proton , hydrogen - atom and molecular hydrogen number densities , @xmath67 is the collision rate , and @xmath68 is the spontaneous transition probability ( bahcall & wolf 1968 ) . cloudy shows that the relative electron density @xmath69 is about @xmath70 at the outside to @xmath71 at the center of the cloud , and the equilibrium temperature is from @xmath72 k in the outside to @xmath73 k in the center . we therefore can roughly neglect the contributions of the fine structure excitation by the proton and molecular hydrogen collisions ( bahcall & wolf 1968 ) . then , @xmath74 where @xmath75 @xmath76 ( bahcall & wolf 1968 ) , and @xmath77 @xmath2 s@xmath12 ( dufton & kingston 1991 ) . taking the observed ratio @xmath78 , t @xmath79 k and @xmath80 , we get @xmath81 @xmath2 . cloudy gives a best fit log u @xmath822.9 and @xmath542.6 for the model b and c , respectively . thus , the upper limit of the neutral hydrogen density implies an upper limit of 1 - 2@xmath83 @xmath5 s@xmath12 for the hydrogen - ionizing photon flux in the a@xmath42 component . this upper limit is about 100 times larger than the milky way value of @xmath84 @xmath5s@xmath12 ( black 1987 ) . because si ii@xmath60 traces warm phase regions outside of the cloud ( cf . morton 1975 ) , the above result is more suitable for outside region of the cloud . for the central part of the absorber cloud , the population ratio of the h@xmath3 j = 4 to j = 0 levels , n(j=4)/n(j=0 ) = 4.5@xmath85 ( songaila & cowie , 1995 ) , provides @xmath86 s@xmath12 , where @xmath87 is the h@xmath3 formation rate , n = n(h ) + 2n(h@xmath3 ) ( see jura 1975 for details ) . we scaled the h@xmath3 formation rate to r @xmath88 @xmath89s@xmath12 , assuming the dust - to - gas ratio is 10% that of the milky way . the density is then @xmath90 20 @xmath2 . we therefore can use this value and other measurements to estimate the physical properties in the central part of the cloud and compare them with the cloudy results . in the central cloud where the kinetic temperature is around 100 k ( songaila & cowie 1995 ) , c ii provides most of the electrons ( e.g. morton 1975 ) , so @xmath91 where we have assumed a spatially homogeneous distribution of c ii ions , electrons and hydrogen atoms . thus , @xmath92 @xmath2 . the equation for c i photoionization equilibrium can be expressed as @xmath93 where we have also assumed a homogeneous distribution of c i ; the photoionization rate , @xmath94 ( s@xmath12 ) , is a function of the radiation field intensity , i ; and @xmath95 ( @xmath96 s@xmath12 ) is the radiative recombination rate coefficient , which is a function of kinetic temperature . the kinetic temperature in the h@xmath3 containing cloud is between 74 k and 270 k , where 74 k is derived from the population ratio of the h@xmath3 in the first excited rotational state to the ground rotational state and 270 k is derived from the b = 1.5 km s@xmath12 for the h@xmath3 absorption lines ( songaila & cowie 1995 ) . therefore we choose @xmath97 @xmath89s@xmath12 ( e.g. snow 1977 ) . from the measurements , we derive n(c i)/n(c ii)@xmath98 . putting these together , we get @xmath99 s@xmath12 which is a factor of few larger than typical value of the @xmath100 s@xmath12 in the milky way ism ( de boer _ et al . this value is consistent with what we expect for the outer region of the cloud . thus , all results derived here are consistent with those derived from the cloudy analysis . we can further use these estimates of the physical parameters to estimate the size of the z = 2.8108 cloud . the averaged value for the electron density is derived to be @xmath101 @xmath2 , n(c ii)@xmath47 n(e)@xmath102 , thus , the physical size for the z = 2.8108 cloud , is @xmath103 pc . for the a@xmath3 component , the lack of highly ionized ions may mean that the a@xmath3 component is not associated with any halo gas . the photoionization models described above can not explain the lack of h@xmath3 and c i , along with the possible detection of co , and special circumstances for molecule formation may apply . in summary , we can account for the z = 2.8108 absorption line system ( a@xmath42 ) containing both hot and cold , neutral gas . the cloud medium contributes most absorption lines of low ionization species , while the hot medium contributes most absorption lines of highly ionized species . this structure is similar to that of the interstellar diffuse clouds in the milky way . the uv flux intensity in this absorber is a few times that of the typical value in the milky way ism . pettini _ et al . _ ( 1994 ) have surveyed about a dozen damped ly@xmath0 systems to measure the abundance of zn and cr and have claimed that the metallicity of the damped ly@xmath0 systems at z @xmath1 2 is about 1/10 of the solar value . they used the relative abundance [ cr / zn ] to deduce the dust - to - gas ratio in the damped systems , which is about 1/10 of the milky way . this result is consistent with that from the dust reddening measurements of quasar spectrum slope by pei _ however , lu _ et al . _ ( 1996 ) recently claimed that the overabundance of zn relative to cr may be intrinsic to the stellar nucleosynthesis in these absorbers instead of dust depletion ( however , see pettini _ et al . _ 1996 ; smith _ et al . _ 1996 ) . here , we assume that the underabundance of cr and ni relative to zn is caused by dust depletion . compared with cr , ni is perhaps a better element to use to deduce depletion . like zn and cr , ni is an iron group element and it traces fe to about [ fe / h ] @xmath104 or even lower ( wheeler _ et al . _ 1989 ; ryan _ et al . ni is also more heavily depleted than cr in the milky way ( jenkins , 1987 ) : 0.35% ni remains in the gas phase compared to 0.62% for cr in the diffuse cloud toward @xmath105 per ( cardelli _ et al . _ 1991 ) . because the ionization potential of ni i is 7.635 ev which is smaller than that of h i , but the ionization potential of ni ii is 18.168 ev which is larger than that of h i , ni ii is the dominant species of ni in the neutral hydrogen dominant region . consequently , the ratio of n(ni ii)/n(h i ) can reflect that of ni / h gas phase abundance without the need to account for unobserved ion stages . for example , under the condition that best fits the ionization structure of the a@xmath42 component in the z = 2.8115 damped ly@xmath0 system , model ( b ) , log u = @xmath106 and n(h)=1 @xmath2 , n(ni ii)/n(ni ) = 97.7% . moreover , there are more uv absorption lines of ni ii than cr ii . if we can observe more than two weak absorption lines of ni ii , we can use a curve - of - growth analysis to get a more accurate estimate of the column density . another potential advantage of using ni ii instead of cr ii is that the ni ii transitions are observable with ground - base telescopes until redshifts about 5 without strong sky emission because the strong uv transitions of ni have rest wavelengths between 1400 and 1700 compared to @xmath1 2000 for cr and zn . our measured equivalent widths of ni ii @xmath18 1709 , ni ii @xmath18 1741 and ni ii @xmath18 1751 in the z@xmath26 system correspond to column densities 3.4@xmath107 @xmath5 , 3.8@xmath108 @xmath5 and 3.2@xmath109 @xmath5 , respectively , when we adopt a doppler parameter b = 30 km s@xmath12 ( meyer _ et al . they are consistent with the values obtained by meyer _ the average column density of ni ii is 3.5@xmath110 @xmath5 . the h i column density in this system is 5@xmath111 @xmath5 ( morton _ et al . thus , ni / h is 7.0@xmath112 , implying that ni is depleted by no more than a factor of 27@xmath1134 in the z@xmath26 damped ly@xmath0 system with respect to the solar ratio of 1.9@xmath114 ( withbroe 1971 ) or [ ni / h ] @xmath115 . the upper limit of n(zn ii ) , 2.6@xmath116 @xmath117 , measured by meyer _ ( 1989 ) indicates that the metallicity in the 2.1408 system is @xmath118 10% of solar abundance . the measured residual depletion in the z = 2.1408 damped ly@xmath0 system is [ ni / zn]@xmath119 . for comparison , [ ni / zn ] @xmath120 in the diffuse cloud toward @xmath105 per of the milky way which has n(h ) @xmath121 @xmath5 ( cardelli _ et al . this is the typical value in the milky way ( c.f . jenkins 1987 ) . the limit for [ ni / zn ] implies that dust grains in the z = 2.1408 damped ly@xmath0 system contain about 70% of the total ni , while dust in our galaxy contain about 99% of the ni . thus , the dust - to - gas ratio is @xmath1187% of that in the milky way . the low dust content implies an inefficient molecular hydrogen formation rate , which suggests low total molecular mass . hence , if the measured dust - to - gas ratio is typical of the interstellar medium in the z = 2.1408 damped ly@xmath0 system , our result is consistent with nondetection of co emission by wiklind & combes ( 1994 ) , who obtained an upper limit for the total molecular mass of @xmath122 m@xmath14 integrating over 1100 km s@xmath12 , but not consistent with the huge amount of molecular mass , m@xmath1237@xmath124 m@xmath14 , reported by brown & vanden bout ( 1993 ) . the column densities for the newly identified ni ii @xmath18 1370 , ni ii @xmath18 1454 and ni ii @xmath18 1467 lines in the z = 2.8115 damped ly@xmath0 system are shown in table 2 . the average column density of ni ii is 6.5@xmath125 @xmath5 in the a@xmath42 component and 3.3@xmath126 @xmath5 in the a@xmath3 component . together , we get 9.8@xmath127 @xmath5 for the two components which is consistent with the column density obtained by meyer _ et al . _ ( 1989 ) obtained by measuring the equivalent widths of ni ii @xmath18 1709 and @xmath18 1741 . the h i column density for the 2 velocity components together in the damped system is 2.24@xmath128 @xmath5 ( mller & warren 1993 ) . thus , ni / h is 4.4@xmath112 , so that ni is depleted by no more than a factor of 43@xmath129 with respect to the solar value or [ ni / h ] @xmath130 . the depletion of zn is [ zn / h ] @xmath131 ( meyer _ et al . _ 1989 ) , so the metallicity is about 10% of the solar value . the residual depletion of ni relative to zn , [ ni / zn ] @xmath132 which means about 80% of the ni is contained in dust grains . consequently , the dust - to - gas ratio is about 8% of that of the galaxy if dust grains cause the depletion of ni relative to zn . in figure 7 , we show our spectra which cover the five ultraviolet co bands ( a - x 0 - 0 , 1 - 0 , 2 - 0 , 3 - 0 , 4 - 0 ) . we mark the central positions of the co lines of the two velocity components ( z = 2.8108 , 2.8132 ) in each spectrum . the co 3 - 0 @xmath18 1447 line exhibits absorption at 5887.47 at the expected position of z = 2.8132 within the uncertainties . if this identification is correct , the co column density is 4.7@xmath133 @xmath5 assuming the line is unsaturated . however , the absorption line at 5887.47 could also be the co ii 1448 line at z = 2.8117 . the corresponding column density is @xmath134 @xmath5 , which is consistent with the upper limit obtained by songaila & cowie ( 1995 ) . in order to improve the co column density limit in the a@xmath42 component , we constructed a composite co spectra from the 5 co lines using a method similar to that employed by levshakov _ ( 1989 ) . to obtain the composite spectrum , we first shifted the spectral regions containing the co absorption bands to rest frame 1477.52 the wavelength of the co a - x 2 - 0 band , which has the largest oscillator strength in the co a - x system ( field _ et al . _ 1983 ) , then normalized to the continuum , and averaged with each pixel weighted by the inverse of its variance . in order to avoid the possible effect of telluric absorption at @xmath18 = 5892.08 and z = 2.8108 c iv absorption at 5900.16 we used the fitted continuum value instead of the observed flux in our coaddition . the final composite spectrum is shown in figure 7 . no absorption of co from the a@xmath42 component is found . the 3@xmath22 upper limit to the equivalent width in the rest frame is 17 m . using the weighted mean of the oscillator strengths of the considered bands , we derive an upper limit on the co column density of the a@xmath42 component of n(co)@xmath135 @xmath5 . thus the ratio n(co)/n(h i)@xmath136 for the a@xmath42 component , provided that the total neutral hydrogen absorption in the z = 2.8115 damped ly@xmath0 system is from this component . figure 2 shows the summed spectrum of co ( j=3@xmath1372 ) from the damped ly@xmath0 system z = 2.8115 toward pks 0528 - 250 . we have not detected any emission from the z = 2.8108 and z = 2.8132 components . the 3@xmath22 upper limit of the observed integrated line intensity i@xmath138 k km s@xmath12 for the a@xmath42 component , and 0.142 k km s@xmath12 for the z = 2.8132 component , where @xmath139 = 100 km s@xmath12 is the integrated velocity interval around the absorption components , and @xmath140 is the number of channels in the velocity interval of 100 km s@xmath12 . the co luminosity for the z = 2.8115 damped ly@xmath0 system can be expressed , @xmath141 where @xmath142 is the brightness temperature of the source , @xmath143 is the solid angle subtended by the source , and @xmath144 is the angular size distance . @xmath146 is the luminosity distance , @xmath147\}.\ ] ] the observed temperature of the source @xmath148 is defined as @xmath149 @xmath150 is the normalized power pattern , and the factor ( 1+z ) is from the expansion of the universe . moreover , the angular size of about 2.5@xmath21 for the ly@xmath0 emission region in the z = 2.8115 damped ly@xmath0 system ( mller & warren 1993 ) is much smaller than the beam size of the telescope of 68@xmath21 , so if the co emission region has similar size as the ly@xmath0 emission region , then t@xmath151 can be further expressed as @xmath152 where @xmath153 is the telescope beam solid angle . then the co line luminosity can be expressed as @xmath154 the molecular mass can be written as @xmath155 where @xmath0 is the co to h@xmath3 conversion factor . adopting the standard conversion factor , @xmath156 ( sanders _ et al . _ 1991 ) , we obtain a 3@xmath22 upper limit for the total molecular mass of @xmath157 in the a@xmath42 component , and 1.88@xmath158 in the a@xmath3 component . these upper limits are about a factor of two better than previous observations of wiklind & combes ( 1994 ) applying the same model assumptions to their t@xmath159 . however , the adopted standard conversion factor could introduce some uncertainty in the total molecular mass derived here . it can be easily shown that the conversion factor @xmath0 for gravitationally bound ( virialized ) clouds , @xmath160 . hence , the total molecular mass in the z = 2.8115 damped ly@xmath0 system could be overestimated if the clouds in it have a higher brightness temperature than the milky way clouds , whereas the total mass could be underestimated if the clouds have higher density . furthermore , there is a weak dependence of @xmath0 on the co abundance , @xmath161^{-1/4}$ ] ( radford _ et al . if the co abundance in the z = 2.8115 damped ly@xmath0 system is considerably lower than the milky way molecular clouds , the abundance effect will lead to an underestimate of the total amount of the molecular gas . from these considerations , the uncertainty in estimating the molecular mass for the z = 2.8115 damped ly@xmath0 system is a factor of a few . for comparison , the total molecular mass in the milky way is 2@xmath162 ( e.g. sanders _ 1991 ) , the total molecular mass in the ultraluminous ir galaxy arp 220 is @xmath163 ( e.g. solomon _ et al . _ 1990 ) , and the total molecular mass of the hyperluminous ir galaxy f10214 + 4724 at z = 2.286 , is @xmath164 ( e.g. downes et al . thus , the derived upper limit of the molecular mass in the z = 2.8115 damped ly@xmath0 system is higher than any ultraluminous ir galaxy . on the other hand , our optical observations suggest that this damped ly@xmath0 system is an analog of a milky way - like normal galaxy at high redshift . in order to detect the molecular mass in this system if it is similar to the milky way , an rms / channel of @xmath110@xmath165 mk is needed , using the same telescope size , system temperature and bandpass . this requires an integration time 10,000 times longer than obtained here . however , interferometers could be used to reach interesting detection levels ( e.g. omont _ et al . _ 1996 ; ohta _ et al _ 1996 ) .

we have obtained a moderate resolution spectrum of the quasar pks 0528 - 250 with the red channel spectrograph on the multiple mirror telescope ( mmt ) in order to study a damped ly absorption line system at z = 2.8115 . we obtain a new upper limit for the co column density for the z = 2.8108 velocity component in the z = 2.8115 damped ly system . the estimated total number density is n(h ) 20 . the physical size for the z = 2.8108 component implied by these models is about 40 parsecs . the derived depletion of nickel by dust confirms previous results that the dust - to - gas ratio in these two damped ly systems is about 10% of the milky way ratio .

we have obtained a moderate resolution spectrum of the quasar pks 0528 - 250 with the red channel spectrograph on the multiple mirror telescope ( mmt ) in order to study a damped ly absorption line system at z = 2.8115 . we obtain a new upper limit for the co column density for the z = 2.8108 velocity component in the z = 2.8115 damped ly system . the ionization of different species in this component rules out a quasar spectral energy distribution ( sed ) as the ionization field , and implies an ultraviolet radiation field intensity a few times that of the milky way value . the estimated total number density is n(h ) 20 . the physical size for the z = 2.8108 component implied by these models is about 40 parsecs . the ionization of different species also suggests a structure with a hot intercloud medium associated with a h i cloud in this component , that is , most low ionized ions are from the cold medium where photoionization and photodissociation dominates . the highly ionized species may be from the intercloud medium where collisional ionization dominates . we also present newly identified ni ii absorption lines in the z = 2.1408 and z = 2.8115 damped ly systems . the derived depletion of nickel by dust confirms previous results that the dust - to - gas ratio in these two damped ly systems is about 10% of the milky way ratio . millimeter wavelength observations obtained at the nrao 12 meter telescope provide new upper limits on co ( 3 - 2 ) emission in the z = 2.8115 damped ly system .

astro-ph9708104

i

our main results are the following . the ionization of different species in the a@xmath42 component of the z = 2.8115 damped ly@xmath0 system rules out the possibility that the quasar uv flux dominates the uv ionizing field in this component , i.e. the quasar should be more than @xmath166 mpc away from the damped ly@xmath0 system . the ionization further suggests that the shape of the uv background radiation field in this component is similar to the milky way . the uv field intensity is a few times that of the milky way value which further implies that the sfr in this component is probably similar to the sfr of the milky way if the total mass in this component is similar to the milky way . this result is consistent with the results from ly@xmath0 observations ( mller & warren 1993 ) . the physical size for this component is about 40 pc . the ionization of different species suggests a structure with a hot intercloud medium associated with a h i cloud in this component , i.e. most lowly ionized ions are from the cold medium where photoionization and photodissociation dominates . most highly ionized ions are from the intercloud medium where collisional ionization dominates . we have not detected co absorption in the rest uv spectrum from the a@xmath42 component of the z = 2.8115 damped system . the 3@xmath22 upper limit of co column density is n(co)@xmath167 @xmath5 for this component . the ratios of the n(co)/n(h i ) and n(co)/n(h@xmath3 ) are in the range of the values for the milky way diffuse clouds ( federman _ et al . _ 1980 ) . the absorption line at 5519.40 could be a co absorption line from the a@xmath3 component ; however , it also could be a co ii absorption line from a@xmath42 component . higher resolution and higher signal - to - noise observations are needed to confirm the identification of this line . analysis of photoionization and photodissociation of h@xmath3 and c i suggests that the ratio n(h@xmath3)/n(c i ) is a good indicator of the shape of the radiation field in the ism of damped ly@xmath0 absorbers . newly identified ni ii absorption lines show that the dust - to - gas ratios in the z = 2.1408 and z = 2.8115 damped ly@xmath0 systems are about 10% of that of the milky way , which are consistent with previous results . we have not detected co ( 3 - 2 ) mm emission from the z = 2.8115 damped ly@xmath0 system . the 3@xmath22 upper limits for the mass of h@xmath3 in the a@xmath42 and a@xmath3 components in the z = 2.8115 damped system are @xmath157 and @xmath168 , respectively . the results still can not rule out the possibility that the z = 2.8115 damped ly@xmath0 system is similar in molecular mass to ultraluminous ir galaxies . we are grateful to dr . a. songaila cowie for providing important comments and data in advance of publication . we thank dr . j. shields for helpful discussions . we thank dr . g. ferland for providing his cloudy program . we thank dr . g. bruzual and dr . s. charlot for providing their galaxy isochrone synthesis spectral evolution library ( gissel ) . we also wish to thank the staffs of mmto and nrao for all of their help . this research was supported by nsf ast-9058510 and nasa grant nagw-2201 . bahcall , j. n. & wolf , r. a. 1968 , apj , 152 , 701 bechtold , j. 1994 , apjs , 91 , 1 bergeson , s.d . , & lawler , j.e . 1993 , apj , 414 , l137 black , j. h. 1987 , in interstellar processes ( reidel publishing company ) , eds . hollenbach , d. j. & thronson , jr . h. a. 731 brown , r. l & vanden bout , p. a. 1993 , apj , 412 , l12 bruzual , g. a. & charlot , s. 1993 , apj , 405 , 538 cardelli j. a. , savage , b. d , bruhweiler , f. c. , smith , a. m. , ebbets , d. c. , sembach , k. r. , & sofia , u. j. 1991 , apj , 337 , l57 chen , j. & morton , d. c. 1984 , mnras , 208 , 167 de boer , k. s. , koppenaal , k. , & pottasch , s. r. , 1973 , a&a , 28 , 145 downes , d. , solomon , p. m. , & radford , s. j. e. , 1995 , apj , 453 , l65 dufton , p. l. & kingston , a. e. 1991 , mnras , 248 , 827 federman , s. r. , glassgold , a. e. , jenkins , e. b. & shaya , e. j. 1980 , apj . 242 , 545 ferland , g. j. 1993 , univ . of kentucky , department of physics and astronomy internal report . field , r. w. , benoist dazy , o. , lavollee , m. , lopez - 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( washington : gpo ) , 127 wolfe , a. m. , turnshek , d. a. , smith , h. e. , & cohen , r. d. 1986 , apjs , 61 , 249 young , p. j. , sargent , w. l. w. , & boksenberg , a. 1982 , apj , 252 , 10 figure 1.the spectrum of pks 0528 - 250 obtained with the mmt red channel spectrograph . the lower curve presents the 1 @xmath22 error as derived from count statistics in the object and night sky spectra . the features identified at better 3@xmath22 significance in table 1 are indicated by tick marks . figure 2.the summed co(3@xmath1372 ) millimeter wavelength spectrum of pks 0528 - 250 observed with nrao 12 meter telescope . the intensity scale is main - beam brightness temperature ( k ) and the velocity scale is the offset ( km s@xmath12 ) from the optical redshift , z = 2.81086 . the two velocity components are marked . a fit to the baseline has been subtracted . the upper line presents the 1 @xmath22 error derived from all scans after removing bad scans . figure 3.spectral energy distributions adopted for photoionization calculations . a(1 ) and a(2 ) are quasar seds . 1 gyr old constant sfr galaxy sed . 0.001 gyr old instantaneous starburst galaxy sed . ( d ) . milky way sed . power - law sed with @xmath169 . ionization potentials for several ions are marked . figure 4.ionization models for the h i dominant region with n(h i ) = @xmath50 @xmath5 . the ordinate is the column density of various ions , the abscissa is the log of the ionization parameter u. the figure shows results of dominant ions , o i , fe ii , si ii , s ii and ni ii in the model e power - law sed model with @xmath169 . solid lines are from cloudy and dotted lines are the observed values . figure 5. the relative ratios of n(h@xmath3)/n(c i ) vs. n(c i ) . the results are shown for sed models described in figure 3 . the vertical lines show the upper limit ( 3@xmath22 ) of n(c i ) . the horizontal lines show the lower limit ( 3@xmath22 ) of the ratio of n(h@xmath3)/n(c i ) . figure 6. model predictions for the highly ionized species , o vi , n v , c iv , si iv , si iii for the different sed models described in figure 3 . solid lines are results from cloudy . dotted lines are the observed values . the cloudy predictions for o vi and n v are out of the range for the sed model ( c ) . o vi is out of the range for the sed model ( b ) . figure 7.spectral regions including the co a - x 0 - 0 , 1 - 0 , 2 - 0 , 3 - 0 , 4 - 0 absorption bands from the z = 2.8108 and 2.8132 components in the rest frame of the z = 2.8108 absorber toward pks 0528 - 250 . the positions of the absorption bands are indicated by tick marks . the lowest right panel is a composite spectrum obtained by combining the 2 - 0 band with the 0 - 0 , 1 - 0 , 3 - 0 , 4 - 0 bands which are shifted to the wavelength of the 2 - 0 band . species & @xmath18 & f@xmath171 & w@xmath172 & n(@xmath5)@xmath173 & n(@xmath5)@xmath174 & w@xmath172 & n(@xmath5)@xmath175 + al ii ( a@xmath42+a@xmath3)@xmath176 & 1670.788 & 1.88&2.100&@xmath177&&2.100&@xmath178 + c i & 1560.310 & 0.0822 & & @xmath179@xmath180 & & @xmath1810.032 & @xmath1811.8@xmath182 + c ii ( a@xmath42+a@xmath3+a@xmath183)@xmath176 & 1334.532 & 0.118 & 2.29 & 1.7@xmath184 & & 2.29 & 1.7@xmath184 + c ii@xmath60 & 1335.702 & 0.118 & & & & 0.312 & 3.6@xmath185 + c iii ( a@xmath42+a@xmath3)@xmath176 & 977.020 & 0.768 & 1.89 & 7.6@xmath6 & & 1.89 & 7.6@xmath6 + c iv & 1548.202 & 0.194&1.28 & 5.6@xmath186 & 1.3@xmath186 & & + c iv&1550.774&0.0970 & 0.976&2.0@xmath186 & 1.1@xmath186 & & + si i@xmath187 & 1845.520 & 0.229 & @xmath1810.105&@xmath1811.6@xmath188&&@xmath189&@xmath1811.6@xmath182 + si ii & 1808.013 & 0.00208 & 0.397&8.5@xmath186&&0.094&1.7@xmath186 + si ii@xmath60@xmath187 & 1533.431 & 0.13 & @xmath1810.031 & @xmath1811.2@xmath182 & & & + si iii & 1206.500 & 1.66 & 1.14&1.9@xmath186&3.6@xmath185 & & + si iv&1393.755 & 0.528 & 0.995 & 7.9@xmath185&3.0@xmath185 & & + si iv&1402.770 & 0.262 & 0.748 & 4.6@xmath185&3.0@xmath185 & & + s i@xmath187&1425.030&0.181&@xmath1810.031&@xmath1819.5@xmath116&&@xmath1810.031&@xmath1819.5@xmath190 + s ii&1250.583 & 0.00535 & 0.157 & 2.7@xmath186 & & 0.131 & 2.6@xmath191 + & 1253.808 & 0.0107 & 0.315 & ... & & 0.236 & ... + s iii ( a@xmath42+a@xmath3)@xmath176&1012.504 & 0.0355 & 0.622 & 3.2@xmath186 & & 0.622 & 3.2@xmath186 + o i&1302.169 & 0.0486 & 1.36 & 2.1@xmath184 & & 0.70 & 1.1@xmath192 + o vi & 1031.927 & 0.13 & 0.97 & 4.0@xmath6&5.2@xmath186 & & + n v & 1238.821 & 0.157&0.247 & @xmath193 & @xmath194 & & + fe ii&2249.879 & 0.0018 & 0.160 & 1.8@xmath186 & & 0.046 & 3.6@xmath195 + & 2260.781 & 0.0028 & 0.260 & ... & & 0.046 & ... + & 2374.461&0.0395&1.201& ... &&0.342 & ... + ni ii & 1741.549&0.068 & 0.116 & 6.9@xmath182&&0.072 & 3.8@xmath182 + & 1709.600 & 0.047&0.101 & ... & & 0.056 & ... + & 1370.132 & 0.100 & 0.103 & ... & & 0.062 & ... + & 1454.842 & 0.0515 & 0.065 & ... & & 0.027 & ... + ni ii ( a@xmath42+a@xmath3)@xmath176 & 1467.756 & 0.0149 & 0.038 & 1.3@xmath185 & & 0.038 & 1.3@xmath185 + co ii ( ? ) & 1448.011 & 0.04516 & 0.032 & 3.9@xmath182 & & & + co a - x ( ? ) & 1447.359 & 0.0360 & & & & 0.032 & 6.4@xmath182 + co ( composite)@xmath187&&&@xmath1810.017&@xmath196 & & & + h@xmath3 & & & & @xmath197 & & & +

the ionization of different species in this component rules out a quasar spectral energy distribution ( sed ) as the ionization field , and implies an ultraviolet radiation field intensity a few times that of the milky way value . the ionization of different species also suggests a structure with a hot intercloud medium associated with a h i cloud in this component , that is , most low ionized ions are from the cold medium where photoionization and photodissociation dominates . the highly ionized species may be from the intercloud medium where collisional ionization dominates . we also present newly identified ni ii absorption lines in the z = 2.1408 and z = 2.8115 damped ly systems .

we have obtained a moderate resolution spectrum of the quasar pks 0528 - 250 with the red channel spectrograph on the multiple mirror telescope ( mmt ) in order to study a damped ly absorption line system at z = 2.8115 . we obtain a new upper limit for the co column density for the z = 2.8108 velocity component in the z = 2.8115 damped ly system . the ionization of different species in this component rules out a quasar spectral energy distribution ( sed ) as the ionization field , and implies an ultraviolet radiation field intensity a few times that of the milky way value . the estimated total number density is n(h ) 20 . the physical size for the z = 2.8108 component implied by these models is about 40 parsecs . the ionization of different species also suggests a structure with a hot intercloud medium associated with a h i cloud in this component , that is , most low ionized ions are from the cold medium where photoionization and photodissociation dominates . the highly ionized species may be from the intercloud medium where collisional ionization dominates . we also present newly identified ni ii absorption lines in the z = 2.1408 and z = 2.8115 damped ly systems . the derived depletion of nickel by dust confirms previous results that the dust - to - gas ratio in these two damped ly systems is about 10% of the milky way ratio . millimeter wavelength observations obtained at the nrao 12 meter telescope provide new upper limits on co ( 3 - 2 ) emission in the z = 2.8115 damped ly system .

1002.1343

i

bl lac objects , being highly continuum - dominated , are a perennial problem for those wishing to study the evolution of agn populations . the lack of visible broad lines and , even more , the low equivalent width of host absorption features makes redshift determinations extraordinarily difficult . yet , since the continuum domination is a manifestation of the good alignment of the relativistic jet outflow to the earth line - of - sight , @xcite knowledge of the distance , and hence luminosity scale , of these sources is very interesting . this problem has become particularly important with gamma - ray detection of large numbers of blazars with the _ fermi _ lat @xcite . it has been known since _ egret _ that radio loud flat spectrum blazars dominate the bright extragalactic sources in the gev sky @xcite ; these objects are flat - spectrum radio quasars ( fsrq ) and radio loud bl lacs . we have good techniques in place to identify likely radio counterparts for the gamma - ray sources . extensive spectroscopy campaigns , especially on the egret - like ` cgrabs ' sample @xcite have provided nearly complete redshifts and characterizations of the fsrq . however , despite extensive observation , including 8+m telescope integrations , less than half of the bl lac counterparts have spectroscopic ids . in some cases , high quality spectroscopy can give useful lower limits on the source redshift @xcite , but many remain unconstrained . in the first lat blazar catalog @xcite , the problem is even more pronounced since the excellent high energy response of the lat favors detection of hard spectrum sources . bl lacs are substantially harder ( @xmath1 ) than fsrq ( @xmath2 ) and so provide a larger fraction , @xmath3% of the _ fermi _ blazar sample , than was seen by _ we attempt here to constrain the redshifts of radio loud bl lacs which have shown no convincing spectroscopic redshift solution , despite sensitive observations on large telescopes , by high dynamic range imaging searches for the agn host . our targets are drawn from the ` crates ' catalog of bright flat - spectrum @xmath4 radio sources @xcite . specifically , in this program we targeted the subset of crates consisting of @xmath5 ) sources selected as likely gamma - ray blazars before the fermi mission ( i.e. cgrabs sources , healey et al . 2008 ) and @xmath6 ) sources that are likely counterparts to lat sources detected early in the mission @xcite . all sources are at declination @xmath7 and all have been shown to display featureless optical spectra @xcite , with sensitive ( 4m+ class ) observations . we were able to image @xmath8 of the sources satisfying these critera at the time of the observing campaigns . it has been claimed @xcite that bl lac host galaxies detected with hst imaging are remarkably uniform giant ellipticals with @xmath9 ; accordingly host detections can give redshift estimates and upper limits on the host flux can give lower limits on the distance . here we do not test this assumption or the possible biases that would select a modest magnitude range for the detected host sample . we simply apply the method to extract redshift constraints , noting that while individual redshifts are doubtless imprecise , the estimates can still be useful for statistical studies of bl lac evolution and as a guide to and comparison with other methods of redshift estimation . conversely , when precision spectroscopic redshifts become available , our measurements can be used to help constrain the host evolution . since we will be searching for de vaucouleurs profile excesses in the wings of the stellar psf of the bright bl lac core , we require good natural seeing and a moderate field of view for adequate comparison stars . for example , while near - ir adaptive optics can deliver superior psf cores , the wings of the source at @xmath1090% encircled energy are extensive and often quite variable over the small corrected fov . this prevents the accurate psf modeling and subtraction required to obtain host measurements whose integrated magnitude can be 10% or less of the core flux .

we have obtained high dynamic range , good natural seeing images of bl lacertae objects ( bl lacs ) to search for the agn host and thus constrain the source redshift . these objects are drawn from a sample of bright flat - spectrum radio sources that are either known ( via recent _ fermi _ lat observations ) gamma - ray emitters or similar sources that might be detected in continuing gamma - ray observations . all had spectroscopic confirmation as bl lac sources , but no redshift solution . the mean of the fit redshifts ( and lower limits ) is higher than those of spectroscopic solutions in the radio- and gamma - ray- loud parent samples , suggesting corrections may be needed for the luminosity function and evolution of these sources .

we have obtained high dynamic range , good natural seeing images of bl lacertae objects ( bl lacs ) to search for the agn host and thus constrain the source redshift . these objects are drawn from a sample of bright flat - spectrum radio sources that are either known ( via recent _ fermi _ lat observations ) gamma - ray emitters or similar sources that might be detected in continuing gamma - ray observations . all had spectroscopic confirmation as bl lac sources , but no redshift solution . we detected hosts for 25/49 objects . as these galaxies have been argued to be standard candles , our measured host magnitudes provide redshift estimates ( ranging from 0.21.0 ) . lower bounds are established on the redshifts of non - detections . the mean of the fit redshifts ( and lower limits ) is higher than those of spectroscopic solutions in the radio- and gamma - ray- loud parent samples , suggesting corrections may be needed for the luminosity function and evolution of these sources .

astro-ph0404148

r

the na d doublet was detected in six of the eight galaxies : ngc 1569 , ngc 1614 , ngc 4214 - 1 and -2 , ngc 4449 , ngc 5253 , and m82 . no absorption was seen in ngc 2363 or i zw 18 . we believe the na d in ngc 5253 , ngc 4214 - 1 , and specific components of ngc 1569 and ngc 4449 are likely stellar in nature , via arguments discussed in section 3.1 . the spectra of the five galaxies in which interstellar sodium absorption was detected are shown in figure 1 ; there are a total of ten interstellar na d absorption components . it is interesting to compare the absorption line kinematics to those of emission - line gas . kinematics were previously measured across large regions in the dwarfs in this paper and m82 to map out superbubbles by martin 1998 . our observations directly measured the h@xmath14 also albeit over a much smaller region . nonetheless , we can use the h@xmath14 along these particular sightlines to tie na d kinematics into these larger structures . the detailed results of these spectra will be discussed individually in 4.2 in order to make a statement about the properties of the interstellar sodium in these galaxies , we need to first determine that the sodium we see is actually interstellar . the na d resonance doublet is prominent in the spectra of cooler stars . the spectrum of a dwarf will be dominated by k - type giants and supergiants if the starburst is older than @xmath810 myr ( leitherer et al . 1999 ) ; these stars show strong photospheric sodium absorption . therefore , we must find a way of deciphering the nature of the neutral sodium observed . we have made use of the available stellar spectral lines in our data to help distinguish between stellar and interstellar sodium . in particular , the mg b band triplet ( 5167.32 , 5172.68 , and 5183.60 ) is a good indicator of the presence of certain stellar populations . the mg b triplet is present in f through m stars , with maximum absorption in the range k0 to m3 , and is not present in the cnm because it is a highly excited line . therefore , we can be certain that any mg b absorption we see is from a stellar atmosphere . the equivalent width of this absorption feature is also well correlated with that of the stellar na d absorption ; we can use the mg b to disjoin the stellar and interstellar sodium by fitting the na d absorption profiles with multiple components , one of which corresponds to a purely stellar feature . using the stellar atlas of jacoby , hunter , & christian ( 1984 ) , we have measured the equivalent widths of the mg b and na d absorption lines in a sample of stars and fit the data with a least - squares fit . we find @xmath19 this is shown with the data from the stellar atlas in figure 2 . this is consistent with the calculations of rupke et al . ( 2002 ) that w(nad ) @xmath8 0.5w(mgb ) . we can use this relationship to predict the strength , width and velocity of the stellar component of the na d absorption . there are two galaxies in our sample , ngc 1569 and ngc 4449 , which have both a stellar and interstellar component . ngc 5253 has what appears to be a purely stellar component , and therefore is not included in the sample of galaxies showing interstellar neutral sodium absorption . the equivalent widths of the stellar and interstellar na d and mg b for these three galaxies are shown in figure 3 , and the spectra are presented in figure 4 . the central component of the m82 absorption profile is near the systemic velocity ( it is redshifted by only 4 km s@xmath1 ) ; however , no mg b absorption is seen to a level of 0.24 . since the equivalent width of the na d absorption in this central component is 1.44 , we can safely say that there is no significant population of cool giants and supergiants contaminating the spectrum at this position , and we will assume this component is purely interstellar . hlsa classify their `` interstellar dominated '' sample galaxies as having a larger line width than their `` strong stellar contamination '' galaxies . since our spectra are well resolved and we are able to distingush between stellar and interstellar lines , it is interesting to note that we can use this method , rather than the overall width of the absorption profile , to categorize the na d. there are only two galaxies ( ngc 1569 and ngc 4449 ) where we have both stellar and interstellar lines , and both of these absorption line systems have a larger interstellar width than stellar . similarly , hlsa found that systems with largers widths are interstellar dominated . to discuss the kinematics of the cnm , it is imperative to know the systemic velocity ( v@xmath20 ) of the galaxy , i.e. the heliocentric velocity of the starburst . however , one may wish to compare data with previous observations in which the velocity of the galactic center of mass was used . usually the center - of - mass velocity and the stellar velocity are similar , unless the galaxy is inclined and the starburst region is far from the axis of rotation ; this could create a velocity offset between the starburst velocity and that of the galactic nucleus . in this case , it may be better to use the velocity of the stars themselves . we were able to get stellar velocities for three galaxies ( ngc 1569 , ngc 4449 , and ngc 5253 ) by using stellar absorption lines ( see 3.1 ) . in the other five galaxies , we set the systemic velocity using ( in order of preference ) co maps ( ngc 1614 , ngc 4214 , and m82 ) , optical lines ( ngc 2363 ) , and stellar velocities ( i zw 18 ) . table 1 gives the systemic velocities used in this analysis and their sources . a heliocentric velocity scale is used throughout the paper . the hlsa sample of 32 lirgs showed significant blueshifts in the na d doublet for their `` interstellar dominated '' outflows , indicating nuclear outflows with typical velocities of @xmath8100 km s@xmath1 . our data for the dwarf galaxies also show the na d absorption to be blueshifted , although with overall slower outflow speeds ( @xmath830 km s@xmath1 ) . ngc 1614 and m82 show both redshifted and blueshifted components ; these are further discussed in 4.2 . the velocities for individual interstellar absorption components are given in table 2 . the line width ( fwhm ) of the interstellar components for the dwarfs and m82 ranges from @xmath830 to @xmath880 km s@xmath1 , with an average of 43 km s@xmath1 . the existence of such broad absorption lines in neutral sodium leads us to conclude that there are multiple clouds of cold gas producing each component of the absorption ; the thermal width of a cloud of cold gas at @xmath8100 k would be only @xmath80.20 km s@xmath1 . moreover , the line widths of cold clouds in the galactic halo are found to be just a few km s@xmath1 ( spitzer & fitzpatrick 1995 ) . the individual line widths in ngc 1614 are significantly larger ( @xmath8100 km s@xmath1 or more ) than those in the dwarfs or m82 ( @xmath845 km s@xmath1 ) . the total width of all components in m82 is relatively large ( 236 km s@xmath1 ) . among the dwarfs in the sample , we do not see a correlation between the fwhm of the lines and the rest - frame equivalent width . however , when the data for m82 and ngc 1614 are added , there is a trend wherein equivalent width increases in proportion to fwhm , for these n points . given the lack of correlation seen by hlsa using a much larger data set , we conclude only that the largest values of fwhm ( and similarly the largest equivalent widths ) are much smaller in dwarfs than in brighter galaxies . the doublet lines are fit with gaussian profiles in pairs with specfit to measure the velocity , fwhm , and equivalent width w of each line ( see table 2 ) . if the absorbing gas is optically thin , then the blue ( @xmath155890 ) line will be twice as strong as the red ( @xmath155896 ) line , and the `` doublet ratio , '' w@xmath21/w@xmath22 = 2 . if the gas is optically thick , w@xmath21/w@xmath22 approaches unity as the optical depth @xmath23 approaches infinity . in our data , just one component is optically thin , the rest are optically thick . we can easily measure how much of the continuum source is being obscured by absorbing gas clouds by studying the residual normalized intensity i@xmath24 of a line at wavelength @xmath15 . if i@xmath24 = 0 for the blue line of a doublet ( i.e. the stronger line ) , then no continuum radiation is `` leaking '' into the absorption line . in other words , the absorbing cloud completely covers the continuum source and the covering factor c@xmath25 = 1 . if a cloud does not cover the whole source , the continuum radiation will `` leak '' into the absorption profile and increase the minimum flux , i@xmath24 , and c@xmath25 @xmath16 1 . specifically , following the derivation of barlow & sargent ( 1997 ) , we can find the covering factor : @xmath26 in our data , the covering factor ranges from 0.23 to 1.0 ( see table 2 ) . now that we know the covering factor of the absorbing gas , we can determine the na d column density . the curve of growth relates the optical depth at line center , @xmath27 , to the doublet ratio via a function f(@xmath27 ) , determined numerically ( spitzer 1978 ) . the column density is then @xmath28 ( spitzer 1968 ) , where @xmath29 is the oscillator strength ( morton 1991 ) , and w@xmath24 and @xmath15 are given in angstroms . using this method , we find that n(nad ) in the dwarfs ranges from 6.2 @xmath18 @xmath30 @xmath5 in ngc 1569 to 5.1 @xmath18 @xmath31 @xmath5 in ngc 4449 . we find the total neutral sodium column densities in ngc 1614 and m82 to be 1.0 @xmath18 @xmath32 @xmath5 and 2.4 @xmath18 @xmath31 @xmath5 , respectively . the measured equivalent widths , and the calculated covering factors and na d column densities , are presented in table 2 . from the column density of sodium , we can then use the metallicity of the galaxy ( given in table 2 ; ( na / h)@xmath10 = 2.04@xmath33 martin & zalubas 1981 ) to find the total column probed . a source of systematic uncertainty is the contingence of neutral sodium column density on the ionization parameter , @xmath34 , as well as the fractional depletion of sodium onto grains , @xmath35 . since dwarfs typically have a low metallicity , we expect lower dust content and depletion level than in larger galaxies . it is the product of these , @xmath36 , which is the important factor in our calculations , as is seen in wakker & mathis ( 2000 ) . they measure the abundance of neutral sodium in galactic high- and intermediate - velocity clouds . using their results and a typical column of 10@xmath37 @xmath5 , we calculate @xmath36 = @xmath8300 . we therefore parameterize the column densities by a simple factor of ( @xmath36/100 ) to reflect the typical correction , and calculate the total column using the equation @xmath38 we find that the corresponding n ( ) in the dwarfs could be as large as 10@xmath37(@xmath39 ) @xmath5 ( ngc 1569 ) to 10@xmath40(@xmath39 ) @xmath5 ( ngc 4449 ) . in m82 and ngc 1614 , this conversion gives a total column of 10@xmath41(@xmath39 ) @xmath5 and 10@xmath40(@xmath39 ) @xmath5 , respectively . in addition to na d , the resonance absorption line ( @xmath42 ) is also present in two of our spectra . and have similar ionization potentials ( 4.34 ev and 5.14 ev , respectively ) and similar depletion levels ( savage & sembach 1991 , wakker & mathis 2000 ) , so it is expected that the species will be spatially coincident in the cnm . it is unfortunate that in nearby galaxies , is found in spectral regions that are strongly contaminated by the fraunhofer a - band absorption from atmospheric o@xmath43 ( near 7600 ) . in only two galaxies were we able to discern the absorption : ngc 1569 and ngc 1614 . ngc 1569 is luckily blueshifted slightly away from the sky absorption , while ngc 1614 is redshifted out of the contaminated region entirely . other galaxies are either completely contaminated by the fraunhofer absorption , the doublet is too weak to measure , or the lines lie between echelle orders . the profile is arguably a better constraint on the cold gas kinematics than the na d profile because the doublet spacing is wider , and the oscillator strength is lower so the lines are less saturated . we fit the profile in ngc 1614 with specfit and found components at -149 km s@xmath1 and + 70 km s@xmath1 . this result helped us pin down the best component velocities for the na d fits , which were previously poorly constrained . due to the low signal - to - noise of the continuum , the doublet ratio and covering factor are uncertain . the results of the fitting are presented in table 3 . without the addition of , the na d profile for ngc 1569 is blended with galactic absorption and atmospheric emission . the stellar profile from the starburst is constrained by absorption , leaving a range of possibilities for the central velocity of the interstellar na d. we find absorption at -24 km s@xmath1 , thereby defining the velocity at which the interstellar na d lies . due to the fraunhofer absorption , the normalization of the continuum in the ngc 1569 spectrum is likely imperfect and the column densities in table 3 are highly uncertain . the spectra do not provide a useful column density constraint .

the absorption features were separated into multiple components and separated into stellar and interstellar parts based on kinematics . we find that three of the dwarfs show outflows , with an average blueshift of 27 km s . we compare the shocked gas velocity ( v ) to the ionized gas velocity ( v ) and interpret the velocity difference as either a trapped ionization front ( ngc 4214 ) or a leaky region ( ngc 2363 ) . the dwarfs show n = 10 , while the na d columns in m82 and ngc 1614 are 10 and 10 , respectively .

we have obtained high resolution echelle spectra ( r = 30,000 - 50,000 ) of the na d absorption doublet ( , 5896 ) for six dwarf starburst galaxies and two more luminous starbursts : m82 and ngc 1614 . the absorption features were separated into multiple components and separated into stellar and interstellar parts based on kinematics . we find that three of the dwarfs show outflows , with an average blueshift of 27 km s . this is small compared to the highest velocity components in ngc 1614 and m82 ( blueshifted by 150 km s and 91 km s , respectively ) ; these two brighter galaxies also show more complex absorption profiles than the dwarfs . none of the outflow speeds clearly exceed the escape velocity of the host galaxy . sightlines in ngc 2363 and ngc4214 apparently intersect expanding shells . we compare the shocked gas velocity ( v ) to the ionized gas velocity ( v ) and interpret the velocity difference as either a trapped ionization front ( ngc 4214 ) or a leaky region ( ngc 2363 ) . the dwarfs show n = 10 , while the na d columns in m82 and ngc 1614 are 10 and 10 , respectively . the mass of expelled gas is highly sensitive to outflow geometry , dust depletion , and ionization fraction , but with a simple shell model we estimate neutral outflow gas masses from m to m .

astro-ph0404148

c

we have obtained high - resolution echelle spectra of six dwarf starburst galaxies , ngc 1614 , and m82 in order to study the cold interstellar gas in dwarf starbursts . interstellar neutral sodium column densities were obtained by measuring the equivalent width of the na d absorption doublet . we find that out of the eight galaxies , ngc 1569 , ngc 1614 , ngc 4214 - 2 , ngc 4449 , and m82 unambiguously show interstellar sodium absorption , while ngc 2363 , ngc 4214 - 1 , ngc 5253 , and i zw 18 do not . the dwarf galaxies ngc 1569 , ngc 4214 , and ngc 4449 exhibit single - component outflows of neutral gas . ngc 1614 and m82 have multiple interstellar components , some outflowing and some infalling , and both galaxies show more absorption from outflowing gas than any dwarf galaxy . the dwarf galaxies show trends similar to brighter , larger galaxies , but on a smaller scale . while samples of lirgs and ulirgs are shown to have average outflow speeds of @xmath8100 km s@xmath1 ( hlsa ) and @xmath8700 km s@xmath1 ( rupke et al . 2002 ; martin & armus 2004 ) , respectively , the three dwarfs show an average outflow speed of only @xmath830 km s@xmath1 . additionally , most ulirgs ( e.g. 73% in rupke et al . 2002 ) show an outflow , whereas only half of the galaxies in our sample have an outflow region . spectral lines in dwarf galaxies also have smaller velocity spreads . it is particularly interesting to see how complex the absorption line spectra become at high resolution . m82 is an excellent example of an absorption line system previously believed to be a single pair of lines , but within each member of the doublet we find a wealth of structure . we resolve at least five line pairs , showing the incredibly complicated nature of the cnm in this galaxy . this is a very intriguing result and prompts us to wonder how many of the galaxies in previous samples could be resolved into complex systems of multiple components . ngc 1614 shows complex absorption as well , though it has a far smoother profile in na d ( and ) than m82 . the three dwarfs with outflows do not seem to exhibit this behavior , showing far simpler spectra . for the first time we are able to combine measurements of the kinematics of the warm , ionized gas in emission with absorption spectra of the cold , neutral gas . for sightlines intersecting a single shell , we can determine whether the ionization front is trapped inside the shock front . this works extremely well for ngc 2363 , which is a simple expanding bubble with an ionization front that has expanded beyond the shock front . ngc 4214 - 2 also presents a relatively simple shell , and this galaxy also shows na d absorption . from the kinematics we postulate that the ionization front is expanding faster than the shock front , though it has clearly not `` caught up '' yet , as there is still a concentric , outer expanding bubble of cold , neutral gas . in other words , the ionization front is still trapped in the shell . the kinematics of na d and h@xmath14 are very different in other galaxies , and can not be easily explained by this straightforward picture . combining our measurements of column density with previous observations of superbubbles and supershells in the sample galaxies , we have parameterized the mass of neutral gas ( or a limiting case thereof ) flowing out of the starbursting region . using a simple spherical shell model , we find the total neutral gas outflow masses to be roughly 10@xmath9 to 10@xmath11 m@xmath10 . ngc 4449 shows far more outflowing cold gas than any other dwarf galaxy . compared to the measurements of outflowing warm and hot gas from these galaxies ( martin 1998 ) , it is likely that the bulk of the energy in the outflow is carried by the warm and hot gas , rather than cold gas . financial support was provided by the david and lucille packard foundation and the alfred p. sloan foundation . this research has made use of the nasa / ipac extragalactic database ( ned ) which is operated by the jet propulsion laboratory , california institute of technology , under contract with the national aeronautics and space administration . this research has made use of the nasa astrophysics data system abstract service . the authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of mauna kea has always had within the indigenous hawaiian community . we are most fortunate to have the opportunity to conduct observations from this mountain . we appreciate comments and clarifications from an anonymous referee . aloisi , a. , savaglio , s. , heckman , t. m. , hoopes , c. g. , leitherer , c. , & sembach , k.r . 2003 , apj , in press alonso - herrero , a. , engelbracht , c. w. , rieke , m. j. , rieke , g. h. , & quillen , a. c. 2001 , apj , 546 , 952 bajaja , e. , huchtmeier , w. k. , & klein , u. 1994 , a&a , 285 , 385 barlow , t. a. , & sargent , w. l. w. 1997 , aj , 113 , 136 becker , r. , henkel , c. , bomans , d. j. , & wilson , t. l. 1995 , a&a , 295 , 302 bica , e. , pastoriza , m. , da silva , l. , dottori , h. , & maia , m. 1991 , aj , 102 , 1702 bushouse , h. a. 1987 , apj , 320 , 49 calzetti , d. , meurer , g. r. , bohlin , r. c. , garnett , d. r. , kinney , a. l. , leitherer , c. , & storchi - bergmann , t. 1997 , aj , 114 , 1834 cameron , a. g. w. 1973 , ssrv , 15 , 121 casoli , f. , dupraz , c. , combes , f. , & kasez , i. , 1991 , a&a , 251 , 1 cervio , m. , & mas - hesse , j. m. 1994 , a&a 284 , 789 dahlem , m. , weaver , k. a. , & heckman , t. m. 1998 , apjs , 118 , 401 gonzalez - delgado , r. , leitherer , c. , heckman , t. , lowenthal , j. , ferguson , h. , & robert , c. 1998 , apj , 495 , 698 hartmann , d. & burton , w. b. 1997 , atlas of galactic neutral hydrogen ( new york : cambridge university press ) heckman , t. , lehnert , m. , strickland , d. , & armus , l. 2000 , apjs , 129 , 493 ( hlsa ) huchra , j.p . , geller , m.j . , gallagher , j. , hunter , d. , hartmann , l. , fabbiano , g. , & aaronson , m. 1983 , apj , 274 , 125 hunter , d. a. , wilcots , e. m. , van woerden , h. , gallagher , j. s. , & kohle , s. 1998 , apj , 495 , l47 jacoby , g. , hunter , d. , & christian , c. 1984 , apjs , 56 , 257 karachentsev , i. d. , makarov , d. i. , & huchtmeier , w. k. 1999 , a&as , 139,97 kobulnicky , h. a. , & skillman , e. d. 1995 , apj , 454 , l121 . 1996 , apj , 471 , 211 kriss , g. 1994 , asp conf . 61 , in astronomical data analysis software and systems iii , ed . d. r. crabtree , r. j. hanisch , & j. barnes ( san francisco : asp ) , 437 kuntz , k. d. & danly , l. 1996 , apj , 457 , 703 lecavelier des etangs , a. , et al . 2004 , a&a , 413 , 131 legrand , f. , tenorio - tagle , g. , silich , s. , knuth , d. , & cervio , m. 2001 , apj , 560 , 630 lehnert , m. d. , & heckman , t. m. 1996 , apj , 472 , 546 lehnert , m. d. , heckman , t. m. , & weaver , k. a. 1999 , apj , 523 , 575 leitherer , c. , vacca , w. d. , conti , p. s. , filippenko , a. v. , carmelle , r. , & sargent , w. l. w. 1996 , apj , 465 , 717 leitherer , c. et al . 1999 , apjs , 123 , 3 lequeux , j. , peimbert , m. , rayo , j. f. , serrano , a. , & torres - peimbert , s. 1979 , a&a , 80 , 155 lequeux , j. , knuth , d. , mas - hesse , j. , & sargent , w. 1995 , a&a , 301 , 18 lo , k .- y . , cheung , k. , masson , c. , phillips , t. , scott , s. , & woody , d. 1987 , apj , 312 , 574 luridiana , v. , peimbert , m. , & leitherer , c. 1999 , apj , 527 , 110 mackenty , j. w. , maz - apellniz , j. , pickens , c. e. , norman , c. a. , & walborn , n. r. 2000 , aj , 120 , 3007 marlowe , a. t. , heckman , t. m. , wyse , r. f. g. , & schommer , r. 1995 , apj , 438 , 563 martin , c. l. 1996 , apj , 465 , 680 . 1998 , apj , 506 , 222 . 1999 , apj , 513 , 156 martin , c. l. & armus , l. 2004 , in preparation martin , w. c. & zalubas , r. 1981 , j. phys . chem . ref . data , 10 , 153 martin , c. l. , kobulnicky , h. a. , & heckman , t. m. 2002 , , 574 , 663 mcintyre , v. j. 1998 , publications of the astronomical society of australia , 15 , 157 meier , d. s. , turner , j. l. , crosthwaite , l. p. , & beck , s. c. 2001 , , 121 , 740 morton , d. c. 1991 , apjs , 77 , 119 mhle , s. , httemeister , s. , klein , u. , & wilcots , e. m. 2001 , astronomische gesellschaft meeting abstracts , 18 , 546 neff , s. g. , hutchins , j. b. , standord , s. a. , & unger , s. w. 1990 , aj , 99 , 1088 ohyama , y. , et al . 2002 , in asp conf . 289 , the proceedings of the iau 8th asian - pacific regional meeting , ed . s. ikeuchi , j. hearnshaw , & t. hanawa ( san francisco : asp ) , 285 papaderos , p. , loose , h .- h . thuan , t. x. , & fricke , k. j.,1996 , a&as , 120 , 207 phillips , a. 1993 , aj , 105 , 486 roy , j .- r . , boulesteix , j. , joncas , g. , & grundseth , b. 1991 , apj , 367 , 141 rupke , d. s. , veilleux , s. , & sanders , d. b. 2002 , apj , 570 , 588 sargent , w. l. w. , & fillipenko , a. v. 1991 , aj , 102 , 107 savage , b. d. , & sembach , k. r. 1991 , apj , 379 , 245 . 1996 , ara&a , 34 , 279 silich , s. a. , & tenorio - tagle , g. 1998 , mnras , 299 , 249 skillman , e. d. , kennicutt , r. c. , & hodge , p. w. 1989 , apj , 347 , 875 sofue , y. 1997 , pasj , 49 , 17 spitzer , l. 1968 , diffuse matter in space ( new york : interscience publication ) . 1978 , physical processes in the interstellar medium ( new york : wiley - interscience ) spitzer , l. & fitzpatrick , e. l. 1995 , apj , 445 , 196 stil , j. m. , & israel , f. p. 2002 , , 392 , 473 storchi - bergmann , t. , calzetti , d. , kinney , a. l. 1994 , apj , 429 , 572 summers , l. k. , stevens , i. r. , strickland , d. k. , & heckman , t. m. 2003 , mnras , 342 , 690 umeda , h. , nomoto , k. , tsuru , t. g. , & matsumoto , h. 2002 , apj , 578 , 855 van zee , l. , westpfahl , d. , haynes , m. p. , & salzer , j. j. 1998 , aj , 115 , 1000 vogt , s. s. , et al . 1994 , proc . spie , 2198 , 362 wakker , b. p. & mathis , j. s. 2000 , apj , 544 , l107 wei , a. , walter , f. , neininger , n. , & klein , u. 1999 , a&a , 345 , l23 wills , k. a. , pedlar , a. , & muxlow , t. w. b. 2002 , , 331 , 313 lcccccccc ngc 1569 & ibm & -40 & 28 & 2.2 & -17.26 & 5.9 & 0.92 & 1 , 2 + ngc 1614 & sb(s)c pec & 4730 & 210 & 64.0 & -20.84 & 170 & 11.25 & 3 , 4 + ngc 2363 & ib(s)m & 70 & 53 & 3.6 & -16.75 & 79 & ... & 5 , 2 + ngc 4214 & iab(s)m & 304 & 35 & 3.6 & -17.65 & 110 & 1.05 & 6 , 2 + ngc 4449 & ibm & 192 & 65 & 3.6 & -17.86 & 135 & 0.34 & 1 , 2 + ngc 5253 & im(pec ? ) & 389 & @xmath1615 & 4.1 & -17.62 & 20 & 0.73 & 1 , 2 + m82 & i0 & 214 & 135 & 3.6 & -18.95 & 88 & 7.98 & 7 , 8 + i zw 18 & ... & 761 & 50 & 10.0 & -13.84 & 2.6 & ... & 9 , 10 + ngc 1569 & -24 & 0.20 & 1.38 & 39.7 & 0.23 & 0.25 & 0.62 @xmath99 0.22 + ngc 1614 & -149 & 4.85 & 1.15 & 294.7 & 0.80 & 0.70 & 42.52 @xmath99 0.20 + & + 70 & 1.13 & 1.08 & 102.7 & 0.52 & ... & 58.93 @xmath99 0.20 + ngc 4214 - 2 & -23 & 0.50 & 1.39 & 39.9 & 0.71 & 0.25 & 2.2 @xmath99 0.28 + ngc 4449 & -34 & 0.17 & 1.07 & 30.9 & 0.27 & 0.25 & 50.9 @xmath99 0.28 + m82 & -91 & 0.62 & 1.36 & 49.1 & 0.69 & 1.0 & 3.0 @xmath99 0.17 + & -35 & 1.03 & 1.11 & 47.2 & 1.00 & ... & 1.7 @xmath99 0.17 + & + 4 & 0.77 & 1.13 & 36.7 & 1.00 & ... & 7.7 @xmath99 0.17 + & + 45 & 1.52 & 1.19 & 78.5 & 1.00 & ... & 9.4 @xmath99 0.17 + & + 86 & 0.46 & 1.98 & 24.6 & 1.00 & ... & 2.4 @xmath99 0.17 + + ngc 2363 & ... & 0.11 & ... & ... & ... & 0.25 & @xmath160.57 + ngc 4214 - 1 & ... & 0.04 & ... & ... & ... & 0.25 & @xmath160.37 + ngc 5253 & ... & 0.07 & ... & ... & ... & 0.37 & @xmath160.20 + i zw 18 & ... & 0.25 & ... & ... & ... & 0.02 & @xmath161.27 + lcccc ngc 1569 & -24 & 500 & 36@xmath991 & @xmath100 + ngc 1614 & -149 & 1000 & @xmath10110 & @xmath102 + & + 70 & 1000 & @xmath10310 & @xmath104 + ngc 2363 & ... & 122 & @xmath161.0 & @xmath105 + ngc 4214 - 1 & ... & 700 & @xmath1642 & @xmath106 + ngc 4214 - 2 & -23 & 500 & 127@xmath9916 & @xmath107 + ngc 4449 & -34 & 1000 & @xmath10865 & 1.4@xmath109 + ngc 5253 & ... & 870 & @xmath1634 & @xmath110 + m82 & -91 & 743 & 381@xmath9921 & @xmath111 + & -35 & 286 & [email protected] & @xmath112 + & + 4 & 500 & 450@xmath9910 & @xmath113 + & + 45 & 500 & 540@xmath9910 & @xmath114 + & + 86 & 500 & 140@xmath9910 & @xmath115 + i zw 18 & ... & 970 & @xmath16275 & @xmath116 +

we have obtained high resolution echelle spectra ( r = 30,000 - 50,000 ) of the na d absorption doublet ( , 5896 ) for six dwarf starburst galaxies and two more luminous starbursts : m82 and ngc 1614 . this is small compared to the highest velocity components in ngc 1614 and m82 ( blueshifted by 150 km s and 91 km s , respectively ) ; these two brighter galaxies also show more complex absorption profiles than the dwarfs . the mass of expelled gas is highly sensitive to outflow geometry , dust depletion , and ionization fraction , but with a simple shell model we estimate neutral outflow gas masses from m to m .

we have obtained high resolution echelle spectra ( r = 30,000 - 50,000 ) of the na d absorption doublet ( , 5896 ) for six dwarf starburst galaxies and two more luminous starbursts : m82 and ngc 1614 . the absorption features were separated into multiple components and separated into stellar and interstellar parts based on kinematics . we find that three of the dwarfs show outflows , with an average blueshift of 27 km s . this is small compared to the highest velocity components in ngc 1614 and m82 ( blueshifted by 150 km s and 91 km s , respectively ) ; these two brighter galaxies also show more complex absorption profiles than the dwarfs . none of the outflow speeds clearly exceed the escape velocity of the host galaxy . sightlines in ngc 2363 and ngc4214 apparently intersect expanding shells . we compare the shocked gas velocity ( v ) to the ionized gas velocity ( v ) and interpret the velocity difference as either a trapped ionization front ( ngc 4214 ) or a leaky region ( ngc 2363 ) . the dwarfs show n = 10 , while the na d columns in m82 and ngc 1614 are 10 and 10 , respectively . the mass of expelled gas is highly sensitive to outflow geometry , dust depletion , and ionization fraction , but with a simple shell model we estimate neutral outflow gas masses from m to m .

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density and concentration fluctuations in fluids and fluid mixtures can be investigated experimentally by light - scattering techniques . the nature of these fluctuations when the system is in equilibrium is a subject well understood@xcite . here we shall consider fluctuations in nonequilibrium steady states ( ness ) , when an external and constant temperature gradient is applied , while the system remains in a hydrodynamically quiescent state . that is , we shall deal with fluctuations that are intrinsically present in thermal nonequilibrium states in the absence of any convective instabilities . such fluctuations have received considerable attention during the past decade@xcite . it was originally believed that , because of the existence of local equilibrium in ness , the time correlation function of the scattered - light intensity would be the same as in equilibrium , but in terms of spatially varying thermodynamic and transport properties corresponding to the local value of temperature . however , it has been demonstrated that qualitative differences do appear . the first complete expression for the spectrum of the nonequilibrium fluctuations in a one - component fluid subjected to a stationary gradient was obtained by kirkpatrick et al.@xcite by using mode - coupling theory . they showed that the central rayleigh line of the spectrum would be substantially modified as a result of the presence of a temperature gradient . because of a coupling between the temperature fluctuations and the transverse - velocity fluctuations through the temperature gradient , spatially long - range nonequilibrium temperature and viscous fluctuations appear , modifying the rayleigh spectrum of the scattered - light intensity . their results were subsequently confirmed on the basis of fluctuating hydrodynamics@xcite . the effect is largest for the transverse - velocity fluctuations in the direction of the temperature gradient which corresponds to the situation that the scattering wave vector , @xmath3 , is perpendicular to the temperature gradient @xmath1 , which configuration will be assumed throughout the present paper . in that case , the strengths of the nonequilibrium temperature and viscous fluctuations are predicted to be proportional to @xmath0 . the dependence on @xmath4 implies that , in real space , the nonequilibrium correlation functions become long ranged@xcite . the spatially long - range nature of the correlation functions in ness is nowadays understood as a general phenomenon arising from the violation of the principle of detailed balance@xcite . experimentally , the long - range nature of the nonequilibrium fluctuations can be probed by light - scattering measurements at small wave numbers @xmath2 , i.e. at small scattering angles @xmath5 . such experiments have been performed in one - component liquids and excellent agreement between theory and experiments has been obtained@xcite . in binary systems , the situation is a little more complicated . in liquid mixtures or in polymer solutions a temperature gradient will induce a concentration gradient through the soret effect . this induced concentration gradient is parallel to the temperature gradient and has the same or opposite direction depending on the sign of the soret coefficient , @xmath6 . in this case , nonequilibrium fluctuations appear , not only because of a coupling between the temperature fluctuations and the transverse - velocity fluctuations through the temperature gradient , but also because of a coupling between the concentration fluctuations and the transverse - velocity fluctuations through the induced concentration gradient . the nonequilibrium rayleigh - scattering spectrum has been calculated for binary liquid mixtures , both on the basis of mode - coupling theory@xcite and on the basis of fluctuating hydrodynamics@xcite , with identical results . in liquid mixtures in thermal nonequilibrium states not only nonequilibrium temperature and nonequilibrium viscous fluctuations , but also nonequilibrium concentration fluctuations exist . the strengths of all three types of nonequilibrium fluctuations are again predicted to be proportional to @xmath0 . the theory was extended by segr et al.@xcite to include the effects of gravity and by vailati and giglio@xcite to include time - dependent nonequilibrium states . the nature of the nonequilibrium fluctuations in the vicinity of a convective instability has also been investigated@xcite , in which case the nonequilibrium modes become propagative . the influence of boundary conditions , which may become important when @xmath3 is parallel to @xmath1 , was considered by pagonabarraga et al.@xcite . experiments have been performed to study nonequilibrium fluctuations in liquid mixtures@xcite . the three types of nonequilibrium fluctuations have been observed in liquid mixtures of toluene and n - hexane@xcite and the strength of all three types of nonequilibrium fluctuations were indeed proportional to @xmath0 , as expected theoretically . initially , it seemed that also the prefactors of the amplitudes of these nonequilibrium fluctuations were in agreement with the theoretical predictions@xcite . however , a definitive assessment was hampered by a lack of reliable experimental information on the soret coefficient@xcite . to our surprise , subsequent accurate measurements of the soret coefficient of liquid mixtures of toluene and n - hexane obtained both by khler and mller@xcite and by zhang et al.@xcite yielded values for the soret coefficient that were about 25% lower than the values needed to explain the quantitative magnitude of the amplitudes of the observed nonequilibrium fluctuations@xcite . subsequent measurements of the nonequilibrium concentration fluctuations in a mixture of aniline and cyclohexane , obtained by vailati and giglio@xcite did not have sufficient accuracy to resolve this issue . as an alternative approach , we decided to investigate nonequilibrium concentration fluctuations in a polymer solution . in a polymer solution the same nonequilibrium enhancement effects are expected to exist , but the mass - diffusion coefficient , @xmath7 , in this case is several orders of magnitude lower than in ordinary liquid mixtures . in addition , the soret coefficient is two orders of magnitude larger that the soret coefficient of ordinary liquid mixtures@xcite . these two facts , as discussed below , simplify the theory because , as also happens in an equilibrium polymer solution , the concentration fluctuations become dominant and they are readily observed by light scattering . both the data acquisition and the data analysis become much easier in this case . thus a polymer solution would seem to be an ideal system to further investigate nonequilibrium concentration fluctuations . for this purpose we have selected solutions of polystyrene in toluene , for which reliable information on the thermophysical properties is available . we have performed small - angle rayleigh - scattering experiments in polystyrene - toluene solutions subjected to various externally applied temperature gradients . a summary of our results has been presented in a physical review letter@xcite . in the present paper we provide a full account of the experiment and of the analysis of the experimental data .

we have performed light - scattering measurements in dilute and semidilute polymer solutions of polystyrene in toluene when subjected to stationary temperature gradients . the experiments confirm the presence of long - range nonequilibrium concentration fluctuations which are proportional to , where is the applied temperature gradient and is the wave number of the fluctuations .

we have performed light - scattering measurements in dilute and semidilute polymer solutions of polystyrene in toluene when subjected to stationary temperature gradients . five solutions with concentrations below and one solution with a concentration above the overlap concentration were investigated . the experiments confirm the presence of long - range nonequilibrium concentration fluctuations which are proportional to , where is the applied temperature gradient and is the wave number of the fluctuations . in addition , we demonstrate that the strength of the nonequilibrium concentration fluctuations , observed in the dilute and semidilute solution regime , agrees with theoretical values calculated from fluctuating hydrodynamics . further theoretical and experimental work will be needed to understand nonequilibrium fluctuations in polymer solutions at higher concentrations . 2

cond-mat9808069

i

two - dimensional electronic systems , as found in single heterojunction interfaces or in more complex structures such as quantum wells , have been studied intensively because of their fundamental interest and for their potential application@xcite . in particular , the two - dimensional electron gas ( 2deg ) with a spatially periodic modulation of its equilibrium density has attracted considerable attention both theoretically@xcite and experimentally@xcite . one way of achieving these systems@xcite is to apply a voltage between a patterned gate and the 2deg , thereby inducing a one - dimensional periodic modulation of the density . as the gate voltage is increased , electrons tend to ` pool ' near the minima of the modulating potential and , in the limit of strong modulation , the system transforms into a periodic array of 1d quantum wires . it is clear that the restricted motion of the electrons along the wires will have a profound effect on the character of the plasma excitations in the system . our main focus in this paper will be to study the evolution of these collective modes with increasing modulation of the 2deg , and in particular , the crossover from 2d to 1d behaviour . the theoretical approaches commonly used to discuss collective excitations in charge - density - modulated systems can be classified broadly as being either hydrodynamic in nature@xcite , or based on the random phase approximation ( rpa)@xcite . the hydrodynamic approaches are appealing because of their relative mathematical and computational simplicity . although they vary in their level of sophistication , they all have in common the objective of describing the dynamics of the electronic system in terms of a closed set of equations for the density and velocity fields . at the simplest level of approximation@xcite , the current density in the electron fluid is determined by a local conductivity , proportional to the equilibrium electron density . poisson s equation is then used to relate the electric field driving the current to the fluctuating electron density . rather than explicitly determining the equilibrium properties of the electronic system , the equilibrium density is simply chosen to have some physically reasonable form . we shall refer to such theories as ` classical ' in that no explicit quantum mechanical aspects are included in either the equilibrium or dynamical properties . although the classical treatment is useful for obtaining a qualitative understanding of the collective modes in a modulated 2deg , it has the shortcoming of not being able to account for nonlocal effects ( e.g. in the magneto - conductivity tensor ) which become important with increasing magnitude of the plasmon wavevector . nonlocal effects in the plasmon dispersion can be included in the hydrodynamic theory through the introduction of an electronic compressibility@xcite . in this way some information about the quantum mechanical equation of state can be built into the theory . in this respect , these theories can be referred to as ` semiclassical ' . the rpa on the other hand , provides a fully quantum mechanical description of both the equilibrium and dynamical behaviour . however , being more general , the computational demands for its implementation are significantly greater . furthermore , since it includes both single - particle and collective aspects , it is sometimes difficult to cleanly identify excitations which are predominantly collective in nature@xcite . for both of these reasons , it is still worthwhile having available hydrodynamic based theories . in this paper , we investigate the collective response of a modulated 2deg using the thomas - fermi - dirac - von weizscker ( tfdw ) hydrodynamics previously developed to treat magnetoplasma excitations in three - dimensional parabolic wells@xcite and electron rings@xcite . one of the primary virtues of this approach is that it is based on a reasonably accurate description of the ground state properties of the electronic system , which are determined self - consistently from the minimization of the tfdw energy functional . thus , unlike most earlier hydrodynamic treatments , the form of the equilibrium density is not chosen arbitrarily . perturbations of the system away from the equilibrium state generate internal forces which drive the system back towards equilibrium . these forces are consistently included in the tfdw hydrodynamic equations used to describe the dynamics of the system . although somewhat more sophisticated , the present approach nevertheless retains much of the mathematical simplicity of the usual hydrodynamic theories . our paper is organized as follows . in sec . [ equilibrium ] we determine the equilibrium properties of a periodically modulated 2deg within the tfdw approximation . [ collective ] then provides the mathematical formalism needed to study the dynamics of the collective modes and includes a derivation of the power absorption which is typically measured in infrared transmission experiments . in sec . [ 2dto1d ] , we consider in detail the crossover from 2d to 1d behavior in the periodically - modulated 2deg , and finally in sec . [ conclusions ] , we present our concluding remarks .

we have studied the collective plasma excitations of a two - dimensional electron gas with an _ arbitrary _ lateral charge - density modulation . the dynamics is formulated using a previously developed hydrodynamic theory based on the thomas - fermi - dirac - von weizscker approximation . in this approach , both the equilibrium and dynamical properties of the periodically modulated electron gas are treated in a consistent fashion . we pay particular attention to the evolution of the collective excitations as the system undergoes the transition from the ideal two - dimensional limit to the highly - localized one - dimensional limit .

we have studied the collective plasma excitations of a two - dimensional electron gas with an _ arbitrary _ lateral charge - density modulation . the dynamics is formulated using a previously developed hydrodynamic theory based on the thomas - fermi - dirac - von weizscker approximation . in this approach , both the equilibrium and dynamical properties of the periodically modulated electron gas are treated in a consistent fashion . we pay particular attention to the evolution of the collective excitations as the system undergoes the transition from the ideal two - dimensional limit to the highly - localized one - dimensional limit . we also calculate the power absorption in the long - wavelength limit to illustrate the effect of the modulation on the modes probed by far - infrared ( fir ) transmission spectroscopy .

1104.4494

i

ngc346 is presently the region of most intense star formation in the entire small magellanic cloud ( smc ) . it contains over 30 o type stars ( massey , parker & garmany 1989 ; evans et al . 2006 ) that ionise the n66 nebula , the largest hii region in the smc ( henize 1956 ) . the presence of these very young ( @xmath20myr ) massive stars in ngc346 has long been established with ground - based spectroscopy ( e.g. walborn 1978 ; walborn & blades 1986 ; niemela et al . 1986 ; massey et al . 1989 ) , but more recently also very young stars of low mass have been detected . observations with the hubble space telescope and spitzer space telescope have revealed respectively a multitude of pre - main sequence ( pms ) star candidates down to the subsolar mass ( nota et al . 2006 ; sabbi et al . 2007 ; gouliermis et al . 2007 ; hennekemper et al . 2008 ) and a large number of candidate young stellar objects ( yso ) with masses as low as @xmath21m@xmath7(bolatto et al . 2007 ; simon et al . 2007 ) . what makes ngc346 and the surrounding regions particularly interesting is that they allow us to study the properties of star formation in a nearby galaxy with a metallicity similar to those in place in the high redshift universe at @xmath22 . the distance modulus for the smc is @xmath23 corresponding to @xmath24kpc ( hilditch et al . 2005 ; keller & wood 2006 ) , whereas the currently accepted values for its metallicity range from @xmath25 to @xmath26z@xmath27 ( see russell & dopita 1992 ; rolleston et al . 1999 ; lee et al . 2005 ; perez montero & diaz 2005 ) . moreover , besides this recent burst , previous star formation episodes have been detected in this area . heap et al . ( 2006 ) and mokiem et al . ( 2006 ) reported the presence of massive stars with an age of @xmath28myr , while massey et al . ( 1989 ) discovered five red supergiants and two b type supergiants that form a spatially distinct subgroup located about @xmath29 sw of the centre of ngc346 and that have an estimated age of @xmath30myr . more recently , sabbi et al . ( 2007 ) detected a small star cluster , located about @xmath31 or @xmath32pc ne of the centre whose colour magnitude diagram ( cmd ) is compatible with an age of @xmath33myr . finally , older populations are also present : sabbi et al . ( 2007 ) find evidence for star formation in this region dating as far back as @xmath34gyr with a moderate enhancement @xmath35myr ago . in addition , an intermediate - age cluster , bs90 , is also present in the field , with an age of @xmath36gyr . it is not easy to establish whether there is any relationship between the very old generations in this field and the more recent star formation episodes . however , it is interesting to investigate whether the @xmath30myr old massive stars of massey et al . ( 1989 ) and the @xmath37myr old small cluster of sabbi et al . ( 2007 ) , although spatially unrelated to one another , could be the precursors of the 30 young massive o type stars and of the recently detected pms stars and yso in this region . it is conceivable that a large number of these @xmath38myr old objects are actually present in ngc346 , many more than those known so far , but that they could belong to a more diffuse population spread throughout the region because of appreciable velocity dispersion motions and , therefore , might not be easy to identify . if the members of such a @xmath39myr old population could be detected , including those of low mass , their spatial distribution and physical properties would allow us to understand whether and how they may have triggered the most recent bursts , as theories of sequential star formation suggest ( e.g. elmegreen & lada 1977 ) . the task of detecting a @xmath39myr old population in a region heavily contaminated by older field stars and younger objects might appear daunting . hennekemper et al . ( 2008 ) attempted to study the presence of an age spread in the pms population of ngc346 through the analysis of the cmd . they showed that the observations are in principle compatible with an upper limit of @xmath34myr to the age , but they concluded that differential reddening and unresolved binaries could be at the origin of the observed colour spread . actually , if these objects have not yet completed their pre - main sequence ( pms ) phase , it should be possible to detect them through the distinctive excess emission features in their spectra that originate from the accretion process , particularly in the uv continuum and in recombination lines such as h@xmath3 , pa@xmath40 and br@xmath41 ( e.g. calvet et al . 2000 ) . although in nearby star forming regions the fraction of pms stars with discs appears to decline quite rapidly during the first 10myr ( e.g. haisch , lada & lada 2001 ; fedele et al . 2010 ) , there is evidence that sustained mass accretion is present also in objects older than this age , particularly above 1m@xmath7 . this is the case for instance of tr37 where sicilia aguilar et al . ( 2006 ) find g - type dwarfs still accreting at ages in excess of 10myr . in the more distant ( @xmath42kpc ) and massive galactic star forming region ngc3603 beccari et al . ( 2010 ) recently found a conspicuous number of pms stars older than 10myr still undergoing mass accretion . in even more distant and dense stellar fields , where spectroscopy of individual stars is limited to the brightest members , romaniello ( 1998 ) , panagia et al . ( 2000 ) and romaniello , robberto & panagia ( 2004 ) have shown that objects undergoing active mass accretion can be efficiently detected with accurate multi - colour photometry and have identified in the regions around sn1987a about 500 pms stars with h@xmath3 equivalent width in excess of 8 and with an age of @xmath43myr . more recently , de marchi , panagia & romaniello ( 2010 , hereafter paperi ) showed that through a suitable combination of broad- and narrow - band photometry it is also possible to derive the mass accretion rate of these objects , with an accuracy comparable to that allowed by spectroscopy . in this work , we build on the method developed in paperi to securely identify bona - fide pms objects in dense stellar fields and apply it to the high - quality hst photometry of the ngc346 region ( sabbi et al . our goal is to measure the physical properties of these objects and study how they depend on age , in order to understand how star formation has proceeded in this area over the past @xmath44myr . the paper is organised as follows : in section[obser ] we briefly describe the observations and address how we correct for differential reddening , whereas section[pmsst ] is devoted to the identification of pms stars via their h@xmath3 excess emission and on the determination of their h@xmath3 luminosity . in section[physi ] we derive the other important physical parameters for these objects , including age , mass and mass accretion rate , while in section[evolu ] we study how the latter evolves in time , how it could affect stellar evolution , and we compare the results to those for similar objects in the milky way and large magellanic cloud . a summary of the most important conclusions of the paper is offered in section[summa ] .

we show that there are at least two , almost equally numerous , young populations with distinct ages of respectively and myr . we provide for all of them accurate physical parameters . this result is consistent with measurements of the mass accretion rate in the 30 dor region and in the milky way and suggests that longer duration for mass accretion could be related to lower metallicity .

we have studied the properties of the stellar populations in the field of the ngc346 cluster in the small magellanic cloud , using a novel self - consistent method that allows us to reliably identify pre - main sequence ( pms ) objects actively undergoing mass accretion , regardless of their age . the method does not require spectroscopy and combines broad - band and photometry with narrow - band imaging to identify all stars with excess h emission and derive the accretion luminosity and mass accretion rate for all of them . the application of this method to existing hst / acs photometry of the ngc346 field has allowed us to identify and study 680 bona - fide pms stars with masses frommtomand ages in the range frommyr tomyr . previous investigations of this region , based on the same data , had identified young (myr old ) candidate pms stars on the basis of their broad - band colours . in this study we show that there are at least two , almost equally numerous , young populations with distinct ages of respectively and myr . we provide for all of them accurate physical parameters . we take advantage of the unprecedented size of our pms sample and of its spread in mass and age to study the evolution of the mass accretion rate as a function of stellar parameters . we find that , regardless of stellar mass , the mass accretion rate decreases with roughly the square root of the age , or about three times slower than predicted by current models of viscous disc evolution , and that more massive stars have systematically higher mass accretion rate in proportion to their mass . a multivariate linear regression fit reveals that , where is the age of the star , its mass and a quantity that is higher at lower metallicity . this result is consistent with measurements of the mass accretion rate in the 30 dor region and in the milky way and suggests that longer duration for mass accretion could be related to lower metallicity . the high mass accretion rates that we find suggest that a considerable amount of mass is accreted during the pms phase , of ordermor possibly of the final mass for stars with massmif their discs are eroded by 20myr , i.e. before they reach the main sequence . therefore , pms evolutionary models that do not account for this effect will systematically underestimate the true age when compared with the observations .

1104.4494

i

we have studied the properties of the stellar populations in the field of the ngc346 cluster in the smc as observed with the acs camera on board the hubble space telescope ( sabbi et al . to this aim , we have employed a novel , self - consistent method that allows us to reliably identify pms stars undergoing active mass accretion , regardless of their age . the method , fully described in paperi , does not require spectroscopy and combines broad - band @xmath0 and @xmath1 photometry with narrow - band @xmath2 imaging to identify all stars with excess h@xmath3 emission and allows us to derive the accretion luminosity @xmath4 and mass accretion rate @xmath78 for all of them . the main results of this work can be summarised as follows . 1 . from the photometry of sabbi et al . ( 2007 ) , we have selected all objects in a region of @xmath48 around the centre of ngc346 that have a combined mean error @xmath50 in the three bands ( @xmath0 , @xmath1 and h@xmath3 ) of less than @xmath51mag , as defined in equation[eq1 ] . a total of 18764 stars satisfy this condition . 2 . the cmd reveals the presence of both young and old populations , but the conspicuous broadening of the upper ms proves that there is also variable extinction . we have determined the reddening towards each of these stars from their colour and magnitude displacements with respect to a 4myr isochrone for metallicity @xmath58 and a distance modulus of @xmath206 . we found that extinction is in the range @xmath207 or @xmath208 ( respectively 17% and 83% limits ) , with a median value of @xmath70 or @xmath71 . we have then used the reddening values towards each of the selected stars to derive a reddening correction for all objects in their vicinity . 3 . following the method developed in paperi , we have identified 791 pms candidates as being objects with h@xmath3 excess above the @xmath91 level with respect to the reference provided by normal stars . their average h@xmath3 luminosity is @xmath96ergs@xmath138 or @xmath97l@xmath27 . we have also determined the equivalent width of the h@xmath3 emission line of these objects and have classified as bona - fide pms stars all those with @xmath158 ( or @xmath209 for stars with @xmath126k ) . these conditions guarantee that our sample is free from contamination due to the chromospheric activity of older objects or to the rotational winds of be stars . a total of 694 objects satisfy these conditions . 4 . by comparing the locations of these objects in the h r diagram with the pms evolutionary models of the pisa group for metallicity @xmath58 , we have been able to derive an accurate value of the mass and age of 680 bona - fide pms stars ( note that previous determinations of these parameters for candidate pms stars in ngc346 that made use of evolutionary models for @xmath124 are necessarily less accurate ) . the masses of these objects range from @xmath194m@xmath7to @xmath210m@xmath7 , with an average value of @xmath9m@xmath7 . their ages show a clear bimodal distribution with two peaks at @xmath9myr and @xmath12myr and very few objects around @xmath118myr , revealing the presence of two distinct but equally populous generations of stars . we address in a companion paper ( de marchi , panagia & sabbi 2011 ) the properties of and the relationships between the two generations . 5 . from the h@xmath3 luminosity and the other physical parameters that we have measured , we have derived the mass accretion rate @xmath5 of all bona - fide pms stars . the median value of @xmath78 is @xmath143m@xmath7yr@xmath138 . this value is about 50% higher than that measured in paperi for a population of 133 pms stars in the field of sn1987a , owing to the much younger median age of pms objects in ngc346 . thanks to the unprecedented size of our pms sample and of its spread in mass and age , we have been able to study the evolution of the mass accretion rate as a function of stellar parameters . regardless of the mass of the star , our analysis shows that the mass accretion rate decreases with roughly the square root of the age , or about three times slower than predicted by current models of viscous disc evolution , and that more massive stars have systematically higher mass accretion rate in proportion to their mass . a multivariate linear regression fit reveals that @xmath211 , where @xmath14 is the age of the star , @xmath15 its mass and @xmath16 a quantity that is higher at lower metallicity . the large mass accretion rates that we find imply that a considerable amount of mass is accreted during the pms phase , at least in low - metallicity environments such as the magellanic clouds . at face value , the observed rates integrated over the entire pms phase would give a total accreted mass of @xmath17m@xmath7 , with negligible dependence of the final mass on the zams , thereby possibly suggesting a lower cut - off mass in the stellar mass function of ngc346 . if , however , the circumstellar discs are eroded on a time scale shorter than the pms lifetime , the total accreted mass will be of course smaller but not negligible . in any case , the pms evolution of moderate - mass stars ( @xmath212m@xmath7 ) should be reconsidered and recalculated taking into account the high @xmath78 values , since for a given ms mass the evolutionary time needed to reach the zams will be longer than what is currently estimated by models that assume @xmath199 after the first few @xmath200yr . we wish to thank an anonymous referee for useful comments that have greatly helped us to improve the presentation of this work . np acknowledges partial support by hst - nasa grants go-11547.06a and go-11653.12a , and stsci - ddrf grant d0001.82435 .

we have studied the properties of the stellar populations in the field of the ngc346 cluster in the small magellanic cloud , using a novel self - consistent method that allows us to reliably identify pre - main sequence ( pms ) objects actively undergoing mass accretion , regardless of their age . the method does not require spectroscopy and combines broad - band and photometry with narrow - band imaging to identify all stars with excess h emission and derive the accretion luminosity and mass accretion rate for all of them . we take advantage of the unprecedented size of our pms sample and of its spread in mass and age to study the evolution of the mass accretion rate as a function of stellar parameters . we find that , regardless of stellar mass , the mass accretion rate decreases with roughly the square root of the age , or about three times slower than predicted by current models of viscous disc evolution , and that more massive stars have systematically higher mass accretion rate in proportion to their mass . a multivariate linear regression fit reveals that , where is the age of the star , its mass and a quantity that is higher at lower metallicity . the high mass accretion rates that we find suggest that a considerable amount of mass is accreted during the pms phase , of ordermor possibly of the final mass for stars with massmif their discs are eroded by 20myr , i.e. before they reach the main sequence .

we have studied the properties of the stellar populations in the field of the ngc346 cluster in the small magellanic cloud , using a novel self - consistent method that allows us to reliably identify pre - main sequence ( pms ) objects actively undergoing mass accretion , regardless of their age . the method does not require spectroscopy and combines broad - band and photometry with narrow - band imaging to identify all stars with excess h emission and derive the accretion luminosity and mass accretion rate for all of them . the application of this method to existing hst / acs photometry of the ngc346 field has allowed us to identify and study 680 bona - fide pms stars with masses frommtomand ages in the range frommyr tomyr . previous investigations of this region , based on the same data , had identified young (myr old ) candidate pms stars on the basis of their broad - band colours . in this study we show that there are at least two , almost equally numerous , young populations with distinct ages of respectively and myr . we provide for all of them accurate physical parameters . we take advantage of the unprecedented size of our pms sample and of its spread in mass and age to study the evolution of the mass accretion rate as a function of stellar parameters . we find that , regardless of stellar mass , the mass accretion rate decreases with roughly the square root of the age , or about three times slower than predicted by current models of viscous disc evolution , and that more massive stars have systematically higher mass accretion rate in proportion to their mass . a multivariate linear regression fit reveals that , where is the age of the star , its mass and a quantity that is higher at lower metallicity . this result is consistent with measurements of the mass accretion rate in the 30 dor region and in the milky way and suggests that longer duration for mass accretion could be related to lower metallicity . the high mass accretion rates that we find suggest that a considerable amount of mass is accreted during the pms phase , of ordermor possibly of the final mass for stars with massmif their discs are eroded by 20myr , i.e. before they reach the main sequence . therefore , pms evolutionary models that do not account for this effect will systematically underestimate the true age when compared with the observations .

astro-ph0404447

c

we have compiled a nearly complete list of bright rgb , hb , and agb stars for the globular cluster m5 reaching from the core of the cluster to @xmath130 from the center . we have used these samples to conduct a thorough comparison with theory in order to test stellar interior physics under the conditions prevalent in these bright stars . we have introduced a new diagnostic @xmath5 for evaluating the evolutionary timescale in the early part of the agb phase , finding that there is a marginal disagreement between the observations and the models of @xcite . on the whole we find good agreement between observations and theory for the cumulative lfs of the rgb above the rgb bump and for the agb , indicating that the evolutionary timescales in both phases are predicted accurately . an apparent exception appears near the tip of the rgb , where there appear to be too few giants compared to theoretical predictions . the chance that this is a statistical fluctuation is less than 2% . this may be an indication that the neutrino emission rates in the cores of these bright stars are underestimated . the most significant result is the large value for the population ratio @xmath4 compared to recent theoretical values . the high value is probably the result of the particular hb morphology of the cluster and not continuing uncertainties in physical inputs like the cross section for the @xmath55 reaction or the core mixing algorithm . we encourage new calculations of hb and agb phases using updated physics because agb stars provide a means of testing predictions for the morphology of evolutionary tracks for stars fusing he into c and o and of constraining the @xmath55 reaction rate . in particular , they stand the greatest chance of identifying the color at which hb stars change from going into or not going into a typical agb phase , and the range of colors for which the agb phase has its maximum duration . we also call attention to a peculiarity of the distribution of stars on m5 s hb . we find that the mass distribution for hb stars peaks at a position corresponding to the blue edge of the instability strip . the instability strip is heavily populated due to the large dispersion in hb masses ( @xmath131 ) . however , the distribution of stars within the instability strip is heavily biased toward the red half of the instability strip . this is consistent with m5 being an oosterhoff group i cluster , but it means that the first overtone instability strip is underpopulated compared to the fundamental strip to the red and compared to the nonvariable stars to the blue . because m5 has one of the bluest hb morphologies of the oo i clusters ( including the more metal - poor m3 ) , it is a severe test of potential explanations of the oosterhoff dichotomy . some mechanism for reducing the evolutionary timescale of stars in the first overtone instability strip seems to be needed . the blue half of m5 s instability strip _ should be _ more heavily populated the big 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storm , j. , carney , b. w. , & beck , j. a. 1991 , , 103 , 1264 straniero , o. , chieffi , a. , & limongi , m .. 1997 , , 490 , 425 straniero , o. , dominguez , i. , imbriani , g. , & piersanti , l. 2003 , , 583 , 878 sweigart , a. v. & catelan , m. 1998 , , 501 , l63 van albada , t. s. & baker , n. 1971 , , 169 , 311 vandenberg , d. a. , swenson , f. j. , rogers , f. j. , iglesias , c. a. , & alexander , d. r. 2000 , , 532 , 430 zinn , r. & west , m. j. 1984 , , 55 , 45 rrrcccl 1 & @xmath132 & @xmath133 & 0.99 & v42 + & 1 & & 12.81 & 10.93 & & pm + 2 & 7.296 & @xmath134 & + & 1 & & @xmath135 & & @xmath136 & ct + 3 & 6.125 & 86.957 & 0.99 + & 2 & & @xmath137 & & @xmath138 & ct + & & & @xmath139 & @xmath140 & & ct + & 2 & & 13.98 & 12.02 & & pm + 4 & 28.847 & @xmath141 & + & 5 & & @xmath142 & & @xmath143 & ct + 5 & 7.478 & @xmath144 & + & 6146 & & @xmath145 & & @xmath146 & cfh + 6 & 35.655 & @xmath147 & + & 6665 & & @xmath148 & & @xmath149 & cfh + 7 & @xmath150 & @xmath151 & 0.99 + & 14 & & @xmath152 & & @xmath153 & ct + & & & @xmath154 & @xmath155 & & ct + & 10 & & 13.87 & 12.37 & & pm + 8 & 30.902 & @xmath156 & + & 15 & & @xmath157 & & @xmath158 & ct + & & & @xmath159 & @xmath160 & & ct + 9 & 53.961 & 69.500 & 0.99 + & 32456 & & @xmath161 & @xmath162 & & hst + & 603 & & @xmath163 & & @xmath164 & cfh + & 22 & & @xmath165 & & @xmath166 & ct + & & & @xmath167 & @xmath168 & & ct + & 15 & & 13.90 & 12.48 & & pm + 10 & 114.220 & 61.938 & 0.99 & i-20 + & 28 & & @xmath169 & & @xmath170 & ct + & & & @xmath171 & @xmath172 & & ct + & 20 & & 14.02 & 12.62 & & pm + [ agb ] rrrcccl 1 & @xmath173 & @xmath174 + & 4873 & & @xmath175 & & @xmath176 & cfh + & 4 & & @xmath177 & & @xmath178 & ct + & & & @xmath179 & @xmath180 & & ct + 2 & 33.925 & 99.017 + & 32361 & & @xmath181 & @xmath182 & & hst + & 6 & & @xmath183 & & @xmath184 & ct + & & & @xmath185 & @xmath186 & & ct + 3 & 15.390 & @xmath187 + & 6680 & & @xmath188 & & @xmath189 & cfh + & 3 & & @xmath190 & & @xmath191 & ct + 4 & @xmath192 & 0.678 + & 210174 & & @xmath193 & @xmath194 & & hst + & 3869 & & @xmath195 & & @xmath196 & cfh + 5 & 442.242 & 184.036 & 0.99 + & 3 & & 13.86 & 12.16 & & pm + 6 & 167.531 & @xmath197 & 0.99 & iv-81 + & 8 & & @xmath198 & & @xmath199 & ct + & & & @xmath200 & @xmath201 & & ct + & 4 & & 13.89 & 12.20 & & pm + 7 & @xmath202 & 45.865 & 0.99 + & 23898 & & @xmath203 & @xmath204 & & hst + & 9 & & @xmath205 & & @xmath206 & ct + & & & @xmath207 & @xmath208 & & ct + & 11 & & 13.93 & 12.38 & & pm + 8 & @xmath209 & @xmath210 & 0.99 & iii-122 + & 10 & & @xmath211 & & @xmath212 & ct + & & & @xmath213 & @xmath214 & & ct + & 5 & & 13.83 & 12.25 & & pm + 9 & @xmath215 & 271.834 & 0.99 + & 6 & & 13.86 & 12.26 & & pm + 10 & 54.805 & 93.936 + & 12 & & @xmath216 & & @xmath217 & ct + & & & @xmath218 & @xmath219 & & ct + [ rgb ] rrrccccccl v1 & 25.226 & 150.907 & 0.99 & & & & 15.107 & 0.493 + v2 & @xmath220 & @xmath221 & 0.99 + v3 & 156.521 & 99.011 & 0.99 & & & & 15.063 & 0.541 + v4 & @xmath222 & 65.207 & & & & & 15.070 & 0.413 & hst 23554 + v5 & @xmath223 & 43.050 & & & & & 15.103 & 0.475 & hst 22389 + v6 & 18.312 & @xmath224 & & & & & 15.011 & 0.515 + v7 & @xmath225 & @xmath226 & 0.99 & 15.035 & 0.344 & s + v8 & 122.626 & @xmath227 & 0.99 & 15.085 & 0.334 & s & 15.072 & 0.514 + v9 & 190.772 & 72.110 & 0.99 + v10 & 111.964 & 369.089 + [ rr ] rrrcccl 1 & @xmath228 & 147.750 & 0.99 & ii469 + & 206 & & 15.32 & 14.58 & & pm + 2 & @xmath229 & 183.246 & 0.99 & ii493 + & 342 & & 15.56 & 15.05 & & pm + 3 & @xmath230 & @xmath231 & 0.99 & ii210 + & 465 & & 15.36 & 15.26 & & pm + 4 & @xmath232 & @xmath233 & 0.99 & ii213 + & 274 & & 15.04 & 14.95 & & pm + 5 & @xmath234 & 132.187 & 0.99 & ii429 + & 263 & & 15.51 & 14.94 & & pm + 6 & @xmath235 & @xmath236 + & 1749 & & @xmath237 & & @xmath238 & ct + & & & @xmath239 & @xmath240 & & ct + 7 & @xmath241 & 128.281 & 0.99 & ii425 + & 759 & & @xmath242 & & @xmath243 & ct + & & & @xmath244 & @xmath245 & & ct + & 399 & & 15.62 & 15.12 & & pm + 8 & @xmath246 & @xmath247 & 0.99 + & 773 & & @xmath248 & & @xmath249 & ct + & & & @xmath250 & @xmath251 & & ct + & 381 & & 15.54 & 15.10 & & pm + 9 & @xmath252 & 295.727 & 0.99 & i43 + & 1075 & & @xmath253 & & @xmath254 & ct + & & & @xmath255 & @xmath256 & & ct + & 431 & & 15.24 & 15.15 & & pm + 10 & @xmath257 & @xmath258 & 0.99 + & 454 & & 15.27 & 15.23 & & pm + [ hb ] rl + 1 & ( v42 ) post - agb star ; pm only + 12 & hst identification ambiguous + 14 & hst identification ambiguous + 22 & hst identification ambiguous , blends with rgb 99 + 23 & hst identification ambiguous + 34 & hst identification ambiguous + 46 & rgb 310 nearby + 60 & rgb star ( hst 10218 ) nearby + [ notes ]

we have tabulated lists of upper red giant , horizontal , and asymptotic giant branch ( rgb , hb , agb ) stars in the globular cluster m5 that are complete to over from the core for the rgb and agb samples , and for the hb sample . samples of hb and agb stars in populous clusters may provide a means of calibrating the masses of horizontal branch stars in globular clusters . we also introduce a new diagnostic that reflects the fraction of the agb lifetime that a star spends in the agb clump . for m5 , we find , in marginal disagreement with theoretical predictions . finally , we note that the blue half of m5 s instability strip ( where first overtone rr lyraes reside ) is underpopulated , based on the large numbers of fundamental mode rr lyraes and on the nonvariable stars at the blue end of the instability strip .

we have tabulated lists of upper red giant , horizontal , and asymptotic giant branch ( rgb , hb , agb ) stars in the globular cluster m5 that are complete to over from the core for the rgb and agb samples , and for the hb sample . the large samples give us the most precise value of to date for a single globular cluster ( ) . this is incompatible with theoretical calculations using the most recent physical inputs . the discrepancy can probably be attributed to the dependence of observed values on horizontal branch morphology . we identify the cluster m55 as being another possible example of this effect . samples of hb and agb stars in populous clusters may provide a means of calibrating the masses of horizontal branch stars in globular clusters . the cumulative luminosity function of the upper red giant branch shows an apparent deficit of observed stars near the tip of the branch . this feature has less than a 2% chance of being due to statistical fluctuations . the slope of the cumulative luminosity function for agb stars is consistent with the theoretically predicted value from stellar models when measurement bias is taken into account . we also introduce a new diagnostic that reflects the fraction of the agb lifetime that a star spends in the agb clump . for m5 , we find , in marginal disagreement with theoretical predictions . finally , we note that the blue half of m5 s instability strip ( where first overtone rr lyraes reside ) is underpopulated , based on the large numbers of fundamental mode rr lyraes and on the nonvariable stars at the blue end of the instability strip . this fact may imply that the evolutionary tracks ( and particularly the colors ) of stars in the instability strip are affected by pulsations .

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assuming the rotation curve of m33 is flat within @xmath32 , kormendy & mcclure ( 1993 ) calculate an upper limit of @xmath125 on the mass of the nucleus . lauer et al . ( 1998 ) calculate a lower limit by determining a core mass of @xmath126 . a better estimate of the mass in the starburst region should be possible from the measured velocity dispersion ( 21 km s@xmath47 , kormendy & mcclure 1990 ) and the size of the starburst . we measured the fwhm of the pc images of the m33 nucleus by fitting them with 2-dimensional gaussian convolved with the tinytim point spread function ( psf ) appropriate for each filter ( @xcite ) . it was not possible to fit the nucleus in the f160bw filter due to its low signal . the results are given in table [ tab_nuc_size ] . lauer et al . ( 1998 ) found the fwhm was @xmath127 ( 0.27 pc ) in the f555w image using a different analytic form for the nuclear profile and taking better care to correct for the effects of the psf and aliasing . the increasing size of the nucleus as a function of wavelength confirms the color gradient measured by kormendy & mcclure ( 1993 ) and lauer et al . ( 1998 ) . lccc f300w & 2.65 & 0.12 & 0.46 f555w & 4.33 & 0.20 & 0.77 f814w & 4.62 & 0.21 & 0.81 f1042 m & 5.58 & 0.25 & 0.98 because they dominate the light , the observed velocity dispersion and size reflect only properties of the more massive stars . this is confirmed by the composite spectral type of the nucleus , for which a range from late - a to early - f main sequence has been reported ( @xcite ; @xcite ; @xcite ; b. garrison , private communication ) . assuming equipartition in kinetic energies , the true velocity dispersion ( @xmath128 ) of the nucleus is then @xmath129 where @xmath130 is the observed velocity dispersion , @xmath131 is the average mass of the stars in the nucleus , and @xmath132 is the average mass of the stars contributing to @xmath130 . assuming the imf given in equation [ eq_imf ] , @xmath133 . from the spectral type of the nucleus , @xmath134 . thus , the true velocity dispersion of the nucleus is 40 km s@xmath47 . the virial mass is computed from @xmath135 where r is the effective radius of the nucleus in pc , @xmath128 is in km s@xmath47 , and @xmath136 is in @xmath137 . estimating @xmath138 for the nucleus is nontrivial and so we will use a measured @xmath138 value and compute a lower limit . we assume @xmath138 to be the size of the nucleus as measured in the f814w image ( hwhm @xmath139 pc ) since @xmath130 was measured from the infrared triplet ( @xcite ) . the mass of the nucleus is then @xmath140 . this is similar to the @xmath141 of the best fit set a models . in addition to the starburst population , it is likely there is at least one other stellar population in the nuclear region . the presence of an older ( @xmath21 gyr ) underlying stellar population with a large @xmath111 is strongly implied by the growth of surface brightness and stellar counts approaching the nuclear region ( @xcite ) and the mass ( @xmath142 ) of the inner @xmath32 of m33 ( @xcite ) . within 4@xmath45 , 3/4 of the observed v band flux comes from the nucleus ( @xcite ) . this implies that the other stellar population in the nuclear region has a @xmath111 ratio of 5.5 assuming the set a best fits or 1.8 assuming the set b best fit . thus , the mass required by the set a models ( @xmath143 ) is more consistant with the available data on the nuclear region . the photometric and spectroscopic evidence indicate that set a models fit the observations of the m33 nucleus better than the set b models , as does the mass determination . the set a models are consistent with the small size of the nucleus and flat profile of the inner disk of m33 . the flat profile implies there is a lack of a substantial density gradient which could funnel gas to the nucleus ( @xcite ) , which means fueling continuous star formation ( as set b fits would require ) would be difficult . the stellar population of the m33 nucleus is described by a 35 to 180 myr burst of star formation with a mass of 0.4 - 1.1 @xmath144 ( table [ tab_best_fit ] ) . the best fit seds in set a for both ses models give very similar results . they imply the best description of the m33 nucleus is a burst of star formation 70 - 75 myrs old and a mass of @xmath20.7 @xmath144 ( table [ tab_best_fit ] ) . our finding that the m33 nucleus is well described by a single burst of star formation enshrouded by a significant amount of dust is quite different than previous studies ( @xcite ; @xcite ; @xcite ) . in these studies , the role of dust was underestimated and , as a result , luminous young and old stellar populations were both needed to reproduce the relatively red ( flat ) spectrum of the m33 nucleus . for example , ciani et al . ( 1984 ) modeled the iue spectrum plus @xmath145 , @xmath146 , and @xmath147 photometry of the m33 nucleus . they found that the data were best represented by two stellar populations , one extremely young ( @xmath148 years ) and one old ( @xmath149 years ) . they argued that the effects of foreground and internal dust were well represented by a screen of mw - type dust with an @xmath150 . schmidt et al . ( 1990 ) obtained a long - slit optical spectrum of the m33 nucleus with a @xmath151 slit and modeled it using a combination of star clusters of different ages . they found that the m33 nucleus was composed of 7 star clusters with ages ranging from @xmath152 to @xmath153 years . this is similar to other studies where over 50% of the v band light was claimed to be from stars with ages @xmath154 years . in addition , schmidt et al.(1990 ) modeled the effects of dust as due to a galactic foreground screen with @xmath155 and a m33 internal screen with @xmath156 . the mass - to - light ratio ( @xmath111 ) we compute from our model fits , corrected for foreground and internal dust , is @xmath20.1 . this is significantly different from previous studies , which found @xmath157 23 ( @xcite ; @xcite ) which is in excess of the value likely to be present from dynamical considerations . by including dust properly , we have arrived at a simpler model of the m33 nucleus which reproduces its observed sed from the uv to the near - ir . we can estimate the peak luminosity of the m33 starburst , although there is some uncertainty because our models do not constrain the rate of star formation with time uniquely . for example , the starburst mass in m33 is roughly 500 times less than that in m82 , assuming similar imfs ( e.g. , imf8 of @xcite ) and the somewhat extended burst which best fits the m82 data . thus , at an age of @xmath210 million years , the m33 starburst would have luminosity of 0.002 times that of m82 , or @xmath158 , alternately , from our abrupt burst model and the current luminosity of @xmath159 , the luminosity at 10 myrs would have been @xmath160 . the center of the milky way contains a very compact ( @xmath161 pc ) cluster of young ( @xmath162 myrs old ) stars with an integrated luminosity of @xmath2@xmath163 ( @xcite ; @xcite ) . the analogy between these two cases is striking . it appears that in m33 we may well be seeing a later development of an event virtually identical to the starburst that currently dominates the galactic center . the relatively young age of the nucleus that we derive from our models may clear up another mystery . the m33 nucleus has a very strong x - ray source with a @xmath164 ergs s@xmath47 ( @xcite ; @xcite ) . the detection of a 106 day period requires that this object be a single source ( @xcite ) . the only known type of object which could reproduce both observed effects is a stellar mass black hole ( @xmath2@xmath165 ) accreting from a companion star . this type of object was mentioned by dubus et al . ( 1997 ) , but discarded as the solution as previous work on the m33 nucleus argued against a significant population of o b stars . the requirements of such an x - ray binary are a black hole with a companion star with enough mass to withstand the supernova blast that created the black hole without being ejected from the binary . for example , a black hole with an early b giant companion would be transfering a significant amount of matter to the black hole , resulting in the observed x - ray luminosity . the type , geometry , and amount of dust associated with the m33 nucleus is fairly well constrained by the observed photometric sed . the dust is best described by a shell of somewhat clumpy mw - like dust ( @xmath166 ) with a radial v - band optical depth of @xmath22 . to show the effects of both foreground and internal dust on the intrinsic sed of the m33 nucleus , we present figure [ fig_dust_ex ] . even in the galactic foreground dust corrected sed , the flux at 2607 ( uit - a1 ) is significantly lower than the flux in the bands around 1600 ( uit - b1 , f160bw , and f170w ) and around 3300 ( f300w , f336w , u ) . the only known way to get such a depression in the sed of a stellar population is to attenuate its sed by dust with a 2175 feature , i.e. mw - type dust . it is interesting to compare this with the result found by gordon e al . they found that smc - like dust was responsible for the attenuation in the 30 starburst galaxies in their sample . they used iue - selected starburst galaxies , which biased their study towards intrinsically bright , lightly attenuated starburst regions . the interstellar environment near an intense starburst is very harsh , associated with an intense uv radiation density and supernovae shocks . there is evidence from the observed dust extinction curves in the magellanic clouds which suggests that star formation modifies nearby dust . in the smc , the only extinction curve outside the star forming bar is very similar to that found in the milky way . the other three extinction curves in the bar are the most extreme known in terms of a non - existent 2175 bump and strong far - uv rise ( @xcite ) . in the lmc , there are two different extinction curves ( @xcite ) . the extinction curve associated with stars near the lmc 2 supergiant shell ( which is itself near the 30 dor star formation region ) has a weak 2175 bump . the extinction curve associated with stars elsewhere in the lmc is similar to that found in the milky way . however , the 30 dor region in the lmc exhibits much more intense star formation than any region in the smc , but the most extreme extinction curves are found in the smc . this fact implies that the relationship between star formation activity and the modification of nearby dust is not a simple one . recent theoretical models of dust exposed to shocks ( @xcite ; @xcite ) illustrate the complicated behavior expected for dust near active star formation . the number of small particles in shocked dust is increased through shattering of larger grains and results in an increased extinction in the far - uv . however , the models which produce a stronger far - uv rise , also produce normal or strong 2175 bumps . this is not what is seen in the behavior of dust in starburst galaxies or the magellanic clouds and probably reflects our incomplete understanding of the carrier of the 2175 feature . the m33 nucleus was also observed by iue , but is not typical of the iue sample used by gordon et al . m33 is much closer than the majority of the iue sample ( 0.795 versus 60 mpc ) and its faintness implies it is intrinsically fainter and/or suffers a higher attenuation than the rest of the sample . in the case of m33 , the starburst is surrounded by a larger optical depth of dust and , since it lacks emission lines , is older than those seen in the iue sample . thus , the dust in the m33 nucleus has likely undergone less processing since it is near a small starburst and self - shielded by a large amount of dust . the amount by which dust can be processed in starburst regions is likely related to the mass and age of the starburst as well as the extent to which the dust can shield itself . additional work on other fairly reddened starburst regions is needed to test this interpretation of the origin of the mw - type dust we find in the m33 nucleus . the low velocity dispersion and extreme compactness of the m33 nucleus have caused lauer et al . ( 1998 ) to suggest that stellar mergers might play an important role in creating the blue stellar population ( see also @xcite ) . these arguments are based on a calculation that a typical star lying within the present - day environment of the m33 nucleus would have a collision / binary capture timescale of about a hubble time . this model could apply if the previous estimate of an old ( @xmath167 yr ) stellar population in the nucleus of m33 is assumed ( @xcite ; @xcite ) . that is , if conditions in the nucleus have not changed over a hubble time , most stars in the nucleus will have undergone such an event . to assess if collisions and mergers are important , we will assume the age of the nucleus is on the order of the hubble time and see if reasonable arguments lead to the observed characteristics of the m33 nucleus . the optical spectrum of m33 ( figure [ fig_id_opt ] ) demonstrates that the nucleus contains many stars of @xmath168 . the observed nuclear b magnitude is 14.6 . corrected for foreground and internal dust , the intrinsic b magnitude is 12.5 , corresponding to a m@xmath169 ( for a distance of 795 kpc ) . for the purposes of this exercise , we attribute most of the nuclear mass of @xmath170 to an old stellar population that creates more massive stars by mergers . the absolute blue magnitude would require the presence of @xmath171 main sequence stars with masses @xmath23 @xmath172 , if these stars were the most massive in the nucleus . this hypothetical population accounts for an uncomfortably large portion of the total nuclear mass . instead , it seems required that the light from the nucleus is dominated by stars closer to the top of the permitted mass range ( @xmath173 ) . we assume the old stellar population is described by an imf similar to the one taken for the starburst , up to a main sequence turnoff mass of @xmath174 . allowing for the mass lost in mergers , stars at the turnoff must undergo on the order of six to eight mergers to build a @xmath175 star . thus , the calculation by lauer et al . ( 1998 ) that , on average , each star might undergo one merger in a hubble time implies that the dominant stars could not be created in this fashion . a more rigorous argument would account for the dynamical evolution of the nucleus . if the age of the m33 nucleus is on the order of the hubble time , then it is possible that it has gone through core collapse ( @xcite ; @xcite ; @xcite ) . lee ( 1987 ) has studied stellar mergers in dynamical models of systems of @xmath176 stars which , in their post core collapse configuration , resemble the m33 nucleus . the merger rate reaches a sharp peak around core collapse . stars that are the result of eight mergers , as required to build the blue stars in the m33 nucleus , are @xmath177 less common than the original population members shortly after core collapse in lee s ( 1987 ) model . we have roughly corrected this result for the approximately three times higher number of seed stars in m33 compared with the modeled cluster . in addition , lee ( 1987 ) made the optimistic assumptions that all binary captures lead to mergers ( rather than the expected @xmath225% ; @xcite ) and that the merged stars have main sequence lifetimes similar to normal stars ( whereas the lifetimes are shortened considerably by the presence of enriched nuclear material ; e.g. , @xcite ) . we project that mergers would yield at best an order of magnitude less than the numbers of massive stars required . this conclusion agrees with the statement by hernquist et al . ( 1991 ) . the merger hypothesis is attractive primarily because of the very small observed core radius in m33 . however , the observations are dominated by the relatively massive stars ; hence we have to examine the time scale for mass segregation to be sure that the radius measured is representative of the distribution of lower mass stars that hypothetically merge due to their high density in this core . we have estimated the dynamical decay time for stars of @xmath178 in a total mass of @xmath179 distributed over a radius of 0.5 pc , assuming that the density goes as @xmath180 , @xmath181 , or is constant within this radius . the calculations are based on equation ( 7 - 18 ) of binney & tremaine ( 1987 ) . we find that the dynamical decay time from formation at a radius of 0.5 pc is in all three cases substantially less than the lifetimes of the stars ; that is , mass segregation is likely to have occurred . the increasing size of the nucleus with wavelength ( see table [ tab_nuc_size ] ) and corresponding observed color gradients ( @xcite ; @xcite ) confirm that the blue , massive stars have probably sunk to the center and are surrounded by a population of lower mass stars . thus , estimates of the merger rate based on the small observed core radius ( e.g. , @xcite and our discussion in the preceding paragraphs ) are likely to be too high . the merger hypothesis can also be tested by examining the properties of the merger products . these products have huge angular momentum compared with normal stars ( e.g. , @xcite ) . if the interiors become convective , the resulting high rotation rates may be spun down through magnetic interaction with circumstellar disks ( @xcite ) . however , the resulting mixing of metal rich material causes the evolution of the stars to differ significantly from that of normal stars ( e.g. , @xcite ; @xcite ) . the possibility of abnormal stellar evolution is made very unlikely by the success in our spectral synthesis evolutionary models in fitting the properties of the nucleus across the entire spectrum , since these models assume normal evolution . the possibility that the nuclear population is characterized by abnormally high rotational velocities is contradicted by the small net velocity dispersion . if the merger mechanism played an important role in m33 , then the conclusions drawn from starburst models would largely be vitiated . however , a variety of arguments show that mergers play a negligible role and hence that the blue stellar population must arise in a starburst as described in section [ sec_stell_pop ] .

the discovery of milky way - type dust ( with a strong 2175 bump ) internal to the m33 nucleus is different from previous work which has found smc - like dust ( no bump ) near starburst regions . the amount by which dust can be processed may be related to the mass and age of the starburst as well as the extent to which the dust can shield itself .

we have thoroughly characterized the ultraviolet to near - infrared ( 0.15 - 2.2 ) spectral energy distribution ( sed ) of the central parsec of the m33 nucleus through new infrared photometry and optical / near - infrared spectroscopy , combined with ultraviolet / optical observations from the literature and the hst archive . the sed shows evidence for a significant level of attenuation , which we model through a monte carlo radiative transfer code as a shell of clumpy milky way - type dust ( ) . the discovery of milky way - type dust ( with a strong 2175 bump ) internal to the m33 nucleus is different from previous work which has found smc - like dust ( no bump ) near starburst regions . the amount by which dust can be processed may be related to the mass and age of the starburst as well as the extent to which the dust can shield itself . our starburst models include the effects of this dust and can fit the sed if the nucleus was the site of a moderate ( at 10 myrs ) episode of coeval star formation about 70 myrs ago . this result is quite different from previous studies which resorted to multiple stellar populations ( between 2 and 7 ) attenuated by either no or very little internal dust . the m33 nuclear starburst is remarkably similar to an older version ( 70 myr versus 10 myr ) of the ultra - compact starburst in the center of the milky way .

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by fitting the uv to near - ir sed of the m33 nucleus with a starburst model which includes stars , gas , and dust , we find the m33 nucleus to be composed of a @xmath270 myr burst of star formation with a mass of @xmath2@xmath182 enshrouded by a shell of mw - type dust ( @xmath9 ) . this result is different from previous work which modeled the nucleus using both young ( @xmath6 years ) and old ( @xmath183 years ) stellar populations subject only to modest reddening . by including the effects of dust internal to m33 , we are able to reproduce the relatively red sed of the m33 nucleus without requiring a luminous old stellar population . as a result , this work is more consistent with the small size and the detection of far - uv flux from the nucleus . the dust in m33 has a strong 2175 bump , in contrast to other uv - bright starbursts that do not show this feature . not much can be said with a sample of one galaxy , but it is possible that the different dust characteristics in m33 nucleus are related to the higher optical depth of dust and/or the age of the starburst . thus , there is not a single type of dust found in starburst galaxies but a range of types varying from that found in the mw to the smc . correcting for the effects of dust in starburst galaxies must be done with care , especially in the uv . the m33 nuclear starburst resembles the ultracompact population of very massive and luminous stars in the center of the milky way , both in the peak luminosity deduced for the starbursts responsible and in the size of the starburst region . it seems likely that ultracompact starbursts ( @xmath184 pc ) are common in the nuclei of normal galaxies and may influence the evolution of these regions significantly . confirmation of our interpretation of the m33 nucleus would be greatly helped by additional uv and far - ir observations . a good uv spectrum of just the nucleus would be easily obtained by the stis instrument on hst due to it s high sensitivity and small apertures . far - ir observations at high spatial resolution would help put stringent constraints on the mass of the dust internal to the nucleus . these observations should be possible with sirtf . we thank the anonymous referee for valuable suggestions which improved the presentation of our work . this work benefited from discussions about ses models with claus leitherer , michel fioc , and brigette rocca - volmerange . in addition , we are indebted to claus leitherer and michel fioc for providing us with new grids of seds from the l98 and pegase ses models . we thank juhan frank for helpful discussion on the x - ray properties of binaries and the intricacies of cluster dynamics . support for this work was provided by nasa through grant number [ ar-08002.01 - 96a ] from the space telescope science institute . additional support was provided by the nsf under grant ast95 - 29190 . mmh received support for this work provided by nasa through hubble fellowship grant # hf-1072.01 - 94a awarded by the space telescope science institute . bailyn , c. d. , & pinsonneault , m. h. 1995 , , 439 , 705 bessell , m. s. 1990 , , 102 , 1181 bessell , m. s. & brett , j. m. 1988 , , 100 , 1134 bessell , m. s. , castelli , f. , & plez , b. 1998 , , 333 , 231 bica , e. & alloin d. 1986 , , 162 , 21 bica , e. & alloin d. 1987 , , 186 , 49 binney , j. , & tremaine , s. 1987 , `` galactic dynamics '' ( princeton univ . press : princeton , n. j. ) , 425 biretta et al . 1996 , wfpc2 instrument handbook , version 4.0 ( baltimore : stsci ) ciani , a. , dodorico , s. , & benvenuti , p. 1984 , , 137 , 223 calzetti , d. , kinney , a. l. , & storchi - bergmann , t. 1994 , , 429 , 582 cardelli , j. a. , clayton , g. c. , & mathis , j. s. 1989 , , 345 , 245 cardelli , j. a. & savage , b. d. 1988 , , 325 , 864 doyon , r. , joseph , r. d. , & wright , g. s. 1994 , , 421 , 101 dubus , g. , charles , p. a. , long , k. s. , & hakala , p. j. 1997 , , 490 , l47 fioc , m. & rocca - volmerange , b. 1997 , , 326 , 950 fioc , m. & rocca - volmerange , b. 1998 , in preparation frogel , j. a. , persson , s. e. , aaronson , m. , matthews , k. 1978 , , 220 , 75 garnett , d. r. , shields , g. a. , skillman , e. d. , sagan , s. p. , & dufour , r. j. 1997 , , 489 , 63 gallagher , j. s. , goad , j. w. , & mould , j. 1982 , , 263 , 101 gordon , k. d. , calzetti , d. , & witt , a. n. 1997 , , 487 , 625 gordon , k. d. & clayton , g. c. 1998 , , 500 , 816 gordon , k. d. , witt , a. n. , & friedmann , b. c. 1998 , , 498 , 522 hernquist , l. , hut , p. , & kormendy , j. 1991 , nature , 354 , 376 holtzman , j. , et al . 1995 , , 107 , 156 hunt , l. k. , mannucci , f. , testi , l. , migliorini , s. , stanga , r. m. , baffa , c. , lisi , f. , & vanzi , l. 1998 , , 115 , 2594 hunter , d. a. , light , r. m. , holtzman , j. a. , lynds , r. , oneil , e. j. , jr . , & grillmair , c. j. 1997 , , 478 , 124 jones , a. p. , tielens , a. g. g. m. , & hollenbach , d. j. 1996 , , 469 , 740 krist , j. & hook , r. 1997 , the tiny tim user s guide , version 4.4 ( baltimore : stsci ) kormendy , j. & mcclure , r. d. 1993 , , 105 , 1793 lanon , a. & rocca - volmerange , b. 1992 , , 96 , 593 lauer , t. r. , faber , s. m. , ajhar , e. a. , grillmair , c. j. , & scowen , p. a. 1998 , , 116 , 2263 lee , h. m. 1987 , , 319 , 801 lee , h. m. , & ostriker , j. p. 1986 , , 310 , 176 leitherer , c. & heckman , t. m. 1995 , , 96 , 9 leitherer , c. et al . 1998 , , submitted lejeune , th . , cuisinier , f. , & buser , r. 1997 , , 125 , 229 leonard , p. j. t. , & livio , m. 1995 , , 447 , l121 massey , p. , bianchi , l. , hutchings , j. b. , & stecher , t. p. 1996 , , 469 , 629 mcquade , k. , calzetti , d. , & kinney , a. l. 1995 , , 97 , 331 minniti , d. , olszewski , e. w. , & rieke , m. 1993 , , 410 , l79 misselt , k. a. , clayton , g. c. , & gordon , k. d. 1998 , , in press monteverde , m. i. , herrero , a. , lennon , d. j. , & kurdritzki , r .- 1997 , , l107 morgan , w. w. & mayall , n. u. 1957 , , 69 , 291 nichols , j. s. , garhart , m. p. , de la pea , m. d. , & levay , k. l. 1994 , new spectral image processing system information manual : low dispersion data - version 1.0 , _ iue _ newsletter no . 53 oconnell , r. w. 1983 , , 267 , 80 odonnell , j. e. & mathis , j. s. 1997 , , 479 , 806 rasio , f. a. , & shapiro , s. l. 1995 , , 438 , 887 rieke , g. h. & lebofsky , m. j. 1982 , in `` the galactic center '' ( am . inst . of phys . : new york ) , 194 rieke , g. h. , loken , k. , rieke , m. j. , & tamblyn , p. 1993 , , 412 , 99 salpeter , e. e. 1955 , , 121 , 161 scalo , j. 1998 , proceedings of herstmonceux conference on imf , in press schmidt , a. a. , bica , e. , & alloin , d. 1990 , , 243 , 620 schulman , e. & bergman , j. n. 1995 , , 441 , 568 shier , l. m. , rieke m. j. , & rieke , g. h. 1996 , , 470 , 222 sills , a. , lombardi , j. c. , bailyn , c. d. , demarque , p. , rasio , f. a. , & shapiro , s. l. 1997 , , 487 , 290 stecher , t. p. , et al . 1997 , , 109 , 584 taylor , j. r. 1982 , an introduction to error analysis ( mill valley , ca : univ . science books ) trinchieri , g. , fabbiano , g. , & peres , g. 1988 , , 325 , 531 van den bergh , s. 1991 , , 103 , 609 voit , m. , et al . 1997 , hst data handbook , version 3.0 ( baltimore : stsci ) wainscoat , r. j. & cowie , l. l. 1992 , , 103 , 332 werner , m. w. & davidson , j. a. 1989 , in `` the center of the galaxy '' ed . m. morris ( kluwer : dordrecht ) , 423 whitmore , b. , heyer , i. , baggett , s. 1997 , instrument science report wfpc2 96 - 4 ( baltimore : stsci ) williams , d. m. , thompson , c. l. , rieke , g. h. & montgomery , e. f. 1993 , , 1946 , 482 witt , a. n. 1977 , , 35 , 1 witt , a. n. & gordon , k. d. 1996 , , 463 , 681 witt , a. n. & gordon , k. d. 1998 , in preparation witt , a. n. , thronson , h. a. , & capuano , j. m. 1992 , , 393 , 611 zaritsky , d. , elston , r. , & hill , j. m. 1989 , , 97 , 97

the sed shows evidence for a significant level of attenuation , which we model through a monte carlo radiative transfer code as a shell of clumpy milky way - type dust ( ) . our starburst models include the effects of this dust and can fit the sed if the nucleus was the site of a moderate ( at 10 myrs ) episode of coeval star formation about 70 myrs ago . this result is quite different from previous studies which resorted to multiple stellar populations ( between 2 and 7 ) attenuated by either no or very little internal dust . the m33 nuclear starburst is remarkably similar to an older version ( 70 myr versus 10 myr ) of the ultra - compact starburst in the center of the milky way .

we have thoroughly characterized the ultraviolet to near - infrared ( 0.15 - 2.2 ) spectral energy distribution ( sed ) of the central parsec of the m33 nucleus through new infrared photometry and optical / near - infrared spectroscopy , combined with ultraviolet / optical observations from the literature and the hst archive . the sed shows evidence for a significant level of attenuation , which we model through a monte carlo radiative transfer code as a shell of clumpy milky way - type dust ( ) . the discovery of milky way - type dust ( with a strong 2175 bump ) internal to the m33 nucleus is different from previous work which has found smc - like dust ( no bump ) near starburst regions . the amount by which dust can be processed may be related to the mass and age of the starburst as well as the extent to which the dust can shield itself . our starburst models include the effects of this dust and can fit the sed if the nucleus was the site of a moderate ( at 10 myrs ) episode of coeval star formation about 70 myrs ago . this result is quite different from previous studies which resorted to multiple stellar populations ( between 2 and 7 ) attenuated by either no or very little internal dust . the m33 nuclear starburst is remarkably similar to an older version ( 70 myr versus 10 myr ) of the ultra - compact starburst in the center of the milky way .

astro-ph0010075

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in 1987 , bothun et al . reported the serendipitous discovery of the extraordinarily large low surface brightness ( lsb ) galaxy now known as malin-1 . in spite of having a projected @xmath8-band central surface brightness of only 26.5 mag arcsec@xmath9 , malin-1 is the largest spiral galaxy known , with a disk scale length of 73 kpc ( assuming @xmath10=75 mpc@xmath3 ) , and an exceptionally high mass ( @xmath11 ) and optical luminosity ( @xmath1223.1 ) . subsequently , through systematic searches of photographic survey plates , other galaxies with similar ( albeit slightly less extreme ) properties to malin-1 have been uncovered ( bothun et al . 1990 ; sprayberry et al . 1993 ; sprayberry et al . we hereafter refer to these as `` lsb giants '' . a handful of lsb giants are also found in the ugc ( nilson 1973 ) , ngc ( dreyer 1953 ) , and eso ( lauberts & valentijn 1989 ) catalogues ( see gallagher & bushouse 1983 ; impey & bothun 1989 ; walsh et al . 1997 ; pickering et al . 1997 ; schombert 1998 ) . nonetheless , while recent photographic and ccd surveys have uncovered large numbers of new small and medium - sized , moderate - to - low surface brightness spiral galaxies ( e.g. , schombert et al . 1992 ; impey et al . 1996 ; oneil et al . 1997 ) , lsb giants have remained relatively rare . having faint , diffuse disks , but sizes , masses , and luminosities at the high end for disk galaxies , the lsb giants occupy a unique realm of physical parameters space and may share evolutionary histories distinct from other lsb galaxies ( e.g. , hoffman et al . 1992 ) . since a continuum of values exists for galaxy properties such as surface brightness , luminosity , and scale length , sprayberry et al . ( 1995b ) proposed to define lsb giants as those objects meeting a `` diffuseness index '' criterion : @xmath13=100 mpc@xmath3 . here we have rewritten the diffuseness criterion for @xmath2=75 mpc@xmath3 , which is assumed throughout this work . ] , where @xmath14 is the extrapolated , deprojected @xmath8-band disk central surface brightness in magnitudes arcsec@xmath9 , and @xmath15 is the disk scale length in kpc . among seven lsb giants described by sprayberry et al . ( 1995b ) , mean properties include : @xmath16 , @xmath17 mags arcsec@xmath9 , and @xmath18 kpc . the colors of these lsb giants are thus comparable to those of normal spirals ( sprayberry et al . 1995b ) , but are redder than typical colors of many small and moderate - sized lsb disks ( e.g. , mcgaugh & bothun 1994 ; matthews & gallagher 1997 ; de blok et al . 1996 ; beijersbergen et al . 1999 ) . in addition , the lsb giants are distinct from other more common lsb spirals in that they often have a significant bulge component ( e.g. , gallagher & bushouse 1983 ; knezek 1993,1998 ) , and frequently their centers harbor an active nucleus ( e.g. , schombert 1998 ) . the origin and evolutionary histories of lsb giant galaxies are still enigmatic . hoffman et al . ( 1992 ) have proposed a formation scenario whereby these systems form in very low density regions from rare , 3@xmath19 density fluctuations . they predict these galaxies should exhibit quiescent , unevolved , gas - rich disks , with rotation curves that flatten near @xmath20300 . knezek ( 1993 ) has suggested an alternative scenario , based on kormendy ( 1989 ) , whereby lsb giants may have dissipatively formed from massive , metal - poor dark matter halos . testing formation and evolution scenarios for lsb giants requires an accurate knowledge of the neutral gas properties and linewidths of these galaxies . and only by combining such measures with optical data can we begin to build a picture of the star - formation histories of these systems and their relationship to other types of lsb galaxies . other motivations also exist for improved observations . hoffman et al . ( 1992 ) have argued that for the enormous disks of lsb giants to remain quiescent over a hubble time , they must be very isolated . yet studies hint that lsb giants are in fact less isolated than other lsb spirals , although redshift surveys in the vicinities of these objects are still incomplete ( sprayberry et al . 1995b ) . pointed observations in the vicinity of lsb giants can thus reveal if these galaxies have any yet - undiscovered gas - rich neighbors . another important use of data is for exploring the tully - fisher ( tf ) relation for giant lsb spirals . sprayberry et al . ( 1995a ) have shown that at least two of the presently known lsb giant galaxies are extreme outliers from the tf relation defined by normal galaxies . this is unlike the bulk of moderate - sized , moderate luminosity lsb galaxies , which tend to follow tf ( sprayberry et al . 1995a ; zwaan et al . 1995 ; verheijen 1997 ) . it is of considerable interest therefore to assess from a larger sample whether lsb giants deviate systematically from the tf relation . while previous observations have established that lsb giants are in general very gas - rich ( @xmath21 ; e.g. , sprayberry et al . 1995b ; walsh et al . 1997 ; pickering et al . 1997,1999 ) , unfortunately existing data for many lsb giants are of dubious quality ( i.e. , the galaxy was confused or resolved by the telescope beam , the spectra are of low signal - to - noise , or measurements from different workers are highly discrepant ; see also table 5 and section [ disc ] ) . for example , based on arecibo 21-cm observations of 3 objects , sprayberry et al . ( 1995b ) suggested that peculiar , asymmetric profiles may be commonplace for lsb giants . however , since the extents of these galaxies were expected to be comparable to the size of the telescope beam , it is important to verify that these `` peculiar '' spectra do not result from some combination of source resolution and telescope mispointing . in addition , independent checks on derived parameters are valuable since it is more difficult to accurately measure integrated fluxes and linewidths when the global profiles are quite broad compared to the bandwidth used , and when sources are at large recessional velocities ( @xmath22 15000 ) , where flux calibration can become increasingly uncertain . finally , there are still a handful of known lsb giants for which no data have previously been obtained . quality single - dish spectra for lsb giants are also a useful precursor and complement to aperture synthesis studies of these galaxies ( e.g. , walsh et al . 1997 ; pickering et al . 1997,1999 ) . mapping is of course a critical part of understanding the dynamics and gas distributions for these galaxies , but since many of the known examples of lsb giants are rather distant ( @xmath2310000 ) and of relatively modest optical angular size ( @xmath24 ) , such observations are challenging and benefit from careful planning based on prior measurements . moreover , because lsb giants are generally expected to have disks with relatively low surface densities ( e.g. , pickering et al . 1997 ) , diffuse emission can be missed in aperture synthesis measurements , and total flux and maximum rotational velocity measures from pencil beam observations serve as an important check . based on the above motivations , we have used the radio telescope to obtain new global observations of a sample of 16 lsb giant galaxies for which existing global measurements were incomplete , required reconfirmation , or were nonexistent . we measure integrated line fluxes , linewidths , and recessional velocities , and attempt to clear up conundrums surrounding several of these objects in the literature .

we have used the radio telescope to obtain new global data for 16 giant low surface brightness ( lsb ) galaxies . our targets have optical luminosities and disk scale lengths at the high end for spiral galaxies ( and kpc for=75 mpc ) , but they have diffuse stellar disks , with mean disk surface brightnesses magnitude fainter than normal giant spirals .

we have used the radio telescope to obtain new global data for 16 giant low surface brightness ( lsb ) galaxies . our targets have optical luminosities and disk scale lengths at the high end for spiral galaxies ( and kpc for=75 mpc ) , but they have diffuse stellar disks , with mean disk surface brightnesses magnitude fainter than normal giant spirals . thirteen of the galaxies previously had been detected in by other workers , but the published observations were either confused , resolved by the telescope beam , of low signal - to - noise , or showed significant discrepancies between different authors . for the other 3 galaxies , no data were previously available . several of the galaxies were resolved by the e - w beam , so global parameters were derived from multiple - point mapping observations . typical masses for our sample are , with.3 - 1.7 ( in solar units ) . all of the observed galaxies have published optical surface photometry , and we have compiled key optical measurements for these objects from the literature . we frequently find significant variations among physical parameters of giant lsb galaxies reported by various workers .

cond-mat0202370

m

the fact that the madelung energy of a random alloy described either by the effective medium model defined by the ss - dft - cpa method or by the supercell model in conjunction with the ss - lsgf method differ from each other , has neither consequences for the final result for the total energy of the random alloy nor even for the partial and local contributions to the total energy . this follows simply from the fact that the density of states and its average local contributions are the same in the two methods , as shown above . in table [ e_iso_pol ] we compare the total energy and its components in a cu@xmath48pt@xmath48 random alloy calculated by the ss - dft - cpa method with @xmath1920.60572 and by the ss - lsgf method on the basis of a 512-atom supercell , in which the atomic positions of cu and pt have been chosen such that the sro parameters are equal zero at the first 7 coordinations shells ( lsgf-1 ) . the agreement between the two calculations is seen to be excellent if one combines the electron - nucleus , the electron - electron , and the madelung contributions to form a total coulomb energy , @xmath193 . the accuracy of the ss - dft - cpa method with the appropriate screening contribution to the madelung potential and energy may be appreciated if one compares the results of a 512-atom supercell calculation performed by the ss - lsgf method ( lsgf-2 ) where the distribution of the cu and pt atoms have not been optimized after the application of the random number generator leading to quite small , but not zero , sro parameters . the values of the sro parameters for the first 7 coordination shells are @xmath640.005208 ( 1 ) , 0.026041 ( 2 ) , 0.007161(3 ) , -0.014323(4 ) , -0.021484(5 ) , 0.0390625(6 ) , @xmath640.0136718 ( 7 ) , respectively , which are approximately the same , as in the lsms calculations in ref . the agreement between ss - dft - cpa results and ss - lsgf calculations with a properly chosen supercell ( lsgf-1 ) is obviously better than between two ss - lsgf calculations .

this allows us to determine the madelung potential energy of a random alloy in the single - site mean field approximation which makes the conventional single - site density - functional- theory coherent potential approximation ( ss - dft - cpa ) method practically identical to the supercell lsgf method with a single - site local interaction zone that yields an exact solution of the dft problem .

we have used the locally self - consistent green s function ( lsgf ) method in supercell calculations to establish the distribution of the net charges assigned to the atomic spheres of the alloy components in metallic alloys with different compositions and degrees of order . this allows us to determine the madelung potential energy of a random alloy in the single - site mean field approximation which makes the conventional single - site density - functional- theory coherent potential approximation ( ss - dft - cpa ) method practically identical to the supercell lsgf method with a single - site local interaction zone that yields an exact solution of the dft problem . we demonstrate that the basic mechanism which governs the charge distribution is the screening of the net charges of the alloy components that makes the direct coulomb interactions short - ranged . in the atomic sphere approximation , this screening appears to be almost independent of the alloy composition , lattice spacing , and crystal structure . a formalism which allows a consistent treatment of the screened coulomb interactions within the single - site mean - filed approximation is outlined . we also derive the contribution of the screened coulomb interactions to the formalism and the generalized perturbation method .

cond-mat0403517

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low dimensional electron systems exhibit a rich variety of surprising effects which are due to the cooperative interplay of impurities and interactions . in one dimension even clean metallic systems are always strongly affected by interactions : at low energy scales physical properties obey anomalous power - laws , known as luttinger liquid behavior , which is very different from the conventional fermi liquid behavior describing most higher dimensional metals.@xcite in luttinger liquids with repulsive interactions already a single static impurity is known to affect the low - energy properties drastically.@xcite the impurity potential in a repulsive luttinger liquid becomes dressed by long - range oscillations which suppress the spectral weight for single - particle excitations near the impurity and also the conductance through the impurity down to zero in the low - energy limit . the _ asymptotic _ low - energy properties of luttinger liquids with a single impurity are rather well understood . universal power - laws and scaling functions have been obtained by bosonization , conformal field theory , and exact solutions for the low - energy asymptotics in special integrable cases.@xcite what remains to be developed , however , is a many - body method for _ microscopic _ models of interacting fermions with impurities , which does not only capture correctly the universal low - energy asymptotics , but allows one to compute observables on all energy scales , providing thus also _ non - universal _ properties , and in particular an answer to the important question at what _ scale _ the ultimate asymptotics sets in . that scale can indeed be surprisingly low , and the properties above it very different from the asymptotic behavior . some of the non - universal properties can be computed numerically by the density matrix renormalization group ( dmrg),@xcite but this method is limited to lattice systems with about 1000 sites , and only a restricted set of observables can be evaluated with affordable computational effort . in the last few years it has been realized that the functional renormalization group ( frg ) is a source of powerful new computation tools for interacting fermi systems , especially for low - dimensional systems with competing instabilities and entangled infrared singularities . the starting point of this approach is an exact hierarchy of differential flow equations for the green or vertex functions of the system , which is obtained by taking derivatives with respect to an infrared cutoff @xmath1.@xcite approximations are then constructed by truncating the hierarchy and parametrizing the vertex functions with a manageable set of variables or functions.@xcite a relatively simple frg approximation for impurities in spinless luttinger liquids has been developed recently by some of us.@xcite the scheme starts from an frg hierarchy for one - particle irreducible vertex functions , as first derived in a field theoretical context by wetterich@xcite and morris,@xcite and for interacting fermi systems by salmhofer and honerkamp.@xcite a matsubara frequency cutoff is used as the flow parameter . the hierarchy is then truncated already at first order , such that the 2-particle vertex remains unrenormalized , and the flow of the self - energy , which describes the renormalized impurity potential , is determined by the bare 2-particle interaction . no simplified parametrization of the self - energy is necessary such that the full spatial dependence of the renormalized impurity potential can be obtained for very large lattice systems . in spite of the striking simplicity of this scheme it was shown that the effects of a single static impurity in a spinless luttinger liquid are fully captured qualitatively , and in the weak coupling limit also quantitatively.@xcite in particular , one obtains that impurity potentials in repulsive luttinger liquids become effectively stronger at lower energy scales , and act ultimately as a weak link between two otherwise separate wires , as predicted by kane and fisher.@xcite the frg also correctly yields the universal low energy power - laws with exponents that do not depend on the bare impurity strength . in addition , it was shown that the asymptotic behavior holds typically only at very low energy scales and for very large systems , except for very strong bare impurities.@xcite the frg approach to impurities in luttinger liquids was originally developed and tested for spectral densities of single - particle excitations , but has been applied very recently also to transport problems , such as persistent currents in mesoscopic rings@xcite and the conductance of interacting wires connected to non - interacting leads.@xcite the full power of the frg with its ability to deal naturally also with complex crossover phenomena emerges most convincingly in the multi - scale problem posed by the transport through a resonant double barrier.@xcite in the present work we further develop the frg approach for impurities in luttinger liquids by including 2-particle vertex renormalization , that is we go one step further in the hierarchy of flow equations than previously.@xcite for spinless fermions this extension does not matter qualitatively , as the lowest order is already qualitatively correct , but the quantitative accuracy of the results improves considerably in particular at intermediate interaction strengths . for spin-@xmath2 systems , which we will treat in a subsequent work,@xcite vertex renormalization is necessary to take into account that backscattering of particles with opposite spins at opposite fermi points scales to zero in the low energy limit . a crucial point is to devise an efficient parametrization of the vertex by a managable number of variables . here we focus on spinless lattice fermions with nearest neighbor interaction as a prototype model . the bulk model is supplemented by site or hopping impurities . we also analyze the influence of boundaries , which can be viewed as infinite barriers or infinitesimal weak links . we choose to parametrize the vertex by a renormalized nearest neighbor interaction , which allows us to capture various advantageous features : the low energy flow of the vertex at @xmath3 in the pure system is obtained correctly to second order in the renormalized couplings ; the non - universal contributions at finite energy scales are correct to second order in the bare interaction ; the algorithm for the flow of the self - energy remains as fast as in the absence of vertex renormalization , such that one can easily deal with up to @xmath0 lattice sites . we compute spectral properties of single - particle excitations near an impurity and the oscillations in the density profile induced by an impurity , or by a boundary . the accuracy of the calculation is checked by comparing with dmrg results for systems with up to 1000 lattice sites and with exact results for the asymptotic behavior , which can be obtained from the bethe ansatz and bosonization . the article is structured as follows . in sec . ii we introduce the microscopic model and various types of impurities . the frg formalism is developed in sec . iii , and worked out explicitly for the spinless fermion model with nearest neighbor interaction . iv is dedicated to results for the renormalized impurity potential , spectral properties , and the density profile . we finally conclude in sec . v with an outline of promising extensions of the present work .

we improve the recently developed functional renormalization group ( frg ) for impurities and boundaries in luttinger liquids by including renormalization of the two - particle interaction , in addition to renormalization of the impurity potential . explicit flow equations are derived for spinless lattice fermions with nearest neighbor interaction at zero temperature , and a fast algorithm for solving these equations for very large systems is presented . results on the relevant energy scales and crossover phenomena at intermediate scales are also obtained .

we improve the recently developed functional renormalization group ( frg ) for impurities and boundaries in luttinger liquids by including renormalization of the two - particle interaction , in addition to renormalization of the impurity potential . explicit flow equations are derived for spinless lattice fermions with nearest neighbor interaction at zero temperature , and a fast algorithm for solving these equations for very large systems is presented . we compute spectral properties of single - particle excitations , and the oscillations in the density profile induced by impurities or boundaries for chains with up to lattice sites . the expected asymptotic power - laws at low energy or long distance are fully captured by the frg . results on the relevant energy scales and crossover phenomena at intermediate scales are also obtained . a comparison with numerical density matrix renormalization results for systems with up to 1000 sites shows that the frg with the inclusion of vertex renormalization is remarkably accurate even for intermediate interaction strengths .

cond-mat0403517

c

in summary , we have shown that the frg provides an ideal tool for computing the intriguing properties of luttinger liquids with static impurities . the method yields ab initio results for microscopic model systems at all energy scales from the fermi energy to the ultimate low energy limit . we have demonstrated the power of the method by computing spectral properties of single - particle excitations as well as the oscillations in the density profile induced by impurities or boundaries for a spinless fermion model with nearest neighbor interaction . with the inclusion of vertex renormalization , in addition to the renormalization of the effective impurity potential , our results agree remarkably well with exact asymptotic results and numerical dmrg data even for intermediate interaction strength . there is a broad range of interesting further applications and extensions of the frg for impurities in luttinger liquids beyond the scope of the present article : _ spin-@xmath2 fermions _ : the inclusion of spin degrees of freedom requires a parametrization of the two - particle vertex with several coupling constants . we have already derived flow equations for the ( extended ) hubbard model , with an effective vertex parametrized by local and nearest neighbor interactions.@xcite _ feedback of impurities on vertex _ : for isolated impurities the influence of impurities on the vertex renormalization is irrelevant for the asymptotic low energy or long distance behavior , although it may contribute quantitatively at intermediate scales . in the case of disordered systems with a finite impurity density the influence of the latter on the two - particle vertex is crucial and must be taken into account.@xcite in principle this is possible by computing the vertex flow with full propagators , which contain the renormalized impurity potential via the self - energy . _ finite temperature _ : the frg approach can be extended without major complications to finite temperature . this is particularly useful for studying the temperature dependence of transport properties.@xcite _ transport _ : in the absence of inelastic processes ( @xmath208 ) the conductance of the interacting wire can be computed from the one - particle green function in the presence of leads.@xcite several results have already been presented in short articles.@xcite _ inelastic processes _ : inelastic processes appear at second order in the interaction and can be included in the flow equations by inserting the second order vertex into the flow equation for the self - energy without neglecting its frequency dependence . this procedure would also capture the anomalous dimension of the bulk system , which is missing in the present work . * acknowledgements : * + we are grateful to manfred salmhofer for useful discussions . this work benefitted from the workshop realistic theories of correlated electron materials in fall 2002 at itp - ucsb . thanks the bundesministerium fr bildung und forschung for financial support .

we compute spectral properties of single - particle excitations , and the oscillations in the density profile induced by impurities or boundaries for chains with up to lattice sites . a comparison with numerical density matrix renormalization results for systems with up to 1000 sites shows that the frg with the inclusion of vertex renormalization is remarkably accurate even for intermediate interaction strengths .

we improve the recently developed functional renormalization group ( frg ) for impurities and boundaries in luttinger liquids by including renormalization of the two - particle interaction , in addition to renormalization of the impurity potential . explicit flow equations are derived for spinless lattice fermions with nearest neighbor interaction at zero temperature , and a fast algorithm for solving these equations for very large systems is presented . we compute spectral properties of single - particle excitations , and the oscillations in the density profile induced by impurities or boundaries for chains with up to lattice sites . the expected asymptotic power - laws at low energy or long distance are fully captured by the frg . results on the relevant energy scales and crossover phenomena at intermediate scales are also obtained . a comparison with numerical density matrix renormalization results for systems with up to 1000 sites shows that the frg with the inclusion of vertex renormalization is remarkably accurate even for intermediate interaction strengths .

1511.07313

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a domain wall is a prototype collective excitation in a physical system , and it is also the paradigm example of a topological soliton @xcite . a domain wall can appear whenever there is a global symmetry that becomes spontaneously broken . it constitutes the boundary that separates two neighbouring domains , in which the order parameter that detects the symmetry breaking has different values . in the case of a one dimensional heisenberg spin chain the order parameter is a three component unit length vector . when one of the three vector components vanishes identically , the heisenberg spin chain reduces to the xy spin chain @xcite . a domain wall along the spin chain is a localised excitation that interpolates between two different , ordered spin states in which the order parameter has different constant values . two major types of domain walls are commonly identified along the heisenberg chain @xcite . these are called the bloch wall and the nel wall , respectively . in the case of a bloch wall , the heisenberg spin variable rotates through the plane of the wall and in the case of a nel wall the rotation takes place within the plane of the wall itself . domain walls that are mixtures of these two , can also occur along the heisenberg spin chain , while along the xy spin chain , only domain walls of the bloch type can be present . in this article we demonstrate that the formation of super - secondary structures , during folding of a protein @xcite , can be understood in terms of a bloch domain wall that forms along a heisenberg spin chain , or along a closely related xy spin chain . we propose that the spin chain interpretation of a protein backbone provides a systematic framework for understanding and describing the process of protein folding . for this we employ all - atom force fields @xcite to scrutinise protein folding dynamics at the level of individual atoms and their oscillations . we analyse the folding pathway using a combination of topological techniques and global analytic tools . we isolate the collective oscillations which are pertinent for the folding process , from the noisy background of thermal and random individual atom fluctuations . in particular , we illustrate how the individual atom motions become organised and combined into a coherent structural excitation which we identify as the bloch wall . as a concrete example we consider an @xmath0-helical subunit of the hiv envelope glycoprotein gp41 @xcite , with protein data bank @xcite ( pdb ) code 1aik . there are six @xmath0-helical subunits in the biological assembly , shown in figure 1 . we consider in isolation the subunit , for which the first amino acid has number 628 in the pdb file . in isolation , the subunit is unstable and starts folding . the transmembrane glycoprotein 41 is itself a subunit of the retrovirus envelope protein complex . in the case of the hiv , its structure has been studied extensively . it is presumed to have substantial biological relevance to the initial viral infection . accordingly , the gp41 protein is a popular target for the development of an anti - viral immune response , to prevent and cure hiv infection . however , medical applications are beyond the direct scope of the present study . here we shall solely address and identify the physical mechanism , why and how an individual , initially @xmath0-helical subunit of 1aik becomes unstable in isolation , and starts folding . for our all - atom molecular dynamics simulations , we utilise the gromacs 4.6.3 package @xcite . we analyse the results using a variety of topological techniques and analytical tools . our approach derives from the mathematical structure of heisenberg and xy spin chains , in combination with properties of a discrete nonlinear schrdinger ( dnls ) hamiltonian @xcite . in particular , the dnls equation that describes the local extrema of the hamiltonian , enables us to analytically identify the profile of the domain wall , and to interpret it in terms of dnls soliton @xcite . here we present results from the detailed investigation of a particular example . however , we expect our observations and conclusions to be generic . indeed , the present results are fully in line with the previous findings @xcite obtained by using the coarse grained unres energy function @xcite in the case of protein a. the similitude of results that are obtained by analysing the protein folding process using different tools , built and based on phenomena with very different characteristic time and length scales , demonstrates that we have correctly identified the relevant collective motions that command the folding process .

we scrutinise collective many - atom motions during all - atom molecular dynamics simulations . the example we consider is an-helical subunit of the hiv envelope glycoprotein gp41 . but in isolation the helix becomes unstable , and the monomer starts deforming . we follow the process computationally . we interpret the evolving structure both in terms of a backbone based heisenberg spin chain and in terms of a side chain based xy spin chain . we find that in both cases the formation of protein super - secondary structure is akin the formation of a topological bloch domain wall along a spin chain . during the process

we inquire how structure emerges during the process of protein folding . for this we scrutinise collective many - atom motions during all - atom molecular dynamics simulations . we introduce , develop and employ various topological techniques , in combination with analytic tools that we deduce from the concept of integrable models and structure of discrete nonlinear schrdinger equation . the example we consider is an-helical subunit of the hiv envelope glycoprotein gp41 . the helical structure is stable when the subunit is part of the biological oligomer . but in isolation the helix becomes unstable , and the monomer starts deforming . we follow the process computationally . we interpret the evolving structure both in terms of a backbone based heisenberg spin chain and in terms of a side chain based xy spin chain . we find that in both cases the formation of protein super - secondary structure is akin the formation of a topological bloch domain wall along a spin chain . during the process we identify three individual bloch walls and we show that each of them can be modelled with a very high precision in terms of a soliton solution to a discrete nonlinear schrdinger equation .

1511.07313

i

molecular dynamics enables the scrutiny of protein folding , at the level of individual atoms and over very short time intervals . however , it can leave us with the conceptual challenge to understand , how the individual atoms cooperate to produce the kind of large scale organisation that appears to be prevalent among crystallographic protein structures . we have performed detailed molecular dynamics simulations , with the aim to find out how organised structure emerges when a protein folds . we have first compared three different force fields using the gromacs 4.6.3 . package , to select the proper tools . we have chosen a c - chain subunit from hiv envelope glycoprotein with pdb code 1aik as a concrete example , partly due to its biomedical relevance even though this is an issue which has not been addressed by us . we have introduced and further developed various tools of modern theoretical physics , to systematise and analyse the data . these include topological tools , conceptual analogies drawn from the notion of spin chains , the notion of wilsonian universality , and methods based on the analytical structure of the discrete nonlinear schrdinger equation . in this manner we have arrived at the conclusion that the protein folding is a process that relates intimately to the emergence and interactions of solitons . in particular , a configuration such as the bloch domain wall along a spin chain appears to be most useful in comprehending how structure emerges and self - organises when a protein folds . we have inspected both the static and dynamic properties of domain wall solitons and observed that concepts which are familiar from the study of lattice systems , such as the peierls - nabarro barrier , also appear along protein backbones lattices , and in fact assume a central role in dictating how the folding proceeds . we hope that our observations help to pave a way for the powerful analytical and topological tools and techniques that have been introduced and developed in the context of integrable spin chains and related solvable models , to become part of the arsenal used describe emergence of structure and organisation in the case of proteins and other biological macromolecules .

we inquire how structure emerges during the process of protein folding . for this we introduce , develop and employ various topological techniques , in combination with analytic tools that we deduce from the concept of integrable models and structure of discrete nonlinear schrdinger equation . the helical structure is stable when the subunit is part of the biological oligomer .

we inquire how structure emerges during the process of protein folding . for this we scrutinise collective many - atom motions during all - atom molecular dynamics simulations . we introduce , develop and employ various topological techniques , in combination with analytic tools that we deduce from the concept of integrable models and structure of discrete nonlinear schrdinger equation . the example we consider is an-helical subunit of the hiv envelope glycoprotein gp41 . the helical structure is stable when the subunit is part of the biological oligomer . but in isolation the helix becomes unstable , and the monomer starts deforming . we follow the process computationally . we interpret the evolving structure both in terms of a backbone based heisenberg spin chain and in terms of a side chain based xy spin chain . we find that in both cases the formation of protein super - secondary structure is akin the formation of a topological bloch domain wall along a spin chain . during the process we identify three individual bloch walls and we show that each of them can be modelled with a very high precision in terms of a soliton solution to a discrete nonlinear schrdinger equation .

math0205030

i

the problem of the existence of periodic orbits for hamiltonian systems has a very far and rich history in the development of mathematics and physics . in fact , some of the major contributions on this question include the celebrated poincar - birkhoff theorem on the existence of periodic orbits for area preserving twist maps on the annulus and the morse - lyusternik - schnirelman theory on the existence of closed geodesics on compact riemannian manifolds . recently , a special class of symplectic invariants was introduced by h. hofer and e. zehnder @xcite as a link between rigidity phenomena of symplectic mappings and the existence of periodic orbits provided by classical variational methods . more precisely , they introduced an axiomatic definition of symplectic capacities in the following way : consider the class of all symplectic manifolds @xmath33 of fixed dimension equal to 2n . a symplectic capacity is a map @xmath34 that associates to @xmath2 a non negative number or @xmath35 and that satisfies the following axioms : * * monotonicity : * if there exists a symplectic embedding @xmath36 then @xmath37 * * conformality : * @xmath38 where @xmath39 is the ball of radius @xmath40 and @xmath41 is the cylinder over the @xmath42-plane . a distinguished symplectic capacity was introduced by hofer and zehnder and is directly related to the question of the existence of periodic orbits on prescribed energy levels of hamiltonian flows : [ defchz ] given a symplectic manifold @xmath2 , define the hofer - zehnder capacity of @xmath18 by @xmath43 where @xmath44 is the set of _ admissible hamiltonians _ @xmath45 defined on @xmath18 , that is , * @xmath46 , where @xmath47 is the set of _ pre - admissible hamiltonians _ defined on @xmath18 , that is , @xmath45 satisfies the following properties : @xmath48 , there exist an open set @xmath49 such that @xmath50 and a compact set @xmath51 satisfying @xmath52 ; * every non - constant periodic orbit of @xmath53 has period greater than 1 . intuitively , this capacity measure the sufficient oscillation for a pre - admissible hamiltonian to have fast periodic orbits , that is , of period less than one . it is easy to see that it satisfies the monotonicity and conformality properties . remarkably , by making use of classical variational methods , hofer and zehnder @xcite showed that it also satisfies the non - triviality axiom , giving , in particular , a dynamical new proof of gromov s nonsqueezing theorem @xcite . moreover , this symplectic invariant has important consequences on the question of the existence of periodic orbits on prescribed energy levels of hamiltonian systems . in fact , it is easy to prove that if a symplectic manifold @xmath2 has _ bounded hofer - zehnder capacity _ , that is , if @xmath54 for every open subset @xmath55 with compact closure , then given any hamiltonian @xmath56 with compact energy levels , there exists a dense subset @xmath57 such that for every @xmath58 the energy hypersurface @xmath59 has a periodic solution . this result was improved by m. struwe in @xcite showing that if the energy hypersurfaces bound a compact submanifold then @xmath22 has total lebesgue measure . this condition is not necessary as was proved recently in @xcite . note that as an immediate consequence we have a proof of the weinstein conjecture @xcite for manifolds with bounded hofer - zehnder capacity , since we can construct in a neighborhood of a contact hypersurface @xmath60 a distinguished parametrized family of hypersurfaces with equivalent flows . unfortunately , it is , in general , a difficult task to determine when a symplectic manifold has bounded hofer - zehnder capacity . for @xmath61 , where @xmath62 denotes the canonical symplectic form , it follows by hofer - zehnder theorem @xcite . for surfaces , it was proved by k. siburg @xcite , that the hofer - zehnder capacity of an open subset @xmath63 coincides with the area of @xmath63 . however , the situation is dramatically different for higher dimensional manifolds . actually , hofer and viterbo showed in @xcite that @xmath64 where @xmath2 is any closed symplectic manifold and @xmath65 is the two dimensional disk of radius @xmath66 , with @xmath40 satisfying the condition @xmath67 , where @xmath68 is the _ index of rationality _ of @xmath2 , that is , @xmath69}\om;\ \ [ u ] \in \pi_2(m ) \text { satisfies } \int_{[u]}\om > 0\bigg\}.\ ] ] if the above set is empty , we define @xmath70 . recall that a 2-form @xmath71 on @xmath18 is _ weakly exact _ if it is closed and @xmath70 . this result was extended by g. lu @xcite to noncompact symplectic manifolds satisfying certain conditions at the infinity . more precisely , he showed that @xmath72 provided that @xmath2 is geometrically bounded and @xmath73 . a symplectic manifold @xmath2 is called _ geometrically bounded _ if there exists an almost complex structure @xmath74 on @xmath18 and a riemannian metric @xmath75 such that * @xmath74 is uniformly @xmath71-tame , that is , there exist positive constants @xmath76 and @xmath77 such that @xmath78 for all tangent vectors @xmath79 and @xmath80 to @xmath18 ; * the sectional curvature of @xmath75 is bounded from above and the injectivity radius is bounded away from zero . the closed symplectic manifolds are clearly geometrically bounded ; a product of two geometrically bounded symplectic manifolds is also such a manifold . moreover , it was proved in @xcite that the cotangent bundle of a compact manifold endowed with any twisted symplectic form is geometrically bounded ( a proof of this fact can also be found in @xcite ) . a _ twisted symplectic structure _ on a cotangent bundle @xmath81 is a symplectic form given by @xmath26 , where @xmath62 is the canonical symplectic form , @xmath82 is the canonical projection and @xmath15 is a closed 2-form on @xmath18 . thus , using the monotonicity property , we can conclude that @xmath83 has bounded hofer - zehnder capacity , where @xmath6 is any compact manifold and @xmath62 is the canonical symplectic form ( because we can embed symplectically any bounded subset of @xmath84 into @xmath85 ) . actually , by the same reason , we can prove that @xmath86 has bounded hofer - zehnder capacity for any geometrically bounded symplectic manifold @xmath18 . it should be noted that it is necessary to consider product symplectic forms @xmath87 . in fact , there is an example due to zehnder @xcite of a symplectic form on @xmath88 with unbounded hofer - zehnder capacity . note that any symplectic form on @xmath89 is weakly exact . other known example of cotangent bundle with bounded hofer - zehnder capacity is @xmath90 endowed with any twisted symplectic form @xmath91 , where @xmath15 is a closed 2-form on @xmath92 and @xmath93 is the canonical projection . it was proved by j. jiang @xcite for @xmath94 and by v. ginzburg and e. kerman @xcite for the general case . we will consider here a refinement of the hofer - zehnder capacity by considering periodic orbits whose homotopy class is contained in a given subgroup @xmath0 of @xmath95 . more precisely , we define the hofer - zehnder semicapacity as follows ; it can be compared with the @xmath96-sensitive hofer - zehnder capacity defined by m. schwarz @xcite and lu @xcite and the relative symplectic capacity introduced by p. biran , l. polterovich and d. salamon @xcite : given a symplectic manifold @xmath2 and a subgroup @xmath3 define the _ hofer - zehnder g - semicapacity _ of @xmath18 ( or _ @xmath0-sensitive hofer - zehnder capacity _ ) by @xmath97 where @xmath98 is the set of _ @xmath0-admissible hamiltonians _ defined on @xmath18 , that is , * @xmath99 , that is , @xmath45 is pre - admissible ( see definition [ defchz ] ) ; * every nonconstant periodic orbit of @xmath53 whose homotopy class belongs to @xmath0 has period greater than 1 . we call it a _ semicapacity _ because given a symplectic embedding @xmath100 such that @xmath101 it can not be expected , in general , that @xmath102 , where @xmath103 is the induced homomorphism on the fundamental group . however , we can state the following _ weak monotonicity property _ ( for a proof see section [ proofthma ] ) : given a symplectic embedding @xmath104 such that @xmath101 then @xmath105 for every subgroup @xmath106 . in particular , if @xmath107 is injective we have that @xmath108 . note that obviously , @xmath109 for every subgroup @xmath3 . moreover , it can be show that if the hofer - zehnder @xmath0-semicapacity is bounded then there are periodic orbits with homotopy class in @xmath0 on almost all energy levels for every proper hamiltonian @xcite . a symplectic manifold @xmath2 has _ bounded hofer - zehnder @xmath0-semicapacity _ if for every open subset with compact closure @xmath110 , we have that @xmath111 we remark that the periodic orbits in @xmath112 given by the theorems of hofer - viterbo and lu are _ contractible_. thus , in terms of symplectic semicapacities , their theorems state the stronger result that @xmath113 for any geometrically bounded symplectic manifold @xmath2 and @xmath114 . by the weak monotonicity property , we can conclude then that @xmath115 is bounded , where @xmath116 is the obvious subgroup generated by the circle in the cylinder @xmath117 . in fact , the kernel of the induced homomorphism on the fundamental group of the symplectic embedding of @xmath118 into @xmath119 is given by @xmath120 . the aim of the first part of this paper is to generalize this result in the following way : note that @xmath121 has a natural hamiltonian free circle action with hamiltonian given by the angle form @xmath122 viewed here as a function on @xmath123 . we will consider the following : is the existence of a hamiltonian free circle action sufficient to ensure the boundedness of the hofer - zehnder semicapacity ( with respect to the subgroup of @xmath95 generated by the orbits of the action ) ? before we state our first result we need a previous topological definition related to free circle actions : let @xmath124 be a free circle action on a connected open subset @xmath6 of a manifold @xmath18 . we define the _ order of the action _ @xmath125 as the order of the cyclic subgroup of @xmath95 generated by the homotopy class of the orbits of @xmath125 . now , we are able to state our first theorem . in what follows we will denote the oscillation of a hamiltonian @xmath45 by @xmath126 . [ thma ] let @xmath2 be a geometrically bounded symplectic manifold and @xmath5 a connected open subset that admits a free hamiltonian circle action @xmath124 ( with period equal to @xmath127 ) given by the hamiltonian @xmath128 . suppose that the order of this action @xmath129 ( considered as an action on @xmath18 ) satisfies @xmath130 . given an open subset @xmath131 with compact closure , suppose that @xmath132 then , we have that @xmath133 where @xmath134 is the induced homomorphism on the fundamental group and @xmath135 is the subgroup generated by the orbits of @xmath125 . * note that the previous theorem can not be stated directly for @xmath6 because we need to assume that @xmath18 is geometrically bounded and it not clear that an open subset of a geometrically bounded symplectic manifold is geometrically bounded . * the circle action above needs to be hamiltonian . in fact , the example of herman - zehnder @xcite has unbounded hofer - zehnder capacity and it is easy to see that it admits a free symplectic circle action with infinite order . before we explain the main ideas involved in the proof of theorem [ thma ] , let us state some corollaries and applications . [ coreulerclass ] let @xmath2 be a geometrically bounded symplectic manifold . suppose that @xmath18 admits a free hamiltonian circle action generated by @xmath136 whose euler class @xmath137 \in h^2(m / s^1,\r)$ ] satisfies @xmath137|_{\pi_2(m / s^1 ) } = 0 $ ] . then , for any open subset @xmath110 with compact closure , we have that @xmath138 provided that @xmath139 . actually , it can be proved that given a free circle action on a manifold @xmath18 such that the euler class @xmath137 \in h^2(m / s^1,\r)$ ] satisfies @xmath137|_{\pi_2(m / s^1 ) } = 0 $ ] then the order of the action is infinite ( see section [ eulerclass ] ) . now , consider the finite subgroup @xmath140 . note that , since the circle action is hamiltonian , the induced action of @xmath141 on @xmath18 is symplectic . since the action is free , the quotient manifold @xmath142 has a induced symplectic structure @xmath143 defined uniquely by the property that the pullback of @xmath143 by the quotient projection is @xmath71 . moreover , @xmath142 has an induced free hamiltonian circle action ( with period @xmath144 ) with order greater than or equal to @xmath145 . consequently , we have the following immediate corollary : [ cor1 ] let @xmath2 be a geometrically bounded symplectic manifold . suppose that @xmath18 admits a free hamiltonian circle action generated by @xmath136 and let @xmath55 be an open subset with compact closure . if @xmath146 and @xmath147 , then @xmath148 where @xmath149 is the quotient projection , @xmath150 is the inclusion , @xmath71 is the induced symplectic form on @xmath142 and @xmath125 is the induced circle action . there are a lot of non - trivial examples of symplectic manifolds admitting such free hamiltonian circle actions . the first one that we will consider is the following : let @xmath18 be a compact manifold admitting a free circle action . then the lift of this action to the cotangent bundle of @xmath18 is hamiltonian with respect to the canonical symplectic form . in fact , it is hamiltonian with respect to any twisted symplectic form @xmath151 , where @xmath15 is a closed two - form on @xmath18 given by the pullback of a closed two - form @xmath152 on @xmath153 . thus , we have the following corollaries : [ cor2 ] let @xmath18 be a compact manifold admitting a free circle action @xmath125 whose euler class @xmath137 \in h^2(m / s^1,\r)$ ] satisfies @xmath137|_{\pi_2(m / s^1 ) } = 0 $ ] and @xmath15 a weakly exact two - form on @xmath18 given by the pullback of a two - form @xmath152 on @xmath153 . then the cotangent bundle @xmath154 has bounded hofer - zehnder @xmath155-semicapacity . let @xmath18 be a compact manifold such that @xmath156 and @xmath157 the total space of a circle bundle @xmath158 . then @xmath159 has bounded hofer - zehnder @xmath155-semicapacity . [ cor3 ] let @xmath18 be a compact manifold admitting a free circle action @xmath125 . then @xmath160 has bounded hofer - zehnder @xmath155-semicapacity for any @xmath161 and any weakly exact 2-form @xmath162 , where @xmath163 is the quotient projection . it is easy to construct specific non - trivial examples of such circle bundles . for instance , the lens spaces @xmath164 @xmath165 over @xmath166 , the heisenberg manifold over the 2-torus and , more generally , any 2-step nilmanifold @xcite . in fact , it can be proved that the group of equivalence classes of circle bundles over a manifold @xmath18 is isomorphic to @xmath167 @xcite . thus , any non - trivial element of @xmath167 for a manifold @xmath18 such that @xmath156 corresponds to a non - trivial circle bundle with infinite order . the heisenberg manifold , for example , corresponds to the cohomology class of the area form on @xmath89 . in the section [ proofthmb ] , we show some applications of the theorem [ thma ] where the circle action is not a lifted action . we will consider circle actions given by the magnetic flow associated to monopoles on surfaces . more precisely , let @xmath168 be a closed riemannian manifold , @xmath15 a closed 2-form on @xmath18 and @xmath25 endowed with the twisted symplectic form @xmath91 , where @xmath62 is the pullback of the canonical symplectic form via the riemannian metric . when @xmath18 is a hyperbolic surface and @xmath15 is the area form , this manifold has remarkable properties and is related to mcduff s example of a symplectic manifold with disconnected contact - type boundary @xcite ( see section [ proofthmb ] , where we give a simple construction of such a manifold ) . the hamiltonian flow @xmath169 given by the kinetic energy @xmath170 with respect to @xmath26 is called the magnetic flow generated by the riemannian metric @xmath75 and the magnetic field @xmath15 . it can be show that , when @xmath18 is a surface of constant negative curvature and @xmath15 is the area form , the magnetic flow defines a free circle action with infinite order on certain subsets of @xmath25 . using this fact and the expanding completion of convex manifolds developed by eliashberg and gromov @xcite , we can prove the following theorem : [ thmb ] let @xmath18 be a surface of genus @xmath171 endowed with the hyperbolic metric @xmath172 and the khler form @xmath173 . let @xmath174 be the usual hamiltonian given by the kinetic energy @xmath175 and @xmath176 a positive real number . consider the open subset @xmath177 . then , @xmath178 as long as @xmath179 , where @xmath31 is the subgroup generated by the fibers of the unitary bundle . in particular , the periodic orbits have contractible projection on @xmath18 . on the other hand , we have that @xmath180 for every @xmath181 . by moser s theorem , we have the following corollary : let @xmath18 be a surface of genus @xmath182 and @xmath15 a symplectic form on @xmath18 . then there exists a riemannian metric @xmath75 on @xmath18 such that @xmath183 as long as @xmath184 , where @xmath185 and @xmath186 is the subgroup generated by the fibers of the unitary bundle as above . when @xmath18 is the 2-torus and @xmath15 is a symplectic form , it is well know that @xmath187 for every open subset @xmath188 with compact closure . in fact , it is easy to prove that @xmath189 is symplectomorphic to @xmath190 , where @xmath191 is the canonical symplectic form on @xmath192 @xcite . this result can also be obtained by the theorem [ thma ] . now , we will use theorem [ thma ] to show that for closed khler manifolds @xmath193 the possible obstruction to the boundedness of the hofer - zehnder capacity is a very thin subset of @xmath18 which , in many situations , can be explicitly described . to prove it , we will need the following nice decomposition result of p. biran @xcite which enable us to represent a khler manifold as a disjoint union of two basic components whose symplectic nature is very standard : [ bir ] let @xmath9 be a closed khler manifold with @xmath11 \in h^2(m,\z)$ ] and @xmath194 a complex hypersurface whose homology class @xmath195 \in h_{2n-2}(m)$ ] is the poincar dual to @xmath13 $ ] for some @xmath196 . then , there exists an isotropic cw - complex @xmath197 whose complement - the open dense subset @xmath198 - is symplectomorphic to a standard symplectic disc bundle @xmath199 modeled on the normal bundle @xmath200 of @xmath12 in @xmath18 and whose fibers have area @xmath201 . the symplectic form @xmath202 is given by @xmath203 where @xmath204 is the bundle projection , @xmath40 is the radial coordinate using a hermitian metric @xmath205 and @xmath206 is a connection form on @xmath19 such that @xmath207 . the form @xmath208 is uniquely characterized by the requirements that its restriction to the zero section @xmath12 equals @xmath209 , the fibers of @xmath204 are symplectic and have area @xmath201 and @xmath202 is invariant under the obvious circle action along the fibers . it is called standard because the symplectic type of @xmath210 depends only on the symplectic type of @xmath211 and the topological type of the normal bundle @xmath200 @xcite . let us recall that the pair @xmath23 is called _ subcritical _ @xcite if @xmath24 is a subcritical stein manifold , that is , if there exists a plurisubharmonic morse function @xmath125 on @xmath24 such that @xmath212 for every critical point @xmath213 of @xmath125 . it is equivalent to the condition that the dimension of @xmath214 ( that is , the maximal dimension of the cells of @xmath214 ) is strictly less than @xmath145 . [ thmc ] let @xmath9 be a closed khler manifold ( @xmath10 ) with @xmath11 \in h^2(m,\z)$ ] and @xmath194 a complex hypersurface whose homology class @xmath195 \in h_{2n-2}(m)$ ] is the poincar dual to @xmath13 $ ] for some @xmath196 . then there exists an open dense subset @xmath19 of @xmath18 symplectomorphic to a standard symplectic disc bundle over @xmath22 whose complement is an isotropic cw - complex @xmath215 such that if @xmath11|_{\pi_2(m)}=0 $ ] then @xmath216 where @xmath217 is the subgroup generated by the orbits of the obvious @xmath218-action on @xmath20 . if @xmath11|_{\pi_2(m ) } \neq 0 $ ] and @xmath17 , we have that @xmath219 moreover , if @xmath23 is subcritical and @xmath11|_{\pi_2(m)}=0 $ ] , then @xmath220 where @xmath221 . * in @xcite it is proved that the hypothesis that @xmath10 and that either @xmath11|_{\pi_2(m ) } = 0 $ ] or @xmath17 are not necessary to ensure that @xmath222 is finite . * the result above can not be stated directly for symplectic disk bundles and concluded as a property of symplectic disk bundles plus biran s decomposition result because symplectic disk bundles are not geometrically bounded . actually , a fundamental ingredient in the proof of theorem [ thmc ] is that , by the lefschetz theorem , the circle action on @xmath20 has the same order considered both as an action on @xmath20 itself and as an action on @xmath24 ( this construction is not necessary in @xcite since we do not need there the topological assumption on the order of the action ) . * under the hypothesis that either @xmath223 or @xmath11|_{\pi_2(m)}=0 $ ] , it was proved by p. biran @xcite that the _ gromov capacity _ of @xmath19 satisfies @xmath224 . these assumptions are not necessary as was proved recently by g. lu @xcite . * the result above for _ subcritical _ manifolds was proved by c. viterbo in @xcite . * when @xmath23 is subcritical we do not consider the case @xmath17 because , as was proved in @xcite , every subcritical polarization has degree 1 . we remark that the cw - complex @xmath214 above is given by the union of the stable manifolds of the gradient flow of a plurisubharmonic function @xmath125 defined on @xmath24 such that it can be explicitly computed in many examples @xcite . the next theorem shows that we can get a similar result in the neighborhood of a symplectic hypersurface of donaldson type @xcite : [ thmd ] let @xmath9 be a closed symplectic manifold ( @xmath10 ) with @xmath11 \in h^2(m,\z)$ ] and @xmath194 a symplectic hypersurface whose homology class @xmath195 \in h_{2n-2}(m)$ ] is the poincar dual to @xmath13 $ ] for some @xmath225 . then there exists @xmath226 such that if @xmath227 there exists an open neighborhood @xmath228 of @xmath22 such that if @xmath11|_{\pi_2(m)}=0 $ ] then @xmath229 where @xmath230 , as above , is the subgroup generated by the orbits of the obvious @xmath218-action on @xmath231 . if @xmath11|_{\pi_2(m ) } \neq 0 $ ] , we have that @xmath232 it is important to remark that an extension of biran s result for symplectic hypersurfaces considered above ( which is generally expected to remains valid ) will enable us to extend theorem [ thmc ] for general symplectic manifolds . the essential idea in the proof of theorem [ thma ] is to relate the hofer - zehnder capacity of a symplectic manifold endowed with a hamiltonian circle action with the hofer - zehnder capacity of its reduced symplectic manifold ( in the sense of marsden - weinstein ) with respect to this action . more precisely , we consider the diagonal hamiltonian circle action on @xmath233 whose reduced symplectic manifold @xmath234 is given by @xmath2 . then , given a pre - admissible hamiltonian @xmath235 we construct a @xmath218-invariant pre - admissible hamiltonian @xmath236 on @xmath157 whose reduced dynamics is given by a reparametrization of the hamiltonian vector field of @xmath45 on @xmath18 . thus , we can apply the results of hofer - viterbo and lu to get a periodic orbit for @xmath237 and so , by reduction , a periodic orbit for @xmath53 . the essential step is to show the non - triviality of the projected closed orbit and it is here that the hypothesis on the order of the action plays an essential role . the idea is to use the condition on the homotopy of the periodic orbit together with an upper bound on the period of the orbit to ensure that the orbit can not be tangent to the trajectories of the diagonal action . in the second part of this paper , we will consider the problem of the existence of periodic orbits on prescribed energy levels for a special class of hamiltonian dynamical systems given by the magnetic flows . this problem was first considered by v. arnold @xcite and s. novikov @xcite and for a discussion of the results in this area we refer to @xcite . it was proved by l. polterovich @xcite that for every nontrivial weakly exact magnetic field on a manifold whose euler characteristic vanishes , there exist non - trivial contractible closed orbits of the magnetic flow in a sequence of arbitrarily small energy levels . the proof uses the geometry of the hofer s metric in the group of hamiltonian diffeomorphisms and the fundamental fact that the displacement energy of the zero section of @xmath25 , with respect to the twisted symplectic form given by a non - vanishing magnetic field , is equal to zero . recently , e. kerman @xcite gives the same result for magnetic fields given by symplectic forms . in @xcite we proved the existence of contractible closed orbits for almost all low energy levels , provided that the magnetic field is also symplectic . we will prove here an extension of polterovich s theorem for any manifold , without the assumption on the euler characteristic . [ thme ] let @xmath18 be any closed riemannian manifold and @xmath15 a non - trivial weakly exact magnetic field . then there exists a sequence of arbitrarily small energy levels containing non - trivial contractible periodic orbits . the main idea in the proof is similar to that of theorem [ thma ] . in fact , we consider a lift of the magnetic flow to @xmath84 and use the topological condition on the periodic orbit to ensure the non - triviality of the projected periodic orbit by symplectic reduction . the details are given in the section [ proofthme ] . i am very grateful to gabriel paternain for many helpful comments and suggestions and to the centro de investigacin en matemtica , guanajuato , mexico for the hospitality while part of this work was in progress . i am also grateful to kai cieliebak , dusa mcduff and felix schlenk for very useful comments .

we introduce the hofer - zehnder-semicapacity of a symplectic manifold ( or-sensitive hofer - zehnder capacity ) with respect to a subgroup ( ) and prove that given a geometrically bounded symplectic manifold and an open subset admitting a hamiltonian free circle action with order greater than two then has bounded hofer - zehnder-semicapacity , where is the subgroup generated by the orbits of the action , provided that the index of rationality of is sufficiently great ( for instance , if|_{\pi_2(m)}=0 $ ] ) . we give several applications of this result . using p. biran s decomposition theorem , we prove the following : let be a closed khler manifold ( ) with \in h^2(m,\z)$ ] and a complex hypersurface representing the poincar dual of $ ] , for some . then there exists a decomposition of into an open dense subset such that has finite hofer - zehnder-semicapacity and an isotropic cw - complex , where is the subgroup generated by the obvious circle action on the normal bundle of . moreover , we prove that if is subcritical then has finite hofer - zehnder-semicapacity . we also show that given a hyperbolic surface and endowed with the twisted symplectic form , where is the khler form on , then the hofer - zehnder-semicapacity of the domain bounded by the hypersurface of kinetic energy minus the zero section is finite if , where is the subgroup generated by the fibers of . finally , we will consider the problem of the existence of periodic orbits on prescribed energy levels for magnetic flows . we prove that given any weakly exact magnetic field on any compact riemannian manifold then there exists a sequence of contractible periodic orbits of energy arbitrarily small , extending a previous result of l. polterovich .

we introduce the hofer - zehnder-semicapacity of a symplectic manifold ( or-sensitive hofer - zehnder capacity ) with respect to a subgroup ( ) and prove that given a geometrically bounded symplectic manifold and an open subset admitting a hamiltonian free circle action with order greater than two then has bounded hofer - zehnder-semicapacity , where is the subgroup generated by the orbits of the action , provided that the index of rationality of is sufficiently great ( for instance , if|_{\pi_2(m)}=0 $ ] ) . we give several applications of this result . using p. biran s decomposition theorem , we prove the following : let be a closed khler manifold ( ) with \in h^2(m,\z)$ ] and a complex hypersurface representing the poincar dual of $ ] , for some . suppose either that vanishes on or that . then there exists a decomposition of into an open dense subset such that has finite hofer - zehnder-semicapacity and an isotropic cw - complex , where is the subgroup generated by the obvious circle action on the normal bundle of . moreover , we prove that if is subcritical then has finite hofer - zehnder-semicapacity . we also show that given a hyperbolic surface and endowed with the twisted symplectic form , where is the khler form on , then the hofer - zehnder-semicapacity of the domain bounded by the hypersurface of kinetic energy minus the zero section is finite if , where is the subgroup generated by the fibers of . finally , we will consider the problem of the existence of periodic orbits on prescribed energy levels for magnetic flows . we prove that given any weakly exact magnetic field on any compact riemannian manifold then there exists a sequence of contractible periodic orbits of energy arbitrarily small , extending a previous result of l. polterovich .

nucl-th0402026

i

the phase transition from partonic degrees of freedom ( quarks and gluons ) to interacting hadrons is a central topic of modern high - energy physics @xcite . in order to understand the dynamics and relevant scales of this transition laboratory experiments under controlled conditions are presently performed with ultra - relativistic nucleus - nucleus collisions . hadronic spectra and relative hadron abundances from these experiments reflect important aspects of the dynamics in the hot and dense zone formed in the early phase of the reaction . here different quark flavors ( @xmath10 ) - as constituents of the final hadrons - provide valuable information on the early high density phase due to the substantial different mass scales for the light ( @xmath11 ) , strange ( @xmath12 ) and charm ( @xmath13 ) or bottom ( @xmath14 ) quarks . furthermore , as has been proposed early by rafelski and mller @xcite in particular the strangeness degree of freedom might play an important role in distinguishing hadronic and partonic dynamics . lattice qcd calculations at vanishing quark chemical potential and finite temperature indicate critical energy densities for the formation of a quark - gluon plasma ( qgp ) of @xmath3 0.7 - 1 gev/@xmath15 @xcite , which might already be achieved at alternating gradient synchrotron ( ags ) energies of @xmath3 10 @xmath0gev for central au+au collisions @xcite . moreover , the recent lattice qcd calculations at finite quark chemical potential @xmath8 @xcite show a rapid increase of the thermodynamic pressure @xmath16 with temperature above the critical temperature @xmath17 for a phase transition ( or cross - over ) to the qgp . the problem is how to relate these numbers to observables from nucleus - nucleus collisions . estimates based on the bjorken formula @xcite for the energy density achieved in central au+au collisions suggest that the critical energy density for the formation of a qgp of @xmath3 0.7 - 1 gev/@xmath15 is by far exceeded during a few fm / c in the initial phase of au+au collisions at relativistic heavy ion collider ( rhic ) energies @xcite . accordingly , a phase transition ( or cross - over ) might already happen at much lower bombarding energies . experimentally , relativistic nucleus - nucleus collisions have been studied at beam energies from 0.1 to 2 @xmath0gev at the schwerionen - synchrotron ( sis ) , from 2 to 11.6 @xmath0gev at the ags and from 20 to 160 @xmath0gev at the super proton synchrotron ( sps ) @xcite . this program has been extended @xcite at rhic with au+au collisions at invariant energies @xmath18 from @xmath19 to 200 gev ( equivalent energies in a fixed target experiment : 0.2 to 21.3 @xmath0tev ) . whereas many previous experimental studies have focused on longitudinal rapidity distributions for hadrons , the transverse mass ( or momentum ) spectra of hadrons are presently in the center of interest . on the one hand a significant suppression of high transverse momentum hadrons in au+au collisions compared to @xmath1 is observed at rhic energies of @xmath20 200 gev @xcite . this suppression is often attributed to the energy loss of highly energetic particles in a hot colored medium ( qgp ) @xcite . in fact , the recent observation by the phenix @xcite , star @xcite and brahms @xcite collaborations , that a similar suppression is not observed in d+au interactions at midrapidities at the same energy , supports this idea . on the other hand , the measured transverse mass ( @xmath21 ) spectra of hadrons ( heavier than pions ) @xmath22 at ags , sps and rhic energies show a substantial _ hardening _ in central au+au collisions relative to @xmath1 interactions ( cf . this hardening of the spectra ( or increase of the inverse slope parameter @xmath9 in ( [ slope ] ) ) for low transverse mass or momentum is commonly attributed to strong collective flow , which is absent in the respective @xmath1 or @xmath2 collisions . the authors of @xcite have proposed to interpret the approximately constant @xmath6 slopes above @xmath23 a@xmath4gev the step as an indication for a phase transition . this interpretation is also based on a rather sharp maximum in the @xmath7 ratio at @xmath3 20 to 30 a@xmath4gev in central of pb+pb collisions ( the horn @xcite ) . however , the present body of experimental data and our theoretical understanding does not allow for a stringent conclusion based only on the step and horn phenomena . in this paper we will address some further theoretical issues , but would like to point out that more experimental data , for example on collisions in the energy range of @xmath24 gev and on weakly interacting hadrons , will be needed to clarify these issues from the experimental side . we will demonstrate in this work , that neither the pressure needed to generate a large collective flow to explain the hard slopes of the @xmath6 spectra with a plateau at sps energies nor the experimental sharp maximum in the @xmath7 ratio at @xmath3 20 to 30 a@xmath4gev is produced in the present transport models by the interactions of hadrons in the expansion phase of the hadronic fireball . some aspects of this work have been published in refs . @xcite before ; however , we here extend the previous studies to rhic energies and consider a wide variety of dynamical scenarios . in particular we will explore two distinct effects : i ) initial state cronin enhancement and ii ) heavy resonance formation on the transverse mass spectra of pions and kaons at all bombarding energies from lower ags to rhic energies . in our studies we use two independent relativistic transport models that employ hadronic and string degrees of freedom , i.e. urqmd @xcite and hsd @xcite . they take into account the formation and multiple rescattering of hadrons and thus dynamically describe the generation of pressure in the hadronic expansion phase . this involves also interactions of leading pre - hadrons that contain a valence quark ( antiquark ) from a primary hard collision ( cf . @xcite ) . in the parton language , the two transport models employed do not include gluon degrees of freedom explicitly nor gluon - gluon and gluon - quark ( antiquark ) interactions . we will use these models to test , whether the description of nucleus - nucleus reactions in terms of pre - hadronic , hadronic and string degrees of freedom and their interactions is sufficient to explain the experimental data . our work is organized as follows : in section ii we briefly recall the ingredients of the hsd and urqmd transport approaches and point out the extensions incorporated in urqmd ( versions 2.0 and 2.1 ) . in section iii the calculated excitation functions for pions , @xmath6 mesons and hyperons for central au+au ( or pb+pb ) collisions from 2 to 21300 a@xmath4gev are shown ( in comparison to the experimental data ) as well as selected particle ratios . section iv is devoted to transverse mass spectra of pions and @xmath6 mesons from @xmath1 to @xmath2 and central @xmath25 reactions in the same energy range . in section v we will discuss various alternative scenarios within the transport calculations to explore their sensitivity to the hadron transverse mass spectra . section vi is devoted to a study of the cronin effect in central au+au collisions , which we attribute to a pre - hadronic initial state scattering effect that also shows up in @xmath2 reactions . section vii includes a comparison of the thermodynamic lagrange parameters @xmath9 and @xmath26 extracted from the urqmd transport model in the central overlap regime of au+au collisions with the experimental systematics on chemical freeze - out configurations in the @xmath27 plane as well as recent lattice qcd results . section viii closes this study with a summary and discussion of open problems .

we investigate hadron production as well as transverse hadron spectra from proton - proton , proton - nucleus and nucleus - nucleus collisions from 2gev to 21.3tev within two independent transport approaches ( hsd and urqmd ) that are based on quark , diquark , string and hadronic degrees of freedom . we investigate various scenarios to explore their potential effects on the spectra . however , the maximum in the ratio at 20 to 30 agev is missed by 40% and the approximately constant slope of the spectra at sps energies is not reproduced either . our systematic analysis suggests that the additional pressure - as expected from lattice qcd calculations at finite quark chemical potential and temperature- should be generated by strong interactions in the early pre - hadronic / partonic phase of central au+au ( pb+pb ) collisions .

we investigate hadron production as well as transverse hadron spectra from proton - proton , proton - nucleus and nucleus - nucleus collisions from 2gev to 21.3tev within two independent transport approaches ( hsd and urqmd ) that are based on quark , diquark , string and hadronic degrees of freedom . the comparison to experimental data on transverse mass spectra from , and c+c ( or si+si ) reactions shows the reliability of the transport models for light systems . for central au+au ( pb+pb ) collisions at bombarding energies above 5 agev , furthermore , the measured transverse mass spectra have a larger inverse slope parameter than expected from the default calculations . we investigate various scenarios to explore their potential effects on the spectra . in particular the initial state cronin effect is found to play a substantial role at top sps and rhic energies . however , the maximum in the ratio at 20 to 30 agev is missed by 40% and the approximately constant slope of the spectra at sps energies is not reproduced either . our systematic analysis suggests that the additional pressure - as expected from lattice qcd calculations at finite quark chemical potential and temperature- should be generated by strong interactions in the early pre - hadronic / partonic phase of central au+au ( pb+pb ) collisions .

cond-mat9811392

i

the presence of an antiferromagnetic ( af ) phase rapidly replaced by an anomalous metallic phase upon doping is one of the prominent features of the phase diagram of high temperature superconducting cuprates @xcite . indeed it was early suggested @xcite that the proximity to an insulating magnetic phase together with the nearly twodimensional structure of these materials could be responsible for the superconducting and anomalous normal - state ( i.e. non - fermi liquid ) properties of these systems via the creation of a quantum - disordered spin liquid ( resonating - valence - bond state ) . since then a great deal of attention has been devoted to the fascinating interplay between magnetism and charge degrees of freedom , leading to various theoretical proposals and to different scenarios for the metal - insulator transition at low doping . one scenario is based on the tendency of a magnetically ordered phase to segregate the additional holes due to doping @xcite . the tendency to phase separation is then frustrated by the coulombic repusion between the segregated carriers @xcite , thus leading to formation of hole - rich domain walls separating af domains in the form of stripe textures . within this scenario , pseudogaps naturally arise in the underdoped phase of the materials as a consequence of stripe fluctuations and local pair formation @xcite . obviously this will substantially affect the transition to the af insulating phase at low doping @xcite . the transition between a magnetically ordered phase and a metallic state can also be strongly affected by extrinsic ingredients like the disorder induced by dopant ions ( sr or zn in the case of @xmath8 ) . this may lead to the formation of local random magnetic moments giving rise to spin - glass ordering between the af insulating and the paramagnetic metallic ( pm ) phases @xcite . the stripe and the spin - glass scenarios clearly illustrate the complicated and rich nature that the af - pm transition may take . however , other proposals are more directly related to magnetism and to the contiguity between the af and the metallic phase . these proposals start from the seminal work of ref . @xcite showing that the materials with half - filled cuo@xmath9 planes are suitably described in terms of a twodimensional quantum heisenberg af model with very small interplanar coupling . following work @xcite suggested that , although the 2d model displays long - range order at @xmath10 , upon doping the added charges enhance the quantum spin fluctuations thus driving the system into a disordered state even at zero temperature ( quantum disordered phase ) @xcite . the occurrence of an af quantum critical point ( qcp ) provides a natural framework to intepret the scaling behavior at low temperatures and low frequencies of the of the @xmath11-integrated magnetic susceptibility @xmath12 . the susceptibility @xmath13 can be experimentally determined via magnetic resonance measurements of the nuclear copper spin - echo decay rate , @xmath14 and spin - lattice relaxation rate , @xmath15 @xcite . it is seen that in a range of temperatures @xmath16 , depending on doping , @xmath17 @xcite . assuming the scaling relations @xcite , @xmath18 and @xmath19 , with @xmath20 a dynamic critical exponent , @xmath21 an anomalous dimension , @xmath22 the antiferromagnetic ordering wave - vector , @xmath23 the correlation length , @xmath24 a scaling function , one gets @xmath25 @xcite . the constancy of this ratio is thus interpreted as the signature of a critical behavior corresponding to a @xmath3 value of the dynamic index @xcite . the strong critical spin fluctuations occurring at the af - qcp have also been claimed to provide a possible source of pairing and normal - state anomalies . despite the apparent simplicity of a scenario involving a direct transition between an insulating af phase and a pm phase , such a transition is far from being trivial and is still an open problem . the main difficulty is in the lack of a microscopic model being able to smoothly interpolate between an insulating af ordered phase with gapped charge excitation and a pm phase . on the one hand , the insulating af phase is suitably represented by the heisenberg model and , in particular , the long - wavelength and low frequency behavior of spin fluctuations in the cuo@xmath9 planes can be well described by the quantum non - linear sigma model @xcite , which at zero temperature and in two spatial dimensions is characterized by the action @xmath26 here @xmath27 is a three - component vector field subject to the real - space constraint @xmath28 which describes the local staggered magnetization , and @xmath29 is a coupling constant . it was first argued in @xcite that this description could be carried over to the case of the lightly doped compounds . in fact , one can think that in this case the @xmath27 field continues giving an effective description of the electron spins localized on the cu sites of the lattice , while the presence of itinerating holes provides a finite renormalization of the coupling constant . the theory described by the action ( [ pura ] ) , besides having the correct symmetries , realizes a zero - temperature transition for a given critical value @xmath30 of the coupling ( see @xcite for the quantum version and @xcite for the classical theory ) thus providing a good model for the physical picture of the af - qcp @xcite . from this point of view the @xmath3 value of the dynamic scaling exponent is a simple consequence of the lorentz invariance of ( [ pura ] ) . however , it is clear that the non - linear @xmath31 model does not properly describe the low - energy charge excitations , which are characteristic of a metallic state possibly providing a damping mechanism for spin - waves ( see , e.g. , case b of ref . @xcite ) . therefore the model in eq . [ pura ] provides a good description of a transition between an insulating ( charge - gapped ) af ( afi ) and an insulating paramagnet ( pi ) . , but it appears to be inappropriate when spin - waves can decay in low - energy particle - hole excitations . on the other hand , attempts have also been made to provide a microscopic basis for the transition to a pm phase . in this regard two distint cases a and b depending on the shape of the fermi surface in the metal were investigated in ref . @xcite within a spin - density - wave approach . in case a the af wavevector @xmath32 ( @xmath33 is the lattice spacing ) was not able to connect points of the fermi surface , so that momentum and energy conservation did not allow the decay of spin - waves in particle - hole pairs . in this case the transition was naturally characterized by a dynamic critical index @xmath34 . in case b , instead , there were ( `` hot '' ) points on the fermi surface connected by @xmath35 so that low - energy particle - hole pairs could be created by the decay of low - energy spin - waves . however , in both cases , a and b , the phase with af long - range order is metallic and therefore the model does not suitably describe a transition between an afi and a pm model would suitably describe the system also in this case despite the metallic character of both the ordered and disordered phases . ] . the case a above shares some common features with a mixed spin - fermion model without a three - body ( i.e. kondo - like ) direct coupling between the local moments and the fermion spins @xcite . this model has been shown @xcite to display a @xmath10 transition between a metallic ( fermi liquid ) phase with spin commensurate long - range order and a metallic ( also fermi liquid ) quantum disordered phase . owing to the absence of the three body coupling responsible for the direct spin - wave decay into particle - hole pairs , also the qcp of this model is characterized by @xmath34 . to the best of our knowledge no simple microscopic modelization is presently available to describe a direct afi - pm transition . of course the possibilities remain open that other extrinsic mechanisms ( stripes , disorder , ... ) provide intermediate steps between the afi and the pm phases . alternatively , one may also envisage that an afi to a pi phase transition occurs first at lower doping , followed at slightly larger doping by a pi - pm transition between two spin - disordered phases . together with the basic difficulty outlined above , the additional question arises concerning the observed @xmath34 critical behavior in the underdoped phase of the cuprates and the way this can be reconciled with the metallic character of this phase . in particular it is believed that the fermi surface of the cuprates in the metallic phase contains `` hot '' points connected by the af wavevector . therefore it should be possible for the spin - waves of arbitrarily low energy to decay into particle - hole pairs and get overdamped . this would lead to a relaxational behavior contrasting with the @xmath34 ( i.e. propagating ) critical behavior of the spin - waves . moreover , by accepting a @xmath36 critical behavior in the metallic phase , it remains to clarify how this may turn into the natural propagating behavior , which characterizes the spin excitations in the ordered side of the qcp . this latter difficulty was also encountered and stressed by the authors of ref . @xcite for their case b : within their mean - field description a @xmath36 behavior was obtained both in the disordered and the ordered af ( metallic ) phases . this suggested that the simple formulation b of the mean - field sdw model was only applicable on the disordered side of ( and not too close to ) the af - qcp . in the present paper we will not attempt to find a microscopic foundation to a direct afi - pm transition , but we will instead start from a semiphenomenological point of view by introducing a field - theoretical generalization of the non - linear @xmath31 model action ( [ pura ] ) to investigate a ) the condition to be fullfilled by a simple ( @xmath37-independent ) damping term in order to maintain a @xmath34 critical behavior ; b ) how in the @xmath38 case an additional crossover energy must behave in the ordered phase to provide a scale separating damped spin excitations at high energy and propagating spin excitations at low energy . the resulting theory will depend on the precise form of the effective damping term . we first discuss the simpler case of the metallic phase on the @xmath39 side of the qcp . within a microscopic model of spins coupled to free itinerant holes , integrating out the holes degrees of freedom in the random phase approximation gives a damping term of the form @xmath40 ( see _ e.g. _ @xcite ) . however , the choice of the adequate low frequency form of @xmath41 should also take in consideration the fact that in underdoped cuprates a significant loss of low - frequency spectral weight is observed at low temperatures in the distribution of quasi - particles , a phenomenon often referred to as `` pseudogap '' ( see _ e.g. _ @xcite ) . the origin of this effect is a debated issue , and has been alternatively interpreted : as the result of spin - fermion scattering @xcite , as due to the intrinsecally non - fermi liquid nature of the system ( luttinger liquid ) @xcite , as a signal of the formation of preformed pairs for @xmath42 @xcite , as due to stripe charge fluctuations @xcite . in all cases , a precise computation of these effects implies solving a difficult self - consistency problem going well beyond the rpa approach . we shall try here a rough , phenomenological approach , assuming that the damping coefficient @xmath43 can acquire at low frequencies an @xmath44-dependence @xmath45 , thus giving rise to an effective damping term of the form @xmath1 , with @xmath46 case corresponds to the case considered in ref . @xcite within a large - n framework . ] . _ _ _ _ once chosen a damping term @xmath47 we perform a renormalization group ( rg ) analysis of the resulting theory in the proximity of the qcp using the momentum - shell method and @xmath5-expansion . we observe the existence of two fixed points , which we shall denote fp1 and fp2 , showing respectively a @xmath3 , undamped spin - wave behavior and a @xmath48 , dissipative behavior . the point fp1 corresponds to the zero - temperature critical point of a pure quantum non - linear sigma model without any damping term , but it becomes unstable in a wide region of the parameters with respect to the dissipative fixed point fp2 . there exists a range of values @xmath49 for which one obtains a @xmath50 dynamic scaling exponent in the proximity of the stable quantum critical point , even in the presence of a damping term . in other words , there are `` soft '' damping terms which do not destroy the @xmath3 , spin - wave behavior . here @xmath51 is the dimension dependent lower bound for the exponents in the soft damping term , which we determine to be @xmath52 , where @xmath53 is the anomalous field dimension and @xmath54 is its value at the fp1 . it is worth noting that this result bears a resemblance to what is found in classical models with long - range interactions @xcite . in particular the scaling exponent of the damping stems from the non - analytic form of @xmath47 , which is not reconstructed by the rg corrections ( for a discussion of this point in classical models see ref . . therefore @xmath55 does not acquire singular corrections but for the anomalous field dimensions . within the framework of an expansion in @xmath56 , where @xmath57 is the spatial dimension of the system and @xmath58 is the bare value of the dynamic scaling exponent in the vicinity of the stable fixed point , one would get @xmath59 , where the 1 or 2 subscripts in @xmath60 refer to fp1 or fp2 respectively . however , the extrapolation of results valid for @xmath61 to the physical region @xmath7 should be done with great care . in particular , using the numerical results for the critical exponents of the @xmath62 model in 2 + 1 dimensions , it appears that @xmath51 is very near to two and the range of `` soft '' @xmath63 values should be a very narrow one . this means that within the here - considered model the appearance of a @xmath3 critical behavior in the cuprates can not be accounted for in the effective framework without assuming a value @xmath64 , _ i.e. _ , an almost linear decay of the quasi - particle spectral weight for low frequencies . this spectral weight suppression is a rather severe condition to be obtained from the magnetic scattering itself , as also suggested by a direct perturbative calculation within a spin - fermion model @xcite , where density of states and vertex corrections to the fermion bubble produced only a minor change of the power - law dependence of the damping term . it is worth noting that a substantial spectral weight reduction is however consistent with anderson s idea that a smooth connection between a charge - gapped insulator and a fermi - liquid metal is hardly conceivable . _ _ as far as the ordered phase is concerned , ( point ( b ) above ) it is necessary to take into account the presence of a non - zero staggered magnetization @xmath65 , which is accompanied by the presence of two quasi - particle bands separated by an energy @xmath66 . this suggests @xcite to introduce a damping term having two distinct asymptotics : @xmath67 for @xmath68 and @xmath69 for @xmath70 , with @xmath71 in the ordered ( as well as in the disordered ) phase , but in a first approximation we ignore this dependence mainly for simplicity reasons , but also because in the insulating phase , where a gap for the charge excitations providing spin - wave decay is present , it would be unnatural to expect a relevant q - dependence . ] the difficult point here is that the scale @xmath72 separating damped and undamped spin excitations vanishes at the transition . this prevents using a conventional rg approach , and we will resort to simple scaling arguments and phenomenological assumptions . our analysis does not attain the same degree of reliability of a traditional landau - ginzburg - wilson theory and has a heuristic character . we shall assume that @xmath73 has a power - law behavior , to be determined by matching the hydrodynamic behaviors on the two sides of the quantum transition . for @xmath74 , _ i.e._for @xmath38 , we find that ( i ) @xmath73 should close at the microscopic " scale as @xmath75 for @xmath76 , where @xmath77 is a correlation length , and that ( ii ) the spin - wave velocity @xmath78 vanishes as @xmath79 , to be consistent with the presence of damping . _ _ the paper is organized as follows : in sec . [ rengreq ] we derive the rg equations for the zero - temperature quantum non - linear sigma model with a damping term of generic form , following the scheme exposed in @xcite . this part is rather technical and it can be skipped in a first reading without loosing the general meaning of the paper . in sec . [ fixpanrgeq ] we perform the fixed point analysis of the rg equations for a damping term @xmath80 . here we show the existence of the two fixed points mentioned above , study their respective regions of stability and compute the relevant critical exponents , with particular regard to the value of the dynamic scaling exponent @xmath81 . in sec . [ ordphase ] we discuss damping in the ordered phase , introducing a phenomenological scale @xmath73 vanishing at the quantum critical point with a critical exponent that we determine by matching the hydrodynamic behaviors on the two sides of the transition . we also compute the critical behavior of the spin - wave velocity @xmath78 in the presence of damping . in sec . [ conclusions ] we present some conclusive remarks and discuss the connection between our model and other physically interesting systems , like macroscopic quantum tunnelling and spin chains with long range interaction .

we find two fixed points : a spin - wave fixed point fp1 showing a dynamic scaling exponent and a dissipative fixed point fp2 with in the framework of the-expansion it is seen that there is a range of values where the point fp1 is stable with respect to fp2 , so that the system realizes a quantum critical behavior even in the presence of a dissipative term . however , reasonable arguments suggest that in this range is very narrow . in the broken symmetry phase we discuss a phenomenological scaling approach , treating damping as a perturbation of the ordered ground state . the relation of these results with the pseudogap effect observed in underdoped layered cuprates is discussed .

we investigate the behavior of the zero - temperature quantum non - linear sigma model in dimensions in the presence of a damping term of the form , with . we find two fixed points : a spin - wave fixed point fp1 showing a dynamic scaling exponent and a dissipative fixed point fp2 with in the framework of the-expansion it is seen that there is a range of values where the point fp1 is stable with respect to fp2 , so that the system realizes a quantum critical behavior even in the presence of a dissipative term . however , reasonable arguments suggest that in this range is very narrow . in the broken symmetry phase we discuss a phenomenological scaling approach , treating damping as a perturbation of the ordered ground state . the relation of these results with the pseudogap effect observed in underdoped layered cuprates is discussed . , and renormalization group , non linear sigma model , quantum critical point , cuprates . 75.10.jm , 75.50.ee , 64.60.ak , 74.72.-h

cond-mat0507035

i

according to ehrenfest s theorem , the expectation values of the position and momentum of an electron obey classical equations of motion . as long as the wavefunction of the electron is a wavepacket with minimal uncertainties in momentum and position , the expectation values are a good description of the quantum state . however , wavepackets disperse , and the ehrenfest theorem looses its relevance after a short time . in a cavity with point scatterers , which split electron wavepackets into partial waves after one scattering event , this time is simply the elastic mean free time . in a ballistic cavity with chaotic classical dynamics , this time is the so - called `` ehrenfest time '' @xmath0 , which depends on the lyapunov exponent @xmath1 of the classical motion in the cavity.@xcite for times longer than @xmath0 , a classical description no longer holds and the wave nature of the electrons becomes visible . the wave nature of electrons is the cause of some striking effects that are absent in classical systems . for transport through cavities coupled to source and drain reservoirs via point contacts , these effects are weak localization , universal conductance fluctuations , and shot noise.@xcite in the limit that transport through cavities is ergodic ( dwell time in the cavity is much longer than the time of flight through the cavity ) , the signatures of quantum transport are ` universal ' , independent of the cavity size and shape , and of the fact whether electron motion inside the cavity is ballistic and chaotic or diffusive , with repeated scattering off impurities with size smaller than the electron wavelength . random matrix theory provides a unified theoretical description of weak localization , universal conductance fluctuations , and shot noise in ballistic or diffusive cavities.@xcite if the electron motion is diffusive , the dynamics is fully quantum mechanical already at times much shorter than the time @xmath2 required for ergodic exploration of the cavity s phase space . for ballistic cavities this is true in most practical applications as well the ehrenfest time @xmath3 usually does not exceed the time of flight through the cavity but there is no fundamental reason why @xmath0 always has to be small . the case of large ehrenfest times is of theoretical interest , as it is one of very few regimes in parameter space in which one can observe differences between signatures of quantum transport in ballistic chaotic and diffusive cavities . the most prominent effects of a large ehrenfest time are found if @xmath0 is larger than the dwell time @xmath4 in the cavity . if @xmath5 , quantum transport is deterministic , and shot noise is suppressed.@xcite the suppression of shot noise has been observed experimentally by varying the dwell time @xmath4 of a chaotic cavity,@xcite and numerically , using a chaotic map as a model for a chaotic cavity.@xcite the effect of a large ehrenfest time on weak localization was first addressed by aleiner and larkin.@xcite their theory predicts a suppression of weak localization @xmath6 , if classical correlations are taken into account properly.@xcite the same suppression was found in an independent calculation by adagideli.@xcite experimental observation of the suppression of weak localization at large ehrenfest times has been reported for transport through antidot arrays.@xcite no semiclassical theory for the ehrenfest - time dependence of universal conductance fluctuations exists . however , semiclassical theories for weak localization and universal conductance fluctuations for the limit @xmath7 are essentially equal,@xcite as are diagrammatic perturbation theories for the same phenomena in diffusive cavities , supporting the expectation that the ehrenfest - time dependencies of weak localization and universal conductance fluctuations will be equal as well.@xcite direct numerical simulation of the effect of a large ehrenfest time on quantum transport through two - dimensional chaotic cavities has been problematic because of the prohibitively high computational cost of the simulations . the reason is that @xmath0 depends only logarithmically on the product of the electron wavenumber @xmath8 and the cavity size @xmath9 , @xmath10 for two - dimensional cavities , system sizes at which @xmath11 can not be simulated with present - day algorithms and processor speeds . in order to circumvent this problem , jacquod , schomerus , and beenakker proposed to replace the cavity by a quantum map.@xcite the map is opened , so that simulation of transport properties is possible . although a map has a one - dimensional phase space , a chaotic map shares many characteristics of the chaotic motion in two - dimensional chaotic cavities.@xcite the reduced dimensionality of the map s phase space made numerical simulations with larger ehrenfest times possible . for an open version of the quantum kicked rotator map , numerical simulations were reported for shot noise,@xcite weak localization,@xcite and universal conductance fluctuations.@xcite simulation results for shot noise were in good agreement with the predictions of the semiclassical theory.@xcite however , for conductance fluctuations , no dependence on @xmath0 was found , despite the fact that ehrenfest times larger than the dwell time were considered . @xcite whereas early numerical simulations of weak localization showed no ehrenfest - time dependence,@xcite we showed that there is a systematic decrease of the weak localization correction to the conductance upon increasing @xmath0 , consistent with the semiclassical theory.@xcite the main technical innovation that allowed us to detect a systematic decrease of the weak localization correction upon increasing the ehrenfest time is that we looked at time - resolved numerical simulations : the map s time evolution is truncated after a time @xmath12 , and weak localization , conductance fluctuations , and shot noise are monitored as a function of @xmath12.@xcite this procedure has two advantages . first , it allows the ensemble average over the quasienergy @xmath13 to be done analytically . ( see sec . [ numerics ] for technical details . ) this made it possible to consider significantly larger ensembles than considered previously . second , monitoring quantum corrections as a function of the ` truncation time ' @xmath12 allows us to determine the minimal time after which quantum corrections can occur . in the semiclassical theory , quantum interference requires a minimal wavepacket to be split _ and _ reunited , which takes a minimal time @xmath14 . a schematic diagram drawing relevant semiclassical trajectories for weak localization and conductance fluctuations is shown in fig . [ fig:1 ] . ( the diagram for conductance fluctuations is taken from ref . and modified to contain the effect of a finite ehrenfest time . ) not being a quantum interference effect , shot noise only requires wavepackets to be split , which happens after a time @xmath0 . comparison of the time when quantum effects appear ( the ` onset time ' ) and the rate of suppression of quantum effects as the ehrenfest time @xmath0 is increased , thus provides a quantitative test of the semiclassical theory . with such a quantitative test of the semiclassical theory , accurate simulations performed at smaller ehrenfest times can still be meaningful . = 0.8 in this paper , we present detailed results of such time - resolved numerical simulation for weak localization , conductance fluctuations , and shot noise . for all three quantum effects , we analyze their ehrenfest - time dependence ( without truncation of the time evolution ) and the onset times ( obtained from simulations with truncation of the time evolution ) . the simulation results are presented in sec.[kicked ] , together with the predictions of random matrix theory for time - resolved transport through open quantum maps . whereas we confirm our earlier conclusion that the numerical simulations for weak localization show a suppression @xmath15 , consistent with the semiclassical theory , we find that simulations for conductance fluctuations show a very small increase if @xmath0 is increased , the effect being small enough to be consistent with the simulation data reported in the literature.@xcite the onset times for conductance fluctuations are more than a factor two smaller than the onset times for weak localization , which is incompatible with the notion that conductance fluctuations arise as wavepackets are split and reunited . a second goal of this paper is to show how classical correlations are taken into account in the semiclassical theory of ref . . the importance of classical correlations no quantum diffraction takes place to or from classical trajectories with classical dwell time shorter than the ehrenfest time was pointed out in the analysis of simulation data for the quantum kicked rotator , most notably the simulations for shot noise.@xcite the original version of the semiclassical theory,@xcite which did not include these correlations , predicted a suppression of weak localization @xmath16 . it is only after accounting for the classical correlations that the proper exponential decay @xmath15 is recovered . ( classical correlations are taken into account correctly in the semiclassical theory of shot - noise suppression at large ehrenfest times.@xcite ) in addition it is demonstrated that this semiclassical theory is unitary , _ i.e. , _ that no probability is lost . our discussion of the semiclassical theory for weak localization can be found in sec . [ alcalculation ] . we conclude in sec . [ discussion ] .

we investigate the behavior of weak localization , conductance fluctuations , and shot noise of a chaotic scatterer in the semiclassical limit . time resolved numerical results , obtained by truncating the time - evolution of a kicked quantum map after a certain number of iterations , are compared to semiclassical theory . considering how the appearance of quantum effects is delayed as a function of the ehrenfest time gives a new method to compare theory and numerical simulations . we find that both weak localization and shot noise agree with semiclassical theory , which predicts exponential suppression with increasing ehrenfest time . however , conductance fluctuations exhibit different behavior , with only a slight dependence on the ehrenfest time .

we investigate the behavior of weak localization , conductance fluctuations , and shot noise of a chaotic scatterer in the semiclassical limit . time resolved numerical results , obtained by truncating the time - evolution of a kicked quantum map after a certain number of iterations , are compared to semiclassical theory . considering how the appearance of quantum effects is delayed as a function of the ehrenfest time gives a new method to compare theory and numerical simulations . we find that both weak localization and shot noise agree with semiclassical theory , which predicts exponential suppression with increasing ehrenfest time . however , conductance fluctuations exhibit different behavior , with only a slight dependence on the ehrenfest time .

hep-ph9701303

c

we have studied in this paper the anomalous dimension representation for the nl bfkl equation and the ensuing resummation formulas , by analysing in detail the @xmath2 contributions to the larger anomalous dimension eigenvalue . our first result ( sec . 2 ) is that the r.g . representation with running coupling and resummed anomalous dimensions is valid at nl level in the regime @xmath226 that is , if the variable @xmath227 is not too large . if the condition ( 5.1 ) is coupled with the saddle point estimate of important @xmath228 values we end up with the limitation @xmath229 which provides a parabola - like boundary in the @xmath230 , @xmath231 plane . conditions of type ( 5.1 ) have been already noticed before @xcite as singularities of the anomalous dimension and those of the type ( 5.2 ) have been known for a while @xcite to be relevant , with different numerical factors , for the occurrence of higher twist unitarization effects [ 27 - 29 ] . here we just emphasize that , within the regions ( 5.1 ) and ( 5.2 ) there is a well defined resummation of anomalous dimensions , provided here , which is able to describe the qcd evolution in agreement with the nl bfkl equation ( fig 7 ) . the renormalization group description in the regime ( 5.1 ) holds independently of the detailed properties of the hard pomeron , i.e. of the leading singularity in the @xmath228-plane which dominates the small-@xmath3 , fixed @xmath143 behaviour . the latter occurs in the coefficient function , and is dependent on the soft region behaviour of the running coupling , in particular on its magnitude and shape around @xmath232 . only if the scale @xmath233 is large enough , the pomeron decouples , and the coefficient function takes a perturbative form , provided the rapidity is not so large to allow diffusion from @xmath233 to @xmath234 . the simplest way to summarize the above results is to write the resummed r.g . representation of the dis structure functions @xmath86 and @xmath235 . by using formulas ( 2.35 ) for the parton densities in the @xmath1-scheme we obtain @xmath236 where @xmath202 and @xmath237 are given by eq . ( 2.26 ) and by the relation @xcite @xmath238 respectively , and @xmath239 are the r.g . expressions of eq . in particular , @xmath240\ ] ] contains the perturbative coefficient of eq . ( 2.19 ) , which provides an additional contribution to the effective anomalous dimension of eq . ( 2.38 ) . note that , once a complete nl computation of @xmath27 will be available , all the relevant coefficient and anomalous dimensions in eq . ( 5.3 ) will be known in the @xmath1-scheme , so as to provide a factorization scheme independent expression for the measurable structure functions . in fact , relating eqs . ( 5.3 ) and ( 2.35 ) is equivalent to computing the quark and gluon coefficient functions in the @xmath1-scheme to all leading orders . by simple algebra , and neglecting subleading contributions , we get @xmath241 , & c_g^l=\g_+h_l(\g_+).\end{aligned}\ ] ] in this paper we have further provided a computation of the @xmath2-contribution to the bfkl kernel , proving the running coupling factorization , and we have evaluated the corresponding nl resummation in the anomalous dimension eigenvalue @xmath27 . we find that higher order effects for the @xmath35 dependent part are small in @xmath27 , while they are not small in the coefficients @xmath202 and @xmath237 . this difference is due to the non - planar nature of the diagrams which yield the most important large @xmath9 contributions . they are suppressed by a colour factor when coupling to gluons , while they are not when coupling to photons . we have also found that running coupling effects , although expected , are particularly important . first of all , they affect the coefficient functions by factors of type @xmath93 in eqs . ( 2.19 ) and ( 5.5 ) due to the fluctuations of the anomalous dimension variable @xmath43 , which are large when @xmath43 approaches the saturation value @xmath203 . ultimately , this is the reason for the breaking of the r. g. representation itself when approaching the critical value ( 5.1 ) , as also noticed in a recent paper @xcite . furthermore , the running of @xmath242 at large @xmath20 values , emphasizes the diffusion towards small values of @xmath26 , and the need of smoothing out the effective coupling around the landau pole . this in turn clarifies the fact that the bare hard pomeron singularity is actually dependent on soft physics , even if small-@xmath3 scaling violations are not . it thus appears that , so far , apart from running coupling effects , large higher order contributions only occur in the @xmath105 entry of the anomalous dimension matrix , which was the basis for an early explanation of the hera data @xcite . note , however , that the absence of higher order effects in @xmath27 may be a feature of the @xmath35-dependent part only , which is mostly nonplanar . for the gluonic part , planar diagrams could also contribute , as it happens in the crude collinear estimate of eq . such possibly large effects renew the present interest in a complete computation , which is hopefully to be obtained soon . * we wish to thank jochen bartels , stefano catani , yuri dokshitzer , jan kwiecinski , al mueller and bryan webber for interesting discussions on the topics presented here . this work is supported in part by murst , italy , and by the e. c. contract chrx - ct96 - 0357 .

we investigate the consistency requirements of the next - to leading bfkl equation with the renormalization group , with particular emphasis on running coupling effects and nl anomalous dimensions . we show that , despite some model dependence of the bare hard pomeron , such consistency holds at leading twist level , provided the effective variable is not too large .

we investigate the consistency requirements of the next - to leading bfkl equation with the renormalization group , with particular emphasis on running coupling effects and nl anomalous dimensions . we show that , despite some model dependence of the bare hard pomeron , such consistency holds at leading twist level , provided the effective variable is not too large . we give a unified view of resummation formulas for coefficient functions and anomalous dimensions in the-scheme and we discuss in detail the new one for the contributions to the gluon channel . pacs 12.38.cy

1310.4122

i

supersymmetry is an important theoretical and phenomenological subject that has dominated theoretical physics for decades , despite the lack ( so far ) of evidence that it actually exists in nature . it assists us in understanding several aspects of low energy physics , from the stability of the higgs vacuum to the unification of forces , and even the low scale of inflation ( relative to the planck mass ) , in a way that is much clearer than in non - supersymmetric frameworks . the embedding of supersymmetry into a gravitational framework by promoting global supersymmetry into a local ( gauged ) symmetry , termed supergravity @xcite , has initiated many interesting avenues of research toward understanding both the unification of gravity with the remaining three fundamental forces of nature , and to some extent quantisation of the gravitational field . in particular , it is well known that supergravity theories constitute consistent low - energy limits of superstring theories , which are thought to provide plausible paths to the quantisation of gravity in concert with other fundamental interactions . + however , supersymmetry is not phenomenologically observed in nature , and thus if it exists , it must be broken in the low energy world . it is therefore desirable to understand the spontaneous or dynamical breaking of supersymmetry under various possible circumstances , of which , thanks to the profusion of gauge and matter sectors that may be consistently coupled into supersymmetry , there are many @xcite . it would be preferable however , to seek a way of breaking local supersymmetry ( supergravity ) directly in a dynamical manner , without the need to couple it to a gauge sector . + one such approach would be to leverage the fermionic ( gravitino ) torsion terms that are generically present in supergravity theories , which consist of four - gravitino self - interaction terms . the latter could conceivably condense under certain circumstances , thereby producing condensates of the gravitino field , which in this way would dynamically acquire a non - zero mass whilst leaving the graviton massless . in this way supergravity would be broken _ dynamically _ , in the same spirit as the breaking of chiral symmetry in the nambu - jona - lasinio model @xcite . + it was conjectured in @xcite that such a dynamical breaking of supergravity could occur via the formation of condensates of the gravitino field , with analyses based on the one - loop effective potential of a simple @xmath2 supergravity model in a flat minkowski space - time ( necessary to allow an unambiguous definition of the gravitino mass via the condensate field ) . the effective potential of the gravitino condensate field , dependent on positive powers of the ultraviolet ( uv ) cutoff scale due to the well - known non - renormalisability of quantum gravity in four space - time dimensions , acquires a non - trivial minimum for some values of the cutoff relative to the gravitational constant ( reduced planck mass ) . in the analyses of @xcite the gravitino thereby acquires a dynamical mass of the order of the planck scale . + it was important for their analyses that the one - loop value of the effective potential _ vanishes _ at the non - trivial minimum , which implies the vanishing of the effective vacuum energy of the resulting low - energy theory . this arguably justifies _ a posteriori _ the minkowski space - time analysis of the effective potential . it was also important for both the entire approach and the double - well shape of the effective potential , appropriate for supergravity breaking , that the deser - zumino super - higgs effect @xcite was incorporated self consistently by coupling the supergravity action with the non - linear volkov - akulov action @xcite of the goldstone particle associated with the ( assumed f - type ) spontaneous global supersymmetry breaking . the latter is a majorana spin 1/2 fermion , the goldstino . + this formalism was essential for two reasons . firstly , the goldstino could be absorbed by the gravitino , under an appropriate field redefinition to make the latter massive , and thus disappear from the physical spectrum secondly , the only subsequent trace of the goldstino would be a ( negative ) cosmological constant @xmath3 in the effective action , which is associated with the scale of global supersymmetry breaking ; namely the vacuum expectation value of the appropriate f - term of the chiral scalar superfield responsible for spontaneous supersymmetry breaking . this is the super - higgs effect @xcite which is essential in keeping track of the right degrees of freedom in the problem of dynamical acquisition of a mass by the gravitino field , and the consequent breaking of local supersymmetry . + from the point of view of the effective potential , this would correspond to a _ positive _ term at the origin in field space of order of @xmath4 , which is responsible for the double - well shape of the potential at the broken symmetry phase . these considerations are consistent with the generic features of dynamical supersymmetry breaking outlined by witten @xcite , according to which the vacuum energy of broken global supersymmetry is _ necessarily positive _ , here @xmath5 , whilst a _ broken local supersymmetry _ ( supergravity ) can still be characterised by _ zero vacuum energy . _ + although physically appealing , the flat minkowski space - time approach of @xcite was criticised in @xcite due to the fact that it ignored the quantum fluctuations of the metric field . following the generic approach of fradkin and tseytlin @xcite of calculating the one - loop effective potential in four - dimensional supergravity theories by means of expanding about a generic ( anti)de sitter , rather than minkowski , background , the authors of @xcite have argued that integrating over metric fluctuations introduces _ imaginary _ parts in the effective potential , for any non - trivial value of the gravitino condensate field , and irrespective of the value of the background cosmological constant @xmath6 ( whose role is to effectively replace @xcite the flat - space uv cut - off of @xcite ) . + the presence of imaginary parts would of course be an indication that the non - trivial - gravitino - condensate ( broken supergravity ) vacuum is _ unstable _ , and thus there would be no possibility of breaking @xmath2 supergravity dynamically in this simple and direct way . of course , the traditional way of breaking supergravity via dynamical global supersymmetry breaking through , say , gaugino condensation @xcite , which would then be communicated to the ( super)gravity sector , evades the arguments of @xcite and thus has appeared to be the only consistent way of dynamically breaking supergravity , carrying the price of necessarily coupling the theory to matter fields . + in this work we shall revisit the arguments and the analysis of @xcite , with a view to incorporating the super - higgs effect that was not included in their analyses . we have been motivated to do so by the compelling nature and simplicity of the possibility of direct dynamical breaking of supergravity by means of its gravitino - torsion self - interactions . + as it turns out , and as is demonstrated below in great detail , the proper incorporation of the super - higgs effect in such a framework enables the dynamical breaking of supergravity ( prior to its coupling to matter or gauge fields ) , in the sense that a one - loop effective potential analysis considering fully metric fluctuations about ( anti)de sitter backgrounds , and thereby fully incorporating any ( weak ) quantum gravitational effects , reveals the existence of non - trivial vacua with _ no imaginary _ parts , contrary to the claims of @xcite . the double - well shape of the effective potential , and its vanishing at the non - trivial minima , fully justifies the flat - space approximate analysis of @xcite and demonstrates that the presence of the cosmological constant @xmath4 due to the super - higgs effect is responsible for the vanishing of the effective vacuum energy of the low - energy effective action of supergravity at the one - loop level . + the structure of the article is as follows . * in section [ sec : superhiggs ] we briefly review the super - higgs effect in the context of simple @xmath7 supergravity , in order to outline to the reader its important features , and the underlying physics that will be used in our analysis of the resultant one - loop effective potential . * in section [ sec : sugra ] we set up the basic formalism and notations underlying the model of @xmath2 supergravity that we shall consider for concreteness in this work . our formalism of course applies in general to more complicated theories of supergravity . * in section [ sec : quadr ] we discuss the quadratic action obtained from previous section by incorporating weak metric fluctuations about a given ( anti)de sitter background , in conjunction with the linearisation of four - gravitino terms by means of appropriate auxiliary fields . this is the first step towards the construction of a ` proper ' ( i.e. incorporating ( weak ) quantum gravitational effects ) one - loop effective potential . we discuss bosonic and fermionic sectors separately as well as their respective gauge fixing procedures . * in section [ sec : potential ] we construct the effective potential and discuss the shape that we require in order to obtain non - trivial local supersymmetry ( supergravity ) breaking , via dynamical condensation of the gravitino field . we discuss carefully the absence of imaginary parts in certain non - trivial vacua , contrary to the claims of @xcite , and explain carefully how this may be achieved . as we also show in subsection [ sec : confsugra ] , phenomenologically realistic values for the gravitino mass and the associated breaking scale of global supersymmetry can be achieved only in appropriate conformal extensions of the @xmath2 supergravity , which may also be relevant for inflation . * conclusions and outlook are then given in section [ sec : concl ] , and some technical aspects of our approach of constructing the one - loop effective potential are discussed in an appendix .

we investigate the dynamical breaking of local supersymmetry ( supergravity ) , including the deser - zumino super - higgs effect , via the corresponding one - loop effective potential for the simple but quite representative cases of , simple supergravity and a ( simplified ) conformal version of it .

we investigate the dynamical breaking of local supersymmetry ( supergravity ) , including the deser - zumino super - higgs effect , via the corresponding one - loop effective potential for the simple but quite representative cases of , simple supergravity and a ( simplified ) conformal version of it . we find solutions to the effective equations which indicate dynamical generation of a gravitino mass , thus breaking supergravity . in the case of conformal supergravity models , the gravitino mass can be much lower than the planck scale , for global supersymmetry breaking scales below the grand unification scale . the absence of instabilities in the effective potential arising from the quantum fluctuations of the metric field is emphasised , contrary to previous claims in the literature . kcl - ph - th/2013-*21 * + lcts/2013 - 12

1004.0843

i

it is generally believed that type ib and type ic supernovae result from core collapse events of naked helium stars . the helium stars are thought to be produced by the loss of the hydrogen envelope , via stellar winds mass loss from massive single stars or via mass transfers in close binary systems . according to recent stellar models adopting the most up - to - date stellar winds mass loss rates @xcite , the final masses ( @xmath5 ) of helium stars produced by mass - losing single stars appear to be too massive to produce typical sne ib / c ( i.e. , @xmath6 @xmath0 at solar metallicity ) . although the limiting mass for bh formation is not yet well determined , given their high binding energy , such massive progenitors of @xmath6 @xmath0 are likely to form black holes ( bhs ) , producing faint supernovae or no supernova at all ( cf . * ? ? ? although very bright sne ib / c like sn 1998bw could be produced from such massive helium stars if , for example , powered by rapid rotation ( e.g. , * ? ? ? * ; * ? ? ? * ) , such events are shown to be rare ( e.g. , * ? ? ? * ; * ? ? ? by contrast , helium stars with a wide range of masses ( @xmath7 ) can be made from @xmath8 @xmath0 primary components in close binary systems via the so - called case a / b mass transfer . many of them may end their life as bright sne ib / c leaving neutron stars as remnants , if their final masses are less than about 7 10 @xmath0 . population studies indeed show that close binary stars can produce a sufficient number of sne ibc to explain their observed rate , without the need of invoking single star progenitors ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? therefore , it is most likely that the majority of typical sne ibc are produced in binary systems . the observational evidence for the connection between sne ibc and long gamma - ray bursts ( grbs ) has particularly motivated many observational studies to better understand sne ibc since the last decade ( see * ? ? ? * for a review ) . theoretical stellar models of sne ibc progenitors are thus highly required nowadays . the most comprehensive studies on the detailed characteristics of sne ibc progenitors in binary systems were conducted by @xcite ( hereafter , wlw95 ) using mass - losing pure helium star models , and by @xcite ( hereafter , wl99 ) using self - consistent binary star models . although more recent theoretical studies on sne ibc progenitors in binary systems can be found in the literature , they have been focused on long grb progenitors or stellar populations , rather than on the detailed nature of typical sne ibc progenitors ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) . in this paper , we revisit the problem of sne ibc progenitors in close binary systems using both binary star and single helium star models up to the neon burning stage , with updated physics of two important ingredients . one is rotation , which was not considered in wlw95 and wl99 , and the other is the mass loss rate of wolf - rayet ( wr ) stars ( sect . [ sect : review ] ) . this paper is organized as follows . in sect . [ sect : review ] , we briefly review recent developments of stellar evolution models regarding the effects of rotation and the wr star mass loss rate , arguing for the need of updated physics in binary star models . our adopted physical assumptions and numerical method are discussed in sect . [ sect : method ] . in the following section ( sec . [ sect : rotation ] ) , using our binary star evolution models including the effect of rotation and the transport of angular momentum due to hydrodynamic instabilities and magnetic torques , we explore the role of tidal interaction and mass transfer in the redistribution of angular momentum in primary stars . in sec . [ sect : sn ] , the nature of sne ibc progenitors is investigated in terms of final masses , masses of helium and hydrogen layers , radii and mass loss rates at the presupernova stage , assuming these properties do not significantly change from neon burning to core collapse . for this purpose , we also present mass - losing single helium star models as a complement to our binary star models , given that the parameter space explored with our binary model sequences is limited . we conclude the paper by discussing observational implications of our results , in sect . [ sect : discussion ] .

we investigate the evolution of type ib / c supernova ( sn ib / c ) progenitors in close binary systems , using new evolutionary models that include the effects of rotation , with initial masses of 12 25 for the primary components , and of single helium stars with initial masses of 2.8 20 . we employ the most up - to - date estimate for the wolf - rayet mass loss rate , and its implications for sn ib / c progenitors are discussed in detail . in terms of stellar structure , sn ib / c progenitors in binary systems at solar metallicity are predicted to have a wide range of final masses up to about 7 , with helium envelopes of .

we investigate the evolution of type ib / c supernova ( sn ib / c ) progenitors in close binary systems , using new evolutionary models that include the effects of rotation , with initial masses of 12 25 for the primary components , and of single helium stars with initial masses of 2.8 20 . we find that , despite the impact of tidal interaction on the rotation of primary stars , the amount of angular momentum retained in the core at the presupernova stage in different binary model sequences converge to a value similar to those found in previous single star models . this amount is large enough to produce millisecond pulsars , but too small to produce magnetars or long gamma - ray bursts . we employ the most up - to - date estimate for the wolf - rayet mass loss rate , and its implications for sn ib / c progenitors are discussed in detail . in terms of stellar structure , sn ib / c progenitors in binary systems at solar metallicity are predicted to have a wide range of final masses up to about 7 , with helium envelopes of . our results indicate that , if the lack of helium lines in the spectra of sne ic were due to small amounts of helium ( e.g. ) , the distribution of both initial and final masses of sn ic progenitors should be bimodal . furthermore , we find that a thin hydrogen layer ( ) is expected to be present in many sn ib progenitors at the presupernova stage . we show that the presence of hydrogen , together with a rather thick helium envelope , can lead to a significant expansion of some sn ib / c progenitors by the time of supernova explosion . this may have important consequences for the shock break - out and supernova light curve . we also argue that some sn progenitors with thin hydrogen layers produced via case ab / b transfer might be related to type iib supernova progenitors with relatively small radii of about .

1004.0843

c

we have presented new evolutionary models of massive close binary stars , considering tidal interaction , and transport of angular momentum and chemical species due to rotationally induced hydrodynamic instabilities and the spruit - tayler dynamo . we have investigated the redistribution of angular momentum in the primary star . although mass transfer and tidal interaction can significantly affect the evolution of the rotation velocity of the primary star on the main sequence , the amount of angular momentum retained in the core in the late evolutionary stages is rather insensitive to the previous history of such binary interactions because of the self - regulating nature of the spruit - tayler dynamo . we have also calculated non - rotating , mass - losing single helium star models and compared them with our primary star models in binary systems . our models adopt a much lower wr mass loss rate than in the previous studies by wlw95 and wl99 , and predict some new important properties of sn ibc progenitors accordingly . the following discussions are based on the models with @xmath16 , unless otherwise specified . 1 . the final masses of sn ibc progenitors in binary systems at @xmath110 @xmath111 are not limited to @xmath112 as predicted by wlw95 and wl99 , but a more wide range @xmath5 is expected ( i.e. , @xmath113 from @xmath114 @xmath0 ; see fig . [ fig : mimf ] ) . 2 . at @xmath115 @xmath111 , significant deficiency of helium ( @xmath116 @xmath0 ) is expected for @xmath117 and for @xmath118 ( fig . [ fig : dmhe ] ) . rather large amounts of helium up to 1.5 @xmath0 are expected for the other final mass range ( i.e. , @xmath119 5.5 @xmath0 ) . at @xmath115 @xmath120 , no such helium deficient sn progenitors are expected for the considered initial masses ( @xmath121 @xmath0 ) . a thin layer of hydrogen with @xmath122 @xmath0 is predicted for sn ibc progenitors with @xmath123 at @xmath124@xmath111 , and @xmath125 at @xmath115@xmath120 , respectively ( fig . [ fig : dmh ] ; table [ tab1 ] ) . 4 . most sn ibc progenitors with @xmath126 @xmath0 rapidly expand during core carbon burning , resulting in @xmath127 at the presuprnova stage . this is much larger than found in wlw95 ( fig . [ fig : radius ] ) . compact progenitors of @xmath128 are only expected for a relatively high mass ( @xmath129 @xmath0 at @xmath110 @xmath111 and @xmath130 @xmath0 at @xmath110 @xmath120 ; fig . [ fig : radius ] ) . our binary star models show that the mass transfer during helium core contraction ( case ab or case b ) in a close massive binary system can not remove the hydrogen envelope promptly enough to avoid the core braking due to the spruit - tayler dynamo during the helium core contraction phase . comparison of our binary star models with the single star models by @xcite and @xcite indicate that the amount of angular momentum retained in the core of the primary star at the presupernova stage should not be much different from those found in single star models if the spruit - tayler dynamo is adopted . i.e. , a specific angular momentum of a few @xmath68 in the innermost @xmath771.4 @xmath0 at the presupernova stage is expected in both single and binary stars . this value is smaller by one or two orders of magnitude than what is necessary to make a long gamma - ray bursts by magnetar or collapsar formation , or very energetic supernovae ( hypernovae ) powered by rapid rotation and strong magnetic fields ( e.g. * ? ? ? * ) , although it may suffice to produce millisecond pulsars @xcite . together with the work by @xcite , our results thus indicate that binary interactions with case ab / b mass transfers at @xmath131 may not particularly enhance the production of strongly rotation - powered events like long grbs or hypernovae . this is consistent with the observational evidence that such events are rare compared to normal core collapse events ( e.g. , * ? ? ? * ; * ? ? ? this also confirms the theoretical consensus that other evolutionary paths are needed to produce long grbs associated with sn ibc , such as the quasi - chemically homogeneous evolution of a metal poor star @xcite , tidal spin - up of a wr star in a very close binary system with a neutron star or black hole companion ( e.g. * ? ? ? * ; * ? ? ? * ) , or binary evolution with case c mass transfer with some specific conditions @xcite . larger radii of our sn ibc progenitor models than those previously found should have consequences in shock break - outs and bolometric light curves . for instance , a shock break - out from a larger envelope would be marked by a lower photosperic temperature . detailed comparison of numerical calculations with observational data may thus give strong constraints on sne ibc progenitor properties ( e.g. , * ? ? ? * ) . recent discovery of the x - ray outburst with sn 2008d by @xcite indeed suggests the usefulness of such a study for the probe of supernova progenitors ( e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) , for which our new models would provide ideal input . we will address this issue in a forthcoming paper . although the weak signature or no evidence of helium in sne ic spectra may indicate the deficiency of helium in their progenitors , it is not well known how much helium can be hidden in the supernova spectra . it may also depend on the degree of mixing of nickel into helium rich layers @xcite . if we assume 0.5 @xmath0 , for instance , as the maximum amount of helium allowed for hiding helium lines in sn spectra , our models indicate that most sne ic progenitors at solar metallicity should belong to two distinct classes in terms of both zams and final masses , as summarized in fig . [ fig : mimf ] for the binary systems that undergo case b mass transfer . the same conclusion was also drawn by wl99 and @xcite . but pols & dewi considered different types of binary systems ( see below ) , and the finding of `` two mass classes '' for the final masses was not obvious in wl99 due to the very high wr rate adopted in their study , although it was clearly seen for the zams masses . if we assume that primary stars of @xmath132 produce low - mass - class sne ic via case bb mass transfer , about 62% of the sne ic from case b systems should belong to the high mass class and the rest ( @xmath7738% ) to the low mass class , at @xmath133 ( see fig . [ fig : mimf ] ) . it is important to note that the two classes are produced by different mechanisms . the high mass class of sne ic progenitors ( i.e. , @xmath134 @xmath0 in fig [ fig : mimf ] ) is a consequence of wr winds mass loss , while the low mass class results from case abb / bb mass transfer as discussed in sect . [ sect : masses ] . the zams mass range for the low mass class may not be much affected by metallicity , while it should be widened with increasing metallicity for the high mass class . this leads to the conclusion that the low and high mass classes would dominate at low and high metallicities respectively . it should also be noted that the final mass range for the low mass class may not change much for different metallicities , while it may decrease with increasing metallicity for the high mass class , due to the increasing wr winds mass loss rates , as implied by the result of wl99 . in the massive close binary systems considered in this paper , the primary star masses become much smaller than those of the secondary stars when case abb or case bb mass transfer begins . if the companion star mass were lower than the helium star in a close binary system , the mass transfer rate should become higher than in the systems of the present study . for example , if a helium star is located in a very short period binary system ( @xmath135 ) with a less massive companion ( e.g. a neutron star ) , mass transfer from the helium star may occur rapidly enough to make a helium - deficient carbon star , even for @xmath136 6.0 @xmath0 as shown by @xcite , @xcite and @xcite . the final masses of such sn ic progenitors may range from 1.5 @xmath0 to 3.0 @xmath0 . this scenario was also suggested by @xcite to explain the fast light curve of type ic sn 1994i . the zams mass of such a sn ic should be in the range of 12 20 @xmath0 @xcite . however , such close helium star plus neutron star systems are supposed to rarely form , and might not contribute much to the population of sne ic , compared to the systems considered in this study . our results should have several observational consequences . as mentioned above , the population of sne ic should be dominated by the high mass class for @xmath137 . they would have higher zams and final masses than those of typical sne ib progenitors ( cf . * ? ? ? * ; * ? ? ? given that the parameter space for the high mass class sne ic may become larger with a higher wr mass loss rate , the number ratio of sne ic to sne ib , and that of high mass class sne ic to low mass class sne ic should increase with increasing metallicity ( cf . * ; * ? ? ? * ; * ? ? ? the existence of the two mass classes of sne ic progenitors may be related to some aspects of the observational diversity of sne ic . for example , sne ic of the low mass class is likely to be characterized by rather fast declining light curves and low luminosities ( cf . * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) , implying that the observed population of sne ic is likely to be baised to high - mass - class sne ic . we should also note the huge difference of the binding energy between the two classes . the binding energy of the envelope above 1.4 @xmath0 in the sn ic progenitor star model of seq . 3 ( @xmath138 @xmath0 ) is only about @xmath139 erg , while it should be one or two orders of magnitude higher for a sn ic progenitor with @xmath140 @xmath0 ( see table [ tab2 ] ) . as a consequence , the energetics of sne ic might be systematically different for the two different classes . on the other hand , the assumption of @xmath141 @xmath0 for sn ic progenitors leads to a ratio of type ic to ib supernova rate ( ic / ib ratio ) of about 0.4 from binary systems at solar metallicity . have @xmath142 @xmath0 with @xmath143 @xmath0 ( see table [ tab1 ] ) . this implies that the low - mass class sne ic would predominantly occur in binary systems at this metallicity . if we assume stars with @xmath144 would produce low - mass class sne ic as in the case of solar metallicity , the sn ic / sn ib ratio would be about 0.1 at smc metallicity . the exploration of the exact mass range for the low - mass class sne ic is a time - consuming task , and we plan to investigate this in near future . ] this appears in contradiction with recent observations that indicate rather a high ic / ib ratio of about 2.0 ( e.g. * ? ? ? this discrepancy would become even larger with @xmath145 , as implied by fig . [ fig : mimf2 ] . this raises a question on the nature of sn ic progenitors , and it should be kept in mind that we still do not fully understand what distinguishes sn ic progenitors from those of sn ib . a recent work by @xcite indicates that the mass fraction of helium in the outermost layers ( @xmath146 ) , rather than the total mass of helium , may be more relevant for the presence of helium lines in supernova spectra . specifically , it is shown that if helium is well mixed with co material such that @xmath146 becomes less than about 0.5 , helium lines are not seen in early time spectra , despite rather a large total amount of helium ( @xmath147 @xmath0 ) , if non - thermal excitation is absent . in our progenitor models , such a small @xmath146 is realized only for @xmath92 5.5 @xmath0 at solar metallicity ( with @xmath16 ) . this is not different from the above - discussed mass limit for having @xmath2 @xmath0 , implying that the initial mass range for sn ic progenitors would not change much even if we adopted @xmath146 as a criterion , at least for the high mass class . on the other hand , we have @xmath148 in the primary star of seq . 3 at carbon exhaustion while the total mass of helium is less than 0.2 @xmath0 . this imples that the initial mass range for the low mass class sn ic progenitors might be affected if the condition of @xmath149 for sn ic progenitors were applied . but @xcite did not yet calculate such a low mass sn progenitor model ( @xmath91 @xmath0 ) , and their analyses were limited to early times of supernovae . it remains to be an important subject of future work to systematically investigate which types of supernova progenitors would lead to the presence or absence of helium lines in the supernova spectra at different epochs , including the effect of non - thermal excitation . therefore , the above discussion on type ic progenitors based on the total amount of helium should only be considered indicative at this stage . it is interesting that , at @xmath133 , the presence of a thin hydrogen layer is only expected for a limited range of the initial / final mass of sn ib progenitors , as shown in figs [ fig : dmh ] , and [ fig : mimf ] . the detection of hydrogen absorption lines at high velocity has been indeed reported in many sne ib ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) , in favor of our model prediction for the presence of a thin hydrogen layer in sne ib progenitors . this might provide a strong constraint for the progenitor masses of observed sne ib , in principle . note also that explosions of such helium stars with thin hydyrogen layers could be recognized as sn iib rather than ib , if hydrogen lines were detected short after supernova explosion , e.g. , as in the case of sn 2008ax @xcite and as recently discussed by @xcite and @xcite . the radii of these progenitor models range from @xmath150 to @xmath151 . they may corredpond to the compact category of sn iib progenitors , which is discussed in @xcite . the relatively low ejecta masses of such sne iib are consitent with our model predictions . on the other hand , case c mass transfer can also leave helium cores covered with small amounts of hydrogen envelope . as the life time of such stars made via case c mass transfer should be rather short , they can retain much more hydrogen ( @xmath152 @xmath0 ) , than what is predicted from our binary models with case ab / b mass transfer . such a star may eventually explode as a sn iib like sn 1993j ( e.g. * ? ? ? * ; * ? ? ? * ) , with a much extended envelope ( @xmath153 ) . therefore , the two categories of sn iib progenitors according to their sizes , which has been recently suggested by @xcite , may be understood within the framework of binary evolution ; sne iib of the compact type may be produced via case ab / b mass transfer ( especially at @xmath154 ) , and sne iib of the extended type via case c mass transfer . this work is supported by the doe scidac program ( doe de - fc02 - 06er41438 ) , the nsf grant ( nsf - arra ast-0909129 ) , and the nasa theory program ( nnx09ak36 g ) . we are grateful to luc dessart for useful discussions . cccccccccccccc 1 & 0.02 & 12 & 8 & 3.0 & 5 & b+bb & 57.9 & 1.40 & 1.21 & 0.17 & 0.0 & 0.33 & onemg wd + 2 & 0.02 & 12 & 11 & 4.0 & 5 & b+bb & 104.4 & 1.48 & 1.24 & 0.20 & 0.0 & 0.35 & onemg wd + 3 & 0.02 & 13 & 11 & 5.0 & 5 & b+bb & 123.3 & 1.64 & 1.43 & 0.18 & 0.0 & 0.22 & sn ic + 4 & 0.02 & 14 & 12 & 3.0 & 5 & a+ab+bb & 118.5 & 1.33 & 1.09 & 0.22 & 0.0 & @xmath155 & onemg wd + 5 & 0.02 & 14 & 12 & 5.0 & 5 & b+bb & 30.7 & 2.97 & 1.66 & 1.24 & 1.9(-4 ) & 0.25 & snib + 6 & 0.02 & 16 & 14 & 2.0 & 5 & a : contact & & & & & & & + 7 & 0.02 & 16 & 14 & 3.0 & 5 & a+ab+abb & 101.8 & 1.54 & 1.33 & 0.17 & 0.0 & 0.39 & onemg wd + 8 & 0.02 & 16 & 14 & 4.0 & 5 & b+bb & 26.2 & 3.66 & 2.05 & 1.47 & 4.5(-3 ) & 0.24 & snib + 9 & 0.02 & 16 & 14 & 5.0 & 5 & b+bb & 33.7 & 3.65 & 2.04 & 1.47 & @xmath156 & 0.25 & snib + 10 & 0.02 & 18 & 12 & 3.0 & 5 & a+ab+abb & 27.9 & 2.66 & 1.58 & 1.01 & @xmath157 & 0.26 & snib + 11 & 0.02 & 18 & 12 & 3.0 & 10 & a+ab+abb & 27.3 & 2.74 & 1.59 & 1.08 & @xmath157 & 0.26 & snib + 12 & 0.02 & 18 & 12 & 5.0 & 10 & b : contact & & & & & & & + 13 & 0.02 & 18 & 17 & 3.0 & 10 & a+ab+abb & 36.2 & 3.03 & 1.68 & 1.27 & @xmath158 & 0.25 & sn ib + 14 & 0.02 & 18 & 17 & 4.0 & 10 & a+ab & 29.7 & 3.79 & 2.14 & 1.49 & @xmath159 & 0.25 & sn ib + 15 & 0.02 & 18 & 17 & 4.0 & 10 & a+ab & 24.0 & 3.97 & 2.27 & 1.53 & @xmath160 & 0.26 & snib + 16 & 0.02 & 18 & 17 & 4.0 & 10 & a+ab & 50.0 & 3.80 & 2.16 & 1.50 & @xmath161 & 0.06 & snib + 17 & 0.02 & 18 & 17 & 4.0 & 10 & a+ab & 25.2 & 3.84 & 2.18 & 1.50 & @xmath162 & 0.26 & snib + 18 & 0.02 & 18 & 17 & 4.0 & 10 & a+ab & 30.6 & 3.73 & 2.14 & 1.43 & @xmath163 & 3.57 & snib + 19 & 0.02 & 18 & 17 & 5.0 & 3 & b & 33.1 & 3.73 & 2.33 & 1.23 & @xmath157 & 0.25 & snib + 20 & 0.02 & 18 & 17 & 5.0 & 5 & b & 32.4 & 4.04 & 2.45 & 1.4 & 0.00 & 0.33 & snib + 21 & 0.02 & 18 & 17 & 5.0 & 10 & b+bb & 31.5 & 4.41 & 2.51 & 1.68 & @xmath164 & 0.26 & snib + 22 & 0.02 & 18 & 17 & 6.0 & 10 & b & 39.3 & 4.39 & 2.56 & 1.62 & @xmath165 & 0.26 & snib + 23 & 0.02 & 25 & 19 & 6.0 & 10 & b : contact & & & & & & & + 24 & 0.02 & 25 & 24 & 2.0 & 10 & a : contact & & & & & & & + 25 & 0.02 & 25 & 24 & 3.0 & 3 & a+ab & 22.7 & 3.70 & 2.46 & 0.98 & 0.0 & 0.24 & snib + 26 & 0.02 & 25 & 24 & 3.0 & 5 & a+ab & 22.4 & 4.33 & 2.80 & 1.30 & 0.0 & 0.25 & snib + 27 & 0.02 & 25 & 24 & 3.0 & 10 & a+ab & 21.3 & 5.07 & 3.17 & 1.67 & 0.0 & 0.25 & snib + 28 & 0.02 & 25 & 24 & 3.0 & 10 & a+ab & 18.9 & 5.08 & 3.19 & 1.66 & 0.0 & 0.32 & snib + 29 & 0.02 & 25 & 24 & 4.0 & 5 & a + ab & 21.5 & 4.45 & 2.91 & 1.22 & 0.0 & 0.26 & snib + 30 & 0.02 & 25 & 24 & 6.0 & 10 & b & 27.4 & 6.49 & 4.45 & 1.63 & 0.0 & 0.39 & snib + 31 & 0.02 & 60 & 40 & 7.0 & 3 & a & 16.8 & 4.95 & 3.70 & 0.25 & 0 & 0.24 & snic + 32 & 0.004 & 16 & 12 & 3.0 & 5 & b+bb & 64.75 & 3.91 & 2.22 & 1.54 & @xmath166 & 0.24 & snib + 33 & 0.004 & 16 & 14 & 3.0 & 5 & b+bb & 19.6 & 3.90 & 2.21 & 1.53 & @xmath166 & 0.24 & snib + 34 & 0.004 & 16 & 14 & 5.0 & 5 & b+bb & 21.8 & 3.84 & 2.19 & 1.51 & @xmath167 & 0.24 & snib + 35 & 0.004 & 18 & 12 & 5.0 & 5 & b+bb & 14.4 & 4.64 & 2.76 & 1.68 & @xmath168 & 0.31 & snib + 36 & 0.004 & 18 & 12 & 8.0 & 5 & b+bb & 24.33 & 4.56 & 2.68 & 1.67 & @xmath169 & 0.33 & snib + 37 & 0.004 & 18 & 17 & 3.0 & 5 & a+ab & 18.4 & 4.42 & 2.55 & 1.67 & @xmath170 & 0.26 & snib + 38 & 0.004 & 18 & 17 & 3.0 & 10 & a+ab & 14.4 & 4.58 & 2.61 & 1.77 & @xmath171 & 0.26 & snib + 39 & 0.004 & 18 & 17 & 6.0 & 5 & b+bb & 27.0 & 4.57 & 2.71 & 1.65 & @xmath166 & 0.27 & snib + 40 & 0.004 & 25 & 12 & 3.0 & 5 & a : contact & & & & & & & + 41 & 0.004 & 25 & 12 & 6.0 & 5 & b : contact & & & & & & & + 42 & 0.004 & 25 & 19 & 3.0 & 5 & a+ab & 10.2 & 7.09 & 4.87 & 2.03 & @xmath172 & 0.32 & snib + 43 & 0.004 & 25 & 24 & 3.0 & 5 & a+ab & 13.0 & 7.31 & 5.05 & 2.07 & @xmath173 & 0.28 & snib + 44 & 0.004 & 25 & 24 & 6.0 & 5 & b : contact & & & & & & + 45 & 0.004 & 40 & 30 & 4.0 & 5 & a+ab & 9.31 & 12.0 & 9.42 & 1.24 & @xmath174 & 0.56 & bh cccccccc 5 & 2.8 & 2.73 & 1.51 & 1.16 & 163.54 & 5.08 & 0.01 + 5 & 3.0 & 2.91 & 1.60 & 1.22 & 33.40 & 1.79 & 0.03 + 5 & 4.0 & 3.72 & 2.15 & 1.43 & 8.01 & 0.73 & 0.18 + 5 & 6.0 & 4.23 & 2.77 & 1.19 & 4.19 & 0.38 & 0.25 + 5 & 8.0 & 4.95 & 3.40 & 0.85 & 3.07 & 0.30 & 0.29 + 5 & 10.0 & 5.49 & 3.93 & 0.54 & 1.59 & 0.22 & 0.47 + 5 & 15.0 & 6.44 & 4.85 & 0.31 & 0.59 & 0.18 & 0.55 + 5 & 20.0 & 7.09 & 5.44 & 0.22 & 0.48 & 0.16 & 0.66 + 10 & 3.0 & 2.95 & 1.60 & 1.27 & 34.96 & 1.84 & 0.03 + 10 & 4.0 & 3.84 & 2.20 & 1.49 & 6.94 & 0.70 & 0.15 + 10 & 6.0 & 4.93 & 3.14 & 1.55 & 4.29 & 0.51 & 0.19 + 10 & 8.0 & 6.06 & 4.13 & 1.41 & 2.55 & 0.35 & 0.33 + 10 & 10.0 & 7.01 & 4.96 & 1.12 & 1.94 & 0.25 & 0.55 + 10 & 15.0 & 8.89 & 6.80 & 0.47 & 0.54 & 0.20 & 0.82 + 10 & 20.0 & 10.33 & 8.21 & 0.31 & 0.40 & 0.16 & 1.17

we find that , despite the impact of tidal interaction on the rotation of primary stars , the amount of angular momentum retained in the core at the presupernova stage in different binary model sequences converge to a value similar to those found in previous single star models . this amount is large enough to produce millisecond pulsars , but too small to produce magnetars or long gamma - ray bursts . our results indicate that , if the lack of helium lines in the spectra of sne ic were due to small amounts of helium ( e.g. ) , the distribution of both initial and final masses of sn ic progenitors should be bimodal . furthermore , we find that a thin hydrogen layer ( ) is expected to be present in many sn ib progenitors at the presupernova stage . this may have important consequences for the shock break - out and supernova light curve .

we investigate the evolution of type ib / c supernova ( sn ib / c ) progenitors in close binary systems , using new evolutionary models that include the effects of rotation , with initial masses of 12 25 for the primary components , and of single helium stars with initial masses of 2.8 20 . we find that , despite the impact of tidal interaction on the rotation of primary stars , the amount of angular momentum retained in the core at the presupernova stage in different binary model sequences converge to a value similar to those found in previous single star models . this amount is large enough to produce millisecond pulsars , but too small to produce magnetars or long gamma - ray bursts . we employ the most up - to - date estimate for the wolf - rayet mass loss rate , and its implications for sn ib / c progenitors are discussed in detail . in terms of stellar structure , sn ib / c progenitors in binary systems at solar metallicity are predicted to have a wide range of final masses up to about 7 , with helium envelopes of . our results indicate that , if the lack of helium lines in the spectra of sne ic were due to small amounts of helium ( e.g. ) , the distribution of both initial and final masses of sn ic progenitors should be bimodal . furthermore , we find that a thin hydrogen layer ( ) is expected to be present in many sn ib progenitors at the presupernova stage . we show that the presence of hydrogen , together with a rather thick helium envelope , can lead to a significant expansion of some sn ib / c progenitors by the time of supernova explosion . this may have important consequences for the shock break - out and supernova light curve . we also argue that some sn progenitors with thin hydrogen layers produced via case ab / b transfer might be related to type iib supernova progenitors with relatively small radii of about .

1702.04206

i

let @xmath9 be an algebraically closed field of arbitrary characteristic . the finite - dimensional algebra @xmath3 is defined as the path algebra of the quiver @xmath11 with vertices @xmath12 , @xmath13 arrows @xmath14 and called the generalized kronecker algebra . we denote by @xmath15 the category of finite - dimensional left - modules of @xmath3 . + it is well known that for @xmath1 the hereditary algebra @xmath3 is of wild representation type @xcite , every regular component in the auslander - reiten quiver of @xmath3 is of type @xmath16 @xcite and there is a bijection between the regular components and the ground field @xmath9 ( * ? ? ? * xviii 1.8 ) . therefore , the problem of completely understanding the category @xmath15 or all regular components is considered hopeless and it is desirable to find invariants which give more specific information about the regular components . + one important invariant @xmath17for any wild hereditary algebra@xmath18 , introduced in @xcite , is the quasi - rank @xmath19 of a regular component @xmath2 . for a quasi - simple module @xmath20 in @xmath2 , @xmath21 is defined as @xmath22 where @xmath23 is the space of non - invertible homomorphisms from @xmath20 to @xmath24 . + another interesting invariant @xmath5 was recently introduced in @xcite . motivated by the representation theory of group algebras of @xmath25-elementary abelian groups of characteristic @xmath26 , the author defines the category @xmath27 of modules with the equal kernels property and the category @xmath28 of modules with the equal images property in the framework of @xmath3 . she shows the existence of uniquely determined quasi - simple modules @xmath29 and @xmath30 in @xmath2 such that the cone @xmath31 of all successors of @xmath29 satisfies @xmath32 and the cone @xmath33 of all predecessors of @xmath30 satisfies @xmath34 . the width @xmath35 of @xmath2 is defined as the unique number @xmath5 such that @xmath36 , i.e. the distance between the two cones . + utilizing homological descriptions of @xmath27 and @xmath28 from @xcite involving a family of elementary modules , we show that the two invariants @xmath21 and @xmath35 are linked by the inequality @xmath37 motivated by this connection , we construct for each @xmath38 a regular component @xmath2 with @xmath39 . in order to do so , we consider representations over the universal covering @xmath40 of @xmath11 . we define classes @xmath41,@xmath42 of representations over @xmath40 such that @xmath43 is in @xmath41 @xmath17resp . @xmath44 if and only if for each arrow @xmath45 of @xmath40 the linear map @xmath46 is injective @xmath17resp . + let @xmath47 be the push - down functor @xcite and @xmath43 be indecomposable . we prove that @xmath48 is in @xmath41 @xmath17resp . @xmath44 if and only if @xmath49 is in @xmath27 @xmath17resp . @xmath50 . since a component @xmath51 of the auslander - reiten quiver of @xmath40 which is taken to a regular component @xmath52 is also of type @xmath16 , we can lift the definition of @xmath35 to @xmath51 . we define @xmath53 as the distance between the cones @xmath54 and @xmath55 and show that @xmath56 . + for @xmath57 , we denote by @xmath58 its quasi - length . if @xmath20 has certain properties , we show how to construct a short exact sequence @xmath59 with indecomposable middle term @xmath60 in a component @xmath61 such that @xmath62 the construction of @xmath63 relies on the fact that @xmath40 is an infinite @xmath64-regular tree with bipartite orientation . using @xmath65 , we construct for each @xmath38 a component @xmath66 with @xmath67 . + in conjunction with a natural action of @xmath68 on @xmath69 , we arrive at our main theorem : let @xmath7 . there is a bijection @xmath70 . as an immediate consequence we get the following statements , which are generalizations of results by kerner and lukas @xcite , @xcite for the kronecker algebra . let @xmath1 , then for each @xmath38 there are exactly @xmath71 regular components with quasi - rank in @xmath72 . assume that @xmath9 is uncountable and @xmath73 . the set of components of quasi - rank @xmath74 is uncountable .

we investigate the generalized kronecker algebra with arrows . given a regular component of the auslander - reiten quiver of , we show that the quasi - rank can be described almost exactly as the distance between two non - intersecting cones in , given by modules with the equal images and the equal kernels property ; more precisley , we show that the two numbers are linked by the inequality utilizing covering theory , we construct for each a bijection between the field and . as a consequence ,

we investigate the generalized kronecker algebra with arrows . given a regular component of the auslander - reiten quiver of , we show that the quasi - rank can be described almost exactly as the distance between two non - intersecting cones in , given by modules with the equal images and the equal kernels property ; more precisley , we show that the two numbers are linked by the inequality utilizing covering theory , we construct for each a bijection between the field and . as a consequence , we get new results about the number of regular components of a fixed quasi - rank .

astro-ph0208132

i

the hubble space telescope has made it possible to measure the masses of black holes ( bhs ) in the centers of many nearby active and quiescent galaxies using stellar and/or gaseous kinematics ( for reviews , see e.g. , richstone et al . 1998 ; van der marel 1999 ; ho 1999 ; de zeeuw 2001 ; kormendy & gebhardt 2001 ) . to date , bh masses have been measured in about 40 galaxies , both spirals and ellipticals , and this number continues to increase . the bh masses correlate loosely with host spheroid luminosity ( kormendy & richstone 1995 ) and more tightly with inner stellar velocity dispersion ( gebhardt et al . 2000 ; ferrarese & merritt 2000 ) . central emission - line gas is detected in virtually all nearby radio galaxies , defined here as galaxies which harbor kpc - scale radio - jets . the equivalent widths of the gas emission lines are generally much larger than those of the absorption lines in the integrated stellar light , so that measurement of the kinematics of nuclear emission - line gas is an efficient way to determine the central gravitational potential and bh mass ( e.g. , harms et al . 1994 ; ferrarese , ford & jaffe 1996 ; macchetto et al . 1997 ; van der marel & van den bosch 1998 ; ferrarese & ford 1999 ; verdoes kleijn et al . 2000 , hereafter vk00 ; sarzi et al . 2001 ; barth et al . . a drawback of this approach is that the gas kinematics might be affected by non - gravitational motions . nevertheless , using the gas kinematics to determine accurate bh masses is particularly interesting for radio galaxies because determining the bh mass and the properties of the gas disk can advance our understanding of radio - jet formation and evolution . in turn , the radio - jet offers an extra diagnostic of the bh accretion and immediate bh surroundings . current questions include : what is the lower - limit to bh masses that can form kpc - scale jets ? is this lower - limit higher or lower than typical bh masses in spirals which ( almost ) never show kpc - scale jets ? is there a correlation between bh mass and jet properties , such as total power or jet velocity ? for these and other reasons we are performing a systematic study of a complete sample of nearby radio galaxies with fanaroff & riley ( 1974 ) type i radio jets , the ` ugc fr - i sample ' ( verdoes kleijn et al . 1999 , hereafter vk99 ; xu et al . 2000 ) using observations at multiple wavelengths . in particular , we have performed a stis spectroscopic survey of the inner gas distributions to measure the kinematics and the physical state of the gas ( noel - storr et al . 2002 ) . here we concentrate on one galaxy from our sample , ngc 4335 , which is a relatively unknown isolated giant elliptical ( @xmath9 ; paturel et al . 1997 ) at 66 mpc . the gas appears embedded in a well - defined dust disk ( diameter @xmath10 ) and gas kinematics can be traced sufficiently far out along the three slits to allow detailed gas dynamical modeling . in addition we perform stellar dynamical modeling for ngc 4335 using the stellar kinematics derived from a wht / isis long - slit observation . the paper layout is as follows . sections [ s : wfpc2 ] and [ s : spec ] present hst / wfpc2 broad- and narrowband imaging , hst / stis gas emission - line spectroscopy and ground - based wht / isis stellar absorption - line spectroscopy , including the basic data reduction and derivation of the gaseous and stellar kinematics . section [ s : modelh ] describes the modeling of the gas disk flux distribution , the derivation of the stellar mass distribution and the fits to the observed gaseous kinematics to estimate the bh mass . section [ s : starkin ] describes two - integral modeling of the wht stellar kinematics to determine the stellar mass - to - light ratio and to constrain the bh mass independently . section [ s : discon ] discusses the implications of the bh mass measurements in ngc 4335 for our understanding of bh demography , and for the techniques used to measure black hole masses . we adopt @xmath11 throughout this paper . this does not directly influence the data - model comparison for any of our models , but does set the length , mass and luminosity scales of the models in physical units . specifically , distances , lengths and masses scale as @xmath12 , while mass - to - light ratios scale as @xmath13 .

we model the gas disk in the customary way , taking into account the combined potential of the galaxy and a putative black hole with mass , as well as the influence on the observed kinematics of the point spread function and finite slit width . the stellar kinematics for ngc 4335 are derived from a ground - based ( wht / isis ) long - slit observation along the galaxy major axis . a two - integral model of the stellar dynamics yields . however , there is reason to believe that this model overestimates . reported correlations between black hole mass and inner stellar velocity dispersion predict to be in ngc 4335 .

we investigate the kinematics of the central gas disk of the radio - loud elliptical galaxy ngc 4335 , derived from hst / stis long - slit spectroscopic observations of h + [ ] along 3 parallel slit positions . the observed mean velocities are consistent with a rotating thin disk . we model the gas disk in the customary way , taking into account the combined potential of the galaxy and a putative black hole with mass , as well as the influence on the observed kinematics of the point spread function and finite slit width . this sets a 3 upper limit of on . the velocity dispersion at is in excess of that predicted by the thin rotating disk model . this does not invalidate the model , if the excess dispersion is caused by localized turbulent motion in addition to bulk circular rotation . however , if instead the dispersion is caused by the bh potential then the thin disk model provides an underestimate of . a bh mass is inferred by modeling the central gas dispersion as due to an isotropic spherical distribution of collisionless gas cloudlets . the stellar kinematics for ngc 4335 are derived from a ground - based ( wht / isis ) long - slit observation along the galaxy major axis . a two - integral model of the stellar dynamics yields . however , there is reason to believe that this model overestimates . reported correlations between black hole mass and inner stellar velocity dispersion predict to be in ngc 4335 . if our standard thin disk modeling of the gas kinematics is valid , then ngc 4335 has an unusually low for its velocity dispersion . if , on the other hand , this approach is flawed , and provides an underestimate of , then black hole masses for other galaxies derived from hst gas kinematics with the same assumptions should be treated with caution . in general , a precise determination of the relation and its scatter will benefit from ( i ) joint measurements of from gas and stellar kinematics in the same galaxies and ( ii ) a better understanding of the physical origin of the excess velocity dispersion commonly observed in nuclear gas disks of elliptical galaxies .

astro-ph0208132

c

before analyzing the implications of the inferred black hole mass we first discuss the two main differences between our gas disk dynamical modeling and the modeling used for ngc 3245 presented by barth et al . ( 2001 ) which constitutes the current state - of - the - art . first , instead of the observed emission - line flux distribution , we have used a double exponential fit to the flux distribution . for ngc 3245 the use of an exponential fit changes the inferred @xmath1 by @xmath225 . moreover , it accounted less well for the wiggles in the velocity profile . in our case the deviations of the exponential model from the observed photometric and spectroscopic emission - line fluxes are estimated to have a @xmath54 effect on bh mass ( see section [ s : bestfit ] ) . second , we do not incorporate the velocity shifts due to asymmetric illumination of the slit by the gas disk in the dispersion direction . in other galaxies this could be important to derive the bh mass as they produce surface brightness caustics ( maciejewski & binney 2001 ) . these caustics are not observed in ngc 4335 . stis observations of stars by one of us show that the velocity shift amounts to at most @xmath226 for a @xmath24 wide slit in the extreme case of a star at the edge of the slit . only the ( central ) apertures in the adjacent slits have an asymmetric flux gradient in the dispersion direction . the kinematics from these apertures are not taken into account in deriving the upper limit to @xmath1 . hence we conclude that the velocity shift has negligible effect on the derived @xmath1 . black hole mass @xmath1 correlates in general rather tightly with observed velocity dispersion @xmath2 in the inner region of galaxies ( gebhardt et al . 2000 ; ferrarese & merritt 2000 ) . recently , tremaine et al . ( 2002 ) completed a detailed analysis of the correlation and we will use their results in what follows . they find a best fit correlation of the form @xmath227 with @xmath228 and @xmath229 for @xmath230 . the observed spread in the correlation indicates that the intrinsic dispersion in @xmath231 is 0.3 dex ( perhaps smaller if observational errors are underestimated ) . measuring the central @xmath2 in similar fashion as in tremaine et al . ( 2002 ) gives @xmath232 for ngc 4335 ( cf . section [ s : stellarkin ] ) which corresponds to a predicted @xmath233 . the @xmath171 upper - limit @xmath234 from the thin disk modeling of the gas mean velocities ( section [ s : bestfit ] ) falls well below the relation , even when including the reported intrinsic dispersion in @xmath1 . the residuals are @xmath235 dex and @xmath236 dex for the upper - limit of @xmath237 ( best - fit model ) and @xmath238 ( for a maximally face - on gas disk ) , respectively ( see figure [ f : bhsigma ] ) . the residuals are even larger if we use the best - fit relation as determined by ferrarese ( 2002 ) who infers a larger @xmath239 . the @xmath219 derived from stellar dynamics corresponds to an equally large , but positive residual of @xmath240 dex . finally , the gravitational modeling of the gas velocity dispersions yields @xmath198 corresponding to a residual of @xmath241 dex , well within the reported intrinsic dispersion of the correlation . which bh mass are we to trust ? the analysis strongly supports a thin rotating gas disk model at @xmath196 . the model provides a reasonable fit to the gas mean velocities and dispersions , the dust disk morphology and gas disk kinematics indicate the same inclination and pa , and the @xmath111 from stellar and gas kinematics is consistent . however , there are doubts for the validity of the model at @xmath4 . the wfpc2 and stis fluxes are consistent with a thin disk surface brightness profile but the signal - to - noise of the wfpc2 image is too low to rule out a more spherical distribution . an excess velocity dispersion with an irregular profile is observed at @xmath242 . only an ad hoc explanation of localized random motion exists for this excess . it is not clear if such quasi - stationary turbulence in a thin disk is physically viable ( e.g. , wada , meurer & norman 2002 ; and references therein ) . if the excess velocity dispersion is ( partly ) due to gravitational motion around the bh , then the thin disk model underestimates the true bh mass . ascribing all gas kinetic energy , including the excess velocity dispersion , as counterbalancing the gravitational potential in a simple manner of isotropically moving collisionless cloudlets yields a bh mass which agrees well with the @xmath8 correlation ( tremaine et al . 2002 ) . ascribing the nuclear velocity dispersion to rotational motion from a spatially _ unresolved _ disk yields an equally good agreement ( section [ s : dispersion ] ) . as discussed in more detail in section [ s : starkin ] , it is not too unreasonable to assume that the stellar dynamical modeling overestimates the bh mass by a factor of @xmath201 . this would be due to radial anisotropy ( often observed in bright ellitpicals such as ngc 4335 ) which the two - integral modeling does not take into account . in conclusion , the gas spheroidal model infers a bh mass in accordance with the empirical @xmath8 relation , but remains very simplistic . if doubts about the validity of the thin disk modeling for @xmath4 were proven true , its inferred bh mass is expected to be an underestimate , driving the expected true bh mass to higher values in better agreement with the @xmath8 relation . similarly , the expected corrections for the stellar dynamical model bring its predicted bh mass in better agreement with the relation . what are the implications if in reality ngc 4335 indeed harbors a bh with @xmath243 ? our results then suggest that gas dynamical modeling assuming thin rotating disks can not be used to derive accurate black hole masses , _ even when all of the following are true _ : ( i ) the gas mean velocities very clearly suggest rotation ; ( ii ) the surrounding dust disk appears regular ; ( iii ) the inclination and position angle of the inner gas disk are well - constrained due to the use of three adjacent slits and these angles are both indicated by the gas disk kinematics and independent methods ; and ( iv ) the derived @xmath130 from gas and stars agree , ruling out asymmetric drift at @xmath196 . this then would cast doubt on other @xmath1 values determined from gas kinematics using similar models . figure [ f : bhsigma ] shows that these measurements have a large influence on the upper - end of the @xmath1 detections and hence on the slope of the correlation . moreover , to date all measurements of @xmath1 in nearby radio galaxies are based on gas kinematics . however , the fact that the inferred bh masses using this method follow the best - fit relation more closely than the stellar dynamical measurements argues against this worry of the validity of the gas dynamical modeling in general . the @xmath126 per degree of freedom as used in deriving the best - fit relation ( cf . equation 3 in tremaine et al . 2002 ) is 0.27 for the gas dynamical measurements while for the stellar dynamical measurements it is 1.30 ( 1.17 if one excludes the milky way bh mass measurement which is obtained from a stellar dynamical model which is completely different from those used for external galaxies ) . moreover , the average residual of the gas dynamical bh mass measurements is positive , counter to what is expected if the gas mean velocities systematically underestimate the circular velocity and hence the inferred bh mass . independent determinations of @xmath1 in galaxies from gaseous and stellar kinematics observed at high spatial resolution are crucial to address the worries about the gas dynamical modeling . this has been performed for ic 1459 ( verdoes kleijn et al . 2000 ; cappellari et al . verdoes kleijn et al . derive from the gaseous kinematics at 6 fos pointings a black hole mass ranging from @xmath244 ( thin disk model ) to @xmath245 ( isotropic spheroidal model ) . however , cappellari et al . ( 2002 ) infer @xmath246 based on three - integral modeling of combined ground - based and hst / stis stellar kinematics . unfortunately , the hst stellar kinematics can not be measured accurately inside the sphere of influence for this bh mass . cappellari et al . also present a more complete view of the gas kinematics from a recent stis long - slit observation . this indicates that while the data are consistent with the earlier fos measurements , and the inferred bh mass is similar ( modeled with independently developed software ) , the gas mean velocities are rather perturbed in this particular case . moreover , ic1459 has an irregular dust distribution . thus , the gas and dust properties in ic 1459 are quite different from the photometrically and kinematically well - behaved central disk in ngc 4335 . an independent @xmath1 measurement based on the stellar kinematics for ngc 4335 at hst resolution , and for other galaxies with similar gas disk kinematics , would test the validity of the gas dynamical modeling in well - behaved gas disks as opposed to irregular gas disks . it is similarly crucial to understand the origin of the excess velocity dispersion commonly seen in nuclear gas disks . presently , it is not clear under which circumstances the thin gas disks become locally turbulent ( for example , gravitational or mhd instabilities ) and if they remain globally stable ( e.g. , wada , meurer & norman 2002 ; and references therein ) . a better idea for the origin of the excess is needed to improve on the highly idealized collisionless spherical model discussed in this paper . in this respect , it is also useful to determine the ionization mechanism of the emission - line gas in nuclear disks . if it is shocks we should be wary about the modeling with unperturbed , infinitely thin rotating disks . furthermore , the disks of gas and dust might perhaps interact with ambient hot x - ray gas which is often present in the centers of bright ellipticals ( e.g. , gunn 1979 ) . the ultimate goal for gas dynamical modeling is thus to explain self - consistently the density , ionization state and dynamical state of the central gas distributions . this requires high s / n two - dimensional photometry , kinematics and line ratios to determine the dynamics , ionization state , density and temperature as a function of disk radius . this will provide not only accurate bh masses but also a vast improvement in our understanding of the fueling of bhs . kiloparsec - scale radio jets are only seen in early - type galaxies but never in spirals ( with one possible exception known to the authors ; ledlow et al . for instance , the ugc fr - i galaxies all have hubble types e - s0 ( cf . prior to this study , only bh masses @xmath247 have been reported in nearby radio galaxies ( i.e. , ngc 4261 , ngc 4374 , m87 , ngc 5128 , ngc 6251 and ngc 7052 , see tremaine et al . 2002 for references ) . interestingly , none of the seven galaxies with a hubble type later than s0 in the the sample compiled by tremaine et al . ( 2002 ) have @xmath248 . we are aware of only one galaxy with a hubble type later than s0 and a @xmath249 , which is the sombrero galaxy ( m104 , hubble type sa ) with @xmath250 , but this measurement is based on models less general than three - integral stellar dynamical models . by contrast , all bh mass upper limits and detections in a sample of 16 mostly early - type disk galaxies ( hubble type s0-sb ; sarzi et al . 2001 ) are below @xmath251 . these results suggest that the differences in bh mass might be the underlying factor for this host preference of radio - jets . however , if our determination of a @xmath171 upper limit of @xmath181 on the bh mass of ngc 4335 is correct , then ngc 4335 would illustrate that bhs with @xmath181 are also capable of producing fr - i radio jets . this would argue against bh mass being the ( only ) parameter underlying the host morphology preference of radio galaxies . it is a pleasure to thank marcella carollo and chris odea for stimulating advice , and to thank chris benn and andy longmore for carrying out our wht service observations and providing helpful suggestions during the analysis . we would like the referee for his / her comments which helped to improve the paper significantly . support for proposal # 8236 was provided by nasa through a grant from the space telescope science institute , which is operated by the association of universities for research in astronomy , inc . , under nasa contract nas 5 - 26555 . this paper made use of the leda database : http://leda.univ-lyon1.fr . g.v.k . is grateful to the leids kerkhoven - bosscha foundation for financial support for a visit to stsci in february 2001 . e & 2 & 0.347 & -0.254 & 101.00 & 9.68 & 115.71 & 9.44 + & 1 & 0.196 & -0.232 & 57.01 & 9.58 & 84.86 & 9.34 + & 1 & 0.096 & -0.217 & 38.39 & 5.65 & 76.64 & 5.62 + & 1 & -0.005 & -0.202 & -2.00 & 5.48 & 80.75 & 5.47 + & 1 & -0.105 & -0.187 & -65.27 & 5.88 & 96.18 & 6.03 + & 1 & -0.205 & -0.171 & -105.18 & 6.50 & 112.63 & 6.26 + & 2 & -0.356 & -0.149 & -126.46 & 8.49 & 141.02 & 7.98 + & 2 & -0.556 & -0.119 & -292.72 & 4.77 & 53.30 & 4.62 + c & 3 & 1.128 & -0.169 & 320.72 & 6.12 & 77.20 & 6.19 + & 3 & 0.828 & -0.124 & 292.35 & 4.25 & 57.35 & 4.17 + & 2 & 0.577 & -0.086 & 284.91 & 5.49 & 55.16 & 5.44 + & 2 & 0.376 & -0.056 & 197.42 & 12.06 & 165.72 & 11.49 + & 1 & 0.226 & -0.034 & 142.31 & 8.88 & 145.00 & 8.72 + & 1 & 0.125 & -0.019 & 64.90 & 4.78 & 197.58 & 4.39 + & 1 & 0.025 & -0.004 & 15.66 & 3.55 & 240.79 & 2.98 + & 1 & -0.075 & 0.011 & -49.96 & 4.06 & 231.24 & 3.32 + & 1 & -0.175 & 0.026 & -89.63 & 5.59 & 142.48 & 5.62 + & 2 & -0.326 & 0.049 & -155.09 & 8.40 & 146.89 & 8.24 + w & 3 & 1.459 & -0.016 & 364.75 & 3.23 & 49.70 & 3.14 + & 3 & 1.158 & 0.029 & 354.71 & 6.85 & 82.90 & 6.86 + & 3 & 0.857 & 0.074 & 310.68 & 5.85 & 92.86 & 5.61 + & 2 & 0.606 & 0.111 & 315.11 & 5.76 & 87.42 & 5.92 + & 2 & 0.406 & 0.141 & 312.75 & 5.11 & 92.93 & 5.06 + & 1 & 0.255 & 0.164 & 209.58 & 11.82 & 147.67 & 11.28 + & 1 & 0.155 & 0.179 & 105.15 & 8.92 & 179.87 & 8.15 + & 1 & 0.055 & 0.194 & 28.02 & 5.92 & 163.13 & 5.79 + & 1 & -0.046 & 0.209 & -12.79 & 6.30 & 159.55 & 6.17 + & 1 & -0.146 & 0.224 & -68.63 & 8.27 & 128.64 & 8.32 + & 2 & -0.296 & 0.247 & -120.31 & 5.39 & 87.64 & 5.36 + & 2 & -0.497 & 0.277 & -155.89 & 9.89 & 113.07 & 9.61 + 36 & 7.39 & 1.04 & 51 & 10 & 210 & 11 + 12 & 3.18 & 0.45 & 95 & 8 & 245 & 9 + 5 & 1.65 & 0.23 & 91 & 8 & 297 & 9 + 3 & 0.92 & 0.13 & 49 & 7 & 296 & 7 + 2 & 0.47 & 0.07 & 34 & 7 & 295 & 7 + 2 & 0.09 & 0.01 & 17 & 8 & 314 & 6 + 2 & -0.28 & -0.04 & -22 & 7 & 291 & 6 + 3 & -0.73 & -0.10 & -46 & 8 & 287 & 7 + 6 & -1.54 & -0.22 & -101 & 7 & 258 & 7 + 16 & -3.52 & -0.50 & -119 & 8 & 232 & 8 +

this sets a 3 upper limit of on . however , if instead the dispersion is caused by the bh potential then the thin disk model provides an underestimate of . a bh mass is inferred by modeling the central gas dispersion as due to an isotropic spherical distribution of collisionless gas cloudlets .

we investigate the kinematics of the central gas disk of the radio - loud elliptical galaxy ngc 4335 , derived from hst / stis long - slit spectroscopic observations of h + [ ] along 3 parallel slit positions . the observed mean velocities are consistent with a rotating thin disk . we model the gas disk in the customary way , taking into account the combined potential of the galaxy and a putative black hole with mass , as well as the influence on the observed kinematics of the point spread function and finite slit width . this sets a 3 upper limit of on . the velocity dispersion at is in excess of that predicted by the thin rotating disk model . this does not invalidate the model , if the excess dispersion is caused by localized turbulent motion in addition to bulk circular rotation . however , if instead the dispersion is caused by the bh potential then the thin disk model provides an underestimate of . a bh mass is inferred by modeling the central gas dispersion as due to an isotropic spherical distribution of collisionless gas cloudlets . the stellar kinematics for ngc 4335 are derived from a ground - based ( wht / isis ) long - slit observation along the galaxy major axis . a two - integral model of the stellar dynamics yields . however , there is reason to believe that this model overestimates . reported correlations between black hole mass and inner stellar velocity dispersion predict to be in ngc 4335 . if our standard thin disk modeling of the gas kinematics is valid , then ngc 4335 has an unusually low for its velocity dispersion . if , on the other hand , this approach is flawed , and provides an underestimate of , then black hole masses for other galaxies derived from hst gas kinematics with the same assumptions should be treated with caution . in general , a precise determination of the relation and its scatter will benefit from ( i ) joint measurements of from gas and stellar kinematics in the same galaxies and ( ii ) a better understanding of the physical origin of the excess velocity dispersion commonly observed in nuclear gas disks of elliptical galaxies .

0911.3652

c

using 3rd and 4th statistical moments of the hi column density image and boothstreping turbulent information from a database of isothermal mhd simulations , we have mapped spatial variations of the sonic mach number across the smc . while most of the hi seen in emission in the smc appears to be subsonic or transonic , several supersonic regions have emerged from our study . it is interesting that these regions do not correlate well with the most recent sites of star formation and seem to point out to large scale shearing or tidal flows . commonly , it is believed that supernovae and superbubbles are the main drivers of galactic turbulence ( mccray & snow 1979 ) , with a typical size of @xmath142 pc . while we do not have high enough resolution to see changes on such small scales ( @xmath143 ) in our derived map of @xmath0 , most of the star - forming bar of the smc appears to have subsonic or transonic properties when viewed at resolution of 30@xmath72 . the most turbulent regions in the smc may be tracing some kind of shearing flows between the smc bar and the surrounding hi . this suggests that smc s chaotic history with the lmc and our own milky way has probably left strong turbulent imprints on the hi gas . the lack of a turnover in the hi spatial power spectrum on the largest observed scales is also indicative of the fact that turbulent energy injection happens largely on scales larger than the size of the smc @xcite . similarly , goldman ( 2000 ) suggested that the hi turbulence in the smc was induced by large - scale flows from tidal interactions with the milky way and the lmc about @xmath144 yrs ago . such large - scale bulk flows could have generated turbulence through shear instabilities , and this turbulence has not have had enough time to decay . most of the hi in the smc has a sonic mach number of 1 - 2 . this is on average at least two times smaller than what we inferred from hi absorption observations for the cnm in the smc , @xmath1453.5 - 4 . similarly , for the cnm in the milky way heiles & troland ( 2003 ) found @xmath146 with a large dispersion . a sonic mach number of about 4 - 5 is commonly assumed for cold gas in molecular clouds ( federrath et al . 2009 ) . for example , heyer et al . ( 2006 ) measured from co observations @xmath147 for the rosette molecular cloud , and @xmath148 for g216 - 2.5 . on the other hand , hill et al . ( 2008 ) found that the distribution of the warm ionized medium ( wim ) in the milky way can be best fit by models for mildly supersonic turbulence with @xmath149 . turbulent properties of the hi in emission in the smc are therefore closer to properties of the wim in the milky way than properties of the cnm . this may suggest a large fraction of warm relative to cold hi being traced in hi emission . in the milky way , the hi is known to consist of at least two components with different temperature : the wnm with @xmath150 k and the cnm with @xmath151 k. in addition , there could be a substantial amount of gas at intermediate temperatures @xcite . due to its lower metallicity , the hi in the smc has different properties . dickey et al . ( 2000 ) found @xmath152 k , in agreement with theoretical expectations by wolfire et al . ( 1995 ) whereby the existence of the two - phase medium is possible only at higher pressures compared with the range that applies for solar neighborhood conditions . they also estimated the fraction of cold hi in the smc to be @xmath153% . this is lower than @xmath154% found for the milky way . as our simulations are isothermal it is obvious to wonder how does the multi - phase hi affect our statistics and conclusions . we investigate this in figure [ fig : ex ] by producing a simulated data cube from a weighted combination of two cubes , one subsonic ( @xmath10=0.7 ) and one supersonic . the subsonic cube represents contribution from warmer gas , while the supersonic cube represents the cold gas . we combined the two cubes with different emphasis on warm vs cold gas , obtained the column density image of the resultant cube , and calculated its moments . figure [ fig : ex ] shows that for the case when the supersonic cube has @xmath10=2.0 skewness of the final cube with up to 50% of subsonic gas will be biased towards supersonic gas and will appear dominated by cold gas . if we increase the sonic mach number of the supersonic cube to 4.0 , the dominance of the higher turbulence is even more pronounced . a cube with up to 60 - 70% of subsonic gas and 25% of supersonic gas , will still have high skewness biased by the supersonic contribution . considering that the hi column density image results in the mean @xmath93 , significantly lower than what is expected for the cold hi , the fraction of the cnm along any los is most likely @xmath155% . this supports the dickey et al . ( 2000 ) estimate of the fraction of cold hi in the smc being about 15% . two different statistical approaches in our study suggest that the hi gas in the smc seen in emission is super - alfvnic . as we have shown in figure [ fig : power ] , in addition to the sonic mach number the spectral slope of the spatial power spectrum is sensitive to the alfvenic mach number for @xmath156 . the sub - alfvnic models generally show steeper slopes due to large scale influence of magnetic fields . thus , if one independently knows the sonic mach number , it is possible to estimate the alfvenic one using just the column density data . while the dependence of the spectral slope on the alfvenic mach number has not received much attention in the past , it is somewhat expected . essentially , magnetization decreases compression in the shocks . strong magnetic forces mix up density clumps preventing formation of isolated peaks , which results in a steeper spectrum . in addition , in the sub - alfvnic case we expect oblique shocks to be disrupted by alfvn shearing , which in turn , produces more small scale shocks @xcite . another indication that the hi in the smc is super - alfvnic comes from the bispectrum . the very sharp decrease in the bispectral amplitudes from large to small scales observed for the smc is the closest to the trend found for simulated data for the case of @xmath85 and @xmath157 . detailed comparison between simulated and observed bispectra awaits future work , however this qualitative comparison is certainly encouraging . assuming on average @xmath84 , the power spectrum slope suggests a super - alfvnic hi in the smc with @xmath158 . this is generally in agreement with the observationally inferred strength of the magnetic field by mao et al . ( 2008 ) . using their estimate for @xmath159 @xmath160 g , a radius of the smc of 2 kpc , the total hydrogen mass of @xmath161 m@xmath162 , and a typical velocity dispersion of 20 ( stanimirovic et al . 2004 ) , we estimate @xmath163 . as the alfvenic mach number shows the nature of the interplay between gas pressure and magnetic fields , it appears that the gas pressure in the smc dominates over the magnetic pressure . our bispectrum analysis of the smc hi data was the first attempt to apply bispectrum on observed astrophysical data . while more detailed comparison between observations and simulations awaits future work , we clearly see trends in the bispectral amplitudes similar to what was found for simulations of supersonic mhd turbulence . the most interesting finding is , however , the effect of small - scale variations in the @xmath124 correlations and a strong break in correlations at a scale of 160 pc . such small - scale variations , or jumps , have not been seen in the bispectrum of simulated data . we can speculate about several possible scenarios that could explain their existence . the jumps could be caused by the energy injection due to processes other than turbulence affecting specific spatial scales . alternatively , the jumps may be marking the presence of colder or multi - phase gas . similarly , the observed break in the bispectrum at about 160 pc is intriguing . as we already pointed out , it is interesting that most expanding shells in the smc ( more than 500 were cataloged so far ) have a diameter of @xmath164 pc . the break could be due to the lack of correlations on scales similar to the distance between two shell centers . obviously this will require further studies . a natural question to ask is how results presented in this paper depend on the resolution of numerical simulations . for example , kritsuk et al . ( 2007 ) investigated how resolution of numerical simulations affects the power spectrum of density . these authors found that the spectral index estimates based on low resolution simulations bear large uncertainties due to the bottle neck contamination , and that the power spectra of @xmath165 simulations are substantially shallower then models with resolution of @xmath166 . however , while kritsuk et al . ( 2007 ) only examined hydrodynamic turbulence , beresnyak et al . ( 2008 ) showed that the slopes were very different between the mhd and pure hydrodynamic cases . for instance , the slopes for hydrodynamic simulations showed a pronounced and well defined bottleneck effect , while the mhd slopes were much less affected . this is indicative of mhd turbulence being less local than the kolmogorov turbulence , and suggests that our simulations will be less affected by resolution . in addition , kritsuk et al . ( 2007 ) found a difference in the slope between hydrodynamic @xmath165 and @xmath166 simulations to be 0.17 . this would result in a change of @xmath167 only and will not change our interpretation . we also add that in the case of higher statistical moments and the bispectrum bfkl confirmed trends noticed by klb at lower resolution of 128@xmath3 . another issue that should be further addressed and that could affect our results is the type of numerical forcing of turbulence . federrath et al . ( 2009 ) recently investigated the effects of solenoidal vs. compressive ( divergence - free vs. curl - free ) forcing on a variety of statistics including pdfs and higher order moments . they found that both types of driving mechanisms are compatible with observations of molecular clouds however , depending on the data studied , one type could be superior then the other in terms of the statistics and reproduced observables . this implies that different regions in the smc may exhibit statistical signatures of either compressive or solenoidally driven turbulence . we have investigated a new method for constraining turbulent properties of the ism , specifically the sonic mach number , by using the hi column density image and a database of numerical simulations with a range of sonic and alfvenic mach numbers . by applying the 3rd and 4th statistical moments on both observed and simulated data we have derived the spatial distribution of the sonic mach number across the smc with angular resolution of 30@xmath72 . to provide an estimate of the alfvenic mach number we used two approaches : the spatial power spectrum and the bispectrum . using the database of numerical simulations we have shown that the spatial power spectrum varies with both the sonic and alfvenic mach numbers . if the sonic number is known the alfvenic number can be constrained from this dependence . the bispectrum shows the level of correlation between turbulent eddies of different size and depends greatly on the sonic mach number , and somewhat on the alfvenic mach number . by comparing the bispectra of observations and simulations we have gauged the importance of magnetic fields relative to the gas pressure in the smc . the following results were discussed in the paper . * skewness and kurtosis of the hi column density generally correlate well and are within the range expected from mhd simulations . this suggests that departures from gaussianity could be interpreted as being governed by mhd turbulence . * most of the hi in the smc bar and the eastern wing is subsonic or transonic with @xmath90 . sites of most recent star formation have @xmath96 . regions with the highest skewness and kurtosis , which could be interpreted as having @xmath91 , correspond to the edges of the bar . the most turbulent regions are most likely tracing tidal or shearing flows . the fraction of the smc with different turbulent properties is : 10% with @xmath94 , 80% with @xmath168 , and about 10% with very low values of @xmath10 . * using hi absorption profiles from dickey et al . ( 2000 ) we have estimated that the cnm in the smc is highly supersonic with @xmath169 . this is at least a factor of two higher than what we measured from the higher statistical moments for the hi gas seen in emission . one possible reason for this discrepancy could be that hi emission is dominated by warm gas and the fraction of the cnm in the smc is @xmath170% . * the slope of the spatial power spectrum and the bispectrum suggest that the hi in the smc is super - alfvenic with @xmath158 . this is implies that the gas pressure dominates over the magnetic pressure . * the bispectrum of the hi column density shows large scale wave correlations suggesting a large scale energy injection mechanism . contrary to simulations which show a smooth decrease of wave - wave correlations from large to small scales , the smc bispectrum shows localized enhancements of correlations and at least one prominent break at @xmath2 pc . we speculate that the multi - phase medium , and/or energy injection by processes other than turbulence , could be responsible for the correlation jumps . the break on the other hand appears at a scale similar to the diameter of the majority of expanding shells in the smc . b.b is thankful for valuable discussions with diego falceta - gonalves and jungyeon cho . bb acknowledges the nasa wisconsin space grant consortium and the national science foundation graduate research fellowship . al acknowledges nsf grant ast 0808118 and the center for magnetic self - organization . ss acknowledges support from the nsf grant ast 0707679 and the research corporation . in figure [ evidence2 ] we plot kurtosis vs. skewness in a manner similar to figure [ evidence ] . the difference between this figure and figure [ evidence ] is that we added seven zero points into the beam ( instead of 3841 points there are now 3848 points ) . this produces almost no change in the supersonic models since they already have high positive skewness and kurtosis . supersonic models still show strong correlation between skewness and kurtosis . however a big change is seen in the subsonic skewness vs. kurtosis . the additional zero points shift the distribution from gaussian ( the mean of our simulations with no scaling applied is unity ) to negative skewness and very peaked kurtosis producing a tight anti - correlation . because this technique only strongly affects subsonic areas we can use it to locate subsonic turbulence in the smc with skewness and kurtosis by looking for anti - correlation and very high values . these properties also hold for simulations with cloud boundaries imposed . note that one must use caution here and carefully examine the distribution of data . the application of this technique to the smc data is shown in figure [ fig : compare ] . this plot shows the skewness and kurtosis maps of the smc side by side with the modified beam . indeed , most regions are unchanged from the analysis in section [ sec : mmaps ] . however a few regions stick out with signatures that are subsonic , that is , anti - correlation between skewness and kurtosis . two regions of the highest kurtosis are located in the area between the hi bar and the eastern wing . while kurtosis reaches values of 4 - 8 , the corresponding skewness values are negative , @xmath171 . again , such combination of skewness and kurtosis may correspond to simulations of subsonic isothermal mhd turbulence , and/or points out additional processes at work . beresnyak , a. , lazarian , a. & cho , j. , 2005 , , 624 , l93 biskamp , d. ( 2003 ) , magnetohydrodynamical turbulence , ( cambridge university press , cambridge ) . brunt , c. , & heyer , m.,2002,apj , 566 , 27 burkert , a. , 2006 , c. r. physique 7 burkhart , b. falceta - goncalves , d. , kowal , g. , lazarian , a. , 2009 , , 693 , 250 ( bfkl ) cho , j. & lazarian , a. 2002 , phys . lett . , 88 , 5001 cho , j. & lazarian , a. , 2003 , , 345 , 325 chepurnov , a. , & lazarian , a. , 2009 , apj , 693 , 1074 chepurnov , a. , lazarian , a. , gordon , j. , & stanimirovic . , s. , apj , 688 , 1021 croviser , j. , & dickey , m. , 1983 , a&a , 122 , 282 deshpande et al.,2000 , apj , 543 , 227 dickey et al . , 2000 , apj , 536 , 756 elmegreen , b. , & scalo , j. , ara&a , 42 , 211 esquivel , a. , & lazarian , a. , 2005 , apj , 631 , 320 esquivel , a. , & lazarian , a. , 2009 , apj in press esquivel , a. , lazarian , a. , pogosyan , d. , & cho , j. , 2003 , mnras , 342 , 325 esquivel et al . , 2007 , mnras , 381 , 1733 federrath , c. , et al.,2009 , aa , in press fry , j. n. 1998 , annals of the new york academy of sciences 848 , 62 gill , a.g . , & henriksen , r.n . , 1990 , , 365 , l27 goodman , a. et al.,2009 , apj , 692 , 91 hatzidimitriou et al . , 2005 , mnras , 360,1771 heiles , c. , troland , t. , 2003 , apj , 586 , 1067 heyer , m. , & zwiebel , e. , 2004 , ap&ss , 292 , 9 hill , a. s. , benjamin , r. a. , kowal , g. , reynolds , r. j. , haffner , . l. m. & lazarian , a. , 2008 , apjs intrator , t. , meassick , s. , browning , j. , majeski , r. & hershkowitz , n. 1989 , phys . fluids b , 1 , 271 - 273 kennicutt et al . 1995 , aj , 109 , 594 kowal , g. , lazarian , a. & beresnyak , a. , 2007 , , 658 , 423 ( klb ) kowal et al . , 2009 , apj , 700,63 kritsuk et al . , 2007 , apj , 665 , 416 lazarian , a. , 2007 , jqsrt , 106 , 225 lazarian , a. , 2009 , ssr , 143 , 357 lazarian et al.,2001 , apj , 555 , 130 lazarian , a. & pogosyan , d. , 2004 , , 616 , 943 lazarian , a . & pogosyan , d . , 2006 , , 652 , 1348 lazarian , a. & pogosyan , d . , 2000 , , 537 , 720 lazarian , a. , & vishniac , e. , 1999 , apj , 511 , 193 levy , d. , puppo , g. & russo , g. , 1999 , mathematical modeling and numerical analysis , 33 , 547 liguori , m. , hansen , f. k. , komatsu , e. , matarrese , s. & riotto , a. , 2006 , phrvd , 73 , 3505 lithwick , y. & goldreich , p. , 2001 , , 562 , 279 liu , x .- d . & osher , s. , 1998 , journal of computational physics , 141 , 1 mao et al . 2009 , apj , 688 , 1029 mccray , r. , & snow , p , 1979 , a&aa , 17 , 213 mckee , c. , ostriker , e. , 2007 , monin , a.s . & yaglom , a.m.,1967 , statistical fluid mechanics , mit press montgomery , d. , brown , m. r. , matthaeus , w. h. , 1987 , j. geophys . , 92 , 282 nordlund , a. k. & padoan , p. , 1999 , interstellar turbulence , proceedings of the 2nd guillermo haro conference , cambridge university press ostriker , e. c. , stone , j. m. & gammie , c. f. , 2001 , apj , 546 , 980 scoccimarro , r. , 2000 , , 544 , 597 stanimirovic , s. , staveley - smith , l. , dickey , j. m. , sault , r. j. , & snowden , s . l. , 1999 , mnras , 302 , 417 ( sx99 ) stanimirovic , s. & lazarian , a. , 2001 , apj , 551 , l53 stanimirovic , s. , 2001 , _ astrophysics and space science _ , 277 , 87 staveley - smith , l. , sault , r. j. , hatzidimitriou , d. , kesteven , m. j. , & mcconnell , d. 1997 , mnras , 289 , 225 stanimirovi , s. , staveley - smith , l. , & jones , p. a. 2004 , apj , 604 , 176 stanimirovi , s.,2007 , iau symposium , 237 , 84 stutzki , j. , bensch , f. , heithausen , a. , ossenkopf , v. , & zielinsky , m. , 1998 , , 336 , 697 tabachnick , b. g. , & fidell , l. s. ( 1996 ) . using multivariate statistics ( 3rd ed . ) . new york : harper collins . tynan , g. r. , moyer , r. a. , burlin , j. & holland , c. 2001 , phys . plasmas , 8 , 2691 westerlund , b. e. 1991 , in the magellanic clouds , iau symp . , 148 , 15

we investigate the nature and spatial variations of turbulence in the small magellanic cloud ( smc ) by applying several statistical methods on the neutral hydrogen ( hi ) column density image of the smc and a database of isothermal numerical simulations . by using the 3rd and 4th statistical moments we derive the spatial distribution of the sonic mach number ( ) across the smc . we find that about 90% of the hi in the smc is subsonic or transonic . however , edges of the smc ` bar ' have and may be tracing shearing or turbulent flows . using numerical simulations this allows us to gauge the alfvn mach number of the smc and conclude that its gas pressure dominates over the magnetic pressure . we find that the bispectrum of the smc hi column density displays similar large - scale correlations as numerical simulations , however it has localized enhancements of correlations . in addition , we find a break in correlations at a scale of pc .

we investigate the nature and spatial variations of turbulence in the small magellanic cloud ( smc ) by applying several statistical methods on the neutral hydrogen ( hi ) column density image of the smc and a database of isothermal numerical simulations . by using the 3rd and 4th statistical moments we derive the spatial distribution of the sonic mach number ( ) across the smc . we find that about 90% of the hi in the smc is subsonic or transonic . however , edges of the smc ` bar ' have and may be tracing shearing or turbulent flows . using numerical simulations we also investigate how the slope of the spatial power spectrum depends on both sonic and alfvn mach numbers . this allows us to gauge the alfvn mach number of the smc and conclude that its gas pressure dominates over the magnetic pressure . the super - alfvnic nature of the hi gas in the smc is also highlighted by the bispectrum , a three - point correlation function which characterizes the level of non - gaussianity in wave modes . we find that the bispectrum of the smc hi column density displays similar large - scale correlations as numerical simulations , however it has localized enhancements of correlations . in addition , we find a break in correlations at a scale of pc . this may be caused by numerous expanding shells of a similar size .

math0305418

i

in this paper we compute and list the fundamental groups of complements of all real conic - line arrangements in @xmath0 with two conics , which are tangent to each other at two points , with up to two additional lines in any position . algorithmically , this paper uses the local computations ( local braid monodromies and their induced relations ) , the braid monodromy techniques of moishezon - teicher ( see @xcite , @xcite , @xcite , @xcite , @xcite and @xcite ) , the enriques - van kampen theorem ( see @xcite ) and some group calculations for studying the fundamental groups . see @xcite for detailed exposition of these techniques . these arrangements may appear in a branch curve of a generic projection to @xmath0 of a surface of general type ( see for example @xcite ) . the main results of this paper are as follows ( where @xmath1 is the unit element in the group and @xmath2 is the free group with two generators ) : [ th1 - 2 ] let @xmath3 be a curve in @xmath0 composed of two tangent conics . then : @xmath4 [ th1 ] there are three possible fundamental groups for a conic - line arrangement which consists of two tangent conics and an additional line : 1 . 2 . @xmath6 . @xmath2 [ th2 ] there are five possible fundamental groups for a conic - line arrangement which consists of two tangent conics and two additional lines : 1 . @xmath7=[x_2 , x_3 x_1 x_3^{-1}]=e \end{array } \right\rangle\ ] ] 2 . @xmath8 3 . @xmath9 4 . @xmath10 5 . @xmath11 the proof of proposition [ th1 - 2 ] is presented completely in section [ sec:1 ] . otherwise , we skip all the braid monodromy computations , and give only the presentation of the fundamental group obtained by the van kampen theorem . these computations and the proofs of propositions [ th1 ] and [ th2 ] appear in sections [ sec:2 ] and [ sec:3 ] , respectively . a group is called _ big _ if it contains a subgroup which is free ( generated by two or more generators ) . by the above results , we have the following corollary : [ bigness ] all the possibilities for fundamental groups of conic - line arrangements consist of two tangent conics and up to two additional lines are big . the proof of this corollary appears in section [ sec_big ] . we rule out some possibilities for conic - line arrangements by the following remark . [ remark ] the only possibility for a line to be tangent to both conics is that this line will pass through one of the tangency points of the two conics ( fourth case in section [ 2conics1line_other ] ) . the reason is the following . if a line was tangented to both conics , it would be a common point of the two duals to the two conics . now , since the dual curve of two tangented conics is two tangented conics too , there are only two common points to the two dual conics . these two common points correspond to the two tangency points between the original two conics . hence , a different line which tangents to both conics is impossible . the paper is organized as follows . section [ local ] presents the local computations related to the singular points appearing in the conic - line arrangements which we deal with . section [ sec:1 ] deals with the proof of proposition [ th1 - 2 ] . in section [ sec:2 ] we compute the different cases of conic - line arrangements which consist of two tangent conics and one additional line . section [ sec:3 ] deals with the different cases of conic - line arrangements which consist of two tangent conics and two additional lines . in section [ sec_big ] we show the simple proof of corollary [ bigness ] . section [ general ] deals with some conjectures concerning the connection between the presentation of the fundamental group of the complements and the geometry of an interesting family of conic - line arrangements . in the appendix , we list all the possibilities for two tangent conics and two additional lines with the corresponding fundamental groups of their complements .

we list all the possible fundamental groups of the complements of real conic - line arrangements with two conics which are tangent to each other at two points , with up to two additional lines . for the computations we use the topological local braid monodromies and the techniques of moishezon - teicher and van - kampen . we also include some conjectures concerning the connection between the presentation of the fundamental group of the complements and the geometry of an interesting family of conic line arrangements .

we list all the possible fundamental groups of the complements of real conic - line arrangements with two conics which are tangent to each other at two points , with up to two additional lines . for the computations we use the topological local braid monodromies and the techniques of moishezon - teicher and van - kampen . we also include some conjectures concerning the connection between the presentation of the fundamental group of the complements and the geometry of an interesting family of conic line arrangements .

0908.0736

i

although the discovery of the planet 51 pegasi b ( mayor & queloz 1995 ) is often hailed as the start of the extrasolar planet revolution , the field of extrasolar planet studies began in 1991 , with the discovery of the two planet - sized bodies orbiting the pulsar psr 1257 + 12 ( wolszczan & frail 1991 ) . subsequent study has confirmed this identification by identifying the effect of mutual gravitational perturbations between the two planets in the timing residuals , thereby also constraining ( wolszczan 1994 ; wolszczan et al . 2000a ; konacki & wolszczan 2003 ) the inclinations and planetary masses , the current values of which are given in table [ params ] . yet , despite their early discovery , the origin of the pulsar planets have received little attention after the initial burst of post - discovery papers ( summarised in podsiadlowski 1992 ) . part of this neglect is no doubt due to the unusual nature of the host star and the relative uniqueness of the planets natal circumstances . however , as has been noted before ( phinney & hansen 1993 ) , the formation scenarios all produce a qualitatively similar outcome namely a gaseous disk on a compact scale around a 1.4@xmath0 pulsar . thus , the exact details of the formation are relevant primarily in the manner in which they determine the size of the original mass and angular momentum budget , and also the disk composition . the subsequent evolution of the gaseous and planetesimal disks are expected to follow a path very similar to the one they would follow if orbiting a normal main sequence star of similar mass . as such , studying the formation of the pulsar planets can offer us insights into the formation of terrestrial planets as a whole . this will be of particular interest in the next few years as the searches for planetary companions to main sequence stars continues to push down into the ` super - earth ' regime ( e.g. rivera et al . 2005 ; udry et al . 2007 ; mayor et al . 2008 ) . in that spirit , we wish to examine the quantitative evolution of pulsar protoplanetary disks that arise from different formation scenarios . in currie & hansen ( 2007 ) , hereafter paper i , we examined the expansion and evolution of gaseous disks for a range of mass and angular momentum , and identified the manner in which they laid down solid material that might eventually coalesce to form planets . in this paper we wish to extend that analysis to the question of how planetesimals , formed from such a distribution , would assemble into a final planetary configuration , and how the resulting planetary systems compare to that observed . in [ setup ] we review the outcomes of paper i and how we construct the initial conditions for the simulations described in this paper . in [ sims ] we describe the qualitative properties of the final planetary systems in each of the simulated scenarios . in [ comp ] we compare these results to the observed system and discuss the issues of broader relevance in [ discuss ] .

we model the assembly of planets from planetary embryos under the conditions suggested by various scenarios for the formation of the planetary system around the millisecond pulsar b1257 + 12 . finally , we examine the results of similar studies of solar system terrestrial planet accumulation and discuss what can be learned from the comparison .

we model the assembly of planets from planetary embryos under the conditions suggested by various scenarios for the formation of the planetary system around the millisecond pulsar b1257 + 12 . we find that the most likely models fall at the low angular momentum end of the proposed range . models that invoke supernova fallback produce such disks , although we find that a solar composition disk produces a more likely evolution than one composed primarily of heavy elements . furthermore , we find that dust sedimentation must occur rapidly as the disk cools , in order that the solid material be confined to a sufficiently narrow range of radii . a quantitative comparison between the observations and the best - fit models shows that the simulations can reproduce the observed eccentricities and masses , but have difficulty reproducing the compactness of the pulsar planet system . finally , we examine the results of similar studies of solar system terrestrial planet accumulation and discuss what can be learned from the comparison .

astro-ph0306380

i

ar lac ( hd 210334 , hr 8448 ) is one of the brightest totally eclipsing rs cvn binaries . since eclipses can help constrain active region geometry , it has been a key system for studying the structure of photospheric spots from visible light modulation , the chromosphere from emission of magnesium , calcium and hydrogen , the transition region through ultraviolet emission lines , and the coronae via emission at extreme ultraviolet ( euv ) , x - ray , and radio wavelengths . there is as yet no comprehensive predictive theory that explains in detail all the aspects of coronal emission based only on fundamental stellar parameters . observational attack is then aimed at increasing the quantity and quality of spectral and photometric data to provide insights and to help constrain the dependence of coronal activity on stellar evolutionary parameters , other magnetic activity indicators or as yet unidentified parameters . with the high energy transmission grating spectrometer ( hetgs ) on the _ chandra_x - ray observatory , we are able to greatly improve the quality of x - ray spectra by resolving a multitude of coronal emission lines due to iron and the hydrogen - like and helium - like lines of a number of abundant elements . these spectra provide both line and continuum fluxes and their time variability . the aim of this study is to model the lines and continuum with the latest atomic data in order to determine the coronal temperature structure , density and absolute elemental abundances . ar lac is comprised of g- and k - type subgiants in a 1.98 day orbit . the components are each of slightly greater than one solar mass ( @xmath5 and @xmath6 , respectively ) and have radii of @xmath7 and @xmath8 . they reach a maximum radial velocity separation of @xmath9 and have rotational velocities of 39 and 70 @xmath10 . at a distance of 42 pc , ar lac is relatively bright . @xcite summarized these and other fundamental properties of ar lac . ar lac was detected in x - rays by heao 1 at a luminosity of @xmath11 @xcite ; @xcite present an early analysis of the x - ray coronae in which it was inferred that emission arose from both stellar components in compact and extended structures . subsequent x - ray studies were undertaken by @xcite ( _ rosat _ ) , @xcite ( _ exosat _ ) , @xcite ( _ beppo - sax _ ) , and @xcite ( _ asca _ ) . observations with _ rosat _ and _ asca _ detected a deep primary eclipse and a smaller secondary eclipse @xcite , while _ exosat _ and _ euve _ observations could only confirm the primary eclipse due to flares or instrumental limitations @xcite . some extended chromospheric material was also detected by @xcite and @xcite . analysis of high resolution _ data @xcite showed a corona dominated by material at @xmath12k , and a substantial amount of material at hotter temperatures of @xmath13k .

we observed the coronally active eclipsing binary ar lac with the high energy transmission grating on _ chandra _ for a total of 97 ks , spaced over five orbits , at quadratures and conjunctions . significant variability in both x - ray and euv fluxes were observed , dominated by at least one x - ray flare and one euv flare . analysis of spectral line widths interpreted in terms of doppler broadening suggests that both binary stellar components are active .

we observed the coronally active eclipsing binary ar lac with the high energy transmission grating on _ chandra _ for a total of 97 ks , spaced over five orbits , at quadratures and conjunctions . contemporaneous and simultaneous euv spectra and photometry were also obtained with the extreme ultraviolet explorer . significant variability in both x - ray and euv fluxes were observed , dominated by at least one x - ray flare and one euv flare . we saw no evidence of primary or secondary eclipses , but exposures at these phases were short and intrinsic variability compromised detection of any geometric modulation . x - ray flux modulation was largest at high temperature , indicative of flare heating of coronal plasma rather than changes in emitting volume or global emission measure . analysis of spectral line widths interpreted in terms of doppler broadening suggests that both binary stellar components are active . based on line fluxes obtained from total integrated spectra , we have modeled the emission measure and abundance distributions . the euv spectral line fluxes were particularly useful for constraining the parameters of the `` cool '' ( k ) plasma . a strong maximum was found in the differential emission measure , characterized by two apparent peaks at and , together with a weak but significant cooler maximum near , and a moderately strong hot tail from . coronal abundances have a broad distribution and show no simple correlation with first ionization potential . while the resulting model spectrum generally agrees very well with the observed spectrum , there are some significant discrepancies , especially among the many fe l - lines . both the emission measure and abundance distributions are qualitatively similar to prior determinations from other x - ray and ultraviolet spectra , indicating some long - term stability in the overall coronal structure .

1405.3294

r

scattering contribution to the total rosseland mean free path as a function of baryon density at several temperatures for both nondegenerate and degenerate neutrinos . all electron - neutrino processes of table [ table : cconsts ] have been included in the total opacity . ] influence of the bag constant , @xmath4 , on the total rosseland neutrino mean free path of degenerate neutrinos ( @xmath102 ) in quark matter . here , @xmath112 and @xmath113 represent @xmath103mev/@xmath2 and @xmath1mev/@xmath2 , respectively . ] influence of the strong coupling constant , @xmath6 , on the total rosseland neutrino mean free path of nondegenerate ( left panel ) and of degenerate neutrinos ( right panel , @xmath102 ) in quark matter . in the panel at the right , only the cases @xmath111 and @xmath114 are considered . the curves corresponding to @xmath115 and @xmath116 lie between the two curves shown and have been omitted for clarity purposes . ] influence of the strange quark mass , @xmath5 , on the total rosseland neutrino mean free path of nondegenerate neutrinos in quark matter with @xmath103mev/@xmath2 . ] the same as fig . [ fig:12 ] but for degenerate neutrinos ( @xmath102 ) . ] the same as fig . [ fig:12 ] but for degenerate neutrinos ( @xmath102 ) . ] mean scattering angle @xmath117 of nondegenerate neutrinos in quark matter . here , @xmath118 , @xmath50 , @xmath51 and @xmath119 indicate the target particle . ] the same as fig . [ fig:16 ] but for @xmath102 . ] electron - neutrino inverse absorption mean free paths in quark matter at two times nuclear saturation density . dashed lines indicate the approximations given in eqs . ( [ eq : iw1982_abs_dnu ] ) ( right panel ) and ( [ eq : iw1982_abs_ndnu ] ) ( left panel ) . ] our results are shown separately in terms of either nondegenerate or highly degenerate neutrinos . to nondegenerate neutrinos we associate a chemical potential @xmath120 . degenerate neutrinos , on the other hand , must have @xmath121 . we represent the latter category in terms of a high net electron - neutrino lepton fraction @xmath122 , where @xmath123 and @xmath124 represent , respectively , electron and electron - neutrino net number densities ( number density of particles minus number density of the corresponding antiparticles ) and @xmath125 is the baryon number density . in fig . [ fig:3 ] we show the inverse neutrino mean free paths associated to the six electron - neutrino processes listed in table [ table : cconsts ] . it must be noted that the factor @xmath126^{-1}$ ] present in eq . ( [ eq : lambda_scatt ] ) has been kept so the curves can be better distinguished in the region @xmath127 . when neutrinos are nondegenerate , neutrino - quark scattering dominates the scattering opacity with respect to neutrino - electron scattering by orders of magnitude . this discrepancy can be explained by the tiny density of electrons present in quark matter . the presence of trapped degenerate neutrinos also increases the electron density and hence the neutrino - electron contribution to the scattering opacity also increases , as can be seen in the lower panel at the left . in both the upper and the lower panels at the left in fig . [ fig:3 ] , it can be seen that neutrino - strange quark scattering differs from the other scatterings mainly at lower neutrino energies . in the panels at the right in fig . [ fig:3 ] we show the neutrino inverse mean free paths associated with absorption . in general , the process of neutrino absorption on @xmath50 quarks dominates the opacity . the contribution of neutrino absorption on @xmath51 quarks , on the other hand , tends to be smaller than that of scatterings , with exception of the very low neutrino energy regime , in which this process dominates the opacity . these results are in agreement with the results found in ref . @xcite . the behavior of the neutrino inverse mean free paths with respect to baryon number density for fixed neutrino energies is shown in figs . [ fig:4 ] and [ fig:5 ] . it can be seen that the contribution of neutrino - electron scattering is always small in comparison with that of neutrino - quark scattering when neutrinos are nondegenerate . it is only when neutrinos are trapped and highly degenerate , implying in an also higher abundance of electrons , that neutrino - electron scattering becomes an important contribution to the total opacity , as it is shown in the lower panels of fig . [ fig:5 ] . it is noticed that , for fixed @xmath128 , the inverse mean free paths vary within one order of magnitude in the baryon number density range of interest . in contrast , the temperature dependence is stronger , e.g. there is a variation of more than two orders of magnitude when @xmath128 goes from @xmath129 mev to a value above @xmath130 mev . the combined scattering processes amount to at least 10% of the total rosseland mean free path , as shown in fig . [ fig:6 ] . in the case of leptonized quark matter , neutrino scattering represents @xmath131 of the total neutrino opacity . it is only when neutrinos are less degenerate in colder quark matter that neutrino absorption becomes dominant . even in this case , as we already mentioned , neutrino scattering will contribute to at least @xmath132 of the total opacity in lower density regions of the star where neutrinos are completely nondegenerate . in figs . [ fig:7 ] and [ fig:8 ] we show the diffusion coefficients @xmath133 , @xmath134 and @xmath135 for both electron - neutrinos and electron - antineutrinos . when neutrinos are nondegenerate , all diffusion coefficients decrease with increasing density . as it can be seen in the panels at the middle , the combined coefficient @xmath136 will be negative . in fig . [ fig:8 ] it can be seen that the behavior of @xmath133 , @xmath134 and @xmath135 for degenerate neutrinos is not the same with respect to increasing density . notoriously , @xmath133 decreases , while @xmath135 increases . this behavior can be anticipated by means of analytic approximations for degenerate neutrinos , as we show in appendix [ ap : dn ] . in figs . [ fig:9 ] through [ fig:11 ] we analyze separately how @xmath5 , @xmath4 and @xmath6 indirectly influence the neutrino rosseland mean opacity through their effects on the equilibrium composition of quark matter as a function of pressure for a given temperature . in eq . ( [ eq : pbag ] ) , it is seen that , for a given @xmath137 , a larger @xmath4 will imply in a larger absolute value of @xmath93 . for fixed @xmath5 and @xmath6 , it follows that the equilibrium chemical potentials will increase accordingly . as verified in fig . [ fig:9 ] , this implies in smaller mean free paths . from eq . ( [ eq : omega_alphac ] ) , it follows that the same reasoning applies for increases in @xmath6 and this is shown in fig . [ fig:10 ] . for last , we analyze the influence of the strange quark mass on the neutrino mean free paths . since @xmath5 enters not only in the equation of state but also directly in the computation of the mean free paths in a nontrivial way , its influence is inferred directly from the numeric results shown in fig . [ fig:11 ] , where it can be seen that an increase in @xmath5 leads to larger mean free paths . it follows then that increases in both @xmath4 and @xmath6 lead to decreases in the neutrino mean free paths . the effect of increasing @xmath6 , however , is distinct from that of increasing @xmath4 in the sense that its effect is more prominent at higher pressures . it can also be noted that the mean free paths of highly degenerate neutrinos in highly degenerate quark matter is less sensitive to changes in @xmath5 or @xmath6 , since in these situations the chemical potentials are already very high . we have seen that scattering may represent a considerable fraction of the total neutrino opacity in quark matter . it is evident then that neutrino scattering must be treated with proper care . now we wish derive an estimate of the error committed when the term containing @xmath45 in eq . ( [ eq : kappa_0 ] ) is neglected and eq . ( [ eq : lambda_scatt ] ) is used as the neutrino inverse scattering mean free path . even though we do not know an explicit form for @xmath45 , it is expected to be much smaller than @xmath28 in magnitude on the regions of higher density , where we expect neutrinos to be almost in thermodynamic equilibrium with the remaining of the matter . in this case , the ratio @xmath138 tends to unity , given that the term containing @xmath45 in eq . ( [ eq : kappa_0 ] ) becomes vanishingly small compared to the first term and eq . ( [ eq : kappa_0 ] ) tends to eq . ( [ eq : lambda_scatt ] ) . on the other hand , on the regions of extremely small neutrino opacity , neutrinos will stream almost freely and , in the limit of free stream , @xmath139 and the ratio @xmath138 deviates maximally from the unity . a fairly general expression relating @xmath45 and @xmath28 on the surface of a stellar core may be written in the form @xcite @xmath140 where @xmath141 is responsible for smoothly shifting the neutrino flux from isotropic to radially outward as the optical depth increases . in fact , as the optical depth becomes larger , eq . ( [ eq : f1_surface ] ) will hold not only on the stellar surface but in a whole thick layer where neutrinos stream freely . in principle , @xmath141 should depend on the neutrino energy , however , to avoid further complications we consider it as a constant geometric factor . in this case , ( [ eq : kappa_0 ] ) reduces to @xmath142 and the ratio @xmath143 represents a bound to the maximum deviation from unity possible . in other words , the ratio @xmath144 will always be closer to @xmath34 than it is @xmath143 . this information can be used as an estimate of the largest possible error committed on the computation of the scattering contribution to the opacity when @xmath145 is used in the place of @xmath44 . when neutrinos are nondegenerate , it can be seen in fig . [ fig:12 ] that which between @xmath145 and @xmath146 is greater depends on the incident neutrino energy . for @xmath147 , @xmath145 tends to be @xmath148 smaller than @xmath146 . for @xmath149 , we see that the contribution of the term containing @xmath150 in eq . ( [ eq : kmaxerr ] ) becomes larger and @xmath146 becomes many times smaller than @xmath145 as the energy of the incident neutrino increases . in fig . [ fig:13 ] we see that when neutrinos are degenerate , there s almost no distinction between the two calculated scattering opacities when @xmath151 . however , for neutrinos with @xmath152 , there is a noticeable difference , that increases with increasing neutrino degeneracy . for instance , when @xmath153mev , @xmath145 is @xmath154 smaller than @xmath146 for @xmath102 . for higher neutrino energies with respect to @xmath155 , @xmath145 becomes several times greater than @xmath146 , similarly to what happens when neutrinos are nondegenerate . in diffusive transport schemes , one is generally interested in the energy - averaged diffusion coefficients as in eqs . ( [ eq : dndef ] ) and ( [ eq : lambda_ross ] ) , whose integrands are weighted with the factor @xmath156 , which quickly cuts off the higher energies , and features a peak centered at @xmath157 when neutrinos are degenerate . it means that in practice , @xmath145 will give scattering opacities at most @xmath148 smaller than the the ones that would be obtained if @xmath158 was used . we have seen that the scattering contribution to the total rosseland mean opacity is in the range @xmath159 for temperatures in the range @xmath160mev when neutrinos are nondegenerate ( fig . [ fig:6 ] ) . it follows then that the error committed in the total neutrino opacity , may be estimated to have an upper bound in the range @xmath161 . in regions where neutrinos are very close to thermodynamic equilibrium , and the anisotropy in the neutrino distribution function is vanishingly small , this error is expected to be much smaller . the situation is very similar when neutrinos are degenerate . in this case , the largest errors will be associated to those shown in fig . [ fig:13 ] for @xmath162 , which we see to be of about @xmath163 when @xmath153mev and smaller for larger temperatures . in this case , neutrino scattering amounts to about @xmath164 of the total neutrino opacity ( fig . [ fig:6 ] ) and the error committed may be estimated to have an upper bound in the range @xmath165 for temperatures increasing in the range @xmath166mev . if neutrinos are not expected to be too strongly degenerate in quark matter with temperatures as low as @xmath129 mev , then in this case the estimated upper bound for the error will be closer to @xmath167 . neutrino - electron scattering has long been known to be an important thermalizing agent in neutron star matter matter @xcite , while neutrino - baryon scattering is usually regarded as an isoenergetic process @xcite . in ref . @xcite , prakash & lattimer work in detail neutrino scattering in neutron star matter with and without hyperons , nevertheless , no attention has been paid to the aspects of neutrino / matter energy exchange or neutrino mean scattering angles . a detailed analysis of neutrino scattering in quark matter , however , is missing in the literature . given that quarks are very degenerate in quark matter and considering , for instance , the large mass of the strange quark with respect to that of electrons , it remains the question of whether neutrino - quark scattering is similar to neutrino - baryon or to neutrino - electron scattering with respect to neutrino - matter energy transfer and mean scattering angles . in this section we show that neutrino - quark scattering is always similar to neutrino - electron scattering with respect to energy exchange and hence non - isoenergetic . both the mean energy transfer and the mean scattering angle are defined in appendix [ ap : etransfer ] . the first thing to be noticed in figs . [ fig:14 ] and [ fig:15 ] , is that neutrino - matter energy exchange vanishes on average for a particular incident neutrino energy , @xmath168 , depending on both the neutrino and matter state of degeneracy . for @xmath169 , neutrinos tend to gain energy on average , while for @xmath170 , they tend to lose energy . this is not to say that neutrinos with @xmath171 do nt exchange energy with matter , but rather , that the net energy exchange vanishes on average . we see that the energy - exchange in neutrino - strange quark scattering is very similar to that in neutrino - electron scattering . the curves representing neutrino - up quark and neutrino - down quark scattering have been omitted since the difference between those and that of neutrino - electron scattering would be barely visible . when neutrinos are nondegenerate , @xmath168 lies between @xmath172 and @xmath173 . when neutrinos are degenerate , @xmath168 lies between @xmath155 and @xmath174 . the exact value depends on the state of degeneracy of the matter , which determines both the mean energy of the particles participating on the reaction and the phase space available for the scattered particles @xcite . regardless of the neutrino / matter particular state of degeneracy , it is a general result that highly energetic neutrinos ( @xmath175 ) will lose on average half their initial energy in each scattering process , a result previously known for the case of neutrino - electron scattering when neutrinos are nondegenerate @xcite , and which we extend here for degenerate neutrinos as well . on the other hand , very low - energetic neutrinos can gain on average several times their initial energy in a given scattering process and it is in this energy regime that neutrino - strange quark and neutrino - electron scatterings differ . it can be seen that low - energetic neutrinos tend to gain more energy from electrons ( and from up and down quarks ) than from strange quarks . figs . [ fig:16 ] and [ fig:17 ] show the neutrino mean scattering angle . less energetic neutrinos will scatter on average by an angle of about @xmath176 degrees . in association with figs . [ fig:14 ] and [ fig:15 ] , this indicates not only high energy transfer but also high momentum transfer . the mean scattering angle decreases as the energy of the incident neutrino increases , as shown in fig . [ fig:16 ] , meaning a more isotropic scenario . when @xmath177 approaches the target s chemical potential , we see a local peak in @xmath117 . more highly energetic neutrinos will on average scatter almost equally on any direction , resulting in small mean scattering angles . when the matter is known to be completely degenerate , it is possible to find approximate expressions for the neutrino mean free paths with respect to the processes of absorption and of scattering , considering that the momenta of all matter constituents are fixed at their fermi surface values . neutrinos , on their turn , are considered to be either completely degenerate or nondegenerate . for the absorption of degenerate neutrinos , it is found @xcite @xmath178&\nonumber\\ & \times\left[1+\frac{1}{2}\frac{p_{f_e}}{p_{f_u}}+\frac{1}{10 } \left(\frac{p_{f_e}}{p_{f_u}}\right)^2\right],\end{aligned}\ ] ] where @xmath179 is the fermi momentum of particle species @xmath17 . ( [ eq : iw1982_abs_dnu ] ) is suitable for the case @xmath180 . in the opposite situation , i.e. , when @xmath181 , the appropriate mean free path is obtained through the replacements @xmath182 and @xmath183 . for the absorption of nondegenerate neutrinos , it is found @xmath184 the strong coupling constant , @xmath6 , makes it appearance in eq . ( [ eq : iw1982_abs_ndnu ] ) through the lowest - order corrections to the quarks chemical potentials due to quark - gluon strong interaction @xmath185 necessary to make the reaction kinematically allowed , since the masses of the @xmath118 and @xmath50 quarks are small and the neutrino momentum is not expected to play any significant role in the momentum conservation when they are nondegenerate , and hence , excluded from the momentum - conservation delta function @xcite . the influence of the neutrino state of degeneracy on neutrino - electron scattering has been analyzed to great extent . the inverse neutrino mean free path for degenerate neutrinos for this process has been found to be approximately @xcite @xmath186\sqrt{\frac{\mu_\nu}{p_{f_e}}x_e } & \nonumber\\ & \times\left[\left(c_{v , e}^2+c_{a , e}^2\right)\left(10+x_e^2\right)+10c_{v , e}c_{a , e}x_e\right],\end{aligned}\ ] ] for @xmath149 . here , @xmath187 @xmath188 and @xmath189 . approximate expressions for neutrino - electron scattering for nondegenerate neutrinos were found for different neutrino energy regimes @xcite @xmath190 \frac{n_e\sigma_0}{6m_e^2}e_\nu p_{f_e}\end{aligned}\ ] ] for @xmath191 , and @xmath192 \frac{n_i\sigma_0}{40 m_e^2}\frac{e_\nu^3}{p_{f_e}},\end{aligned}\ ] ] for @xmath193 . neglecting the quark masses , the same results of eqs . ( [ eq : iw1982_scatt_dnu])-([eq : iw1982_scatt_ndnu_low ] ) are expected to be valid for neutrino - quark scattering , with appropriate coupling constants . it is important to note that in all of eqs . ( [ eq : iw1982_abs_dnu])-([eq : iw1982_scatt_ndnu_low ] ) it is assumed that also electrons are completely degenerate . tubbs & schramm show approximations for neutrino - electron scattering when both neutrinos and electrons are nondegenerate @xcite . in fig . [ fig:18 ] we show a comparison between full numeric results and analytic approximations of eqs . ( [ eq : iw1982_abs_dnu ] ) and ( [ eq : iw1982_abs_ndnu ] ) for the process @xmath194 . in the case of degenerate neutrinos , we have divided the numeric results by the factor @xmath195 , already included in the analytic results . in the nondegenerate case , we have used @xmath196 in eq . ( [ eq : iw1982_abs_ndnu ] ) ( with @xmath111 in the thermodynamic potential of quark matter ) . larger values for @xmath6 may result in better agreement with the numeric results for @xmath197 for this particular combination of temperature and density , but the same value for the strong coupling constant will not always give the better results for higher temperatures or densities for a given bag constant . using eq . ( [ eq : iw1982_abs_ndnu ] ) requires then fixing @xmath6 to an optimal value , whenever this is physically acceptable , so the approximation may give the best results in its domain of validity . ( [ eq : iw1982_abs_dnu ] ) , for absorption of degenerate neutrinos , on the other hand is shown to give good results only on the vicinity of @xmath157 and the results are better the higher the neutrino degeneracy is . in the upper panels of fig . [ fig:19 ] we compare the results given by eqs . ( [ eq : iw1982_scatt_ndnu_high ] ) and ( [ eq : iw1982_scatt_ndnu_low ] ) with the numeric results for the indicated scattering processes of nondegenerate neutrinos . it is clear that the range of energies @xmath198 is in general not covered by the approximations . for the case of neutrino - electron scattering , eq . ( [ eq : iw1982_scatt_ndnu_high ] ) gives the better results for the whole range of energies , even though its domain of validity is @xmath199 . nonetheless , it must be noticed that , in this case , results share only the same order of magnitude and , roughly , the same qualitative behavior . in the lower panels of of fig . [ fig:19 ] , we show how the results of eq . ( [ eq : iw1982_scatt_dnu ] ) compare to the exact results . as in the case of absorption , the results are better for @xmath177 near @xmath155 , nonetheless , the approximate results are in good qualitative agreement and same order of magnitude as the exact results also for @xmath200 . in the panel of the middle , we show how the strange quark mass affects the scattering cross section . using the approximate mean free paths given by eqs . ( [ eq : iw1982_abs_dnu])-([eq : iw1982_scatt_ndnu_low ] ) , we calculate the neutrino rosseland mean free path and compare the results against exact calculations . since we considered only the cases of either highly degenerate or completely nondegenerate neutrinos , we did not use any interpolating procedure to join the different regimes , such as the one suggested by @xcite . also , it must be noted that , for scatterings of nondegenerate neutrinos , only eq . ( [ eq : iw1982_scatt_ndnu_low ] ) was used . even though an interpolating scheme to join smoothly eqs . ( [ eq : iw1982_scatt_ndnu_high ] ) and ( [ eq : iw1982_scatt_ndnu_low ] ) can be proposed , this is not expected to improve the results too much , since this energy range is strongly cut - off by the factor @xmath201 . the results shown in fig . [ fig:20 ] reflect the fact that the approximations are , in general , good only on a limited range of neutrino energies . as one would expect , the analytic approximations of eqs . ( [ eq : iw1982_abs_dnu])-([eq : iw1982_scatt_ndnu_low ] ) imply in generally poor agreement with exact results of energy - averaged opacities . notoriously , the results are better for degenerate neutrinos . this can be understood from the fact that the approximations to the mean free paths tend to be better for neutrino energies near @xmath155 and the integrands of eq . ( [ eq : lambda_ross ] ) are highly weighted in the same region . nevertheless , even in this case , the results agree only by order of magnitude and they share roughly the same qualitative behavior .

our numerical results for the neutrino mean free paths are compared against known analytic approximations . we conclude that neutrino scattering constitutes a significant portion of the total neutrino opacity in leptonized quark matter and neutrino - quark scattering is , in general , very similar to neutrino - electron scattering with respect to both mean energy transfer per scattering and mean scattering angle .

we perform an extensive analysis of neutrino diffusion in quark matter within the mit bag model at arbitrary temperature and degeneracy . we examine in detail the contribution of each of the relevant weak interaction processes to the total neutrino opacity and evaluate the effect of the strange quark mass , the bag constant , and the qcd perturbative corrections to the mit bag model . we also investigate the anisotropic contribution to the neutrino distribution function in scatterings , the mean energy transfer and the mean scattering angle . the density and temperature dependence of the diffusion coefficients that govern the cooling and deleptonization of a compact star is shown in detail . finally , our numerical results for the neutrino mean free paths are compared against known analytic approximations . we conclude that neutrino scattering constitutes a significant portion of the total neutrino opacity in leptonized quark matter and neutrino - quark scattering is , in general , very similar to neutrino - electron scattering with respect to both mean energy transfer per scattering and mean scattering angle .

hep-ph9511204

i

@xmath5 colliders have made important contributions to our understanding of the electroweak interactions@xcite and it is expected that this tradition will continue with the advent of higher luminosity and higher energy machines . in the near future the cern lep-200 @xmath5 collider@xcite will begin operation and beyond that there is a growing effort directed towards the design and construction of future high energy @xmath5 linear colliders with @xmath22 gev which we will refer to generically as the next linear collider ( nlc)@xcite . one of the primary physics goals of lep-200 and an important goal of the nlc is to make precision measurements of @xmath3 boson properties including @xmath23 , @xmath24 , and @xmath3-boson interactions with fermions and the photon and @xmath25 . the latter measurements , that of the trilinear gauge boson vertices ( tgv s ) provides a stringent test of the gauge structure of the standard model@xcite . the current measurement of these couplings are rather weak . using a popular parametrization of the cp conserving gauge boson couplings , indirect measurements of tgv s via radiative corrections to precision electroweak measurements@xcite give the following limits@xcite : @xmath26 , @xmath27 , @xmath28 , @xmath29 , and @xmath30 . however , there are ambiguities in these calculations associated with running the couplings down from the scale of new physics to low energy so that these limits are not particularly rigorous and it is necessary to use direct measurements for more reliable bounds . the cdf and d0 collaborations at the tevatron @xmath31 collider at fermilab , using the processes @xmath32 , have obtained the direct 95% c.l . limits of @xmath33 , @xmath34 , @xmath35 , and @xmath36 @xcite . these measurements are quite weak but it is expected that they will improve as the luminosity of the tevatron increases . in the longer term measurements at the large hadron collider at cern will improve these limits considerably@xcite . it is expected that measurements at high energy @xmath5 colliders will surpass those at the hadron colliders . as a result , many processes have been studied to determine their usefulness for measuring the tgv s ; @xmath37 @xcite , @xmath38 @xcite , @xmath39@xcite , @xmath40 @xcite , @xmath41@xcite , @xmath42 @xcite and more detailed studies of various four fermion final states in the process @xmath43 @xcite . probably the most useful of the @xmath42 channels for these studies is @xmath44 . with only one unobserved neutrino this channel has several advantages : it can be fully reconstructed using the constraint of the initial beam energies , the @xmath45 and @xmath46 can be discriminated using lepton charge identification , it does not have the qcd backgrounds that plague the fully hadronic decay modes , and it offers much higher statistics than the fully leptonic modes . as a result of the importance of this channel there have been numerous studies of this process . in particular , there is a growing list of analysis of @xmath47 , @xmath5 to four fermion final state processes @xcite , single @xmath3 production@xcite , electroweak radiative corrections to these reactions including the important contribution from initial state radiation @xcite , and the sensitivity of these processes to anomalous @xmath1 and @xmath48 gauge boson couplings ( tgv s ) . in this paper we examine in detail the four fermion final state @xmath49 where @xmath50 is either @xmath51 or @xmath52 and @xmath53 can be either @xmath54 or @xmath55 . we study this process for the centre of mass energies @xmath4 gev appropriate to lep200 , and @xmath6 and 1000 gev appropriate to the nlc . to obtain results we included all tree level diagrams to the four fermion final states using helicity amplitude techniques . for the @xmath56 final state 10 diagrams contribute and for the @xmath57 final state 20 diagrams contribute . our primary interest is to study the sensitivity of these processes to anomalous gauge boson couplings . to do so we examined numerous distributions . for the purpose of comparing theory to experiment we also examined the question of whether the approximation of only including the resonant diagrams is adequate or whether the full four - fermion final state calculation is needed . using helicity amplitudes we are able to study the usefulness of initial state polarization in extracting the tgv s . in the @xmath58 final state single @xmath3 production can also be studied@xcite where the @xmath1 vertex can be isolated from the @xmath2 vertex by imposing an appropriate cut on the outgoing electron . in this case , when only hadronic jets are observed and not the outgoing lepton , there are ambiguities in identifying the charge of the @xmath3 besides problems with hadronic backgrounds which we do not deal with here . a detailed analysis of single @xmath3 production will be presented elsewhere @xcite . in the next section we discuss effective lagrangians and the various parametrizations used to describe gauge boson self interactions which have appeared in the literature . in section iii we describe our calculation . section iv comprises the bulk of the paper which is used to present and discuss our results . we summarize our conclusions in section v.

we performed a detailed analysis of the process where we included all tree level feynman diagrams that contribute to this final state . we concentrated on lep-200 energies , taking gev , and energies appropriate to the proposed next linear collider ( nlc ) , a high energy collider with center of mass energies and 1 tev . at 175 gev 8888 , succ . centre - ville , montral , qubec , canada , h3c 3p8

we performed a detailed analysis of the process where we included all tree level feynman diagrams that contribute to this final state . we studied the sensitivity of this process to anomalous trilinear gauge boson couplings of the and vertices using two popular parametrizations . we used a maximum likelihood analysis of a five dimensional differential cross - section based on the and decay product angular distributions . we concentrated on lep-200 energies , taking gev , and energies appropriate to the proposed next linear collider ( nlc ) , a high energy collider with center of mass energies and 1 tev . at 175 gev , can be measured to about , to and to , to and to . at 95% c.l . assuming 500 pb integrated luminosity . although these will be improvements of existing measurements they are not sufficiently precise to test the standard model at the loop level and are unlikely to see deviations from sm expectations . at 500 gev with 50 fb integrated luminosity , can be measured to about , and to and and to at 95% c.l . while at 1 tev with 200 fb integrated luminosity , and can be measured to about and respectively . the 500 gev measurements will be at the level of loop contributions to the couplings and may show hints of new physics while the 1 tev should be sensitive to new physics at the loop level . w - pair production in the process + and measurement of the and couplings ottawa - carleton institute for physics + department of physics , carleton university , ottawa canada , k1s 5b6 dpartement de physique , universit du qubec montral + c.p . 8888 , succ . centre - ville , montral , qubec , canada , h3c 3p8

hep-ph9511204

c

we performed a detailed analysis of the measurement of tri - linear gauge boson couplings in the process @xmath220 . we included all tree level contributions to this final state and included finite gauge boson width effects . the off - shell @xmath3 contributions contribute from 20% for the @xmath179 mode at lep200 to 30% and 100% for the electron mode at a 500 gev and 1 tev nlc respectively ( with the kinematic cuts we used ) . clearly , the non - resonant contributions must be included to properly account for the experimental situation . to gauge the sensitivity of this process to anomalous gauge boson couplings we used the @xmath3 decay distributions as a polarimeter to distinguish the longitudinal @xmath3 modes , which are more sensitive to anomalous coupings , from the transverse modes . we implemented this through the use of a quintic differential cross section , with each angular variable divided into 4 bins , and then calculating the likelihood function of non - standard model couplings as compared to the standard model . using this approach we found that at lep200 operating at 175 gev and assuming integrated luminosity of 500 pb@xmath14 , @xmath7 @xmath9 , @xmath10 , @xmath12 , and @xmath13 could be measured to roughly @xmath8 and @xmath180 and @xmath181 to @xmath221 and @xmath222 respectively . it is extremely unlikely that measurements of this precision would reveal anomalous couplings . at a 500 gev nlc with an integrated luminosity of 50 fb@xmath14 , @xmath7 , @xmath18 and @xmath19 , could be measured to roughly @xmath15 , @xmath16 and @xmath223 respectively and @xmath180 and @xmath181 to @xmath224 and @xmath197 respectively . at the 1 tev nlc with 200 fb@xmath14 the corresponding numbers are @xmath225 , @xmath226 , @xmath227 and @xmath228 . the 500 gev nlc measurements are sensitive enough that they should be sensitive to loop contributions to the tgv s while the 1 tev will be able to measure such effects . we studied the sensitivity of the off - mass shell cross sections to anomalous couplings by imposing kinematic cuts on the invariant mass distributions of the outgoing fermion pairs . a cursory analysis found that the off - resonance cross section is relatively sensitive to anomalous couplings and that useful information could be extracted from this region of phase space . although the inclusion of @xmath3 decays to fermions and the non - resonant diagrams does not alter the precision to which the tgv s can be measured they do change the cross sections and kinematic distributions at the same level as radiative corrections and must be taken into account for an accurate comparison between experiment and theory . the optimal strategy to maximize the information contained in each event is to construct a likelihood function based on the four vector of each of the outgoing fermions on an event by event basis , putting them through a realistic detector simulation . this would make the best use of the information whether it be on the @xmath3 resonance or not . kinematic cuts should only be introduced to reduce backgrounds . since the precision of these measurements is beyond the level of loop induced radiative corrections it is crucial that radiative corrections are well understood and included in event generators used in the study of these processes . progress is being made along these lines as exemplified by the monte carlo event generators ; excalibur @xcite , whopper , @xcite eeww @xcite , wwf @xcite , and wwgenp @xcite . the authors benefited greatly from many helpful conversations , communications , and suggestions during the course of this work with tim barklow , genevieve blanger , pat kalyniak , dean karlen , and paul madsen . this research was supported in part by the natural sciences and engineering research council of canada and les fonds fcar du quebec . d. schaile , _ proceedings of the xxvii int . conf . on high energy physics _ , bussey , i.g . knowles , glasgow , uk , 20 - 27 july 1994 ( inst . of physics publishing , 1995 ) p. 27 . k. hagiwara _ et al _ , nucl b282 * , 253 ( 1987 ) . d. zeppenfeld , phys . let . * 183b * , 380 ( 1987 ) ; d. treille _ et al _ , proceedings of the ecfa workshop on lep 200 , ed . a. bhm and w. hoogland , aachen ( 1986 ) , cern 87 - 08 , vol.2 , p.414 . dicus , k. kallianpur , phys . rev . * d32 * , 35 ( 1985 ) ; m.j . duncan , g.l . kane , phys . lett . * 55 * , 773 ( 1985 ) ; e.n.argyres and c.g.papadopoulos , phys . b263 * , 298(1991 ) . g.kane , j. vidal , c.p . yuan , phys . rev . * d39 * , 2617 ( 1990 ) , and references therein . some recent reviews on physics at high energy @xmath5 colliders are : m. peskin , proceedings of the 1987 slac summer institute on particle physics , slac - pub-4601 ( 1988 ) ; d. treille , proceedings of the workshop on physics and experiments with linear @xmath5 colliders , waikoloa hawaii , april 1993 ( world scientific ; in press ) ; a. djouadi and p.m. zerwas , proceedings of _ beyond the standard model iii _ , ed . s. godfrey and p. kalyniak , ottawa canada , june 1992 , ( world scientific , singapore , 1993 ) p. 204 . a. miyamoto , proceedings of workshop on physics and experiments with linear @xmath5 colliders , waikoloa , hawaii , ed . f.a . harris , s.l . olsen , s. pakvasa , and x. tata , ( world scientific , singapore , 1994 ) p 141 . b. wiik , proceedings of the workshop on physics and experiments with linear @xmath5 colliders , waikoloa hawaii , ed . f.a . harris , s.l . olsen , s. pakvasa , and x. tata , ( world scientific , singapore , 1994 ) . proceedings of the first workshop on japan linear collider ( jlc ) , kek , oct 24 - 25 , 1989 , kek report 90 - 2 ( 1990 ) ; 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a. de rjula , m.b . gavela , p. hernandez and e. mass , nucl . phys . * b384 * , 3 ( 1992 ) d. zeppenfeld , j.a.m . vermaseren and u. baur , nucl . phys . * b375 * , 3 ( 1992 ) . u. baur and d. zeppenfeld , mad / ph/878 . r. kleiss and w. j. stirling , nucl . * b262 * , 235 ( 1985 ) ; z.xu d .- h.zhang l. chang nucl . phys . * b291 * , 392 ( 1987 ) . see for example v. barger and r. phillips , _ collider physics _ , ( addison - wesley publishing company , 1987 ) . m. peskin , proceedings of the 1987 slac summer institute on particle physics , slac - pub-4601 ( 1988 ) . burke , proceedings of the 1990 slac summer institute on particle physics , slac - pub-5418 ( 1991 ) . h. anlauf _ proceedings of workshop on physics and experiments with linear @xmath5 colliders , waikoloa , hawaii , ed . f.a . harris , s.l . olsen , s. pakvasa , and x. tata , ( world scientific , singapore , 1994 ) p 708 . g. montagne , o. nicrosini , f. piccinini , comp . . commun . * 90 * , 141 ( 1995 ) . lccccccc mode & @xmath180 & @xmath181 & @xmath232 & @xmath233 & @xmath234 & @xmath12 & @xmath13 + + @xmath179 & @xmath235 & @xmath236 & @xmath237 & @xmath238 & @xmath239 & @xmath240 & @xmath241 + @xmath178 & @xmath242 & @xmath243 & @xmath244 & @xmath245 & @xmath246 & @xmath247 & @xmath248 + combined & @xmath249 & @xmath250 & @xmath251 & @xmath252 & @xmath253 & @xmath254 & @xmath255 + + @xmath179 & @xmath256 & @xmath257 & @xmath258 & @xmath259 & @xmath16 & @xmath16 & @xmath260 + @xmath178 & @xmath256 & @xmath257 & @xmath261 & @xmath259 & @xmath16 & @xmath16 & @xmath260 + combined & @xmath262 & @xmath256 & @xmath263 & @xmath264 & @xmath223 & @xmath223 & @xmath223 + + @xmath179 & @xmath265 & @xmath266 & @xmath15 & @xmath267 & @xmath268 & @xmath267 & @xmath267 + @xmath178 & @xmath265 & @xmath266 & @xmath15 & @xmath267 & @xmath268 & @xmath267 & @xmath267 + combined & @xmath269 & @xmath270 & @xmath271 & @xmath268 & @xmath272 & @xmath273 & @xmath273 + ccccccccc initial state & cut & @xmath180 & @xmath181 & @xmath274 & @xmath233 & @xmath234 & @xmath12 & @xmath13 + + @xmath140 & @xmath275 gev & @xmath276 & @xmath277 & @xmath278 & @xmath279 & @xmath280 & @xmath281 & @xmath282 + + @xmath206 & @xmath283 gev & @xmath284 & @xmath285 & @xmath286 & @xmath287 & @xmath288 & @xmath289 & @xmath290 + @xmath291 & @xmath283 gev & @xmath292 & @xmath292 & @xmath293 & @xmath294 & @xmath295 & @xmath296 & @xmath297 + @xmath140 & @xmath283 gev & @xmath298 & @xmath299 & @xmath300 & @xmath301 & @xmath302 & @xmath303 & @xmath304 + + @xmath206 & @xmath283 gev & @xmath305 & @xmath306 & @xmath307 & @xmath308 & @xmath309 & @xmath310 & @xmath311 + @xmath291 & @xmath283 gev & @xmath292 & @xmath312 & @xmath313 & @xmath314 & @xmath315 & @xmath316 & @xmath316 + @xmath140 & @xmath283 gev & @xmath317 & @xmath318 & @xmath319 & @xmath320 & @xmath316 & @xmath311 & @xmath311 +

we studied the sensitivity of this process to anomalous trilinear gauge boson couplings of the and vertices using two popular parametrizations . we used a maximum likelihood analysis of a five dimensional differential cross - section based on the and decay product angular distributions . although these will be improvements of existing measurements they are not sufficiently precise to test the standard model at the loop level and are unlikely to see deviations from sm expectations . at 500 gev with 50 fb integrated luminosity , can be measured to about , and to and and to at 95% c.l . while at 1 tev with 200 fb integrated luminosity , and can be measured to about and respectively . the 500 gev measurements will be at the level of loop contributions to the couplings and may show hints of new physics while the 1 tev should be sensitive to new physics at the loop level . w - pair production in the process + and measurement of the and couplings ottawa - carleton institute for physics + department of physics , carleton university , ottawa canada , k1s 5b6 dpartement de physique , universit du qubec montral + c.p .

we performed a detailed analysis of the process where we included all tree level feynman diagrams that contribute to this final state . we studied the sensitivity of this process to anomalous trilinear gauge boson couplings of the and vertices using two popular parametrizations . we used a maximum likelihood analysis of a five dimensional differential cross - section based on the and decay product angular distributions . we concentrated on lep-200 energies , taking gev , and energies appropriate to the proposed next linear collider ( nlc ) , a high energy collider with center of mass energies and 1 tev . at 175 gev , can be measured to about , to and to , to and to . at 95% c.l . assuming 500 pb integrated luminosity . although these will be improvements of existing measurements they are not sufficiently precise to test the standard model at the loop level and are unlikely to see deviations from sm expectations . at 500 gev with 50 fb integrated luminosity , can be measured to about , and to and and to at 95% c.l . while at 1 tev with 200 fb integrated luminosity , and can be measured to about and respectively . the 500 gev measurements will be at the level of loop contributions to the couplings and may show hints of new physics while the 1 tev should be sensitive to new physics at the loop level . w - pair production in the process + and measurement of the and couplings ottawa - carleton institute for physics + department of physics , carleton university , ottawa canada , k1s 5b6 dpartement de physique , universit du qubec montral + c.p . 8888 , succ . centre - ville , montral , qubec , canada , h3c 3p8

astro-ph9912427

i

an increasingly large number of investigations has recognized the importance of dwarf spheroidal galaxies for our understanding of galaxy formation and evolution ( see mateo @xcite and da costa @xcite for recent reviews ) . while new studies of the central , densest regions of the more distant local group galaxies have benefited from the exceptional resolution of hst , the nearby dwarf spheroidal satellites of the milky way can still be investigated in great detail using ground based wide - field data . thanks to recent improvements in detector efficiency ( in particular , in the blue part of the optical spectrum ) and size , cmd s with long color baselines and high statistical significance can be obtained in affordable exposure times . the fornax dwarf spheroidal ( dsph ) galaxy represents one of the most interesting cases for studying the complexity of stellar populations in dwarf galaxies . this galaxy was one of the first dsph in which an intermediate age population was detected . the presence of upper asymptotic giant branch ( agb ) stars , brighter and redder than the tip of the red giant branch ( rgb ) , indicated that about @xmath16 of the galaxy could be of intermediate age ( 2 to 8 gyr ) ( aaronson & mould @xcite , @xcite ) . surveys for agb stars led to discovery of 111 carbon stars , for which follow up near - infrared photometry indicated a wide range of bolometric luminosities , a mass dispersion among the progenitors , and hence an age spread ( frogel et al . @xcite ; westerlund et al . @xcite ; lundgren @xcite ; azzopardi et al . fornax is also known to contain a planetary nebula whose abundance patterns are consistent with an origin from a second or third generation star ( danziger et al . @xcite ; maran et al . the presence of such an intermediate - age population is confirmed by a conspicuous red hb clump ( demers et al . @xcite ; stetson et al . @xcite ) . most recently , an hst study of a central fornax field sampling the main - sequence turnoffs of the intermediate - age and old populations has been carried out by buonanno et al . ( @xcite ) . the analysis of the resulting cmd has shown evidence for a star formation starting about 12 gyr ago and continuing until 0.5 gyr ago . a variable star formation rate is revealed by gaps between separate subgiant branches , and major star formation episodes probably occurred nearly 2.5 , 4 , and 7 gyr ago . also , fornax certainly harbors an old stellar population , since it contains five globular clusters whose ages do not differ from those of m68 and m92 ( buonanno et al . @xcite ; smith et al . @xcite ) , except perhaps for cluster 4 that appears to be 2 - 3 gyr younger ( buonanno et al . @xcite ) . these clusters have unusually red horizontal branches for their low metallicity , with no counterparts in the outer galactic halo or the magellanic clouds . also for cluster 4 , the recent wfpc2 color - magnitude diagrams of buonanno et al . ( @xcite ) unambiguously indicate a low metallicity , [ fe / h]@xmath17 , although integrated spectra pointed to a metallicity similar to that of field stars ( beauchamp et al . an old population is present among the field stars of fornax as well , as demonstrated by detection of a red horizontal branch slightly fainter than the red clump , and of rr lyrae variables ( buonanno et al . @xcite ; stetson et al . @xcite , hereafter shs98 ) . fornax also hosts a significant population of young stars . buonanno et al . ( @xcite ) had already noticed a handful of faint blue stars in their cmd of the fornax field , tentatively explained as belonging to a @xmath18 yr population ( cf . also gratton et al . @xcite ) . the deeper cmd of beauchamp et al . ( @xcite ) clearly revealed a young main - sequence , and comparison with theoretical isochrones indicated recent star formation . the brightest turnoff was located at @xmath19 , implying a minimum age of @xmath20 yr . this young population is best shown by the recent wide - area survey of shs98 . notwithstanding this young stellar component , fornax appears to be devoid of any interstellar medium ( ism ) . a large - area search for neutral hydrogen has given no detectable hi emission or absorption ( young @xcite ) , the upper limit for hi emission being @xmath21 @xmath22 at the galaxy center . thus the interstellar medium that must have been present a few @xmath23 yr ago to form stars , appears to be all gone . there is also the possibility that the ism has been ionized and heated up by the interstellar uv field . however , this hypothesis conflicts with the lack of detection of x - ray emission in the direction of fornax ( gizis et al . the various stellar subpopulations in fornax have different spatial distributions , which have been carefully investigated by shs98 . the oldest population , represented by the rr lyrae variables , has the most extended distribution . the intermediate - age stars ( red clump stars ) are more centrally concentrated , while the young population of blue ms stars , as well the reddest agb ( carbon ) stars , are even more concentrated in a bar - like distribution roughly aligned in the ew direction , with the brightest stars located at the ends of the bar . also the red clump population displays an asymmetrical structure ( cf . hodge @xcite ; eskridge @xcite ; demers et al . @xcite ) , with a peculiar `` crescent '' shape ( shs98 ) . despite all these pieces of knowledge accumulated in recent years , the star formation history of fornax is not yet fully understood . several questions need to be answered before a reconstruction of the star formation and chemical enrichment history of fornax can be attempted . the metallicity should be measured for stellar populations of different age and location within the galaxy , so as to determine the run of metal enrichment as a function of time . the star formation history needs to be evaluated using critical features in the cmd as tracers of star formation at different epochs , to understand to what extent star formation proceeded continuously or in bursts , and how it propagated throughout the body of the galaxy . the nature of the wide red giant branch ( rgb ) is still quite puzzling , though all previous investigations agree on the fact that it is broader than expected on the basis of the photometric errors . further , there is a lack of observational data with which to study features such as the rgb and agb bumps or the precise location of central helium - burning stars as a function of age and metal abundance , as a test of stellar evolution models . large field observations of local group dsph galaxies , being able to sample a significant number of stars , can address these issues . with these open questions in mind , we have investigated the stellar populations of fornax as part of a wide - field study of nearby dwarf spheroidals . we present here a large area @xmath24 photometric study of the fornax field , yielding magnitudes and colors for about 40,000 stars down to @xmath25 mag below the horizontal branch , in four regions located at different distances from the galaxy center . the use of standard passbands , together with the size of our stellar sample , allowed us to derive the basic physical properties of fornax with high accuracy and measure details in its cmd that trace the less numerous populations and faster evolutionary phases . in particular , the @xmath26 band turned out to be invaluable for studying the hot stars , be they old or young , whereas the wide baseline of the @xmath9 color provides the best resolution of the different evolutionary phases in the color - magnitude diagrams ( cf . smecker - hane et al . @xcite ; held et al . @xcite ) . also , the availability of a comparison field allowed us to estimate the foreground and background contamination . the present photometry will be the input database to model the star formation history ( sfh ) of fornax ( held et al . , in preparation ) using population synthesis techniques . the paper is organized as follows . the observations and data reduction are presented in sect . [ sec_obsred ] . in sect . [ sec_cmd ] we present @xmath27 , @xmath9 color - magnitude diagrams of the fornax field stars and discuss several interesting features with the help of theoretical isochrone fitting . the @xmath27 , @xmath28 luminosity function is derived in sect . [ sec_lf ] and used to estimate the distance to fornax . this is confirmed by an independent distance estimate based on the @xmath27 luminosity of old - hb stars ( sect.[sec_disthb ] ) . in sect . [ sec_metal ] we compare the cmd of fornax with template globular cluster rgb sequences using the standard @xmath29 colors , and discuss the mean abundance and age of the dominant population . the color distribution of red giant stars in fornax is analyzed in detail in sect . [ sec_coldistrib ] , where the size of an intrinsic abundance spread is discussed . some light on the nature of the wide rgb of fornax is shed by a comparison of the spatial gradient of different populations ( sect . [ sec_popratios ] ) . our results and conclusions are summarized in sect . [ sec_conclu ] .

the large baseline of the colors together with the size of the stellar sample allowed us to analyze in detail the color distribution of the red giant stars . while these stars could be either old or young red giants , we show that their spatial distribution is consistent with the radial gradient of old horizontal branch stars , and completely different from that of the younger population . this result clarifies the nature of the red giant branch of fornax , suggesting that its exceptional color width is due to the presence of two main populations yielding a large abundance range ( } < -0.7 $ ] ) .

we present ccd photometry of about 40000 stars in four regions of the fornax dwarf spheroidal galaxy down to , the largest three - color data set obtained for this galaxy until now . the resultant color - magnitude diagrams , based on a wide color baseline , show a variety of features tracing the history of star formation of this dwarf galaxy . one of the most distinctive features in our diagrams is the conspicuous young main sequence , indicating recent star formation until approximately yr ago . a plume of stars brighter than the red hb clump , with , trace the helium - burning phase of the young population . a comparison of the color and extension of this feature with model isochrones suggests a relatively metal - rich population ( [ fe / h] ) with age 300400 myr . this represents an important constraint for understanding the chemical enrichment history of fornax . an extended upper agb tail and a prominent red hb clump sign the presence of the well - known dominant intermediate - age population with an age range 2 - 10 gyr , for which we have estimated a mean age . about 0.2 mag below the red clump , an extended hb is indicative of an old population . we show that blue hb stars may be present in the outer regions . together with previous detection of rr lyrae , this provides evidence for a minority field population that is as old and metal - poor as that in the fornax globular clusters . we have identified the agb bump , a clustering of stars that occurs at the beginning of helium shell - burning evolution , at a luminosity . this is an example of the short - lived evolutionary phases that can be revealed in stellar populations using adequately large star data samples , whose measurements provide powerful tests of theoretical models . based on precise detection of the tip of the rgb in a selected rgb sample , we measure a corrected distance modulus . an independent estimate of the distance to fornax was also obtained from the mean magnitude of old horizontal branch stars , yielding a distance modulus , in good agreement with the distance estimated from the red giant branch tip and previous results . the large baseline of the colors together with the size of the stellar sample allowed us to analyze in detail the color distribution of the red giant stars . we find that it can be approximately described as the superposition of two populations . the dominant component , comprising% of the red giant stars , consists of relatively metal - enriched intermediate - age stars . its mean metallicity is [ fe / h]= , based on a comparison of the fiducial locus of the bulk of the fornax red giants with the homogeneous galactic globular cluster set of da costa & armandroff ( ) . once the younger mean age of fornax is taken into account , our best estimate for the mean abundance of the bulk of the galaxy is [ fe / h] . the dominant intermediate - age component has an intrinsic color dispersion mag , corresponding to a relatively low abundance dispersion , } = 0.12 \pm 0.02 $ ] dex . further , there is a distinct small population of red giants on the blue side of the rgb . while these stars could be either old or young red giants , we show that their spatial distribution is consistent with the radial gradient of old horizontal branch stars , and completely different from that of the younger population . this unambiguously qualifies them as old and metal - poor . this result clarifies the nature of the red giant branch of fornax , suggesting that its exceptional color width is due to the presence of two main populations yielding a large abundance range ( } < -0.7 $ ] ) . this evidence suggests a scenario in which the fornax dsph started forming a stellar halo and its surrounding clusters together about 1013 gyr ago , followed by a major star formation epoch ( probably with a discontinuous rate ) after several gyr .

astro-ph9912427

c

the red giant luminosity function ( lf ) and distance to fornax was derived using stars within @xmath101 from the fiducial sequence . as shown in sect . [ sec_coldistrib ] , this implies selecting the dominant stellar population in fornax . luminosity distributions were obtained both in @xmath27 and in @xmath28 by counting stars in 0.2 mag bins down to below the red clump . since at these bright magnitudes our photometry is virtually complete , there was no need to correct the observed lf s for incompleteness . foreground and background contamination is not a concern , either , because the number of field objects in the proximity of the rgb is negligible . the cutoff in the @xmath28 luminosity function corresponding to the maximum luminosity reached by red giants before they ignite the he burning , has proven to be a good distance indicator ( madore & freedman @xcite ; see also salaris & cassisi @xcite ) . we measured the @xmath28 magnitude of the rgb tip separately for our 4 fornax fields , following the methods of lee et al . ( @xcite ) . the mean of the four values is @xmath102 . although the scatter of the individual measurements is small ( @xmath103 mag ) , we have adopted a larger uncertainty to take into account both the intrinsic precision of the tip detection method , which is about a half of the 0.2 mag bin , and the zero point uncertainties . we then calculated the distance to fornax using the relations of da costa & armandroff ( @xcite ) . this procedure , often applied to derive the distance of dwarf galaxies , implicitly assumes that the @xmath28 magnitude of the tip is little affected by age . theoretical models indeed show a dependence of the tip luminosity on the age , but this is more pronounced for very metal - poor populations ( [ fe / h]@xmath104 ) and ages younger than 5 gyr ( e.g. , caputo et al . @xcite ) . the relations of da costa & armandroff ( @xcite ) give the @xmath28 bolometric correction as a function of color of the stars near the rgb tip , and the bolometric luminosity of the tip as a function of metallicity . the dereddened color of the rgb tip in fornax , calculated as the median ( @xmath105 ) within 0.1 mag from the tip , is @xmath106 , where the error reflects the scatter of the values obtained in our four fields plus the absolute zero point uncertainty . we adopted a reddening @xmath107 from burstein & heiles ( @xcite ) , yielding @xmath108 and @xmath109 . the bolometric correction is then @xmath110 , while a metallicity @xmath111 } = { -1.39}\pm { 0.15}$ ] ( cf . [ sec_metal ] ) implies @xmath112 . we thus obtain @xmath113 , and a distance modulus @xmath114 , corresponding to @xmath115 kpc . previous distance estimates range from @xmath116 ( buonanno et al . @xcite ) to 20.76 ( demers et al . @xcite ; buonanno et al . sagar et al . ( @xcite ) found @xmath117 . the present estimate therefore confirms earlier results . this value is also consistent with the distance moduli of fornax globular clusters ( buonanno et al . @xcite ) , yielding an average modulus @xmath118 . using this distance estimate , we plot in fig . [ f_lf ] the @xmath27 luminosity function of the red giant stars in the inner region of fornax . besides the obvious red clump at @xmath119 , we notice the small yet significant peak near @xmath120 that we identify with the agb bump , a clustering of stars that occurs at the beginning of helium shell - burning evolution . gallart ( @xcite ) has recently discussed the presence of this feature in the lmc and m31 where its location agrees with the prediction of stellar evolution models ( bertelli et al . we have measured the location of the agb bump in fornax by performing a gaussian fit to the lf in the region of the bump . we found @xmath121 , where the error is mainly set by the zero point uncertainty . this corresponds to a luminosity @xmath122 , with an additional 0.1 mag uncertainty on the @xmath123 extinction . similarly , we measured a mean @xmath27 magnitude for the red clump @xmath124 mag , corresponding to @xmath125 . thus the detected clump is @xmath126 mag brighter in @xmath27 than the red hb clump . for an assumed age of 5 gyr and the mean metallicity of fornax , these measurements confirm the identification with the agb bump and rule out alternative identifications with the rgb bump . the rgb bump is expected to be near the hb level for a metallicity [ fe / h]@xmath127 and age 5 gyr ( alves & sarajedini @xcite ) . in lyndsay 113 , a 5 gyr old cluster in the small magellanic cloud having metallicity comparable with that of fornax , the rgb bump is found to be @xmath128 mag brighter than hb stars in the same cluster ( mighell et al . clearly , stars in the rgb bump will be outnumbered by the overwhelming red clump . observational data like those presented here for the fornax dwarf are important to constrain evolutionary models , which in turn are necessary to interpret the stellar population of local group galaxies . an independent estimate of the distance to fornax was obtained from the mean level of its old- hb field stars . the mean magnitude of the hb was measured by fitting a gaussian to the @xmath27 mag distribution of the stars in the range @xmath129 , @xmath130 . we necessarily included only the red part of the hb@xmath89 , since the bluer horizontal - branch stars appear to be mixed with the blue stars on the young main sequence . note , however , that we do not include any rc stars ( which are brighter than the hb@xmath89 and rr lyrae variables ) . the mean level of the red hb is @xmath131 , where the uncertainty reflects the scatter of the values measured in the different fields ( larger than the formal error on the mean magnitude ) , and the systematic error of the @xmath27 zero point . buonanno et al . ( @xcite ) found a mean level @xmath132 for the hb@xmath89of four globular clusters in fornax . using this value for @xmath133 , and @xmath134 , we calculated the distance modulus of fornax on the lee et al . ( @xcite ) distance scale , using their relation for the absolute visual magnitude of rr lyrae variables , @xmath135 } + 0.82\ ] ] for a helium abundance of @xmath136 . assuming for red hb stars the relatively metal - rich nominal metal content of rgb stars , [ fe / h]@xmath137 , this relation would give @xmath138 mag and a distance modulus @xmath139 for a population with age comparable to that of galactic globular clusters . this uncertainty includes internal and photometric errors only . however , the mean metallicity of the old - hb stars is probably lower . if the old population in fornax is relatively metal - poor , of the order [ fe / h]@xmath140 ( as we suggest in sect.[sec_popratios ] ) , the relation given by lee et al . ( @xcite ) would imply @xmath141 mag and a distance modulus @xmath142 . the level of the red hb ( distinct from the clump ) is probably the result of contributions from stars in a range of ages and metallicities . for this reason we refrained from applying any uncertain correction to convert the measured mean magnitude of the red hb@xmath89 to an equivalent magnitude of rr lyrae variables . further , this distance modulus based on the hb level is affected by the uncertainties on the luminosity of hb stars as a function of age and metallicity . a discussion of the alternative distance scales , however , is beyond the scope of this paper . this measurement of the distance to fornax based on its old horizontal branch star luminosity confirms the distance modulus estimated from the rgb tip . this consistency is not unexpected , since both the rgb tip method of da90 and the hb absolute magnitude obtained for the hb@xmath89 are based on the distance scale of lee et al . ( @xcite ) . these two distance measurements use @xmath28 and @xmath27 magnitudes , respectively , which are observationally independent . the mean metal abundance of the bulk of the fornax population was derived by direct comparison of the red giant branch in the @xmath28 , ( @xmath105 ) color - magnitude diagram with the ridge lines of globular clusters from da costa & armandroff ( @xcite ) ( see fig . [ f_da90 ] ) . our procedure is fully described in paper i and ii , and is only briefly outlined here . in short , we calculated the average color shift , @xmath143 , between the fornax rgb and the galactic cluster fiducial loci . an interpolation of the relation between the mean color shifts and the globular cluster metallicities ( actually a quadratic fit ) provides an estimate of [ fe / h ] for the dwarf spheroidal . this procedure was applied to the @xmath144-selected rgb sample ( cf.sect . [ sec_lf ] ) , in two luminosity intervals ( @xmath145 and @xmath146 ) , yielding a metallicity [ fe / h]@xmath147 and [ fe / h]@xmath148 dex , respectively . the mean of the abundances determined in these two magnitude bins was adopted as our final estimate . the resultant value , [ fe / h]@xmath149 , is in good agreement with previous work . we find no evidence for a metallicity gradient among the regions studied here , to within the errors . however , the measurements of mean abundance based on the color of the rgb are subject to the well - known difficulty in disentangling the effects of age and metallicity on the effective temperature of red giant stars ( the `` age - metallicity degeneracy '' ) . thus we need to estimate the mean age of fornax before discussing further its mean metal abundance . when compared with the predictions of stellar evolution models ( e.g. , bertelli et al . @xcite ; caputo et al . @xcite ) , the position of core he burning stars in color - magnitude diagrams may provide a useful age indicator ( e.g. , caputo et al . @xcite ; girardi @xcite ; and references therein ) . the rc comprises core helium - burning stars of different ages , so that its location bears information on the _ mean age _ of the intermediate age population , weighted by the age distribution function . thus , similarly to what we had done for the hb , we measured the mean @xmath9 color in addition to the @xmath27 luminosity for the red clump . the mean magnitude , already reported above , is @xmath150 mag , corresponding to @xmath125 , in excellent agreement with demers et al . this means that the rc is @xmath151 mag more luminous in @xmath27than the old hb stars , a value that appears consistent with the difference in age of a 13 gyr old population and a 5 gyr old bulk component ( see caputo et al . the clump is quite extended in luminosity ( @xmath152 mag ) , comparable with that of carina ( hurley - keller et al . @xcite ) , but less than that of leo i ( cf . gallart et al . the mean color is @xmath153 . the uncertainties include the field - to - field scatter , comparable with the photometric measurement errors , and the zero - point uncertainty . the relation @xmath154 , obtained from a linear fit to the color - color relations for the fornax red giants in the range @xmath155 , yields @xmath156 . this value shows excellent agreement with the results of buonanno et al . ( @xcite ) . by fitting a parabola to the fiducial points of the rgb , we estimated the interpolated rgb color at the rc level ( @xmath157 mag ) , a value also confirmed by inspection of the wfpc2 color - magnitude diagram ( buonanno et al . the difference in color between the red clump and red giant stars at the same luminosity is then @xmath158 mag , with an estimated uncertainty of 0.02 mag . this result can be compared with the model predictions of girardi ( @xcite ; and priv . comm . ) based on the models of girardi et al . ( @xcite ) , which are in accord with the empirical calibration of hatzidimitriou ( @xcite ) . for a metallicity z=0.001 ( but @xmath159 is relatively independent of abundance for metal - poor populations ) our result is consistent with a mean age of the order @xmath5 gyr . this value is close to the estimate of sagar et al . ( @xcite ) , based on best fitting of yale isochrones , and definitely larger than the age estimated by demers et al ( @xcite ) . most interestingly , the mean age obtained from the clump location appears to be consistent with the presence of ms evolved stars in the same age interval , as observed with hst ( buonanno et al . this results is quite encouraging for application of this age indicator to more distant local group galaxies , whose main - sequence turnoff can not be directly measured . if we now assume a mean age of approximately 5 gyr for the bulk of the fornax stars , the observed rgb color would imply a metallicity significantly larger than the formal result obtained above from a comparison with globular clusters . we have estimated the effects of age by comparing theoretical isochrones of different ages ( e.g. , 5 and 15 gyr ) at a given metallicity ( from bertelli et al . @xcite ) . by measuring the ( @xmath105 ) colors at @xmath160 predicted by model isochrones with z=0.001 ( [ fe / h]@xmath161 ) , we find that a 5 gyr isochrone is bluer by @xmath162 mag than a 15 gyr model isochrone . this effect mimics a metallicity difference of @xmath163 dex using the fiducial loci of globular clusters ( cf . paper ii ; caputo et al . @xcite ; gallart et al . @xcite ) . thus , if the body of fornax stars is @xmath164 gyr old , the measured location of the peak of the rgb is necessarily indicative of a higher mean metallicity , of the order [ fe / h]@xmath165 ( clearly the correction is somewhat model dependent ) . we regard this value as the most appropriate estimate of the mean metal abundance of the dominant stellar population in fornax . with this correction , the fornax metallicity turns out to be very close to that of sagittarius , a dsph which has a comparable total luminosity ( e.g. , bellazzini et al . @xcite ) . ccccccc & & & & & & + 17.20 & 0.082 & 0.067 & 0.024 & 0.029 & 0.078 & 0.060 + 18.20 & 0.063 & 0.077 & 0.036 & 0.042 & 0.052 & 0.065 + 19.20 & 0.088 & 0.093 & 0.061 & 0.073 & 0.063 & 0.058 + one of the main results of this paper , made possible by the size of our stellar sample and photometric baseline , is a detailed analysis of the color distribution function ( cdf ) of the red giant stars in fornax . [ twogauss ] shows the distribution of the ( @xmath166 ) color residuals about a preliminary fiducial sequence , in the magnitude range @xmath167 ( @xmath168 ) , for the inner and outer field . while these histograms confirm the well - known wide color range of the rgb stars in fornax ( e.g. , buonanno et al . @xcite ; sagar et al . @xcite ; grebel et al . @xcite ; beauchamp et al . @xcite ) , they also show that the color distributions can not merely be described using a single `` color dispersion '' . rather , the cdf is more appropriately described as roughly bimodal , showing a principal peak and a bluer component extending to @xmath169 . this color distribution function is quite well modeled by the sum of two gaussians . the main component of the distribution represents the bulk of the red giant population , a mix of old and ( mostly ) intermediate - age stars . the secondary peak is centered at about @xmath170 . on the other hand , we notice a relatively well - defined cutoff on the red side of the rgb , indicating the lack of any significant metal - rich component similar to the stellar population of 47 tuc , or even less metal - rich if we assume a mean age younger than that of milky way globular clusters . this absence sets an important constraint for modeling the chemical enrichment of the fornax dwarf . both components are wider than accounted for by instrumental errors . the dispersions of the two components , in the luminosity range @xmath171 , are @xmath172 ( central peak ) and @xmath173 ( blue component ) in the inner region , and @xmath174 , @xmath175 in the outer field . table [ t_sigmas ] gives the observed dispersions for the main component of the fornax field population for the inner and outer region in 3 magnitude intervals . also given in table [ t_sigmas ] are the instrumental errors @xmath176 obtained by fitting a gaussian to the color residuals of artificial stars , exactly in the same way as for the real data . the observed and instrumental dispersions are also compared in fig . [ f_cfsigmas ] . the intrinsic ( @xmath166 ) color dispersions , calculated as the quadratic difference between the observed and the instrumental scatter , are given in the last two columns of table [ t_sigmas ] . in the luminosity interval @xmath177 the intrinsic color spread of the main rgb population is @xmath178 mag . using again the color - color relations for the fornax red giants to convert ( @xmath179 ) color spreads into equivalent dispersions in ( @xmath105 ) , and the calibration of rgb color shifts as a function of metal abundance variations , we obtained a metallicity spread @xmath14 } = 0.12 \pm 0.02 $ ] dex for the dominant field population . then the ( @xmath144 ) metallicity range for the bulk population of fornax would be approximately @xmath180 } < -1.15 $ ] , or @xmath181 } < -0.75 $ ] if a correction for the mean age is applied . this intrinsic metallicity range is significantly lower than the abundance spread quoted by most previous studies for the red giant branch as a whole . according to beauchamp et al . ( @xcite ) , the total range in [ fe / h ] is 0.8 dex , comparable to that found by sagar et al . ( @xcite ) and grebel et al . ( @xcite ) . a smaller spread ( @xmath182 dex ) was found by geisler ( @xcite ) . this discrepancy probably results from the coarser metallicity resolution of the colors employed in past studies , with the notable exception of the washington colors of geisler ( @xcite ) . we conclude that a small abundance spread seems in fact more appropriate to describe the intermediate - age field population in fornax . while the metallicity dispersion given above is comparable to that of leo i ( e.g. , gallart et al . @xcite ) , it appears to be smaller than the abundance spread found in the majority of dwarf spheroidal galaxies ( da costa @xcite ; mateo @xcite ) . in a few cases , wide range in metallicity has been confirmed by low- and high - dispersion spectroscopy ( e.g. , cot et al . @xcite ; shetrone et al . the mean value of the metallicity spread for galactic dsph and satellites of m31 is @xmath183 dex ( cot et al . had we considered our fornax rgb color distribution as a whole , we would have obtained a metallicity spread of the same order ( @xmath15 } < -0.7 $ ] , @xmath184 range ) , in good agreement with previous studies . since age is known to affect the rgb color , [ fe / h ] dispersions derived by the width of the giant branch should be taken with caution in view of a possible contribution of an age spread . as argued above , an age range of the order 5 gyr ( which is that of stars making up the main rgb ) is sufficient to mimic a metallicity range of @xmath185dex . thus we might assume that the width of the rgb main component is entirely due to the age spread of its populations . the situation is more complex , though , and the effects of a metallicity and age range on the color distribution depend on the details of the star formation and chemical enrichment history . successive stellar generations are expected to be progressively more metal - enriched , so that younger stars ( implying a bluer rgb ) will generally have higher metal abundance ( leading to a redder rgb ) . the two effects of a younger age and higher metallicity will act in opposite directions , and may even compensate each other as it appears to be the case for carina ( smecker - hane et al . @xcite ) . similarly to carina , the abundance spread we have found for the dominant population of fornax may represent a _ lower limit _ ( see also paper ii ; gallart et al . @xcite ; for similar considerations for other dsph s ) . this issue shall be more quantitatively investigated in a following paper . we return now to discuss the nature of the population making up the blue tail of the cdf , which is until now far from established . qualitative examination of the cmd s is not sufficient to establish whether the blue tail of the cdf represents an old , population , or is made up of young red agb stars . however , we will show in sect . [ sec_popratios ] that there is definite evidence that the bluer rgb stars are old and metal - poor , which implies that the extended color distribution shown in fig . [ twogauss ] can be interpreted as a metallicity distribution . in conclusion , a model involving two populations seems to provide a good description of the star content of the fornax dsph , with the older population having [ fe / h]@xmath186 with a dispersion of 0.20 dex , and the dominant , intermediate - age population with [ fe / h]@xmath12 . our large - field data confidently rule out the presence of a distinct metal - rich population with abundance comparable to that of 47 tuc , even accounting for a mean age of 5 gyr for the fornax bulk population . this complexity is common to most of the other dwarf spheroidals . for example , two distinct star formation epochs have been recently revealed in sculptor by majewski et al . ( @xcite ) . in this galaxy , a detailed analysis of the rgb morphology showed the presence of two distinct rgb bumps consistent with the presence of a metal - poor population of [ fe / h]@xmath187 , and a population of [ fe / h]@xmath188 . also the recent study of the star formation history of leo i by gallart et al . ( @xcite ) indicate that most of the star formation activity ( 80% ) occurred between 7 and 1 gyr ( mean 4 gyr ) while the contribution of the older phase was small . a wide metallicity range and a composite population , although with a higher mean abundance , has also been inferred in the sagittarius dsph , a galaxy similar in many respects to fornax ( bellazzini et al . also , the metallicity distribution of stars in the small elliptical m32 shows a metal - rich peak ( [ fe / h]@xmath189 ) with a low - metallicity tail extending to about [ fe / h]@xmath190 ( grillmair et al . it is also interesting to note the analogy with the extremely broad metallicity range found in the halo of the nearby elliptical ngc 5128 ( harris et al . @xcite ) , where the shape of the metallicity distribution suggested a two - phase _ in situ _ model . rrrrrr & & & & & + 1.2 & 4.2 & 7.0 & 36.6 & 1.7 & 30.5 + 2.6 & 5.5 & 6.3 & 45.7 & 3.3 & 39.8 + 4.2 & 7.4 & 9.3 & 53.6 & 4.3 & 36.1 + 5.9 & 5.7 & 7.4 & 46.2 & 3.4 & 35.2 + 7.5 & 5.4 & 5.9 & 37.0 & 3.8 & 40.9 + 9.2 & 5.6 & 5.2 & 24.4 & 4.0 & 38.1 + 10.9 & 8.0 & 6.0 & 19.2 & 3.6 & 39.5 + 12.5 & 8.2 & 6.1 & 20.2 & 4.1 & 34.0 + 14.2 & 9.3 & 4.4 & 13.0 & 2.9 & 33.4 + 15.9 & 7.9 & 5.7 & 11.9 & 2.3 & 41.5 + a comparison of the color - magnitude diagram in the different regions in this study provided important clues regarding the origin of the stellar populations in fornax , and in particular on the nature of its complex red giant branch . were the bluer rgb stars old and metal - poor , one would expect a higher fraction of them in the outer fields , on the basis of the population gradient detected by shs98 . clearly the opposite finding , i.e. a larger rgb blue tail in the inner regions , would indicate a connection to the more recent bursts of star formation . in order to measure the radial gradient in the stellar populations in fornax , stars in different evolutionary phases were counted separately in different radial bins . the cmd regions chosen for counts include the red clump , the red part of the hb@xmath89 , the blue - loop helium - burning stars ( bl ) , the young main sequence ( yms ) , and the red giants ( those in the mainstream giant branch , rgb , and in the bluer component , @xmath191rgb ) . the reader is referred to the boxes outlined in fig . [ 1cmdbvi ] . the results of star counts are presented in table [ t_popratios ] , where we list the effective galactocentric distance and the percentage of stars in all the cmd regions relative to the number of rc stars . the fraction of young main sequence , old hb , blue - rgb and mainstream rgb stars are also plotted on a logarithmic scale in fig . [ f_popratios ] . as previously noticed by shs98 , the young stars are more centrally concentrated than the dominant intermediate age component , indicating that recent star formation took place preferentially in the central regions . the counts on the rgb as expected follow those of rc stars . conversely , the hb stars are preferentially found in the outer regions . most importantly , the bluer rgb stars _ closely follow the radial trend of the horizontal - branch stars _ ( fig . [ f_popratios ] ) . this result unambiguously demonstrates that the sparse sequence on the blue side of the fornax rgb belongs to the _ old and metal - poor _ population ( @xmath192 gyr ) along with the old - hb stars and rr lyrae variables .

the resultant color - magnitude diagrams , based on a wide color baseline , show a variety of features tracing the history of star formation of this dwarf galaxy . a comparison of the color and extension of this feature with model isochrones suggests a relatively metal - rich population ( [ fe / h] ) with age 300400 myr . this represents an important constraint for understanding the chemical enrichment history of fornax . we have identified the agb bump , a clustering of stars that occurs at the beginning of helium shell - burning evolution , at a luminosity . the dominant component , comprising% of the red giant stars , consists of relatively metal - enriched intermediate - age stars . its mean metallicity is [ fe / h]= , based on a comparison of the fiducial locus of the bulk of the fornax red giants with the homogeneous galactic globular cluster set of da costa & armandroff ( ) . once the younger mean age of fornax is taken into account , our best estimate for the mean abundance of the bulk of the galaxy is [ fe / h] . further , there is a distinct small population of red giants on the blue side of the rgb . this unambiguously qualifies them as old and metal - poor . this evidence suggests a scenario in which the fornax dsph started forming a stellar halo and its surrounding clusters together about 1013 gyr ago , followed by a major star formation epoch ( probably with a discontinuous rate ) after several gyr .

we present ccd photometry of about 40000 stars in four regions of the fornax dwarf spheroidal galaxy down to , the largest three - color data set obtained for this galaxy until now . the resultant color - magnitude diagrams , based on a wide color baseline , show a variety of features tracing the history of star formation of this dwarf galaxy . one of the most distinctive features in our diagrams is the conspicuous young main sequence , indicating recent star formation until approximately yr ago . a plume of stars brighter than the red hb clump , with , trace the helium - burning phase of the young population . a comparison of the color and extension of this feature with model isochrones suggests a relatively metal - rich population ( [ fe / h] ) with age 300400 myr . this represents an important constraint for understanding the chemical enrichment history of fornax . an extended upper agb tail and a prominent red hb clump sign the presence of the well - known dominant intermediate - age population with an age range 2 - 10 gyr , for which we have estimated a mean age . about 0.2 mag below the red clump , an extended hb is indicative of an old population . we show that blue hb stars may be present in the outer regions . together with previous detection of rr lyrae , this provides evidence for a minority field population that is as old and metal - poor as that in the fornax globular clusters . we have identified the agb bump , a clustering of stars that occurs at the beginning of helium shell - burning evolution , at a luminosity . this is an example of the short - lived evolutionary phases that can be revealed in stellar populations using adequately large star data samples , whose measurements provide powerful tests of theoretical models . based on precise detection of the tip of the rgb in a selected rgb sample , we measure a corrected distance modulus . an independent estimate of the distance to fornax was also obtained from the mean magnitude of old horizontal branch stars , yielding a distance modulus , in good agreement with the distance estimated from the red giant branch tip and previous results . the large baseline of the colors together with the size of the stellar sample allowed us to analyze in detail the color distribution of the red giant stars . we find that it can be approximately described as the superposition of two populations . the dominant component , comprising% of the red giant stars , consists of relatively metal - enriched intermediate - age stars . its mean metallicity is [ fe / h]= , based on a comparison of the fiducial locus of the bulk of the fornax red giants with the homogeneous galactic globular cluster set of da costa & armandroff ( ) . once the younger mean age of fornax is taken into account , our best estimate for the mean abundance of the bulk of the galaxy is [ fe / h] . the dominant intermediate - age component has an intrinsic color dispersion mag , corresponding to a relatively low abundance dispersion , } = 0.12 \pm 0.02 $ ] dex . further , there is a distinct small population of red giants on the blue side of the rgb . while these stars could be either old or young red giants , we show that their spatial distribution is consistent with the radial gradient of old horizontal branch stars , and completely different from that of the younger population . this unambiguously qualifies them as old and metal - poor . this result clarifies the nature of the red giant branch of fornax , suggesting that its exceptional color width is due to the presence of two main populations yielding a large abundance range ( } < -0.7 $ ] ) . this evidence suggests a scenario in which the fornax dsph started forming a stellar halo and its surrounding clusters together about 1013 gyr ago , followed by a major star formation epoch ( probably with a discontinuous rate ) after several gyr .

astro-ph9912427

i

we have presented a large area study of the field population in the fornax dwarf spheroidal galaxy , based on @xmath24 data for about 40000 stars . the size of our sample , together with the wide photometric baseline employed in this work , provide new information on the stellar content of fornax . one of the most distinctive features in our diagrams is the conspicuous young main sequence . in this paper we have shown that the plume of stars just above the red clump is made up of intermediate mass stars ( 2.42.9 @xmath96 ) burning helium in the core , counterparts of the young main sequence stars in the age range 0.30.4 gyr . the comparison with isochrones suggests us that these blue - loop stars must be as metal - rich as [ fe / h]@xmath4 , which represents an important constraint for the metal enrichment history in fornax . an extended upper agb tail and a prominent red hb clump testify the presence of a dominant intermediate - age population in the age range 2 - 10 gyr , corresponding to 0.91.4 @xmath96stars . from the difference in the mean ( @xmath105 ) colors of the red clump and the rgb at the same luminosity , we have estimated a mean age @xmath5 for the bulk of the intermediate - age population in fornax , in agreement with the morphology of the ms turnoffs in wfpc2 color - magnitude diagrams ( buonanno et al . this suggests that the location of the red hb clump may indeed prove to be a useful age indicator for distant lg galaxies . about 0.2 mag below the red clump , an extended hb is indicative of an old population . in particular , our data point to the presence of blue hb stars in the outer regions . together with previous detection of rr lyrae , this provides evidence for a minority field population that is as old and metal - poor as that in the fornax globular clusters . the fornax dsph clearly started forming stars in a halo nearly at the same epoch when most of its surrounding clusters were formed . evolutionary phases that gave barely discernible features in small field observations are easily measurable in our color - magnitude diagrams . we could reliably measure the agb bump , a small clump produced by a clustering of stars at the base of the agb , at @xmath6 . measurements of such minor evolutionary features may provide useful tests of stellar models for stars of different masses and metallicities . the sharp cutoff in the luminosity function of fornax has been used to estimate its distance using the rgb tip method . the corrected distance modulus of fornax , @xmath114 , agrees with previous determinations . this estimate is confirmed by the mean level of old horizontal - branch stars . by measuring the average magnitude of the red hb ( distinct from the red clump ) we estimated a distance modulus @xmath193 on the distance scale of lee et al . ( @xcite ) . fornax , as many other dsph , has been known for a long time to have a wide rgb color distribution . the `` color scatter '' has been usually taken to represent an abundance spread . we have analyzed in detail the color distribution of the red giant stars across the fiducial line , and found that it is reasonably well fitted by a two - component model . this approximately bimodal distribution is remarkably similar in all fields . about 70% of the red giants belong to an intermediate - age rgb component which is itself wider than expected from instrumental errors . by comparing the bulk of the fornax rgb with the ridge lines of standard globular clusters , we have estimated a mean metallicity [ fe / h]@xmath194 . this nominal value should be corrected for the age difference between the fornax population and the milky way globulars . accounting for an age difference of 10 gyr , we find an _ age - corrected _ mean metallicity [ fe / h]@xmath195 for the dominant intermediate - age population of fornax . interestingly , this is also the metallicity found for sagittarius , the nearest milky way dsph satellite that has luminosity comparable to that of fornax . the _ intrinsic _ color scatter of stars in the rgb main component is @xmath196 mag implying a relatively modest metallicity spread @xmath14 } = 0.12 \pm 0.02 $ ] dex . then the ( @xmath144 ) metallicity range for the bulk population of fornax is @xmath181 } < -0.75 $ ] if a correction for the mean age is applied . the secondary component or `` bluer tail '' is also quite broad . in principle , these bluer stars could be either young or old and metal - poor . star counts of different subpopulations at various locations confirm and extend the evidence for radial population gradients emerged in previous studies . recent star formation is clearly concentrated in the central regions , though with some degree of asymmetry ( e.g. , shs98 ) . old stars are more easily seen in the outer fields . a blue hb population can be noticed in our outermost field , coming from the minority old , metal - poor field component . the stars populating the blue side of the wide rgb closely follow the spatial distribution of the old - hb stars . this is perhaps our most important finding , since it demonstrates that the bluer rgb stars are themselves old and metal- poor , and clearly establishes the nature of the wide rgb of fornax . thus the roughly bimodal color distribution can be interpreted as a metallicity distribution , implying that the bulk of the fornax galaxy was built during two rather distinct star - forming epochs . the older population has [ fe / h]@xmath197 dex with ( @xmath101 ) and an wide abundance range @xmath198 } < -1.4 $ ] . the emerging picture is one in which the evolution of fornax is characterized by two major star formation epochs , each consisting of many episodes . the first episode took place at an early epoch , being presumably coeval to the birth of the old galactic globular clusters , from metal - poor gas . after a relatively quiescent period , fornax formed the bulk of stellar populations between 7 and 2.5 gyr ago from the pre - enriched gas . star formation continued at a lower rate in the central regions until as recently as 10@xmath199 yr ago . the modest internal abundance spread found in each main population seen in the metallicity distribution , and the different metallicities of populations of different age , trace the progressive metal enrichment and represent the basis for an age - metallicity relation in fornax . the constraints found in this paper provide the physical input for a quantitative analysis of the star formation and chemical enrichment history of fornax , which will be done in a forthcoming study using the methods of stellar population synthesis . we thank l. girardi for useful discussions and for kindly providing us with unpublished theoretical red clump colors . stetson is thanked for helpful comments on the manuscript . i. s. acknowledges support from antares , an astrophysics network funded by the hcm program of the european community . alves d.r . , sarajedini a. , 1999 , apj 511 , 225 aparicio a. , gallart c. , chiosi c. , bertelli g. , 1996 , apj 469 , l97 aparicio a. , dalcanton j.j . , gallart c. , martnez - delgado d. , 1997 , aj 114 , 1447 azzopardi m. , breysacher j. , muratorio g. , westerlund , b.e . 1999 , in iau symp 192 , the stellar content of local group galaxies , eds . p. whitelock r. cannon ( asp , san francisco ) , in press beauchamp d. , hardy e. , suntzeff n.b . , zinn r. , 1995 , aj 109 , 1628 bellazzini m. , ferraro f.r . , buonanno r. , 1999 , mnras 307 , 619 bersier d. , wood p.r , 1999 , iau symp . 192 , the stellar content of local group galaxies , p. whitelock r. cannon eds . ( asp , san francisco ) , in press bertelli g. , bressan a. , chiosi c. , fagotto f. , nasi e. , 1994 , a&as 106 , 275 buonanno r. , corsi c. e. , fusi pecci f. , hardy e. , zinn r. , 1985 , a&a 152 , 65 buonanno r. , corsi c.e . , zinn r. , et al . , 1998 , apj 501 , l33 buonanno r. , corsi c.e . , castellani m. , et al . , 1999 , aj 118 , 1671 d. , heiles c. , 1982 , aj 87 , 1165 caputo f. , castellani v. , deglinnocenti s. , 1995 , a&a 304 , 365 caputo f. , cassisi s. , castellani m. , marconi g. , santolamazza p. , 1999 , aj 117 , 2199 cole a.a . , tostoy e. , gallagher j.s . , et al . , 1999 , aj 118 , 1657 da costa g.s . , 1998 . in aparicio a. , herrero a. , sanchez f. ( eds . ) , _ stellar astrophysics for the local group _ , cambridge university press , cambridge , p. 351 g.s . , armandroff t.e . , 1990 , aj 100 , 162 danziger i.j . , webster b.l . , dopita m.a . , hawarden t.g . , 1978 , apj 220 , 458 demers s. , grondin l. , kunkel w.e . , 1990 , pasp , 102 , 632 gallart c. , 1998 , apj 495 , l43 gallart c. , freedman w. l. , mateo m. , et al . , 1999a , apj 514 , 665 gallart c. , freedman , w. l. , aparicio a. , bertelli g. , chiosi c. , 1999b , aj in press geisler d. , 1994 , in : layden a. , smith r.c . , storm j. ( eds ) proc . 3rd ctio / eso workshop , the local group : comparative and global properties . eso , garching , p. 141 girardi l. , 1999 , mnras 308 , 818 girardi l. , bressan a. , bertelli g. , chiosi c. , 1999 , a&as , in press gizis j.e . , mould j.r . , djorgovski s. , 1993 , pasp 105 , 871 gratton r.g . , ortolani s. , richter o.g . , 1986 , mem . sait 57 , 561 grebel e.k . , roberts w.m . , van de rydt f. , 1994 , in : layden a. , smith r.c . , storm j. ( eds ) proc . 3rd ctio / eso workshop , the local group : comparative and global properties . eso , garching , p. 148 grillmair c.j . , lauer t.r . , worthey g. , et al . , 1996 , aj 112 , 1975 harris g.l.h . , harris w.e . , poole g.b . , 1998 , aj 117 , 855 hatzidimitriou d. , 1991 , mnras 21 , 545 held e.v . , saviane i. , momany y. , 1999 , a&a 345 , 747 ( paper ii ) hodge p.w . , 1961 , aj 66 , 249 hurley - keller d. , mateo m. , nemec j. , 1998 , aj 115 , 1840 b. f. , freedman w. l. , 1995 , aj 109 , 1645 majewski s.r . , siegel m.h . , patterson r.j . , , 1999 , apj 520 , l33 maran s.p . , gull t.r . , stecher t.p . , aller l.h . , keyes c.d . , 1984 , apj 280 , 615 mateo m. , 1998 , ara&a 36 , 435 mighell k.j . , sarajedini a. , french r.s . , 1998 , aj 116 , 2395 minniti d. , zijlstra a.a . , alonso m.v . , 1999 , aj 117 , 881 sagar r. , hawkins m.r.s . , cannon r.d . , 1990 , mnras 242 , 167 salaris m. , cassisi s. , 1998 , mnras 298 , 166 saviane i. , held e.v . , piotto g. , 1996 , a&a 315 , 40 ( paper i ) t. a. , stetson p. b. , hesser j. e. , lehnert m. d. , 1994 , aj 108 , 507 smith e.o . , rich r.m . , neill j.d . , 1998 , aj 115 , 2369 stetson p. b. , 1987 , pasp 99 , 191 stetson p.b . , hesser j.e . , smecker - hane t.a . , 1998 , pasp 110 , 533 ( shs98 )

we present ccd photometry of about 40000 stars in four regions of the fornax dwarf spheroidal galaxy down to , the largest three - color data set obtained for this galaxy until now . one of the most distinctive features in our diagrams is the conspicuous young main sequence , indicating recent star formation until approximately yr ago . a plume of stars brighter than the red hb clump , with , trace the helium - burning phase of the young population . an extended upper agb tail and a prominent red hb clump sign the presence of the well - known dominant intermediate - age population with an age range 2 - 10 gyr , for which we have estimated a mean age . about 0.2 mag below the red clump , an extended hb is indicative of an old population . we show that blue hb stars may be present in the outer regions . together with previous detection of rr lyrae , this provides evidence for a minority field population that is as old and metal - poor as that in the fornax globular clusters . we find that it can be approximately described as the superposition of two populations . the dominant intermediate - age component has an intrinsic color dispersion mag , corresponding to a relatively low abundance dispersion , } = 0.12 \pm 0.02 $ ] dex .

we present ccd photometry of about 40000 stars in four regions of the fornax dwarf spheroidal galaxy down to , the largest three - color data set obtained for this galaxy until now . the resultant color - magnitude diagrams , based on a wide color baseline , show a variety of features tracing the history of star formation of this dwarf galaxy . one of the most distinctive features in our diagrams is the conspicuous young main sequence , indicating recent star formation until approximately yr ago . a plume of stars brighter than the red hb clump , with , trace the helium - burning phase of the young population . a comparison of the color and extension of this feature with model isochrones suggests a relatively metal - rich population ( [ fe / h] ) with age 300400 myr . this represents an important constraint for understanding the chemical enrichment history of fornax . an extended upper agb tail and a prominent red hb clump sign the presence of the well - known dominant intermediate - age population with an age range 2 - 10 gyr , for which we have estimated a mean age . about 0.2 mag below the red clump , an extended hb is indicative of an old population . we show that blue hb stars may be present in the outer regions . together with previous detection of rr lyrae , this provides evidence for a minority field population that is as old and metal - poor as that in the fornax globular clusters . we have identified the agb bump , a clustering of stars that occurs at the beginning of helium shell - burning evolution , at a luminosity . this is an example of the short - lived evolutionary phases that can be revealed in stellar populations using adequately large star data samples , whose measurements provide powerful tests of theoretical models . based on precise detection of the tip of the rgb in a selected rgb sample , we measure a corrected distance modulus . an independent estimate of the distance to fornax was also obtained from the mean magnitude of old horizontal branch stars , yielding a distance modulus , in good agreement with the distance estimated from the red giant branch tip and previous results . the large baseline of the colors together with the size of the stellar sample allowed us to analyze in detail the color distribution of the red giant stars . we find that it can be approximately described as the superposition of two populations . the dominant component , comprising% of the red giant stars , consists of relatively metal - enriched intermediate - age stars . its mean metallicity is [ fe / h]= , based on a comparison of the fiducial locus of the bulk of the fornax red giants with the homogeneous galactic globular cluster set of da costa & armandroff ( ) . once the younger mean age of fornax is taken into account , our best estimate for the mean abundance of the bulk of the galaxy is [ fe / h] . the dominant intermediate - age component has an intrinsic color dispersion mag , corresponding to a relatively low abundance dispersion , } = 0.12 \pm 0.02 $ ] dex . further , there is a distinct small population of red giants on the blue side of the rgb . while these stars could be either old or young red giants , we show that their spatial distribution is consistent with the radial gradient of old horizontal branch stars , and completely different from that of the younger population . this unambiguously qualifies them as old and metal - poor . this result clarifies the nature of the red giant branch of fornax , suggesting that its exceptional color width is due to the presence of two main populations yielding a large abundance range ( } < -0.7 $ ] ) . this evidence suggests a scenario in which the fornax dsph started forming a stellar halo and its surrounding clusters together about 1013 gyr ago , followed by a major star formation epoch ( probably with a discontinuous rate ) after several gyr .

1403.0361

c

in this work , we have developed a family of kernels for data analysis in dynamical systems , which incorporate empirical information about the dynamical flow in phase space . compared to canonical isotropic gaussian kernels , the kernels presented here assign higher affinity to pairs of data samples whose relative displacement vector lies on a small - angle cone with axis parallel to the dynamical vector field @xmath0 on the data manifold . the latter is estimated through finite differences of time - ordered samples , i.e. , without requiring prior knowledge of the equations of motion . due to the presence of the angular term , we refer to the new kernels as cone kernels . cone kernels also feature a scaling factor introduced heuristically in earlier work on so - called nlsa algorithms @xcite , whose role is to locally decrease ( increase ) the rate of decay of the kernel in regions of phase space where the dynamical flow is fast ( slow ) in the sense of the norm @xmath135 of the dynamical vector field in data space . moreover , the strength of the angular dependence is controlled by a parameter @xmath1 , such that @xmath2 and @xmath3 correspond to zero or maximal influence of the angular term . thus , cone kernels include the earlier nlsa kernels as the special case @xmath2 . we evaluated the metric tensor @xmath116 induced on the data manifold by cone kernels ( lemma [ lemmahmetric ] ) using the asymptotic analysis framework of berry @xcite , and also studied the associated diffusion operator @xmath65 . by virtue of the @xmath135-dependent scaling , the induced metric is invariant for all @xmath52 under conformal transformations of the original ambient space metric @xmath24 . moreover , for @xmath285 , @xmath116 contracts local distances between points on the data manifold whose relative displacement is parallel to @xmath0 , becoming degenerate as @xmath52 approaches 1 . in that regime , @xmath65 becomes along @xmath0 @xcite , in the sense that the associated codifferential operator asymptotically annihilates all differential 1-forms @xmath118 with the property @xmath144 ( lemma [ lemmaalong ] ) . intuitively , one thinks of @xmath65 in the @xmath3 limit as generating diffusions along the integral curves of the dynamical vector field . because @xmath0 and its integral curves do not depend on the ambient space metric , this feature is intrinsic to the dynamical system under study . more generally , as @xmath3 , the action of @xmath65 on functions depends on the ambient space metric only through the ratio @xmath286 for an @xmath7-dimensional manifold . the latter is invariant under conformal transformations of @xmath24 , as well as more general transformations . a further important property arising in the @xmath3 limit is that the dirichlet form associated with @xmath65 depends on the directional derivative of functions along @xmath287 , as opposed to the canonical dependence on the gradient operator [ see ] . this property has significant bearing on the structure of the corresponding diffusion eigenfunctions , which are useful in a wide range of dimension reduction , signal processing , and learning problems . in particular , the leading eigenfunctions are expected to be adapted to the dynamical system generating the data , in the sense of varying weakly along the integral curves of @xmath0 . we discussed the utility of cone kernels in a suite of numerical experiments involving nonlinear flows on the 2-torus and north pacific sea surface temperature ( sst ) data from a comprehensive climate model . in the torus experiments , we explicitly demonstrated the adaptivity of the diffusion eigenfunctions associated with @xmath57 cone kernels to the dynamics ( figures [ figphii ] and [ figphiii ] ) , as well as the robustness of those eigenfunctions to non - conformal deformations of the data ( figure [ figphiideformed ] ) . in the north pacific sst experiments , cone kernels were found to have superior feature extraction capabilities , in the sense of requiring fewer basis functions than their @xmath2 counterparts to describe the salient coherent structures of north pacific sst variability , while also providing better separation between the timescales associated with the annual solar forcing and low - frequency ( interannual ) variability of the ocean . we attribute this improvement of skill to the ability of @xmath57 cone kernels to take into account changes in the direction of the dynamical flow due to the annual cycle . this feature should be generic in datasets with prominent quasiperiodic behavior . there are several open questions generated by this work which lie outside the scope of the present paper . on the theory side , a more detailed understanding of the diffusion eigenfunctions obtained from cone kernels would be desirable ; e.g. , their properties as embedding coordinates @xcite . furthermore , it would be useful to explore generalizations of the deterministic framework adopted here to stochastic dynamical systems . such approaches might involve replacing the ambient - space distances and inner products with suitable statistical metrics @xcite , retaining the explicit dependence on aspects related to the drift of the system in phase space . even in the deterministic dynamical system context , potential shortcomings of cone kernels may arise due to sensitivity to observational noise and/or poor performance of the directional term in high intrinsic dimensions . such scenarios would warrant modification of the cone kernel formulation put forward here , but we expect the general approach of incorporating empirically accessible information about the dynamics in kernel design to remain fruitful .

we present a family of kernels for analysis of data generated by dynamical systems . these so - called cone kernels feature an explicit dependence on the dynamical vector field operating in the phase - space manifold , estimated empirically through finite - differences of time - ordered data samples . in particular , cone kernels assign strong affinity to pairs of samples whose relative displacement vector lies within a narrow cone aligned with the dynamical vector field . as a result , in a suitable asymptotic limit , the associated diffusion operator generates diffusions along the dynamical flow , and is invariant under a weakly restrictive class of transformations of the data , which includes conformal transformations . we demonstrate the utility of cone kernels in nonlinear flows on the 2-torus and north pacific sea surface temperature data generated by a comprehensive climate model .

we present a family of kernels for analysis of data generated by dynamical systems . these so - called cone kernels feature an explicit dependence on the dynamical vector field operating in the phase - space manifold , estimated empirically through finite - differences of time - ordered data samples . in particular , cone kernels assign strong affinity to pairs of samples whose relative displacement vector lies within a narrow cone aligned with the dynamical vector field . as a result , in a suitable asymptotic limit , the associated diffusion operator generates diffusions along the dynamical flow , and is invariant under a weakly restrictive class of transformations of the data , which includes conformal transformations . moreover , the corresponding dirichlet form is governed by the directional derivative of functions along the dynamical vector field . the latter feature is metric - independent . the diffusion eigenfunctions obtained via cone kernels are therefore adapted to the dynamics in that they vary predominantly in directions transverse to the flow . we demonstrate the utility of cone kernels in nonlinear flows on the 2-torus and north pacific sea surface temperature data generated by a comprehensive climate model . kernel methods , diffusion operators , eigenfunctions , manifold embedding , vector field , delay coordinates 37m10 , 37n10

1010.0759

i

this is the second in a series of two papers devoted to a relativistic computation of torques from an external perturber on a thin disc due to interactions at the lindblad resonances , i.e. locations in the disc where the orbital frequency @xmath4 and the radial epicyclic frequency @xmath5 satisfy @xmath6 , where @xmath7 is the pattern speed of the perturbation . such resonances have been extensively studied in the nonrelativistic case ( e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? in the first paper ( `` paper i '' ) , we performed this computation for a general time - stationary , axisymmetric , spacetime with an equatorial plane of symmetry and a metric perturbation @xmath8 that respects the equatorial symmetry . this paper ( `` paper ii '' ) completes the evaluation of the lindblad torque in the case of most interest : the perturbation of the accretion disc surrounding a schwarzschild or kerr black hole by a small secondary also orbiting in the equatorial plane . such computations of the lindblad resonant strengths may be relevant in the context of electromagnetic counterparts to binary black hole mergers , particularly if an inner disc is involved @xcite . ( the more complicated case of perturbations outside of the equatorial plane as may occur in the case of a merger where the primary hole is rotating and the secondary is in an inclined orbit is left to future work . ) the resonant torque formula in paper i depended on the geodesic properties in the unperturbed spacetime as well as being proportional to the square of the absolute value of the resonant amplitude @xmath9 , which was a function of the @xmath10 fourier component of the metric perturbation @xmath8 and its spatial derivative @xmath11 . the construction of these perturbations generally depends on the solution for the weyl tensor component @xmath12 , which may be solved using a separable wave equation with a source given by the stress - energy tensor associated with the perturber @xcite ; and then @xmath8 may be obtained by applying a second - order differential operator to a master potential @xcite , which may be derived from @xmath12 @xcite . fortunately , for our computations there is a way to circumvent the @xcite procedure : paper i showed that the particular combination of metric perturbations we require is related to @xmath13 , the power delivered to a test particle in a slightly eccentric orbit by the @xmath10 component of the perturbation . by replacing the perturber with an equivalent gravitational wave source either incoming from past null infinity in the case of an inner lindblad resonance ( ilr ) , or emerging from the past horizon in the case of an outer lindblad resonance ( olr ) we may equate @xmath13 with the power absorbed from the gravitational wave . however , energy is conserved on a time - independent background metric , and thus @xmath13 can be related to the interference between the equivalent gravitational wave representing the perturbation and the gravitational wave emitted by the test particle . this allows us to express the resonant amplitude and hence the resonant torque in terms of the waveforms emitted by the perturber and the test particle ( both to future null infinity and into the future horizon ) , so that standard methods to solve for @xmath12 are sufficient . the outline of this paper is as follows . in section [ sec : metric ] , we introduce the kerr metric and review the associated standard notation . section [ sec : geodesics ] reviews the geodesics in the kerr spacetime and their description with action - angle variables , and section [ sec : modes ] describes the compuation of the perturbation in the weyl scalar @xmath12 ; while both of these subjects are standard , there are some differences in our treatment that are particularly suited to the problem at hand , and we make frequent use of intermediate results when taking the nonrelativistic limit , so an extended discussion is warranted . section [ sec : resonantamp ] presents the key new theoretical result of this paper , relating the behaviour of @xmath12 near the horizon and at infinity to the resonant amplitude @xmath9 . we recompute the resonant amplitudes in the kepler problem in section [ sec : kepler ] , and then proceed to investigate the lindblad resonances in the schwarzschild problem in section [ sec : schwarzschild ] . section [ sec : kerr ] then considers the lindblad resonance amplitudes associated with equatorial orbits in the kerr spacetime . we conclude in section [ sec : discussion ] .

we present a fully relativistic computation of the torques due to lindblad resonances from perturbers on circular , equatorial orbits on discs around schwarzschild and kerr black holes . the computation proceeds by establishing a relation between the lindblad torques and the gravitational waveforms emitted by the perturber and a test particle in a slightly eccentric orbit at the radius of the lindblad resonance . we show that our result reduces to the usual formula when taking the nonrelativistic limit . discs around a black hole possess an inner lindblad resonance ( ilr ) with no newtonian keplerian analogue ; however its strength is very weak even in the moderately relativistic regime ( few tens ) , which is in part due to the partial cancellation of the two leading contributions to the resonant amplitude ( the gravitoelectric octupole and gravitomagnetic quadrupole ) . for equatorial orbits around kerr black holes , we find that the ilr strength is enhanced for retrograde spins and suppressed for prograde spins . accretion , accretion discs relativistic processes black hole physics .

we present a fully relativistic computation of the torques due to lindblad resonances from perturbers on circular , equatorial orbits on discs around schwarzschild and kerr black holes . the computation proceeds by establishing a relation between the lindblad torques and the gravitational waveforms emitted by the perturber and a test particle in a slightly eccentric orbit at the radius of the lindblad resonance . we show that our result reduces to the usual formula when taking the nonrelativistic limit . discs around a black hole possess an inner lindblad resonance ( ilr ) with no newtonian keplerian analogue ; however its strength is very weak even in the moderately relativistic regime ( few tens ) , which is in part due to the partial cancellation of the two leading contributions to the resonant amplitude ( the gravitoelectric octupole and gravitomagnetic quadrupole ) . for equatorial orbits around kerr black holes , we find that the ilr strength is enhanced for retrograde spins and suppressed for prograde spins . we also find that the torque associated with the ilrs is enhanced relative to the nonrelativistic case ; the enhancement is a factor of 2 for the schwarzschild hole even when the perturber is at a radius of . accretion , accretion discs relativistic processes black hole physics .

0903.3541

i

classical level raising results typically show that if the reduction mod @xmath0 of a level @xmath4 modular form @xmath5 has certain properties ( depending on a prime @xmath6 ) , then there exists a modular form @xmath7 of level @xmath8 , new at @xmath3 , with @xmath9 . an example of a level raising result for classical modular forms is the following , due to ribet @xcite : let @xmath10 be an eigenform , and let @xmath11 be a finite place of @xmath12 such that @xmath13 and @xmath5 is not congruent to an eisenstein series modulo @xmath14 . if @xmath15 is a prime number such that the following condition is satisfied , @xmath16 then there exists a @xmath3-new eigenform @xmath17 congruent to @xmath5 modulo @xmath14 . in this paper we prove an analogous level raising result for families of @xmath0-adic automorphic forms . in @xcite and part iii of @xcite , buzzard defines modules of overconvergent @xmath0-adic automorphic forms for definite quaternion algebras , and constructs from these a so - called ` eigencurve ' . the eigencurve is a rigid analytic variety whose points correspond to certain systems of eigenvalues for hecke algebras acting on these modules of automorphic forms . this space @xmath0-adically interpolates the systems of eigenvalues arising from classical automorphic forms . emerton has constructed eigenvarieties in a cohomological framework @xcite , but in the following we will work with buzzard s more concrete construction . since we first wrote the present text , we have also proven some cases of level raising for @xmath0-adic modular forms using the completed cohomology spaces investigated by emerton ( see @xcite ) . the first construction of an eigencurve was carried out for modular forms ( automorphic forms for @xmath18 ) in coleman and mazur s seminal paper @xcite . an important recent result is the construction of a @xmath0-adic jacquet - langlands map between an eigencurve for a definite quaternion algebra and the @xmath18 eigencurve ( interpolating the usual jacquet - langlands correspondence ) , as carried out in @xcite . we follow the general approach of the first part of diamond and taylor s paper @xcite , and our theorem [ supporttheorem ] is an analogue of theorem 1 in that paper , but several new features appear in our work . in particular , the level raising results in @xcite and @xcite for definite quaternion algebras are proved by utilising a pairing on finite dimensional vector spaces of automorphic forms . in our setting , the spaces of automorphic forms are banach modules over an affinoid algebra , so we introduce spaces of ` dual ' automorphic forms and work with the pairing between the usual space of automorphic forms and the dual space . we then prove suitable forms of ihara s lemma , our theorem [ lemma : trivialtorsion ] ( cf . lemma 2 of @xcite ) , for the usual and dual spaces of automorphic forms . an interesting asymmetry between the two situations can be observed . this investigation of level raising results was motivated by a conjecture made by a. paulin , prompted by results on local - global compatibility on the eigencurve in his thesis @xcite . paulin s conjecture was made for the @xmath18-eigencurve ; we may apply our theorem to the image of the @xmath0-adic jacquet - langlands map there to prove many cases of his conjecture . since we have applications to the eigencurve for @xmath19 in mind we work with definite quaternion algebras over @xmath2 in this paper , but some of the methods of section [ mainbody ] should apply to definite quaternion algebras over any totally real number field , although we do use the fact that weight space is one - dimensional in our arguments . we end this introduction by stating the conjecture made by paulin . we fix two distinct primes @xmath0 and @xmath3 , and an integer @xmath4 coprime to @xmath20 . let @xmath21 be the cuspidal eigencurve of tame level @xmath22 , parametrising overconvergent cuspidal @xmath0-adic modular eigenforms ( see @xcite for its construction ) . if @xmath23 is a point of @xmath21 , corresponding to an eigenform @xmath24 , paulin defines an associated representation of @xmath25 , denoted @xmath26 . we call an irreducible connected component @xmath27 of the eigencurve _ generically special _ if the @xmath25-representations associated to the points of @xmath27 away from a discrete set are special . we define _ generically unramified principal series _ similarly . denote by @xmath28 and @xmath29 the roots of the polynomial @xmath30 , where @xmath31 and @xmath32 are the @xmath33 and @xmath34 eigenvalues of @xmath24 . paulin makes the conjecture : suppose @xmath27 is generically unramified principal series . suppose further that there is a point @xmath23 on @xmath27 where the ratio of @xmath28 and @xmath29 becomes @xmath35 and @xmath26 is special . then there exists a generically special component @xmath36 intersecting @xmath27 at @xmath23 . chenevier raised the same question ( in a slightly different form ) in relation to the characterisation of the zariski closure of the @xmath3-new classical forms in the eigencurve . we address this issue in section [ neweigen ] . finally , in a recent preprint @xcite paulin has proved versions of his level raising ( and lowering ) conjectures ( even for ramified principal series ) . his techniques are completely different to ours , making use of deformation theory and requiring a recent important result of emerton showing that the space @xmath37 constructed by kisin in @xcite is equal to the @xmath18-eigencurve ( if one restricts to pieces of the two spaces where certain conditions are satisfied by the relevant mod @xmath0 galois representations ) .

we present a level raising result for families of-adic automorphic forms for a definite quaternion algebra over . the main theorem is an analogue of a theorem for classical automorphic forms due to diamond and taylor . we show that certain families of forms old at a prime intersect with families of-new forms ( at a non - classical point ) . one of the ingredients in the proof of diamond and taylor s theorem ( which also played a role in earlier work of taylor ) is the definition of a suitable pairing on the space of automorphic forms . in our situation one can not define such a pairing on the infinite dimensional space of-adic automorphic forms , so instead we introduce a space defined with respect to a dual coefficient system and work with a pairing between the usual forms and the dual space . a key ingredient is an analogue of ihara s lemma which shows an interesting asymmetry between the usual and the dual spaces .

we present a level raising result for families of-adic automorphic forms for a definite quaternion algebra over . the main theorem is an analogue of a theorem for classical automorphic forms due to diamond and taylor . we show that certain families of forms old at a prime intersect with families of-new forms ( at a non - classical point ) . one of the ingredients in the proof of diamond and taylor s theorem ( which also played a role in earlier work of taylor ) is the definition of a suitable pairing on the space of automorphic forms . in our situation one can not define such a pairing on the infinite dimensional space of-adic automorphic forms , so instead we introduce a space defined with respect to a dual coefficient system and work with a pairing between the usual forms and the dual space . a key ingredient is an analogue of ihara s lemma which shows an interesting asymmetry between the usual and the dual spaces .

1310.8196

i

with the abundant data provided by _ sdo _ and modern advanced numerical models , we have unprecedented opportunities to examine in a realistic and quantitative way many proposed mechanisms for solar eruptions , e.g. , how the eruptive core field is built up , how the favorable magnetic topology is formed , and when the system runs into a unstable regime and erupts . in this paper we studied a sigmoid eruption event in ar 11283 from its building up to disruption for over three days , which involves a number of magnetic processes and thus is attractive for our study . based on a recently developed nlfff model @xcite , we compute a time sequence of static coronal fields to follow the slow buildup of the sigmoidal fr . as opposed to most other nlfff methods constrained by vector magnetograms , our cese mhd nlfff code can reproduce the structure of the evolving fr very well , as is demonstrated by the perfect matching with the observations . a detailed analysis of the fields compared with the _ sdo_/aia observations suggests the following scenario for the evolution of this region . within the first day , a new bipole emerges into the negative polarity of a pre - existing bipolar mature ar , forming a fan - spine topology of a coronal null point on the separatrix surface between the two flux systems . in the following two days , a fr is built up slowly in the embedded core region through tether - cutting reconnections in both the photosphere ( i.e. , flux cancellation ) and corona , which is driven by photospheric shearing , converging and rotating flows . in this process , bpss forms between the fr and its ambient field , and develops into a fully s - shape . with more and more flux fed into the fr , the fr expands and the apex of the fr axis runs slowly into the ti domain near the end of the third day . however the fr does not erupt instantly since it is still attached at the bottom to the photosphere . by the combined effects of the ti - driven expansion of the fr and the line - tying at the bp , the fr is broken into two parts by reconnection within the rope . this reconnection dynamically perturbs the bpss and results in the transient enhanced brightening of the sigmoid . then the upper portion of the fr freely expands as it is driven by the ti , while the lower portion remains . the fast expansion of the rope pushes strongly outward its envelope flux near the null point and triggers breakout reconnection at the null , which further facilitates the eruption . as to how a sigmoidal fr forms and erupts is still a subject of intense debate , we summarize here the important results which are concluded from the studied event but might also apply to other events with similar magnetic configurations : 1 . magnetic flux emergence into an inverse - polarity preexisting field can form a fan - spine topology configuration with a coronal null on the separatrix surface between the two flux systems @xcite . flare ribbons with closed circular shapes trace the footpoints of the fan separatrix , and thus can usually be regarded as a signature of the presence of a null - related topology , along with the flux distribution of positive ( negative ) polarity surrounded by negative ( positive ) polarity . 2 . a fr does not emerge bodily from below the photosphere , but forms gradually in the corona after the apparent new flux injection observed at the photosphere . the building up of a fr is largely driven by shear / rotation flows on the photosphere , which is possibly associated with the emergence . this is consistent with the numerical investigations of the flux emergence @xcite that a twist flux tube in the convection zone can not emerge bodily into the corona , but transport its twist by torsional alfvn wave which manifests as the photospheric flows @xcite . both flux cancellation @xcite and tether - cutting @xcite reconnections contribute to the in situ formation of fr in the corona from sheared arcades , but do not trigger the eruption @xcite . such quasi - static evolution of the fr can be characterized well by a time sequence of static nlfff models based on continuously observed magnetograms . the result also supports store - and - release cme models with fr existing in the corona prior to eruption , but not a by - product of eruption . comparison of the magnetic fields with aia observations suggests that the prominent high - temperature euv emission is largely produced by the current sheets developing along separatrix surfaces ( and qsls ) but not by the extended volume current of the fr , because the dissipation rate of the extended currents is much smaller than that of the current sheets . in particular , the sigmoid is produced by the bpss current sheet @xcite . although it has been shown that the ti triggers the eruption , the present case is different from that of the standard ti in which the fr is fully developed , i.e. , is elevated off the photosphere away from a bpss configuration for hours before eruption ( e.g. , * ? ? ? here we demonstrate a case where the instability sets in before the fr is detached from the photosphere , and the photosphere can exert an additional restraining force to the fr at the bp . as a result , the fr does not erupt instantly even though its axis runs into the ti domain , and a splitting of the fr body is expected for the fr to expel partially @xcite . unlike the finding of @xcite that the partial expulsion of a fr ( i.e. , there are bpss and fr remaining below post - flare loops ) only occurs in the case of ki , we suggest that it can also occur in the case of ti . an eruption is usually jointly produced by multiple mechanisms ( e.g. , * ? ? ? for the studied event , in addition to the ti , the reconnection that splits the fr and the breakout reconnection that occurs at the null contribute to the final expulsion of the fr . 7 magnetic fields experience abrupt changes through the eruption : the transverse field along the main pil on the photosphere is enhanced ; the long s - shaped bpss shrinks significantly and reforms below the post - flare arcades , which is consistent with the enhanced photospheric field ; the free energy is released mostly at a height of several mms above the photosphere with a distinct downward compaction of its distribution . these results support the `` magnetic implosion '' conjecture . as a consequence , the non - potentiality of the photospheric fields might even increase after flare , and it is necessary to look at the 3d coronal field to disentangle these effects . although the basic scenario of the ar evolution has been drawn , questions remain for the dynamical evolution of the coronal field during the eruption , in particular , how does the reconnection occur within the fr , how does the bpss evolve during this reconnection , and how is the breakout reconnection triggered . a solution to these requires an mhd simulation which is beyond the scope of this paper , and will be investigated in detail using the recipe given by @xcite in a future paper of this series . we thank the anonymous referee for helpful comments which significantly improved the manuscript . this work is jointly supported by the 973 program under grant 2012cb825601 , the chinese academy of sciences ( kzzd - ew-01 - 4 ) , the national natural science foundation of china ( 41204126 , 41231068 , 41274192 , 41174151 , 41031066 , and 41074122 ) , and the specialized research fund for state key laboratories . the work performed by stw is supported by nsf - ags1153323 , and qh is supported by nsf shine ags-1062050 . numerical calculations were completed on our sigma cluster computing system . data from observations are courtesy of nasa/_sdo _ and the hmi science teams . gibson , s. e. , fletcher , l. , zanna , g. d. , pike , c. d. , mason , h. e. , mandrini , c. h. , demoulin , p. , gilbert , h. , burkepile , j. , holzer , t. , alexander , d. , liu , y. , nitta , n. , qiu , j. , schmieder , b. , & thompson , b. j. 2002 , the astrophysical journal , 574 , 1021 , c. j. , derosa , m. l. , metcalf , t. , barnes , g. , lites , b. , tarbell , t. , mctiernan , j. , valori , g. , wiegelmann , t. , wheatland , m. s. , amari , t. , aulanier , g. , dmoulin , p. , fuhrmann , m. , kusano , k. , rgnier , s. , & thalmann , j. k. 2008 , , 675 , 1637 , s. t. & guo , w. p. 1997 , a self - consistent numerical magnetohydrodynamic ( mhd ) model of helmet streamer and flux - rope interactions : initiation and propagation of coronal mass ejections ( cmes ) , coronal mass ejections , geophys . 83 , edited by n. crooker , j. joselyn , and j. feynman , agu , washington , d. c. tech .

we present a magnetic analysis of the formation and eruption of an active region ( ar ) sigmoid in ar 11283 from 2011 september 4 to 6 . to follow the quasi - static evolution of the coronal magnetic field , we reconstruct a time sequence of static fields using a recently developed nonlinear force - free field model constrained by the _ sdo_/hmi vector magnetograms . a detailed analysis of the fields compared with the _ sdo_/aia observations suggests the following scenario for the evolution of the region . initially , a new bipole emerges into the negative polarity of a pre - existing bipolar ar , forming a null point topology between the two flux systems . a weakly twisted flux rope ( fr ) is then built up slowly in the embedded core region , largely through flux - cancellation photospheric reconnections , forming a bald patch separatrix surface ( bpss ) separating the fr from its ambient field . the fr grows gradually until its axis runs into a torus instability ( ti ) domain near the end of the third day , and the bpss also develops a fully s - shape . unlike in the case of standard ti , the fr does not erupt instantly since it is still attached at the photosphere along the bald patch ( bp ) portion of the polarity inversion line . this process dynamically perturbs the bpss and results in the transient enhanced brightening of the sigmoid . the accelerated expansion of the upper portion of the fr strongly pushes its envelope flux near the null point and triggers breakout reconnection at the null , as evidenced by a remarkable circular flare ribbon , which further facilitates the eruption .

we present a magnetic analysis of the formation and eruption of an active region ( ar ) sigmoid in ar 11283 from 2011 september 4 to 6 . to follow the quasi - static evolution of the coronal magnetic field , we reconstruct a time sequence of static fields using a recently developed nonlinear force - free field model constrained by the _ sdo_/hmi vector magnetograms . a detailed analysis of the fields compared with the _ sdo_/aia observations suggests the following scenario for the evolution of the region . initially , a new bipole emerges into the negative polarity of a pre - existing bipolar ar , forming a null point topology between the two flux systems . a weakly twisted flux rope ( fr ) is then built up slowly in the embedded core region , largely through flux - cancellation photospheric reconnections , forming a bald patch separatrix surface ( bpss ) separating the fr from its ambient field . the fr grows gradually until its axis runs into a torus instability ( ti ) domain near the end of the third day , and the bpss also develops a fully s - shape . unlike in the case of standard ti , the fr does not erupt instantly since it is still attached at the photosphere along the bald patch ( bp ) portion of the polarity inversion line . the combined effects of the ti - driven expansion of the fr and the line - tying at the bp tear the fr into two parts with the upper portion freely expelled and the lower portion remaining behind the post - flare arcades . this process dynamically perturbs the bpss and results in the transient enhanced brightening of the sigmoid . the accelerated expansion of the upper portion of the fr strongly pushes its envelope flux near the null point and triggers breakout reconnection at the null , as evidenced by a remarkable circular flare ribbon , which further facilitates the eruption . we discuss the important implications of these results for the formation and disruption of sigmoid region with fr . = 1 utf8gbsn

1609.05864

i

by probing the thermal response at timescales and lengthscales on the order of the phonon relaxation times and free paths , respectively , thermal spectroscopy provides a potentially powerful means of extracting information about these intrinsic transport properties of real materials @xcite . as a result , thermal spectroscopy has recently received a lot of attention for applications related to the development of thermoelectric materials @xcite . the success of this technique relies on reliably extracting the information embedded in the material response , an inverse problem of considerable complexity that currently remains open . in order to use precise language , in this paper we focus on time - domain thermoreflectance . we believe that the methodology proposed in this paper can be straightforwardly extended to complementary approaches based on frequency - domain thermoreflectance @xcite . traditional approaches to time - domain thermoreflectance data analysis start by matching ( in a least - squares - fit sense ) the experimental response to numerical solutions of the heat conduction equation with the thermal conductivity treated as an adjustable , effective " , quantity @xcite . the free path distribution is subsequently extracted by assuming that the fitted effective thermal conductivity is given by the convolution of the differential free path distribution in the material with a suppression function that is assumed to be geometry dependent @xcite . an approximate suppression function has been developed for the thermal grating geometry @xcite ; suppression functions for other , more complex , geometries have yet to be developed . robust optimization frameworks for inverting the resulting integral equations have also been developed @xcite . however , since , by design , the material response in the experiment is not in the traditional fourier regime defined by characteristic timescales and lengthscales being much longer than the phonon mean free time and mean free path , respectively approaches based on fitting the material response using fourier theory can only be accepted as approximate . as shown in section [ discussion ] , the requirement of long times is particularly difficult to satisfy even if lengthscale corrections are applied . in general , in situations where the requirements for fourier behavior are not carefully met , the effective thermal conductivity obtained by such fits will depend on the fitting time window , the measurement location @xcite , and the experimental geometry , highlighting the fact that it is not a material property and casting doubt over the reliability of the inverse calculation . to avoid these conceptual but also practical problems , in the present work , we propose a methodology for reconstructing the relaxation time distribution in the material from thermal spectroscopy experimental results using an approach that at no time makes an assumption of an underlying fourier behavior . in our work , the reconstruction problem is formulated as a non - convex optimization problem whose goal is to minimize the difference between the experimental material response and the response as calculated by a bte - based model of the experimental process . here , we note the recent paper @xcite in which reconstruction is based on a fourier - space solution of a bte model of the two - dimensional transient thermal grating experiment . despite emphasizing the bte more than in previous approaches , the work in @xcite , ultimately , still reverts to a fourier - based formulation by fitting effective thermal diffusivities and introducing related approximations ( e.g. late times compared to the mean phonon relaxation time ) . a further distinguishing feature of our work is the use of deviational monte carlo ( mc ) simulation @xcite as a method to solve the bte which expands the domain of applicability of the approach , since it does not rely on the simplicity of the experimental setup or the degree to which it is amenable to analytical treatment . the remainder of the paper is organized as follows . in section [ formulation ] , we formulate the reconstruction as an optimization problem requiring only solutions of the bte and present the optimization framework used for the reconstruction . in section [ application / validation ] , we discuss the implementation of the proposed method in the context of an archetypal experimental setup , namely that of a transient thermal grating @xcite . in the same section , we validate our proposed method using synthetic data generated through monte carlo ( mc ) simulation . in section [ discussion ] we provide some comparison to effective thermal conductivity approaches and a discussion on the validity of the latter . in section [ conclusion ] we provide a summary of our work and suggestions for future improvement .

we present a method for reconstructing the phonon relaxation time distribution ( including polarization ) in a material from thermal spectroscopy data . the distinguishing feature of this approach is that it does not make use of the effective thermal conductivity concept and associated approximations . the proposed method is illustrated using monte carlo solutions of thermal grating relaxation as synthetic experimental data .

we present a method for reconstructing the phonon relaxation time distribution ( including polarization ) in a material from thermal spectroscopy data . the distinguishing feature of this approach is that it does not make use of the effective thermal conductivity concept and associated approximations . the reconstruction is posed as an optimization problem in which the relaxation times are determined by minimizing the discrepancy between the experimental relaxation traces and solutions of the boltzmann transport equation ( bte ) for the same problem . the latter may be analytical , in which case the procedure is very efficient , or numerical . the proposed method is illustrated using monte carlo solutions of thermal grating relaxation as synthetic experimental data . the reconstruction is shown to agree very well with the relaxation times used to generate the synthetic monte carlo data and remains robust in the presence of uncertainty ( noise ) .

1204.6045

i

understanding the properties of stars and the history of star formation in galaxies remains one of the most fundamental subjects in astrophysics . the _ hubble space telescope _ ( @xmath7 ) provides an important tool for this endeavor , since it enables the detailed study of stars and star clusters , not only in the milky way and its nearest neighbors , but in galaxies well beyond the local group . the wide field camera 3 ( wfc3 ) provides a particularly valuable new panchromatic imaging capability , with spectral coverage from the near - uv to the near - ir . this capability is especially useful for studying the stellar populations in nearby galaxies where individual stars are resolved . a good example of a multi - wavelength survey of nearby galaxies which employs resolved stars and star clusters is the acs nearby galaxy treasury ( angst ) program @xcite . this study includes @xmath065 galaxies out to @xmath03.5 mpc , and provides uniform multi - color ( @xmath8 ) catalogs of tens of thousands of individual stars in each galaxy . although the angst program provides an excellent survey for a wide range of studies , it does not provide observations in the @xmath9-band since the observations were obtained before wfc3 was installed on @xmath7 . the @xmath9-band is particularly useful for age - dating populations of young stars , which is the focus of the current paper . phat ( panchromatic hubble andromeda treasury ) is a related study that does take advantage of the new @xmath9-band capability on wfc3 . while nowhere as extensive as the multiple cycle treasury program phat survey , the current study of m83 is complementary in the sense that it provides similar observations of the resolved stellar component of a nearby spiral galaxy , and uses quite different analysis techniques , as will be discussed in sections 2 and 3 . future observations of m83 ( id:12513 , pi : william blair ) will expand the wfc3 dataset available for m83 from 2 to 7 fields . m83 ( ngc5236 ) , also known as the `` southern pinwheel '' galaxy , is a slightly barred spiral galaxy with a starbursting nucleus located at a distance of @xmath3mpc , i.e. , @xmath10 @xcite . the h@xmath11 emission can be used to pinpoint regions of recently formed massive stars along the spiral arms , while red supergiants can be found throughout the galaxy . the color - magnitude diagram ( cmd ) of resolved stars is a powerful diagnostic tool for understanding the stellar evolution and history of star formation of galaxies in detail . by comparing stellar evolution models to observed cmds , we are able to determine the ages of the stellar populations in galaxies . however , in active star - forming regions , the stars are often partially obscured by dust . applying a single extinction correction value for the whole galaxy often results in over- or under - estimates of the ages of individual stars . if the cmd is the only tool used to determine the ages , the spatial variations of dust extinction in galaxies and their effects on the determined ages are not readily apparent . the additional information available from the color - color diagram can remedy this problem . by using techniques developed in this paper , we can constrain the variations of dust extinction across m83 , and make corrections for individual stars . we also focus on spatial variations in the stellar properties throughout the galaxy . the @xmath7 wfc3 observations of m83 were performed in august 2009 as part of the wfc3 science oversight committee ( soc ) early release science ( ers ) program ( id:11360 , pi : robert oconnell ) . the central region ( [email protected] ) of m83 was observed in august , 2009 . a second adjacent field to the nnw was observed in march 2010 , and will be included in future publications . details of the wfc3 ers data calibration and processing are given by @xcite and @xcite . in this paper we present @xmath13 photometry of resolved stars in m83 and the resulting color - color and color - magnitude diagrams . we use @xmath14 vs. @xmath15 color - color diagrams to constrain the variation of dust extinction along the line - of - sight of each individual star , and correct @xmath16 vs. @xmath15 cmds for the extinction of individual stars to determine their ages . the high sensitivity and the superb resolving power in the wfc3 f336w - band plays a key role in allowing us to develop our extinction correction techniques , and demonstrate the performance of the newly installed wfc3 . this results in improved stellar age estimates , and a better understanding of the recent star - formation history of m83 . our investigations are focused on the followings : 1 . do we see spatial variations of stellar ages in m83 ? if so , can we use these variations to learn more about the evolution of the galaxy and what triggers star formation ? 2 . how well do various age estimates correlate ( i.e. , resolved stars , integrated light , clusters , number ratio of red - to - blue stars , h@xmath11 morphology , stellar surface brightness fluctuations , presence of wolf - rayet stars ) ? this paper is organized as follows . in 2 , we describe the observations , photometric analysis , and the extinction correction method . cmds and color - color diagrams of the 50 selected regions are then used to provide stellar age estimates , as described in 3 . comparisons with other age estimates ( i.e. , integrated light and star clusters ) are also made . in 4 , we compare the stellar ages to a variety of other parameters that correlate with age , including red - to - blue star ratios , @xmath17 morphology , and surface brightness fluctuations . section 5 includes a discussion of how these comparisons can be used as diagnostics , with special attention paid to the question of what spatial variations can tell us about the star formation history in m83 , and on the question of how star clusters might dissolve and populate the field . a summary of our primary results is provided in 6 . in appendix a , we investigate the locations of sources of wolf - rayet stars in our m83 field and discuss the correlation with the positions of young regions . in appendix b , we describe how the spatial resolution affects our measured colors and magnitudes , and our age estimates of stars in our m83 field .

we present a multi - wavelength photometric study of,000 resolved stars in the nearby spiral galaxy m83 ( ngc5236 ,mpc ) based on wide field camera 3 observations using four filters : f336w , f438w , f555w , and f814w . the locations of wolf - rayet stars are found to correlate with the positions of many of the youngest regions , providing additional support for our ability to accurately estimate ages .

we present a multi - wavelength photometric study of,000 resolved stars in the nearby spiral galaxy m83 ( ngc5236 ,mpc ) based on wide field camera 3 observations using four filters : f336w , f438w , f555w , and f814w . we select 50 regions ( an average size of 260pc by 280pc ) in the spiral arm and inter - arm areas of m83 , and determine the age distribution of the luminous stellar populations in each region . this is accomplished by correcting for extinction towards each individual star by comparing its colors with predictions from stellar isochrones . we compare the resulting luminosity weighted mean ages of the luminous stars in the 50 regions with those determined from several independent methods , including the number ratio of red - to - blue supergiants , morphological appearance of the regions , surface brightness fluctuations , and the ages of clusters in the regions . we find reasonably good agreement between these methods . we also find that young stars are much more likely to be found in concentrated aggregates along spiral arms , while older stars are more dispersed . these results are consistent with the scenario that star formation is associated with the spiral arms , and stars form primarily in star clusters and then disperse on short timescales to form the field population . the locations of wolf - rayet stars are found to correlate with the positions of many of the youngest regions , providing additional support for our ability to accurately estimate ages . we address the effects of spatial resolution on the measured colors , magnitudes , and age estimates . while individual stars can occasionally show measurable differences in the colors and magnitudes , the age estimates for entire regions are only slightly affected .

1602.08329

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the experimental technique of trapped one - dimensional atomic gases @xcite has now become a fundamental tool for revealing nontrivial effects in quantum many - body systems @xcite . for the interacting bose gas in one dimension ( 1d ) , the first set of exact results goes back to the pioneering work of girardeau @xcite on the impenetrable bose gas where the strong interacting limit is considered . the 1d bose gas interacting with the delta - function potentials , i.e. the lieb - liniger ( ll ) model , gives a solvable model for interacting bosons in 1d @xcite , where it is integrable even when the interaction parameter is generic . for the impenetrable bose gas which corresponds to the tonks - girardeau ( tg ) limit , i.e. the strong interacting limit of the ll model , the one - body reduced density matrix is derived and successfully expressed in terms of the determinant of a fredholm operator @xcite . the exact result is followed by several important developments in mathematical physics @xcite . furthermore , dynamical correlation functions of the ll model are now systematically derived @xcite . soliton - like localized excitations in a periodic 1d bose gas have attracted much interest recently and have been studied theoretically @xcite . here we remark that dark solitons are created experimentally in cold atoms @xcite , for instance , by the phase - imprinting method @xcite ( see also @xcite ) . localized quantum states are important for investigating dynamical responses of interacting quantum systems . quantum dark solitons in confining potentials are studied by semiclassical quantization @xcite , and those in thermal equilibrium of a quasi-1d bose gas by generating classical field ensembles @xcite . however , it is not clear even at zero temperature how we can construct quantum states associated with dark solitons in the many - body system of the ll model . let us consider the gross - pitaevskii ( gp ) equation , which describes bose - einstein condensation ( bec ) in the mean - field approximation @xcite . we also call it the nonlinear schrdinger equation . the gp equation has dark soliton solutions for the repulsive interactions , while it has bright soliton solutions for the attractive interactions @xcite . it was conjectured that dark solitons are closely related to lieb s type - ii excitations , i.e. one - hole excitations , by carefully studying the dispersion relations @xcite . the dispersion relations of the ll model are briefly compared with those of the classical nonlinear schrdinger equation in the weak coupling limit @xcite . however , it has not been shown how one can construct such a quantum state that leads to a dark soliton in the classical limit or what kind of physical quantity can show a property of a dark soliton for some quantum state . here we remark that each of the type - ii eigenstates has a flat density profile since the bethe ansatz eigenstates are translationally invariant . moreover , we consider dark solitons under the periodic boundary conditions , which are expressed in terms of elliptic functions @xcite . in this paper we demonstrate that a quantum state derived from the bethe ansatz eigenvectors of the ll model by taking the fourier transform of the type - ii excitations over a branch @xcite has many aspects closely related to classical dark solitons of the gp equation under the periodic boundary conditions . we call the state the _ quantum dark soliton state _ and a classical dark soliton under the periodic boundary conditions simply a _ classical dark soliton_. through the bethe ansatz we show several corresponding aspects in the weak coupling regime . firstly , the density profile of the quantum dark soliton state at an initial time is consistent with that of a classical dark soliton . here we call the graph of the expectation value of the local density operator for a given state versus the position coordinate the density profile of the state , and for a quantum dark soliton state we simply call it the density profile of quantum dark soliton ; we call the graphs of the square amplitude and phase in the complex scalar field of a classical dark soliton versus the position coordinate the density profile and phase profile of classical dark soliton , respectively . secondly , in time evolution the density profile of quantum dark soliton coincides with that of the corresponding classical dark soliton over the whole graph and they move together with the same velocity for a long period of time . thirdly , for the matrix element of the bosonic field operator between two quantum dark soliton states where one state has @xmath0 particles and another @xmath1 particles , the profiles of the square amplitude and phase at the initial time graphically agree with those of classical dark soliton , respectively . in time evolution the profiles of square amplitude and phase overlap with those of classical dark soliton , respectively , over the whole region and the corresponding profiles move together in time for a long period of time . here we remark that a classical dark soliton parametrized by elliptic functions becomes a standard dark soliton with open boundaries by simultaneously sending the system size to infinity and the elliptic modulus to unity . furthermore , in order to illustrate the method for constructing quantum dark solitons , in the 1d free fermions we show from the anti - commutation relations that a notch appears in the density profile of some superposition of one - hole excitations . interestingly , the density profile of the fermionic state coincides with that of quantum dark soliton for the 1d bose gas in the large coupling case , i.e. near the tg limit , not only at an initial time but also during the quantum dynamics for some period of time . the time evolution of the expectation value of the local density operator in the 1d bose gas should be important also from the renewed interest on the fundamentals of quantum statistical mechanics @xcite . the density profile of a quantum dark soliton state has initially a localized notch but collapses slowly to a flat profile in time evolution @xcite . the relaxation behavior is consistent with the viewpoints of equilibration of an isolated quantum system @xcite and thermalization due to the typicality of quantum states @xcite . we now argue that the density profile of quantum dark soliton has a finite lifetime but it is much longer than the quantum speed limit time of the quantum state in the weak coupling case . here we remark that the lifetime of a generic state is given by the quantum speed limit time for it @xcite . by observing the exact time evolution of the density profile of quantum dark soliton we estimate its lifetime . we shall show in section 5 that the observed life time is inversely proportional to the coupling constant . we thus suggest that the localized density profile of a quantum dark soliton is much more stable than the density profile of a generic quantum state in the weak coupling case . here we remark that girardeau and wright discussed a permanent quantum soliton for impenetrable bosons in 1d @xcite , which corresponds to the infinite coupling case of the ll model . we also argue that the behavior of the wavefunctions is nontrivial in the weak coupling limit for the ll model . the wavefunctions do not simply become close to such wavefunctions of the 1d free bosons that could be consistent with the mean - field picture , when the coupling constant approaches zero but it takes a nonzero value . the exact bethe ansatz wavefunctions consist of a large number of terms such as @xmath2 . furthermore , we can show that many - body correlations increase if we increase the particle number @xmath1 while we keep the coupling constant small but fixed and the particle density constant . for instance , the zero mode fraction in the ground state of the 1d bose gas , which we regard as the condensate fraction of bec , becomes small and decreases to zero if the number of particles increases while the coupling constant and the particle density are fixed @xcite . we suggest that it is also the case for quantum dark solitons i.e. , that some properties of quantum dark solitons corresponding to classical dark solitons do not necessarily hold if we increase the particle number @xmath1 while we keep the coupling constant small but fixed and the density of particles fixed . in fact , it is not _ a priori _ clear how valid the mean - field approximation is for quantum dark solitons even in the weak coupling case . here we remark that the breakdown of mean - field theory is addressed for impenetrable bosons @xcite , and a long - wavelength theory beyond the mean - field approximation is discussed for low - dimensional bose liquids @xcite . let us consider the hamiltonian of the ll model for @xmath1 bosons with coupling constant @xmath3 @xmath4 here we impose periodic boundary conditions with length @xmath5 . we employ a system of units with @xmath6 , where @xmath7 is the particle mass . we introduce the canonical bose field operator @xmath8 with the commutation relations @xcite @xmath9=\delta(x - x ' ) , \\ & [ \hat { \psi}(x , t ) , \hat { \psi}(x',t)]=[\hat { \psi}^{\dagger}(x , t ) , \hat { \psi}^{\dagger}(x',t)]=0 . \end{aligned}\ ] ] the second - quantized hamiltonian of the ll model is written in terms of the field operator @xmath8 as @xmath10 , \label{h2}\end{aligned}\ ] ] where @xmath11 is the chemical potential . the heisenberg equation of motion of this system has the form @xmath12 in the classical limit where the quantum field operator @xmath8 is replaced by a complex @xmath3-number field @xmath13 , equation ( [ eq : qnse ] ) becomes the following partial differential equation @xmath14 we call it the nonlinear schrdinger equation . the equation ( [ eq : nse ] ) can be solved by the inverse scattering method and has soliton solutions @xcite ( see also @xcite ) . we recall that it has dark soliton solutions for the repulsive interactions @xmath15 , while it has bright soliton solutions for the attractive interactions @xmath16 . for the attractive case , bright solitons are analytically derived from the quantum wave packets constructed through the fourier transform of the bound states @xcite . the construction was extended for optical fibers @xcite . time evolution of quantum states of bright solitons was investigated theoretically @xcite and experimentally @xcite . the effect of quantum noises on the quantum states of bright solitons was also studied @xcite . the contents of the paper consists of the following . in section 2 we briefly introduce the notation for the bethe ansatz , characterize the type ii excitation branch , and then construct quantum dark soliton states . we argue that the structure of quantum dark soliton states is analogous to the dirichlet kernel , and show for free fermions that the density profile of a superposition of one - hole excited states has a notch . it illustrates the construction of quantum dark soliton states . in section 3 we derive one - soliton solutions of the nonlinear schrdinger equation ( [ eq : nse ] ) under the periodic boundary conditions . we express the classical dark solitons in terms of elliptic functions similarly as in ref . @xcite . by sending the elliptic modulus @xmath17 to 1 , the classical dark solitons under the periodic boundary conditions become the standard classical dark solitons of the nonlinear schrdinger equation with open boundaries . furthermore , we calculate the logarithmic corrections to them , in particular , to the chemical potential and the soliton velocity , by which we can confirm the numerical estimates of the soliton parameters shown in section 4 at least approximately . in section 4 we show several corresponding aspects between the quantum dark soliton states and the corresponding classical dark solitons , which hold in the weak coupling case and should be rigorously valid when the coupling constant approaches zero with the density and the particle number @xmath1 fixed . firstly , we show that the density profile of quantum dark soliton at an initial time is consistent with that of classical dark soliton . secondly , we show that in exact time evolution the density profile of quantum dark soliton as a whole coincides with that of classical dark soliton for a long period of time . thirdly , we show that both the square amplitude and phase profiles for the matrix element of the quantum field operator @xmath18 in the ll model between the quantum dark soliton states with @xmath0 and @xmath1 particles overlap with those of classical dark soliton , respectively , all over the profiles . the square amplitude and phase profiles move in time evolution with exactly the same speed as those of classical dark soliton , respectively . furthermore , we remark that the density profile of a sum of one - hole excitations in the 1d free fermions overlap with that of quantum dark soliton in the 1d bose gas with the large coupling constant , i.e. in a regime close to the tg limit . for the matrix element of the fermionic field operator between two such fermionic states the square amplitude and phase profiles have several features in common with those of quantum dark soliton in the 1d bose gas for the large coupling case , respectively , although they do not overlap each other . we thus obtain useful tools to describe approximately the profiles of quantum dark soliton in the large coupling case . however , it is still quite nontrivial that the profiles of quantum dark soliton in the weak coupling case are consistent with those of classical dark soliton . in section 5 we argue that the lifetime of a notch in the density profile of quantum dark soliton is much longer than that of a generic state when the coupling constant @xmath3 is very small . we compare the lifetime of a notch in the density profile of quantum dark soliton with the quantum speed limit time , and show that the ratio of the former to the latter increases as the coupling constant decreases . it becomes infinitely large as the coupling constant approaches zero . thus , although the localized density profile collapses in time evolution , we call the quantum states quantum dark soliton states .

the classical solutions satisfy the periodic boundary conditions and we simply call them classical dark solitons . through exact solutions we show corresponding aspects between the states and the solitons in the weak coupling case : the quantum and classical density profiles completely overlap with each other not only at an initial time but also at later times over a long period of time , and they move together with the same speed in time ; the matrix element of the bosonic field operator between the quantum states has exactly the same profiles of the square amplitude and the phase as the classical complex scalar field of a classical dark soliton not only at the initial time but also at later times , and the corresponding profiles move together for a long period of time . we suggest that the corresponding properties hold rigorously in the weak coupling limit . furthermore , we argue that the lifetime of the dark soliton - like density profile in the quantum state becomes infinitely long as the coupling constant approaches zero , by comparing it with the quantum speed limit time . thus , we call the quantum states _ quantum dark soliton states_.

we present a series of quantum states that are characterized by dark solitons of the nonlinear schrdinger equation ( i.e. the gross - pitaevskii equation ) for the one - dimensional ( 1d ) bose gas interacting through the repulsive delta - function potentials . the classical solutions satisfy the periodic boundary conditions and we simply call them classical dark solitons . through exact solutions we show corresponding aspects between the states and the solitons in the weak coupling case : the quantum and classical density profiles completely overlap with each other not only at an initial time but also at later times over a long period of time , and they move together with the same speed in time ; the matrix element of the bosonic field operator between the quantum states has exactly the same profiles of the square amplitude and the phase as the classical complex scalar field of a classical dark soliton not only at the initial time but also at later times , and the corresponding profiles move together for a long period of time . we suggest that the corresponding properties hold rigorously in the weak coupling limit . furthermore , we argue that the lifetime of the dark soliton - like density profile in the quantum state becomes infinitely long as the coupling constant approaches zero , by comparing it with the quantum speed limit time . thus , we call the quantum states _ quantum dark soliton states_.

1005.3909

i

we carry out a study based on stellar population synthesis result of a type i lirg , irasf13308 + 5946 . we find that : \3 . we estimate the past ir luminosity during the starburst epoch . we find it has probably experienced a type i ulirg phase from @xmath237myr ago . when the star formation activity weakened recently , the ir luminosity decrease to the present level ( @xmath238 ) as a lirg . nuclear starburst and agn activity both contribute to the ir luminosity budget , with @xmath170% from starburst . it locates at the transitional position between ir qsos and pg qsos on the plots @xmath240 versus @xmath241 and @xmath228 versus @xmath242 . combining the results above , we conclude that irasf13308 + 5946 is probable an evolutionary transition object from a type i ulirg to a pg qso . the authors are grateful to dr . cai - na hao for her data through private communication . we thank r. cid fernandes for his warm - hearted explanation of and very valuable advices to the paper . we thank dr . stijn wuyts for valuable discussions . this project is supported by nsfc grant 10833006 , 10773014 and the 973 program grant 2007cb815406 . this work is based on the data from first , iras , 2mass and sdss observations . funding for the sdss and sdss - ii has been provided by the alfred p. sloan foundation , the participating institutions , the national science foundation , the u.s . department of energy , the national aeronautics and space administration , the japanese monbukagakusho , the max planck society , and the higher education funding council for england . the sdss web site is http://www.sdss.org/. the 2mass project is a collaboration between the university of massachusetts and the infrared processing and analysis center ( jpl / caltech ) . funding is provided primarily by nasa and the nsf . the university of massachusetts constructed and maintained the observatory facilities , and operated the survey . all data processing and data product generation is being carried out by ipac . survey operations began in spring 1997 and concluded in spring 2001 . alongi m. , bertelli g. , bressan a. , chiosi c. , fagotto f. , greggio l. , nasie . , 1993 , a&as , 97 , 851 arribas , s. , & colina , l. 2003 , apj , 591 , 791 arribas , s. , bushouse , h. , lucas , r. a. , colina , l. , & borne , k. d. 2004 , aj , 127 , 2522 binney , j. , & tremaine , s. 1987 , galactic dynamics ( princeton : princeton univ . press ) blanton , m. r. , et al . 2003 , aj , 125 , 2348 boller , t. , gallo , l. c. , lutz , d. , & sturm , e. 2002 , mnras , 336 , 1143 boroson , t. a. , & green , r. f. 1992 , apjs , 80 , 109 ( bg92 ) bressan a. , fagotto f. , bertelli g. , chiosi c. , 1993 , a&as , 100 , 647 bruzual g. , & charlot s. , 2003 , mnras , 344 , 1000 ( bc03 ) bushouse h. a. , borne k. d. , colina l. et al . 2002 , apjs , 138 , 1 calzetti , d. 1997 , in aip conf . 408 , the ultraviolet universe at low and high redshift : probing the progress of galaxy evolution , eds . w. h. waller , m. n. fanelli , j. e. hollis , & a. c. danks ( woodbury : aip ) , 403 calzetti , d. , armus , l. , bohlin , r.c . et al . , 2000 . apj 533 , 682 calzetti , d. , kinney , a.l . , storchi - 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we present a stellar population synthesis study of a type i luminous infrared galaxy ( lirg ) : irasf13308 + 5946 . ( 2000 ) and leitherer et al.s ( 2002 ) extinction curves , we estimate the past infrared ( ir ) luminosities of the host galaxy and find it may have experienced an ultraluminous infrared galaxy ( ulirg ) phase for nearly 300myr , so this galaxy has probably experienced a type i ulirg phase . both nuclear starburst and active galactic nuclei ( agn ) contribute to the present ir luminosity budget , and starburst contributes% . these results indicate that irasf13308 + 5946 is probably at the transitional phase from a type i ulirg to a classical qso .

we present a stellar population synthesis study of a type i luminous infrared galaxy ( lirg ) : irasf13308 + 5946 . it is a quasar with absolute magnitude and has a spectral feature of a seyfert 1.5 galaxy . optical images show characteristics of later stages of a merger . with the help of the stellar synthesis code ( cid fernandes et al . 2005 ) and both calzetti et al . ( 2000 ) and leitherer et al.s ( 2002 ) extinction curves , we estimate the past infrared ( ir ) luminosities of the host galaxy and find it may have experienced an ultraluminous infrared galaxy ( ulirg ) phase for nearly 300myr , so this galaxy has probably experienced a type i ulirg phase . both nuclear starburst and active galactic nuclei ( agn ) contribute to the present ir luminosity budget , and starburst contributes% . the mass of supermassive black - hole ( smbh ) is and the eddington ratio is 0.12 , which both approximate to typical values of pg qsos . these results indicate that irasf13308 + 5946 is probably at the transitional phase from a type i ulirg to a classical qso .

astro-ph0202216

i

we have predicted the properties of the low-@xmath6 dla population from an hi - selected galaxy survey of the local universe . the strong linear correlation between hi cross - section and hi mass means that selection effects should be very similar and allows us to use the statistics available for the properties of adbs galaxies to predict those of low-@xmath6 dlas . we find a much higher value of @xmath0 at @xmath6=0 from the adbs than was found for the optically - selected , spiral dominated sample of rao et al . the rao et al . data have been used as evidence that there was evolution of the dla population between @xmath6=0.5 and @xmath6=0 . however , the adbs prediction for the total cross - section at @xmath46 is consistent with @xmath0 for mg ii absorbers with fe ii absorption , systems that are good candidates for damped absorption and both of these data sets indicate that no evolution is required to explain the dla population . with the large error bars on all of the @xmath0 points , we can not rule out some evolution on the dla population , but it is not required . the @xmath0 distribution of galaxies as a function of hi mass is peaked around @xmath66 , and 50% of the galaxies should fall within a factor of @xmath93 of this value . to date only 2 dla absorbers have been studied in emission at 21 cm : one has a m@xmath67 of 1.3 @xmath68 ( bowen et al . 2001b ) , the other was not detected with a 3@xmath69 upper limit of 2.25 @xmath68 ( kanekar et al . 2001 ) . these results do not provide a statistical test of our hi mass distribution , but the results are consistent with what we would expect . the adbs sample indicates that the stellar luminosities of dlas should be distributed fairly evenly over several orders of magnitude . as with the hi masses , there are few galaxy / dla associations for which the galaxy redshift is confirmed and a luminosity is measured . the absorber candidates that have been identified ( steidel et al . 1994 , lebrun et al . 1997 , lanzetta et al . 1997 , rao & turnshek 1998 , pettini et al . 2000 ) span a wide range of luminosities . this range of dla luminosities is a warning for high redshift dla candidate searches the absorber candidates are not necessarily the nearest l@xmath70 galaxy to the line of sight . we have compared the internal kinematics of the adbs galaxies with those for high redshift dlas ( a low redshift sample does not exist ) . prochaska & wolfe ( 1997 ) , through simulations of gas disks , rule out galaxies with small velocity widths as the primary source of damped emission at a 97% confidence level . the adbs galaxies that we associate with the dlas locally have larger line widths than the prochaska & wolfe dwarf " galaxies , but the sample consists of a range of galaxy types dominated by galaxies with hi masses of @xmath90.1 and luminosities below l@xmath71 . we find that we can not rule out evolution in the kinematics of hi - rich galaxies , but it is not required and more massive hi disks then found in our local sample are not necessary to account for the kinematics . we thank jason x. prochaska for helpful discussions about the kinematics of dlas and the referee for a thoughtful reading of this paper . we would also like to thank the vla staff for their assistance in the observations and reduction of this data , and the 2mass team for all of the hard work that went into making the survey a reality .

we present a study of the expected properties of the low redshift damped absorber population determined from a sample of hi - selected galaxies in the local universe . we use measurements of the number density and hi cross - section of galaxies to show that the total hi cross - section at column densities sufficient to produce damped absorption is consistent with no evolution of the absorber population . however , because of the large dispersion in the correlation between hi mass and stellar luminosity , we find that the distribution of as a function of l is fairly flat . additionally , we examine the line widths of the hi - selected galaxies and show that there may be evolution in the kinematics of hi - rich galaxies , but it is not necessary for the higher redshift population to contain a greater proportion of high mass galaxies than we find locally .

we present a study of the expected properties of the low redshift damped absorber population determined from a sample of hi - selected galaxies in the local universe . because of a tight correlation between the hi mass and hi cross - section , which we demonstrate spans all galaxy types , we can use our hi - selected sample to predict the properties of the absorption line systems . we use measurements of the number density and hi cross - section of galaxies to show that the total hi cross - section at column densities sufficient to produce damped absorption is consistent with no evolution of the absorber population . we also find that the distribution is dominated by galaxies with hi masses near 10 . however , because of the large dispersion in the correlation between hi mass and stellar luminosity , we find that the distribution of as a function of l is fairly flat . additionally , we examine the line widths of the hi - selected galaxies and show that there may be evolution in the kinematics of hi - rich galaxies , but it is not necessary for the higher redshift population to contain a greater proportion of high mass galaxies than we find locally .

1401.8247

r

we have carried out brownian dynamics ( bd ) simulation for a wide range of chain length ( @xmath46=16 - 2048 ) and bending constant ( @xmath22 = 0 - 320 ) . because of the argument given in sec . [ scaling_section ] very long chains were needed to clearly identify the crossover regimes . first we present the equilibrium properties of the chains in section [ eqlb_section ] followed by the dynamical quantities presented in sec . [ dynamics_section ] . from the bd simulation we have monitored the average @xmath113 and replacing @xmath114 in eqn . [ lp1 ] calculated the chain persistence length for various values of @xmath22 . one expects that eqns . [ lp2d ] and [ lp1 ] must give results that agree with each other when the persistence length is much larger than the range of the excluded volume interaction , but that the two results agree even for small value of @xmath115 we believe is a nontrivial result . the comparison of calculated @xmath1 by different methods is shown in table [ table ] . we also observe that the @xmath1 calculated using eqn . [ lp1 ] practically has no dependence on chain length @xmath46 . we have used eqn . [ lp1 ] for further analysis of our data in the subsequent sections . note that this behavior differs from the result found by hsu _ for a lattice model @xcite , where a renormalization of @xmath1 by excluded volume was shown to occur . thus on length scales of order @xmath1 there is no strict universality between different models . we emphasize , however , that the persistence length , when it is supposed to measure the local intrinsic stiffness of the chain ( as supposed in the kratky - porod model ) , can not be estimated from the asymptotic decay of the bond vector correlation function @xmath116 with the `` chemical distance '' @xmath23 along the chain , that is the conventional definition given in all the polymer physics textbooks : as will be shown below ( sec . [ bond_section ] ) , we verify the predicted @xcite power law behavior for very long chains and large @xmath23 , previously seen already for a lattice model of semi - flexible chains by hsu _ et al . _ although lattice and continuum models have different statistical properties when one considers lengths of the scale @xmath1 , for much larger scales the behavior should be universal , and hence this power law decay is expected . we also note that a definition of the persistence length dating back to flory , where one considers the correlation of the first bond vector @xmath117 with the end - to - end vector @xmath60 , @xmath118 which has been advocated by cifra @xcite as an `` exact expression '' , must similarly be refuted : in 2d , redner and privman @xcite have shown that @xmath119 for large @xmath46 is logarithmically divergent with @xmath46 already for a simple self - avoiding walk ( saw ) . for completeness , we mention that an analogous definition for inner bond vectors @xmath120 even shows a power - law divergence , @xmath121 , both in 2d and 3d ( see hsu et al . @xcite and @xcite ) . thus we urge that the results and discussion presented in this section need to be taken seriously in writing future review articles and newer edition of the existing textbooks . the extension of flory theory for a semi - flexible chain has been done by schaefer , joanny , and pincus @xcite and nakanishi @xcite which states that the rms of the end - to - end distance @xmath122 in @xmath123 spatial dimensions exhibits the following scaling relation @xmath124 where @xmath125 is the bond length ( @xmath109 in our simulation ) . for @xmath17 this reduces to @xmath126 . in other words if the end - to - end distance is scaled by the appropriate power of the persistence length @xmath1 , then this renormalized end - to - end distances @xmath127 for different values of the chain stiffness parameter @xmath22 will fall onto the same master plot . for a large combination of chain length @xmath46 and stiffness parameter @xmath22 we observe excellent fit to our equilibrium data for @xmath128 to eqn . [ scaling ] as shown in fig . [ r1n ] . versus @xmath129 for various values of the chain stiffness parameter . all the data for different stiffness parameter collapse on the same master plot . the solid line is a fit to a straight line . only data points for which the contour length exceeds the persistence length were included in this plot . ] -0.5truecm it is worth noting that the persistence length calculated from eqn . [ lp1 ] using the formula from wlc model uses the local correlation , namely the angle between the subsequent bond vectors and hence is expected to provide a decent value of the persistence length when ev is also included . the excellent collapse of the data for @xmath130 for various values of the stiffness parameter ( @xmath131 ) on the same master curve indicates that eqn . [ lp1 ] _ can be used as the standard definition of persistence length even in presence of the ev effect_. having established the definition of persistence length which validated eqn . [ scaling ] , we now use eqn . [ rn_wlc ] presented in section [ wlc_section ] to analyze the bd simulation results for the end - to - end distance . please note that limiting cases of eqn . [ rn_wlc ] are either a gaussian coil ( @xmath28 for @xmath132 ) or a rod ( @xmath30 for @xmath133 ) . we have used simulation results to plot @xmath134 for a large number of values(@xmath135 ) of @xmath12 ( @xmath136 ) . as a function of @xmath12 obtained from different combinations of chain length @xmath46 and stiffness parameter @xmath22 ( log - log scale ) . the solid ( maroon ) line is a fit to the formula @xmath137 for @xmath138 . the inset shows the same for small values of @xmath139 which clearly indicates that limiting slope of unity ( @xmath140 ) for @xmath141 . ] -0.5truecm we have also taken additional care that a given value of @xmath12 is generated for different combinations of @xmath0 and @xmath1 . these results are shown in fig . for @xmath142 we observe that @xmath143 while for @xmath15 the data very nicely fit with @xmath144 . this is consistent with prior mc results using a lattice model by hsu _ et al . _ . however , since our studies are done in continuum we are able to get data that is for much shorter length scales . the fact that in the rod - like regime ( @xmath145 ) the best fit " exponent is 0.95 rather than the asymptotic value 1.0 is due to the fact that for @xmath22=32 and 64 the rods " still exhibit nonnegligible transverse fluctuation unlike truly stiff rods . the gaussian behavior that eqn . [ rn_wlc ] implies @xmath146 for large @xmath0 would mean a horizontal straight line in fig . [ rn ] , but no indication of such a behavior is seen . the simulation data then implies the strict absence of a gaussian limit for 2d swollen semi - flexible chains due to severe dominance of the ev interaction . this result should be contrasted with the simulation results in 3d , where one sees a gradual crossover from rod limit to the ev limit ( in 3d ) passing through a gaussian regime @xcite . it is reasonable to define an average axis for a polymer chain in the rod limit ( @xmath147 ) . in this limit using wlc chain hamiltonian the transverse fluctuation with respect to this average axis has been shown @xcite to obey the following equation @xmath148 the above equation implies that the roughness exponent @xcite @xmath149 ( @xmath150 ) for a weakly bending rod . starting from an extremely stiff chain where the transverse fluctuations are expected to be governed by the roughening exponent @xmath149 , if we approach the limit of fully flexible chain , then the fluctuations become isotropic and in this limit one can expect that @xmath151 , so that in 2d @xmath152 . in order to calculate the transverse fluctuation , in our simulation , for each configuration of the polymer chain , we choose @xmath153 as the longitudinal axis and calculate transverse fluctuations as follows : @xmath154 where @xmath155 is the perpendicular distance of the @xmath156 monomer with respect to the instantaneous direction @xmath60 . we have repeated this calculation for several chain lengths from extremely stiff chains to fully flexible chains . this is shown in fig . [ tfl](a ) . if one does not analyze the data carefully , one might be misled to conclude that the exponent @xmath157 increases gradually with the chain stiffness @xmath22 . however , as we will see that the proper interpretation requires a scaling description in terms of @xmath12 as scaling variable . the interesting aspect of this rescaled dimensionless transverse fluctuation is shown in fig . [ tfl](b ) as a function of rescaled length @xmath12 where the rescaled fluctuations collapse on the same master curve . this plot exhibits a maximum and then decreases gradually for large value of @xmath12 . it is worth noting that analytical results do not exist for chains with intermediate stiffness . the physical origin of this maximum can be interpreted as follows . starting from the stiff chain limit when @xmath142 it increases for a more flexible chain when the chain undergoes shape changes from rod to ellipsoid - like blob , and finally to isotropic spherical blobs . naturally , when chain flexibility is defined in units of the persistence length for some value of @xmath12 ( @xmath158 3 from fig . [ tfl](b ) ) the fluctuation becomes maximum before it becomes isotropic . to the best of our knowledge this result is new and in principle can be used to measure the persistence length of a semiflexible polymer by measuring the transverse fluctuations using fluorescence probes . this would require numerically analyzing a large number of images of semiflexible chains ( of a given kind of polymer ) with varying contour length . for each image of a chain one can extract @xmath0 as well as the end - to - end vector @xmath60 and then use eqn . [ lbot ] to extract @xmath159 . plotting then @xmath11 versus @xmath0 one would find @xmath160 from the position of the maximum of this plot . the orientational correlation between successive bonds decays exponentially in a wlc model according to eqn . however , recent monte carlo ( mc ) studies by hsu , paul , and binder have verified that a swollen semiflexible chain in 2d exhibits a power law decay as a function of the separation @xmath23 between the beads @xcite given by @xmath161 for a fully flexible chain @xmath162 in 2d so that @xmath163 . it is then expected that a semiflexible chain will exhibit the same behavior when @xmath15 . while for very stiff chain one needs to have extremely long chain to see this asymptotic regime for large @xmath15 , yet satisfying the condition @xmath164 , from our simulation we clearly see this trend for moderate values of @xmath22 . we calculated the bond correlation function from its definition and tested both eqn . [ bexp ] and [ bpower ] . first in fig . [ semilog ] we show the semi - log plot of eqn . [ bexp ] . is calculated from the slope of the fitted line , which is very close to the values ( correspondingly 105.8 , 52.6 , 25.9 , 12.6 , 6.05 , 3.31 ) from @xmath165 ( see table [ table ] ) . ] the straight lines are fitted only with the first several data points in order to get values of @xmath1 which are close to those calculated from @xmath165 . the deviation from the initial slope ( only after few points ) clearly shows that eqn . [ bexp ] predicted by the wlc model does not hold good for a 2d swollen chain as expected from the result of fig . [ rn ] . fig . [ loglog ] shows the log - log plot of eqn . [ bpower ] where we have also included the graph for a fully flexible chain for reference . as a function of @xmath23 for various combinations of @xmath46 and @xmath22 . while for large @xmath22 the asymptotic slope of @xmath166 is preempted by finite size effect , for @xmath167 and @xmath168 the slope of @xmath169 is clearly visible ; ( b ) same as in ( a ) but using rescaled variable @xmath170 which shows excellent data collapse for @xmath171 . the inset shows the same but only for the cases to emphasize that in the limit @xmath172 there is a perfect data collapse for the power law scaling . , title="fig : " ] + as a function of @xmath23 for various combinations of @xmath46 and @xmath22 . while for large @xmath22 the asymptotic slope of @xmath166 is preempted by finite size effect , for @xmath167 and @xmath168 the slope of @xmath169 is clearly visible ; ( b ) same as in ( a ) but using rescaled variable @xmath170 which shows excellent data collapse for @xmath171 . the inset shows the same but only for the cases to emphasize that in the limit @xmath172 there is a perfect data collapse for the power law scaling . , title="fig : " ] please note that even for a fully flexible chain it requires a rather long chain length ( @xmath173 ) to clearly see the regime with slope with @xmath174 over an appreciably broad range of abscissa values . for comparison we put the graph for a shorter fully flexible chain of @xmath175 . here the curve starts to decrease faster before it reaches the slope corresponding to @xmath174 . naturally for stiffer chains ( which could be thought of a flexible chain of length @xmath12 for this purpose ) for the maximum chain length @xmath176 considered in this paper we only see the regime characterized by @xmath163 only for @xmath177 and 4.0 . it is expected that the bond vector correlation also exhibits a scaling behavior when studied as a function of @xmath170 , as even for moderate values of @xmath178 ( see fig . [ semilog ] ) , this length rescaling @xmath179 overrides the exponential decay for small @xmath170 . with a choice of distance between monomers in units of @xmath1 all chains are expected to behave as fully flexible chains . therefore , if we use the renormalized distance @xmath170 to replot fig [ loglog](a ) then one expects that the power law correlation for chains with different stiffness will collapse on the same master plot . this is shown in fig . [ loglog](b ) . we observe excellent data collapse for @xmath171 . deviations from this collapse occur at a progressively larger value of @xmath170 as the ratio @xmath12 increases either by increasing the contour length @xmath0 for a fixed @xmath1 or for the same contour length @xmath0 and lowering the value of @xmath1 . this is expected , since eqn . [ bpower ] can hold only for @xmath164 . of course , a numerical study of the regime @xmath180 for large @xmath1 is prohibitively difficult . however , the inset shows both the data collapse and the @xmath163 regimes for two chain lengths ( @xmath173 and 2048 ) and for two values of @xmath22 ( @xmath115 and @xmath181 ) which proves beyond doubt that for @xmath182 the bond autocorrelation exhibits a power law decay of a fully flexible chain . the hamiltonian for the wlc chain model has been studied by many analytic technics assuming that for moderate chain lengths and stiff enough chains the ev effect will not dominate . since we already established the severe dominance of the ev effect , gaussian regime is absent for a 2d swollen chain . here we compare the radial distribution functions for chains with different stiffness . in particular , we compare the results from our simulation with analytic results of wilhelm and frey @xcite in 2d . for the wlc model wilhelm and frey @xcite have derived expressions for the radial distribution functions @xmath183 ( both in 2d and 3d ) in terms of infinite series . in 2d the expression for @xmath183 is given as follows . \times \nonumber \\ \mathrm{exp}\left [ -\frac{(l+1/4)^2}{2t(1-r)}\right ] d_{3/2}\left [ \frac{2l+1/2}{\sqrt{2t(1-r ) } } \right ] , \label{frey}\end{aligned}\ ] ] where @xmath185 , @xmath186 and @xmath187 is a parabolic cylinder function . for the whole range of values of @xmath22 in our simulation , when we plot the analytic result of eqn . [ frey ] we find that this series is fully dominated by the first term and we did nt see visual differences from the plot that includes the first four terms . therefore , in fig . [ distri ] we plot only the first term of this series ( @xmath188 ) term given by @xmath189^{5/4 } \times \nonumber \\ \mathrm{exp}\left [ -\frac{(1/4)^2}{2t(1-r)}\right ] d_{3/2}\left [ \frac{1/2}{\sqrt{2t(1-r ) } } \right ] \label{freyl0}\end{aligned}\ ] ] please note that for the radial distribution function wilhelm and frey @xcite does not take into account excluded volume effects . in fig . [ distri ] we have also included the distribution for a completely flexible chain ( @xmath190 ) for comparison purposes . for @xmath181 and 8 ( _ i.e. _ , @xmath191 ) the simulated distribution still is intermediate between the behavior of fully flexible chains ( which we expect to result for @xmath192 for all @xmath22 ! ) and the distribution of the kratky - porod model . we now look at the dynamics of a swollen semi - flexible chain . we are using a brownian dynamics ( bd ) scheme and therefore , hd effects are not included in our studies . however , for polymers adsorbed on a flat surface simulation studies have shown that the hd effects are negligible for no - slip boundary conditions @xcite . thus we expect the results are relevant for a fair comparison of experimental studies . also we would like to point out that unlike equilibrium properties , computational time increases dramatically to study time dependent properties for the same chain length . thus the diffusion and relaxation studies for the longest chain length reported in this paper took significant time for well converged runs . we verified that the diffusion constant @xmath193 is independent of the persistence length @xmath1 and depends only on the chain length @xmath46 and scales as @xmath194 with very good accuracy , as expected in a bd formalism . next we consider monomer relaxation dynamics of the chain . following previous work for the relaxation of a fully flexible chain @xcite we have monitored various quantities pertaining to a single monomer relaxation . these quantities have been studied in the past using bd algorithm @xcite , and dynamical monte carlo algorithms ( dmc ) @xcite , including the bond - fluctuation model ( bfm ) @xcite . the dynamics of the individual monomers and the collective dynamics for the whole chain have been characterized by the functions @xmath42 , @xmath195 , @xmath196 , @xmath197 , and @xmath198 . they are defined as follows : @xmath199 ^ 2\rangle , \label{g1}\\ & g_2(t ) = \nonumber \\ & \langle \left [ \left(\mathbf{r}_{n/2}(t ) - \mathbf{r}_{cm}(t ) \right ) - \left ( \mathbf{r}_{n/2}(0 ) - \mathbf{r}_{cm}(0)\right ) \right]^2 \rangle,\label{g2}\\ & g_3(t ) = \langle \left [ \mathbf{r}_{cm}(t ) - \mathbf{r}_{cm}(0)\right]^2 \rangle , \label{g3}\\ & g_4(t ) = \langle \left [ \mathbf{r}_{end}(t ) - \mathbf{r}_{end}(0)\right]^2 \rangle , \label{g4}\\ & g_5(t ) = \nonumber \\ & \langle \left [ \left ( \mathbf{r}_{end}(t ) - \mathbf{r}_{cm}(t)\right ) - \left(\mathbf{r}_{end}(0 ) - \mathbf{r}_{cm}(0)\right ) \right]^2 \rangle . \label{g5}\end{aligned}\ ] ] the quantities @xmath42 , @xmath196 , and @xmath197 reflect the time dependence of the position of the middle monomer , the center of mass , and the end monomer of the chain respectively . at late times for distances greater than the gyration radius the functions @xmath42 , @xmath196 and @xmath197 will describe the motion of the entire chain . consequently , @xmath200 for @xmath201 where @xmath57 is given by eqn . [ tau2 ] . the quantities @xmath195 and @xmath198 on the contrary measure the relative displacement of the middle and the end monomer with respect to the center of mass of the chain . the functions @xmath195 and @xmath198 saturate at finite static values @xmath202 and @xmath203 respectively , since for @xmath204 the orientations of the vectors @xmath205 , @xmath206 are uncorrelated with their counterparts at @xmath207 . to study monomer dynamics , we have carried out bd simulation for various chain lengths @xmath208 and for chain stiffness @xmath209 . we only show a limited set of data . as a reference and for comparison with the data for chains with @xmath210 , we first show data for a fully flexible chain where we expect to see a single crossover dynamics from @xmath81 at an early time for @xmath211 to a purely diffusive dynamics for the entire chain ( @xmath212 ) . this is shown in fig . [ kappa0 ] for chain length @xmath175 and 1024 respectively . ( @xmath213 ) for a fully flexible chain ( @xmath214 ) of length @xmath175 . ( b ) @xmath215 ( @xmath216 ) for a fully flexible chain of length @xmath173.,title="fig : " ] + ( @xmath213 ) for a fully flexible chain ( @xmath214 ) of length @xmath175 . ( b ) @xmath215 ( @xmath216 ) for a fully flexible chain of length @xmath173.,title="fig : " ] we have checked that the graphs for other chain length are similar and have the @xmath217 dependence for the fully flexible chain . at late times the functions @xmath218 and @xmath219 saturates and the functions @xmath72 , @xmath220 and @xmath221 grow linearly as a function of time , becoming practically indistinguishable from each other . similar studies have been reported earlier by grest and kremer @xcite and by gerroff , milchev , paul , and binder @xcite . however , our studies are much more exhaustive and quantitatively captures the crossover from @xmath217 to the purely diffusive regime which were only qualitative in previous studies and for shorter chains . we now show data for the double crossover to support our scaling analysis for @xmath210 . in particular we show data for chain length @xmath175 with @xmath2222.0 and @xmath173 with @xmath2222.0 , 4.0 respectively . unlike fig . [ kappa0 ] for @xmath190 , plots for @xmath42 , @xmath195 shown in fig . [ kappa_2_4 ] are characterized by a @xmath41 slope which then crosses over to the regime characterized by @xmath223 and that @xmath42 eventually merges with @xmath196 . when we compare fig . [ kappa_2_4](a ) and fig . [ kappa_2_4](b ) consistent with the prediction of scaling theory we observe that the extent of the @xmath41 region in both the graphs are the same as they have the same value of @xmath224 , although the chain lengths are different . likewise , comparing fig . [ kappa_2_4](b ) and fig . [ kappa_2_4](c ) we note that since both plots have the same chain length the beginning of the second crossover occur almost at the same time ( @xmath225 ) but since the latter chain is twice as stiff it has a wider @xmath41 regime resulting in a narrower span of @xmath217 regime . thus fig . [ kappa_2_4 ] unambiguously confirms predictions from the scaling theory . we observe that at early time @xmath226 ; however the width of the region @xmath227 is narrower than that of @xmath81 and it exhibits a slightly lower value of slope before saturation . considering that the crossovers are broad , we believe that this is due to finite size effect as it is evident if we compare fig . [ kappa_2_4](a ) and fig . [ kappa_2_4](b ) . in the latter case , which is for a larger chain length , the difference between @xmath42 and @xmath195 are much smaller and we notice that the difference begins at a later time . ideally for very large system the point when @xmath42 would change its slope towards @xmath212 , @xmath195 also tend to saturate . the sharpness of this feature would require a much larger system . we also note the same feature in fig . [ kappa0 ] . ( black ) , @xmath195 ( red ) and @xmath196 ( green ) as a function of time on a log - log scale for chain length @xmath175 and @xmath228 . the blue and magenta dashed lines correspond to straight lines @xmath229 , and @xmath230 , respectively , where @xmath231 and @xmath232 are constants . ( b ) same but for @xmath173 and @xmath228 . ( c ) same but for @xmath173 and @xmath233 . note that for a fully flexible chain the slope of the curve @xmath234 would monotonously increase with time , unlike the present case.,title="fig : " ] + ( black ) , @xmath195 ( red ) and @xmath196 ( green ) as a function of time on a log - log scale for chain length @xmath175 and @xmath228 . the blue and magenta dashed lines correspond to straight lines @xmath229 , and @xmath230 , respectively , where @xmath231 and @xmath232 are constants . ( b ) same but for @xmath173 and @xmath228 . ( c ) same but for @xmath173 and @xmath233 . note that for a fully flexible chain the slope of the curve @xmath234 would monotonously increase with time , unlike the present case.,title="fig : " ] + ( black ) , @xmath195 ( red ) and @xmath196 ( green ) as a function of time on a log - log scale for chain length @xmath175 and @xmath228 . the blue and magenta dashed lines correspond to straight lines @xmath229 , and @xmath230 , respectively , where @xmath231 and @xmath232 are constants . ( b ) same but for @xmath173 and @xmath228 . ( c ) same but for @xmath173 and @xmath233 . note that for a fully flexible chain the slope of the curve @xmath234 would monotonously increase with time , unlike the present case.,title="fig : " ] + but the plots for @xmath42 quite clearly show three distinct scaling regimes of @xmath52 crossing over to @xmath81 and then merging with @xmath67 at late times . we have further confirmed the existence of this double crossover by plotting @xmath235 as shown in fig . [ g1_min ] . the existence of an initial plateau ( @xmath236 ) , followed by a decay ( @xmath237 ) , and of a minimum ( near @xmath57 ) before the diffusion ( @xmath238 ) starts further demonstrates quite conclusively that the exponent changes from @xmath239 . we would like to mention that because of the width of the @xmath217 regime becomes narrower for stiffer chains we were unable to see this regime unambiguously in simulation of shorter chains and/or larger @xmath22 ( _ e.g. _ , for @xmath175 and @xmath240 ) . while for @xmath175 the double crossover is clear for @xmath177 , but becomes ambiguous for @xmath241 which required an increased chain length of @xmath173 . as expected , the crossovers are rather gradual , spread out over a decade in time @xmath43 each , and hence for chains that are not long enough the existence of these regimes is missed in previous work . as a function of @xmath43 corresponding to the plots of fig . [ kappa_2_4](a ) ( red ) , ( b ) ( blue ) and ( c ) ( green ) respectively . in each graph the minimum occurs in the intermediate regime characterized by @xmath217 . , title="fig : " ] + the interplay of rouse modes and the bending modes with respect to the monomer dynamics of semiflexible chains was considered in early work by harnau _ et al . _ @xcite , in the framework of a rouse model generalized by higher order terms to account for chain stiffness . they ignored excluded volume , and considered a single chain length , attempting to model @xmath242 alkanes in a melt . they found that their results were neither consistent with the rouse behavior ( @xmath243 ) nor with the power law due to bending modes ( @xmath244 ) . in our view , the chain length studied in this work was too small to observe both power laws separately , rather all their data fall in a regime of smooth crossover . having established the double - crossover we now further investigate the consequence of scaling prediction that the first crossover occurs at time @xmath245 when @xmath246 . [ g1g2 ] shows a plot of @xmath247 as a function of rescaled time @xmath248 which shows data collapse for @xmath249 and @xmath250 for various combinations of chain length @xmath46 and @xmath22 confirming the length and the time scales for these crossovers . note that the scaling theory of section [ scaling_section ] implies @xmath251 where @xmath47 , @xmath57 are the times defined in eqn . [ tau1 ] and [ tau2 ] . if the first argument of the scaling function @xmath252 , @xmath253 is small in comparison to unity , we can approximate eqn . [ gtilde ] as @xmath254 , which reduces to eqn . [ granek ] . for @xmath255 we can rewrite the scaling function as @xmath256 note that @xmath257 remains constant when we increase @xmath46 and @xmath1 by the same factor : this observation explains that the scaling of the data in fig . [ g1g2 ] encompasses the full range of times . and @xmath258 as a function of @xmath259 on a log - log scale for chain lengths @xmath260 , 1024 with @xmath177 , 4.0 respectively . the dot - dashed and dashed lines correspond to slopes 0.75 ( maroon ) and 0.6 ( magenta ) respectively . ]

our theory captures the early time monomer dynamics of a stiff chain characterized by dependence for the mean square displacement(msd ) of the monomers , but predicts a first crossover to the rouse regime of for , and a second crossover to the purely diffusive dynamics for the entire chain at . we further observe that the normalized transverse fluctuations of the semiflexible chains for different stiffness as a function of renormalized contour length collapse on the same master plot and exhibits power law scaling at extreme limits , where for extremely stiff chains ( ) , and for fully flexible chains . finally , we compare the radial distribution functions obtained from our simulation studies with those obtained analytically .

we present a unified scaling description for the dynamics of monomers of a semiflexible chain under good solvent condition in the free draining limit . we consider both the cases where the contour length is comparable to the persistence length and the case . our theory captures the early time monomer dynamics of a stiff chain characterized by dependence for the mean square displacement(msd ) of the monomers , but predicts a first crossover to the rouse regime of for , and a second crossover to the purely diffusive dynamics for the entire chain at . we confirm the predictions of this scaling description by studying monomer dynamics of dilute solution of semi - flexible chains under good solvent conditions obtained from our brownian dynamics ( bd ) simulation studies for a large choice of chain lengths with number of monomers per chain n = 16 - 2048 and persistence length lennard - jones ( lj ) units . these bd simulation results further confirm the absence of gaussian regime for a 2d swollen chain from the slope of the plot of which around changes suddenly from , also manifested in the power law decay for the bond autocorrelation function disproving the validity of the wlc in 2d . we further observe that the normalized transverse fluctuations of the semiflexible chains for different stiffness as a function of renormalized contour length collapse on the same master plot and exhibits power law scaling at extreme limits , where for extremely stiff chains ( ) , and for fully flexible chains . finally , we compare the radial distribution functions obtained from our simulation studies with those obtained analytically .

1401.8247

i

in conclusion , we have studied conformations , fluctuations , and crossover dynamics of a swollen semiflexible chain in 2d . we first developed a scaling theory which generalizes early time monomer dynamics of a fully flexible chain for a semiflexible chain characterized by its contour length and the persistence length . we predict a double crossover which arises due to the presence of an additional length scale introduced through the chain persistence length . monomer dynamics up to a length scale @xmath1 is independent of chain length and is characterized by the @xmath41 power law . at a later time @xmath261 when the size of the fluctuations becomes bigger than @xmath1 the dynamics begin to look like that of a fully flexible chain and characterized by the well known @xmath262 growth . both of these exponents have been discussed in the literature separately but have not been emphasized that before the entire chain reaches purely diffusive regime , there ought to be two and not one crossover , the first crossover differentiates chains of different stiffness . previously the dynamics of monomer msd of semiflexible polymers has also been studied by harnau _ et al . _ @xcite , using a rouse - type model generalized to include chain stiffness . they saw a gradual crossover , in between bending modes and rouse modes , but did not consider the scaling description of the crossover . note that excluded volume effects were absent in their model , and hence it is not applicable in @xmath17 dimensions . motivated by recent lattice mc results for a swollen chain in 2d predicting the absence of a gaussian regime we undertook similar studies in 2d continuum using bd simulation . while checking our data for the rms end - to - end distance for chain of different contour length and persistence length we discovered that we regain the well known results for the end - to - end distance due to schaefer , joanny , and pincus @xcite and nakanishi @xcite provided we use the definition of the persistence length given by either the lattice or continuum version of the kratky - porod wlc model . we explain this by noting that the persistence length being a local property of a chain does not depend on the ev interaction . this is further reassured when we note that the persistence length calculated this way does not depend on the chain length unlike well used textbook definition of persistence length where the projection of the end - to - end vector on the first bond is used as the definition and does depend on the chain length . therefore , we emphasize that the latter definition needs to be discarded . we also confirm the absence of the gaussian regime in the continuum bead - spring model where the swollen chain for @xmath142 behaves like a rod and thereafter always behaves like a swollen chain . considering that there are increased number of activities to explore the properties of biomolecules on a surface , our result ( fig . [ rn ] ) will be extremely valuable to analyze the experimental data correctly for stiff molecules on flat surfaces . it has not escaped our attention that many such reported analyses are still done using the wlc model and/or calculating the chain persistence length from projected end - to - end to the first bond . transverse fluctuations in a stiff chain has been addressed analytically in the literature only in the extremely stiff chain limit where one finds that it is described by the roughening exponent . analytic calculations for moderately stiff chains are hard to carry out , and to date there are no results for transverse fluctuations spanning the entire regime from a stiff to a fully flexible chain . we have numerically obtained this result and pointed out that the appropriate length variable to analyze the data is to use the persistence length as the unit of length . when we use @xmath12 as the length scale to plot transverse fluctuation we discover the non - monotonic behavior of this fluctuation reaching a maximum for some @xmath263 . we point out that this universal scaling of the transverse fluctuation can be used to measure the persistence length of the chain . another accompanying consequence of the absence of gaussian regime for a swollen chain in 2d is the decay of the bond correlation function which exhibits a power law decay . again , by choosing the normalized contour segment @xmath170 as the appropriate variable we regain the exponent @xmath163 which describes the decay of bond autocorrelation for a fully flexible chain . we must point out that many of these results and analyses on chain conformations and equilibrium fluctuations point to a common theme . in the limit @xmath15 we recover the expected behavior of a fully flexible chain and chains with different stiffness exhibit universal scaling behavior when persistence length is chosen as the unit of length . this general idea extends to our study of monomer dynamics as well . we have provided a new scaling theory of monomer dynamics for semiflexible polymers in 2d . our theory predicts novel crossover dynamics at an intermediate time when the fluctuations of the monomers @xmath264 . around this time the monomer dynamics become the same as that of a fully flexible swollen chain characterized by @xmath265 in 2d . the theory expands the existing scaling theory for monomer dynamics for a wlc and that of a fully flexible chain to include the effect of the chain persistence length . fully flexible swollen chains are self - similar objects , while a polymer segment up to its own persistence length is not . therefore , it is expected that for length scales up to @xmath1 the dynamics will have different characteristics due to bending modes arising out of the chain stiffness . the ev effect is almost negligible for the @xmath41 regime and therefore , our result is the same as that of previous studies using wlc hamiltonian @xcite . for the @xmath217 regime originating from the ev effect , where the monomer dynamics are governed by rouse relaxation of a fully flexible chain , our theory elucidates the exact role of chain persistence length neither contained in wlc model nor studied before . we also validate our new scaling theory by extensive bd simulation results . a subtle issue concerns the limit @xmath22 towards infinity while keeping the contour length @xmath0 fixed . then transverse motions of the monomers relative to each other , in a coordinate system where the @xmath266-axis is fixed along the rod - like polymer , are completely suppressed . in the laboratory coordinate system " , however , the rod still can make random transverse motions , namely rigid body rotations and translations . however , in addition to those motions still motions of the monomers relative to each other along the axis of the rod are possible . these motions may give rise to a transient @xmath267 behavior , as a model calculation for a one - dimensional harmonic chain shows @xcite . however , our data for @xmath268 for large @xmath22 due to the smoothness of crossovers did not allow to clearly separate this mode of motions from the displacements due to transverse fluctuations . in the present manuscript we have ignored hd interactions as they are not significant for 2d swollen chains on a substrate . however we now present simple estimates of generalization of our results in 3d and/or in presence of hd interactions which will be relevant for a 3d swollen chain . in the free draining limit , the results @xmath41 will remain the same in 3d @xcite , but the intermediate rouse relaxation regime will be characterized by @xmath269 ( @xmath270 in 3d ) , for the case where the ev is relevant ( _ i.e. _ , msds exceeding @xmath271 ) . for msd in between @xmath272 and @xmath273 gaussian behavior prevails , @xmath274 , and hence @xmath275 in that regime . the crossover between flexible and stiff chain dynamics in 3d in the free draining limit was studied by steinhauser _ et al . _ @xcite , but no scaling analysis is done . replacing rouse relaxation by zimm relaxation one immediately sees that in presence of hd interaction the intermediate regime is characterized by @xmath276 @xcite . notice that in this case @xmath59 cancels out and this relaxation should be the same in 2d and 3d . however , as shown by hinczewski and netz @xcite , very complicated crossovers occur in this case . we now make some comments about some recent experiments to study monomer dynamics . this is typically done using fcs where a tagged monomer can be directly watched in real time . however , as has been mentioned by petrov _ et al . _ @xcite that since the @xmath41 regime or the intermediate regimes ( either @xmath40 or @xmath277 ) occur at much shorter time scales compared to the longest relaxation time , unless extreme caution is taken for the measurement of msd of a labeled particle , the interpretation can be misleading , especially for shorter dna fragments @xcite . for dsdna of length @xmath278 base pairs ( which is equivalent to @xmath279 fluorescence correlation spectroscopy ( fcs ) studies of petrov _ et al . _ observed the zimm regime characterized by a @xmath277 power law . however , a clear demonstration of the double crossover is lacking in recent experiments with biopolymers @xcite . this is partly due to lack of resolution of the experiments and partly due to the fact that lacking any theoretical predictions for this phenomenon , researchers did not specifically investigate the precise behavior of msd before the onset of overall chain diffusion very carefully . we will provide some physical arguments why the experimental detection can be hard : a simple calculation for fig . [ phase ] shows that in order for the width of the @xmath41 and @xmath280 to be equal ( in logarithmic scale ) one needs @xmath281 in 2d . in other words for a stiffer chain one needs a very long chain to see the @xmath280 regime . indeed in our simulation we found ( not shown here ) that for @xmath282 , 32 , and 64 , the results with chain length up to @xmath175 are largely dominated by the @xmath41 regime and we did not clearly see the @xmath280 regime . it is only after we lowered the value of @xmath22 and used longer chain ( @xmath173 ) , we identified these two regimes quite conclusively ( fig . 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we confirm the predictions of this scaling description by studying monomer dynamics of dilute solution of semi - flexible chains under good solvent conditions obtained from our brownian dynamics ( bd ) simulation studies for a large choice of chain lengths with number of monomers per chain n = 16 - 2048 and persistence length lennard - jones ( lj ) units . these bd simulation results further confirm the absence of gaussian regime for a 2d swollen chain from the slope of the plot of which around changes suddenly from , also manifested in the power law decay for the bond autocorrelation function disproving the validity of the wlc in 2d .

we present a unified scaling description for the dynamics of monomers of a semiflexible chain under good solvent condition in the free draining limit . we consider both the cases where the contour length is comparable to the persistence length and the case . our theory captures the early time monomer dynamics of a stiff chain characterized by dependence for the mean square displacement(msd ) of the monomers , but predicts a first crossover to the rouse regime of for , and a second crossover to the purely diffusive dynamics for the entire chain at . we confirm the predictions of this scaling description by studying monomer dynamics of dilute solution of semi - flexible chains under good solvent conditions obtained from our brownian dynamics ( bd ) simulation studies for a large choice of chain lengths with number of monomers per chain n = 16 - 2048 and persistence length lennard - jones ( lj ) units . these bd simulation results further confirm the absence of gaussian regime for a 2d swollen chain from the slope of the plot of which around changes suddenly from , also manifested in the power law decay for the bond autocorrelation function disproving the validity of the wlc in 2d . we further observe that the normalized transverse fluctuations of the semiflexible chains for different stiffness as a function of renormalized contour length collapse on the same master plot and exhibits power law scaling at extreme limits , where for extremely stiff chains ( ) , and for fully flexible chains . finally , we compare the radial distribution functions obtained from our simulation studies with those obtained analytically .

1611.02947

i

intersections are natural bottlenecks and crucially influence the dynamics of urban traffic . traffic lights trigger a switching process meant to manage conflicting traffic flows . the coordination is sometimes done dynamically , according to sensor data of currently existing traffic flows ; otherwise it is done statically , by the use of timers . while intersections can be studied in isolation @xcite , the larger picture of networks of multiple intersections is increasingly important , also in view of the rapid growth of urbanization @xcite . this paper contributes to the theoretical underpinning of traffic networks by extending classical models for isolated intersections to models for networks of intersections with static signaling . think of a series of traffic lights designed to let traffic flow over several intersections in one main direction . any vehicle traveling along ( at an approximate prescribed speed ) wants to meet a progressive cascade of green lights , and not have to stop at intersections . in practical use , only a group of vehicles referred to as _ platoon _ can pass the intersection before the time band is interrupted to give way to other traffic flows . the platoon sizes are governed by the signal times . our method to model such situations consists of two ingredients : an extension of a classical queueing model for one isolated intersection that can deal with correlated input and that allows for a detailed characterization of the output process of an intersection , and an algorithm for network analysis that decomposes the series of queues into multiple isolated queues . while interesting in their own right , and likely to find more applications in transportation science , network analysis of intersections requires the delicate combination of both ingredients . we now discuss each of them separately . * queueing model for one intersection . * the classical model for an isolated intersection that we adopt and extend in this paper is the fixed - cycle traffic - light ( fctl ) queue ; one of the most well - studied stochastic models in traffic engineering @xcite . vehicles arrive to an intersection controlled by a traffic light and form a queue . the time scale is divided into time intervals of unit length , and the traffic light alternates between red and green periods of fixed durations @xmath0 and @xmath1 time units . delayed vehicles depart during the green period , where it takes one time unit for each delayed vehicle to depart ; departures thus occur at equally spaced times until either the queue dissipates or the green phase terminates . darroch @xcite obtained the probability generating function ( pgf ) of the steady - state overflow queue ( the number of vehicles waiting in front of the traffic light at the end of a green period ) and the pgf of the steady - state delay was obtained in van leeuwaarden @xcite . hence , all information about the distribution of the steady - state overflow queue and steady - state delay in the fctl queue can be obtained from the results in @xcite , including all moments of the steady - state queue length and delay , and the distribution of the output process ( the way vehicles leave the intersection ) . the output process of the first intersection is of crucial importance for the present paper , because it will serve as input process for some other signalized intersection . moreover , the output process of a second intersection serves as input for a third intersection , and so forth . this network effect acts as a filter that modifies , and perhaps streamlines , the arrival process at consecutive intersections . therefore , we shall address in this paper the technical challenge of extending the classical fctl queue to allow for nonuniform and hence time - dependent correlated arrival processes . we call this extended model the generalized fctl queue . * network algorithm . * a network of intersections with correlated input and output processes appears not solvable . we therefore develop an approximation scheme to evaluate the system performance based on decomposition . while this approach has been successfully applied to classic queueing networks @xcite , a network of generalized fctl queues poses additional challenges due to the non - synchronized cyclic structures and inherently correlated arrival processes . we decompose the network into isolated generalized fctl queues , which are then analyzed separately by assuming specific arrival processes , and in particular the output process of one intersection serves as the input process of an upstream intersection , hence creating the correlation structure that comes with network topologies . * outline of the paper . * in section [ sec : queuelengths ] we provide a detailed model description of the generalized fctl queue . in section [ sec : main ] we present the full analytic solution of the generalized fctl queue , both in terms of a formal characterization of the probability generating functions of the queue length distribution , and in terms of practically implementable algorithms for calculating the queue length distribution , for any given correlated arrival pattern . in section [ sec : networks ] we design the network algorithm based on decomposition and the results in section [ sec : main ] . we also compare our analytical results with extensive discrete - event simulation of the same network model . in section [ sec : conclusions ] we present conclusions .

we present an algorithmic method for analyzing networks of intersections with static signaling , with as primary example a line network that allows traffic flow over several intersections in one main direction . the method decomposes the network into separate intersections and treats each intersection in isolation using an extension of the fixed - cycle traffic - light ( fctl ) queue . the network effects are modeled by matching the output process of one intersection with the input process of the next ( downstream ) intersection . this network analysis provides insight into wave phenomena due to vehicles experiencing progressive cascades of green lights and sheds light on platoon forming in case of imperfections . our algorithm is shown to match results from extensive discrete - event simulations and can also be applied to more complex network structures . * keywords : * fixed - cycle traffic - light queue ; performance evaluation ; queueing theory ; steady - state distribution ; traffic engineering ; transform solution ; stochastic networks + * ams 2000 subject classification*. 60e10 , 60j10 , 60k25 , 68m20 , 90b20

we present an algorithmic method for analyzing networks of intersections with static signaling , with as primary example a line network that allows traffic flow over several intersections in one main direction . the method decomposes the network into separate intersections and treats each intersection in isolation using an extension of the fixed - cycle traffic - light ( fctl ) queue . the network effects are modeled by matching the output process of one intersection with the input process of the next ( downstream ) intersection . this network analysis provides insight into wave phenomena due to vehicles experiencing progressive cascades of green lights and sheds light on platoon forming in case of imperfections . our algorithm is shown to match results from extensive discrete - event simulations and can also be applied to more complex network structures . * keywords : * fixed - cycle traffic - light queue ; performance evaluation ; queueing theory ; steady - state distribution ; traffic engineering ; transform solution ; stochastic networks + * ams 2000 subject classification*. 60e10 , 60j10 , 60k25 , 68m20 , 90b20

astro-ph0301278

c

we have presented @xmath0 observations for the open cluster m67 , and have discussed the light curves for the known w uma contact binaries and the monitoring of the majority of the blue stragglers for variability . we find that all of the known w uma binaries show light curve variations that occur on timescales of days to months . two systems ( s757 and iii-79 ) show large changes in the shapes of their light curves . the relative brightnesses of both the two maxima and the two minima in the light curve of s757 have been observed to change on timescales of less than a month . the faint system iii-79 shows a substantial change in the shape of the light curve between the january 1998 of svmv and our observations in march 2001 . the other two systems ( s1036 and s1282 ) show smaller variations . s1282 changed between a w - type and an a - type configuration between the 1973 observations of whelan et al . ( 1979 ) and the 1988 observations of gilliland et al . the existence of two systems which appear to change between these subtypes indicates that the classification is perhaps not a robust indicator of the evolutionary state of the stellar components . the blue straggler system s 1036 shows smaller light curve variations , but a stronger and more stable oconnell effect . we have verified that s 1282 is a highly - inclined totally - eclipsing system with @xmath79 and @xmath80 . because this system falls right at the cluster turnoff , we strongly encourage further spectroscopic work to provide a constraint on the cluster turnoff mass , and thus on the cluster age . this system has also shown unusual short disturbances in its light curve that may relate to magnetic activity , and which should be followed up . among the blue stragglers , in addition to the two known @xmath3 scuti pulsating variables , we find possible evidence of longer period variations in the stars s752 , s968 , and s1263 . while these stars did not satisfy our criteria for a definite claim of variability , we see trends in the photometry and apparent changes in the mean brightness level that should be investigated . finally , we present a series of observations of two long - period binary systems . for the poorly understood sub - subgiant branch system s 1063 , there are indications of quasi - periodicity on timescales similar to the orbital period , as well as variations in the mean brightness level of the light curve . for the giant - white dwarf system s 1040 , we find evidence of a drop in brightness at phases corresponding to the passage of the white dwarf in front of the giant using the ephemeris derived by mathieu et al . although this drop in brightness can not be due to an eclipse of the giant by the white dwarf itself , there may be associated material within the system that could account for the variability . this information can probably be used to contrain the inclination of the system . we would especially like to thank m. van den berg and k. stassun for the loan of data from their photometry papers . e.l.s . would like to thank m. blake , s. rucinski , w. welsh , r. taam , and p. etzel for helpful conversations during the course of this work . we would also like to thank the director of mount laguna observatory ( p. etzel ) for generous allocations of telescope time . this work has been partly supported by nsf grant ast-0098696 to e.l.s . ahumada , j. , & lapasset , e. 1995 , , 109 , 375 bailyn , c. d. 1995 , , 22 , 133 belloni , t. , verbunt , f. , & mathieu , r. d. 1998 , , 339 , 431 daz - cordovs , j. , claret , a. , & gimnez , a. 1995 , , 110 , 329 dinescu , d. i. , demarque , p. , guenther , d. b. , & pinsonneault , m. h. 1995 , , 109 , 2090 duerbeck , h. w. 1978 , , 32 , 361 fan , x. et al . 1996 , , 112 , 628 gilliland , r. l. & brown , t. m. 1992 , , 103 , 1945 gilliland , r. l. , brown , t. m. , duncan , d. k. , suntzeff , n. b. , lockwood , g. w. , thompson , d. t. , schild , r. e. , jeffrey , w. a. , & penprase , b. e. , 1991 , , 101 , 541 girard , t. m. , grundy , w. m. , lopez , c. e. , & van altena , w. f. 1989 , , 98 , 227 hauschildt , p. h. , allard , f. , & baron , e. 1999 , , 512 , 377 hills , j. g. & day , c. a. 1976 , astrophys . lett . , 17 , 87 honeycutt , r. k. 1992 , , 104 , 435 hurley , j. r. , tout , c. a. , aarseth , s. j. , & pols , o. r. 2001 , , 323 , 630 kim , s .- l . , chun , m. y. , park , b .- , & lee , s .- w . 1996 , jkas , 29 , 43 kurochkin , n. e. 1979 , astron . circular ussr , 1076 , 2 lafler , j. & kinman , t. d. 1965 , , 11 , 216 landsman , w. , aparicio , j. , bergeron , p. , di stefano , r. , & stecher , t. p. 1997 , , 481 , l93 latham , d. , mathieu , r. , milone , a. , & davis , r. 1992 , in binaries as tracers of stellar formation , ed . a. duquennoy and m. mayor ( cambridge : cambridge university press ) , 132 latham , d. w. , & milone , a. a. e. 1996 , in asp conf . 90 , the origins , evolution , and destinies of binary stars in clusters , ed . e. f. milone , and j .- c . mermilliod ( san francisco : asp ) , 385 maceroni , c. , milano , l. , & russo , g. 1984 , , 58 , 405 mathieu , r. d. , latham , d. w. , & griffin , r. f. 1990 , , 100 , 1859 mathieu , r. d. , van den berg , m. , torres , g. , latham , d. w. , verbunt , f. , & stassun , k. 2002 , aj , submitted milone , a. a. e & latham , d. w. 1994 , , 108 , 1828 mochnacki , s. w. 1981 , , 245 , 650 mochnacki , s. w. & doughty , n. a. 1972 , , 156 , 51 montgomery , k. a. , marschall , l. a. , & janes , k. a. 1993 , , 106 , 181 nissen , p. e. , twarog , b. a. , & crawford , d. l. 1986 , , 92 , 1100 . oconnell , d. j. k. 1951 , riverview coll . publ . , 2 , 85 pamyatnykh , a. a. 2000 , in delta scuti and related stars , ed . m. breger and m. h. montgomery ( san francisco : asp ) , 215 peterson , r. c. , carney , b. w. , & latham , d. w. 1984 , , 279 , 237 portegies zwart , s. f. , mcmillan , s. l. w. , hut , p. & makino , j. 2001 , , 321 , 199 rajamohan , r. , bhattacharyya , j. c. , subramanian , v. , & kuppuswamy , k. 1988 , bull . india , 16 , 139 rasio , f. a. 1996 , , 444 , l41 rucinski , s. m. 1997 , , 113 , 1112 rucinski , s. m. 1998 , , 116 , 2998 rucinski , s. m. 2001 , , 122 , 1007 rucinski , s. m. & duerbeck , h. w. 1997 , , 109 , 1340 sanders , w. l. 1977 , , 27 , 89 sandquist , e. l. , latham , d. w. , shetrone , m. d. , & milone , a. a. e. 2003 , , in press scargle , j. d. 1982 , , 263 , 835 simoda , m. 1991 , ibvs , 3675 , 1 stassun , k. g. , van den berg , m. , mathieu , r. d. , & verbunt , f. 2002 , , 382 , 899 ( svmv ) stetson , p. b. 1990 , , 102 , 932 van den berg , m. , orosz , j. , verbunt , f. , & stassun , k. 2001 , , 375 , 375 van den berg , m. , stassun , k. g. , verbunt , f. , & mathieu , r. d. 2002 , , 382 , 888 ( vsvm ) van hamme , w. 1993 , , 106 , 2096 welch , d. l. & stetson , p. b. 1993 , , 105 , 1813 whelan , j. a. j. , worden , s. p. , ruciski , s. m. , & romanishin , w. 1979 , , 186 , 729 cccc 1 & dec . 5/6 , 2000 & 1884.878 & 60 + 2 & dec . 7/8 , 2000 & 1886.806 & 111 + 3 & dec . 11/12 , 2000 & 1890.817 & 57 + 4 & dec . 12/13 , 2000 & 1891.820 & 116 + 5 & jan . 23/24 , 2001 & 1933.675 & 206 + 6 & jan . 25/26 , 2001 & 1935.673 & 176 + 7 & jan . 29/30 , 2001 & 1939.676 & 44 + 8 & jan . 30/31 , 2001 & 1940.657 & 130 + 9 & jan . 31/feb . 1 , 2001 & 1941.663 & 161 + 10 & feb . 17/18 , 2001 & 1958.655 & 63 + 11 & feb . 18/19 , 2001 & 1959.790 & 75 + 12 & mar . 1/2 , 2001 & 1970.619 & 205 + 13 & mar . 3/4 , 2001 & 1972.631 & 205 + 14 & mar . 5/6 , 2001 & 1974.721 & 32 + 15 & jan . 21/22 , 2002 & 2296.687 & 89 + 16 & jan . 24/25 , 2002 & 2299.690 & 124 + 17 & feb . 5/6 , 2002 & 2311.649 & 119 + 18 & feb . 10/11 , 2002 & 2316.638 & 167 + 19 & mar . 18/19 , 2002 & 2352.625 & 131 + [ obs ] lcccc @xmath81 & 2451800.129 & 2450500.047 & & 2450000.036 + @xmath82 ( d ) & @xmath83 & @xmath84 & 0.360452 & 0.2704 + @xmath85 & 0.08 & 0.13 & 0.39 & @xmath86 + @xmath87 & 0.06 & 0.06 & 0.33 & 0.11 + @xmath88 & 13.51 & 12.81 & 13.44 & 15.90 + @xmath89 & 0.61 & 0.50 & 0.52 & 1.11 + @xmath36 & & @xmath90 & @xmath91 & + @xmath37 & & & @xmath92 & + [ wuma ] ccrcrlrl 145 & & & & & none & & + 277 & & & & & none & & + 751 & 12.70 & & 0.008 & 0.53 & @xmath95 & 777 & no variation + 752 & 11.32 & 0.30 & 0.018 & 0.75 & @xmath96 & 1418 & am star ; possible flare detected + 792 & 11.99 & 0.60 & 0.007 & 1.01 & @xmath97 & 1610 & no variation + 968 & 11.25 & 0.13 & 0.010 & 0.74 & @xmath98 & 1261 & am star ; possible low amplitude , + & & & & & & & timescale @xmath99 days + 975 & 11.05 & 0.43 & 0.077 & 7.26 & @xmath100 & 1659 & photometry affected by faint companion + 977 & 10.02 & @xmath101 & 0.006 & 0.69 & @xmath102 & 504 & no variation + 984 & 12.26 & 0.57 & 0.014 & 1.64 & @xmath100 & 1732 & no variation + 997 & 12.13 & 0.46 & 0.006 & 0.92 & @xmath100 & 1655 & no variation + 1005 & 12.68 & 0.52 & 0.010 & 1.57 & @xmath100 & 1654 & no variation + 1031 & 13.29 & 0.46 & 0.007 & 0.32 & @xmath100 & 1644 & no variation + 1036 & 12.81 & 0.49 & 0.046 & 90.59 & @xmath100 & 1651 & w uma variable ( ev cnc ) + 1066 & 10.95 & 0.11 & 0.003 & 0.24 & @xmath103 & 2061 & no variation + 1072 & 11.31 & 0.61 & 0.006 & 0.97 & @xmath103 & 2073 & no variation + 1082 & 11.20 & 0.42 & 0.024 & 33.59 & @xmath103 & 2097 & rs cvn variable ( es cnc ) + 1165 & & & & & none & & + 1183 & 12.66 & & 0.011 & 0.07 & 15 & 66 & no variation + 1195 & 12.29 & & 0.003 & 0.40 & 15 & 78 & no variation + 1263 & 11.06 & 0.19 & 0.007 & 0.98 & @xmath104 & 1275 & possible low amplitude , + & & & & & & & timescale @xmath105 10 days + 1267 & 10.90 & & 0.005 & 0.45 & @xmath106 & 484 & no variation + 1273 & 12.25 & 0.57 & 0.006 & 0.63 & @xmath103 & 1451 & no variation + 1280 & 12.23 & 0.26 & 0.009 & 2.55 & @xmath103 & 1685 & @xmath3 scu variable ( ew cnc ) + 1282 & 13.44 & 0.52 & 0.133 & 108.08 & @xmath107 & 1864 & w uma variable ( ah cnc ) + 1284 & 10.93 & 0.22 & 0.012 & 9.41 & @xmath103 & 2015 & @xmath3 scu variable ( ex cnc ) + 1434 & 10.70 & 0.11 & & & none & & + 1440 & & & & & none & & + 1947 & & & & & none & & + 2204 & 12.89 & 0.45 & 0.013 & 1.03 & @xmath100 & 1717 & no variation + 2223 & 13.30 & 0.50 & 0.012 & 0.92 & @xmath103 & 2084 & no variation + 2226 & & & & & none & & + [ straggler ] cccr 1884.9294 & 11.5231 & 0.0006 & 33 + 1885.0391 & 11.5243 & 0.0008 & 27 + 1886.8586 & 11.5184 & 0.0007 & 36 + 1886.9615 & 11.5157 & 0.0006 & 43 + 1887.0468 & 11.5177 & 0.0007 & 32 + 1890.8688 & 11.5076 & 0.0007 & 42 + 1890.9386 & 11.4998 & 0.0014 & 14 + 1891.8734 & 11.5064 & 0.0008 & 37 + 1891.9872 & 11.5092 & 0.0006 & 51 + 1892.0607 & 11.5101 & 0.0008 & 28 + 1930.7983 & 11.5395 & 0.0058 & 1 + 1933.7305 & 11.5209 & 0.0005 & 55 + 1933.8308 & 11.5210 & 0.0005 & 63 + 1933.9312 & 11.5191 & 0.0005 & 57 + 1934.0118 & 11.5181 & 0.0007 & 31 + 1935.7288 & 11.5128 & 0.0007 & 45 + 1935.8314 & 11.5152 & 0.0005 & 60 + 1935.9333 & 11.5138 & 0.0006 & 54 + 1936.0000 & 11.5114 & 0.0010 & 17 + 1939.8739 & 11.4991 & 0.0008 & 36 + 1939.9386 & 11.4952 & 0.0018 & 8 + 1940.7053 & 11.5028 & 0.0007 & 37 + 1940.8386 & 11.4972 & 0.0007 & 46 + 1940.9371 & 11.5010 & 0.0007 & 47 + 1941.7175 & 11.5034 & 0.0005 & 49 + 1941.8186 & 11.5074 & 0.0005 & 48 + 1941.9199 & 11.5052 & 0.0005 & 50 + 1941.9883 & 11.5018 & 0.0010 & 14 + 1958.6849 & 11.4962 & 0.0036 & 7 + 1958.8989 & 11.4972 & 0.0006 & 50 + 1958.9531 & 11.4961 & 0.0017 & 5 + 1959.8451 & 11.5077 & 0.0006 & 47 + 1959.9218 & 11.5017 & 0.0009 & 28 + 2296.7175 & 11.5428 & 0.0008 & 21 + 2300.0020 & 11.5423 & 0.0008 & 20 + 2311.6980 & 11.5368 & 0.0009 & 23 + 2311.7991 & 11.5394 & 0.0005 & 44 + 2311.8994 & 11.5383 & 0.0005 & 46 + 2311.9536 & 11.5345 & 0.0019 & 5 + 2316.6882 & 11.5028 & 0.0009 & 46 + 2316.7888 & 11.5104 & 0.0006 & 53 + 2316.8887 & 11.5079 & 0.0007 & 45 + 2316.9590 & 11.5038 & 0.0011 & 23 + 2352.6743 & 11.5638 & 0.0006 & 47 + 2352.7751 & 11.5613 & 0.0005 & 50 + 2352.8530 & 11.5622 & 0.0006 & 34 + [ s1040tab ] cccr 1884.9297 & 13.4520 & 0.0010 & 33 + 1885.0391 & 13.4550 & 0.0014 & 27 + 1886.8594 & 13.4854 & 0.0011 & 36 + 1886.9609 & 13.4899 & 0.0008 & 43 + 1887.0469 & 13.4912 & 0.0010 & 32 + 1890.8711 & 13.5676 & 0.0011 & 43 + 1890.9375 & 13.5754 & 0.0025 & 13 + 1891.8750 & 13.5556 & 0.0012 & 37 + 1891.9883 & 13.5590 & 0.0010 & 52 + 1892.0625 & 13.5538 & 0.0015 & 27 + 1933.7305 & 13.5066 & 0.0007 & 55 + 1933.8320 & 13.5129 & 0.0006 & 64 + 1933.9336 & 13.5140 & 0.0007 & 58 + 1934.0117 & 13.5138 & 0.0010 & 29 + 1935.7305 & 13.5668 & 0.0008 & 45 + 1935.8320 & 13.5704 & 0.0007 & 60 + 1935.9336 & 13.5697 & 0.0007 & 54 + 1936.0000 & 13.5757 & 0.0013 & 17 + 1939.8750 & 13.6060 & 0.0010 & 36 + 1939.9375 & 13.6033 & 0.0027 & 7 + 1940.7070 & 13.5926 & 0.0009 & 37 + 1940.8398 & 13.5944 & 0.0010 & 47 + 1940.9375 & 13.5924 & 0.0011 & 46 + 1941.7188 & 13.5715 & 0.0008 & 50 + 1941.8242 & 13.5696 & 0.0007 & 49 + 1941.9258 & 13.5693 & 0.0007 & 49 + 1941.9922 & 13.5667 & 0.0016 & 12 + 1958.6797 & 13.5500 & 0.0104 & 4 + 1958.8984 & 13.5577 & 0.0008 & 49 + 1958.9531 & 13.5658 & 0.0025 & 5 + 1959.8984 & 13.5886 & 0.0010 & 51 + 1970.6875 & 13.5418 & 0.0008 & 63 + 1970.7930 & 13.5450 & 0.0008 & 75 + 1970.8828 & 13.5474 & 0.0009 & 67 + 1972.6914 & 13.5598 & 0.0007 & 97 + 1972.7930 & 13.5630 & 0.0010 & 89 + 1972.8594 & 13.5639 & 0.0022 & 17 + 1974.6758 & 13.5433 & 0.0024 & 30 + 2296.7188 & 13.5082 & 0.0008 & 21 + 2300.0000 & 13.5386 & 0.0009 & 20 + 2311.6992 & 13.6108 & 0.0010 & 24 + 2311.8008 & 13.6122 & 0.0006 & 44 + 2311.9023 & 13.6116 & 0.0006 & 48 + 2311.9531 & 13.6154 & 0.0027 & 3 + 2316.6875 & 13.5574 & 0.0016 & 42 + 2316.7891 & 13.5538 & 0.0008 & 53 + 2316.8906 & 13.5541 & 0.0009 & 46 + 2316.9609 & 13.5599 & 0.0019 & 22 + 2352.6758 & 13.5144 & 0.0007 & 48 + 2352.7773 & 13.5164 & 0.0006 & 51 + 2352.8555 & 13.5183 & 0.0008 & 32 + [ s1063tab ]

we present an analysis of over 2200 images taken on 14 nights at the mt . we have also monitored cluster blue stragglers for variability , and we present evidence hinting at low level variations in the stragglers s752 , s968 , and s1263 , and we place limits on the variability of a number of other cluster blue stragglers . finally , we provide photometry of the sub - subgiant branch star s1063 showing variability on timescales similar to the orbital period , while the `` red straggler '' s1040 shows evidence of an unexplained drop in brightness at phases corresponding to the passage of the white dwarf in front of the giant .

we present an analysis of over 2200 images taken on 14 nights at the mt . laguna 1 m telescope of the open cluster m67 . our observations overlap but extend beyond the field analyzed by gilliland et al . ( 1991 ) , and complement data recently published by van den berg et al . ( 2002 ) and stassun et al . ( 2002 ) . we show variability in the light curves of all 4 of the known w uma variables on timescales ranging from a day to decades ( for ah cnc ) . we have modeled the light curve of ah cnc , and the total eclipses allow us to determine and . the position of this system near the turnoff of m67 makes it useful for constraining the turnoff mass for the cluster . we have also detected two unusual features in the light curve of ah cnc that may be caused by prominences . we have also monitored cluster blue stragglers for variability , and we present evidence hinting at low level variations in the stragglers s752 , s968 , and s1263 , and we place limits on the variability of a number of other cluster blue stragglers . finally , we provide photometry of the sub - subgiant branch star s1063 showing variability on timescales similar to the orbital period , while the `` red straggler '' s1040 shows evidence of an unexplained drop in brightness at phases corresponding to the passage of the white dwarf in front of the giant .

0912.0518

i

our understanding of planet formation has rapidly improved over the past 15 years . prior to the discovery of the first extrasolar planet orbiting a solar - type star ( 51 peg b ; @xcite ) , it was widely assumed that extrasolar giant planet semimajor axes would mimic those of the gas giants in our own solar system , which orbit at distances @xmath14 5 au . in the years that followed it became apparent that an _ in situ _ formation model was not universally applicable because radial velocity surveys were finding jovian planets in abundance well inside the canonical ice line . over 350 planets have now been discovered , 282 of which reside around stars within 200 pc . sufficiently large samples are available for the statistical properties of exoplanets to reveal themselves , providing information about the planet formation and migration processes . for solar - type stars ( f , g , and k dwarfs ) , jovian planets fall into two rough populations : `` hot planets '' with @xmath15 @xmath1 0.1 au ( @xcite ) and those that orbit beyond @xmath0 1 au ( figure [ f1.eps ] ) . these observations were explained _ a posteriori _ in terms of orbital migration ( @xcite ) and planet - planet scattering ( @xcite ; @xcite ; @xcite ) , with the dearth of planets with periods between @xmath0 10 - 100 days ( the `` period valley '' ) possibly resulting from differential mass - dependent orbital migration ( @xcite ; @xcite ; @xcite ) . while much is known about planets around sun - like stars ( e.g. , @xcite ; @xcite ; @xcite ; @xcite ; @xcite ) , comparatively little is known about planets around intermediate - mass ( i m ) stars with @xmath16 @xmath14 1.5 @xmath17 . main sequence a- and f - type stars are problematic doppler targets because of their high jitter levels and rotationally - broadened absorption features ( @xcite ) . on the other hand , evolved i m stars have lower jitter levels as well as narrower and more numerous absorption lines resulting from their slow rotation and cool photospheres . as a consequence , nearly all radial velocity surveys of i m stars are targeting evolved g- or k - type subgiants and giants ( @xcite , @xcite , @xcite ; @xcite , @xcite , @xcite , @xcite , @xcite ) , although at least one survey is targeting their main sequence progenitors ( @xcite ; @xcite ) . recently @xcite showed that planets orbiting evolved a - type stars have large semimajor axes compared to planets around solar - type stars . this trend has become even stronger with the discovery of more planets orbiting i m stars ( @xcite ) . specifically , over 20 planets have been discovered around stars with minimum masses @xmath14 1.5 @xmath18 but none have semimajor axes @xmath19 0.6 au . this `` planet desert '' is shown in figure [ f1.eps ] and a summary of known planets around i m stars is presented table [ evolvedtab ] . lcccccccc hd 13189 & 2 - 6 & k2 ii & & 8 - 20 & 1.5 - 2.2 & 0.27 ( 0.06 ) & 1 , 2 + @xmath20 tau & 2.7 ( 0.1 ) & k0 iii & 13.7 ( 0.6 ) & 7.6 ( 0.2 ) & 1.93 ( 0.03 ) & 0.151 ( 0.023 ) & 3 + ngc 2423 no . 3 & 2.4 ( 0.2 ) & & & 10.6 & 2.10 & 0.21 ( 0.07 ) & 4 + 81 cet & 2.4 ( 2.0 - 2.5 ) & g5 iii : & 11 ( 10 - 13 ) & 5.3 & 2.5 & 0.206 ( 0.029 ) & 5 + hd 104985 & 2.3 & g9 iii & 11 & 8.3 & 0.95 & 0.090 ( 0.009 ) & 6 , 7 + 18 del & 2.3 & g6 iii & 8.5 & 10.3 & 2.6 & 0.08 ( 0.01 ) & 6 + hd 17092 & 2.3 ( 0.3 ) & k0 iii & 10.9 ( 2.8 ) & 4.6 ( 0.3 ) & 1.29 ( 0.05 ) & 0.166 ( 0.052 ) & 8 + @xmath21 aql & 2.2 & k0 iii & 12 & 2.8 & 0.68 & 0.0 ( fixed ) & 6 + 14 and & 2.2 ( 2.0 - 2.3 ) & k0 iii & 11 ( 10 - 12 ) & 4.8 & 0.83 & 0.0 ( fixed ) & 5 + hd 81688 & 2.1 & k0iii - iv & 13 & 2.7 & 0.81 & 0.0 ( fixed ) & 6 + hd 173416 & 2.0 ( 0.3 ) & g8 iii & 13.5 ( 0.9 ) & 2.7 ( 0.3 ) & 1.16 ( 0.06 ) & 0.21 ( 0.04 ) & 9 + hd 11977 & 1.91 ( 0.21 ) & g5 iii & 10.09 ( 0.32 ) & 6.54 & 1.93 & 0.40 ( 0.07 ) & 10 , 11 + hd 102272 & 1.9 ( 0.3 ) & k0 iii & 10.1 ( 4.6 ) & 5.9 ( 0.2 ) & 0.614 ( 0.001 ) & 0.05 ( 0.04 ) & 12 + & & & & 2.6 ( 0.4 ) & 1.57 ( 0.05 ) & 0.68 ( 0.06 ) & 12 + @xmath12 gem & 1.86 , 1.7 ( 0.4 ) & k0 iii & 8.8 ( 0.1 ) & 2.9 ( 0.3 ) & 1.69 ( 0.03 ) & 0.06 ( 0.04 ) & 13 , 14 , 15 , 16 + hd 89744 & 1.86 ( 0.18 ) & f7 iv & 2.08 ( 0.06 ) & 7.2 & 0.88 & 0.70 ( 0.02 ) & 17 , 18 + hd 210702 & 1.85 ( 0.13 ) & k1 iv & 4.45 ( 0.07 ) & 1.97 ( 0.11,0.18 ) & 1.20 ( 0.02,0.03 ) & 0.036 ( @xmath190.106 ) & 19 , 20 + @xmath22 crb & 1.84 ( 0.13 ) & k0 iv & 4.71 ( 0.08 ) & 2.01 ( 0.11,0.17 ) & 2.80 ( 0.07,0.08 ) & 0.044 ( @xmath190.123 ) & 21 , 20 + 6 lyn & 1.82 ( 0.13 ) & k0 iv & 5.2 ( 4.9 - 5.6 ) & 2.21 ( 0.11,0.16 ) & 2.18 ( 0.05,0.06 ) & 0.059 ( @xmath190.125 ) & 20 , 5 + hd 167042 & 1.72 ( 0.12 ) & k1 iv & 4.30 ( 0.07 ) & 1.70 ( 0.09,0.12 ) & 1.32 ( 0.03,0.04 ) & 0.089 ( 0.028,0.065 ) & 21 , 20 , 5 + hd 192699 & 1.69 ( 0.12 ) & g8 iv & 3.90 ( 0.06 ) & 2.40 ( 0.15,0.21 ) & 1.15 ( 0.02,0.03 ) & 0.129 ( 0.029,0.060 ) & 19 , 20 + hd 175541 & 1.65 ( 0.12 ) & g8 iv & 3.80 ( 0.09 ) & 0.70 ( 0.06,0.08 ) & 1.03 ( 0.02,0.03 ) & 0.083 ( @xmath190.283 ) & 19 + hd 5319 & 1.59 ( 0.18 ) & g5 iv & 3.26 ( 0.50,0.41 ) & 1.94 & 1.75 & 0.12 ( 0.08 ) & 22 there are several explanations for this observational result . one possibility is that the swollen radii of evolved stars have engulfed or tidally disrupted short - period planets . the current census of i m exoplanet - host stars mostly consists of red clump giants ( core helium and hydrogen shell burning post - rgb stars ) and subgiants ( stars with contracting inert helium cores and hydrogen - burning shells ) . planet - hosting stars in the clump giant phase have radii between @xmath0 8 - 14 @xmath23 ( @xmath0 0.03 - 0.06 au ) so any planets orbiting inside @xmath0 0.1 au will likely have been engulfed by an expanding radius during post - main sequence stellar evolution . however , a tidal torque from an expanding stellar surface can also decay the orbits of short period planets . @xcite numerically trace the semimajor axis evolution of short - period planets around evolving rgb stars and show that , in their past , i m clump giants may have engulfed or disrupted the orbits of planets out to @xmath0 0.5 au . with radii between @xmath0 2 - 5 @xmath23 ( @xmath0 0.01 - 0.02 au ) , planets orbiting i m subgiants are the least affected by stellar evolution . stellar evolution may therefore explain the lack of short - period planets around i m clump giants , but the same result for i m subgiants suggests that the observed trend is not due to post - main sequence engulfment . the observed semimajor axis distribution can also be explained as a result of inward orbital migration combined with mass - dependent disk dispersal lifetime . the rocky progenitors of jovian planets ( @xmath010 @xmath24 cores ) can form at distances @xmath25 8 au for stellar masses between @xmath0 1.5 - 3 @xmath18 ( @xcite ) . @xcite performed monte carlo simulations of jovian planet formation and migration around i m stars and , using simple stellar mass - dependent gas disk lifetime relations ( @xcite ) and type ii migration models ( @xcite ) , was able to successfully reproduce the observed dearth of short - period planets . in this scenario inward migration is halted once rapid disk dispersal occurs , stranding migrating planets at semimajor axes that depend on stellar mass . an alternative explanation was offered by @xcite . they found that the protoplanetary disks of young i m stars will develop a maximum surface density at @xmath0 1 au as a result of magnetrotational instability of the inner disk , leading to a trapping and accumulation of solids that can then grow to form rocky cores and jovian planets . this formation scenario provides a mechanism for _ in situ _ formation of jovian planets interior to the ice line , which is located near 3 au at 10 myr for a 2 @xmath18 star ( @xcite ) . models of jovian planet formation around i m stars make few quantitative predictions that can be observationally tested . simple disk depletion plus migration models for i m planet hosts ( 1.5 - 3.0 @xmath18 ) by @xcite predict occurrence rates for jovian planets with semimajor axes @xmath19 0.5 au to be @xmath1 1.5% and for jovian planets with semimajor axes @xmath14 0.5 au to be @xmath25 7.5% . @xcite use a semianalytic model of protoplanetary disk evolution to study snow line locations and planet formation rates around stars of varying masses . for stellar masses between 1.5 - 2.0 @xmath18 , their models predict that jovian planet occurrence rates reach frequencies of @xmath010 - 15% . @xcite suggest that multiple planetary systems may form more efficeintly around i m stars compared to other stellar mass regimes . the semimajor axis distribution of planets with minimum masses between @xmath0 2 - 10 @xmath4 orbiting i m stars is beginning to be better constrained by observations , but little is known about planets with masses @xmath19 1.5 @xmath4 . this poor understanding is a direct result of the dearth of low - mass planets currently known , with only one having a minimum mass below 1.5 @xmath4 ( hd 175541b with @xmath26sin@xmath27 = 0.70 @xmath4 ) . it is unclear , however , whether this scarcity is a result of a detection bias caused by higher jitter levels in i m stars or whether it reflects an intrinsic shortage of low - mass planets . unfortunately , models of planet formation in this stellar mass regime have made few predictions about low - mass planetary companions . for solar - type stars , @xcite estimate the frequency of neptune - mass planets with periods @xmath19 50 days to be at least 30% . this raises the exciting possibility that low - mass planets could be abundant around i m stars , especially in light of recent studies suggesting that the frequency of jovian - mass planets scales with stellar mass ( @xcite ) . testing these theories requires an understanding of the detection limits of radial velocity surveys . the goal of this study is twofold : to derive the occurrence rate of jovian planets around i m stars and to characterize the distributions of planet periods ( @xmath10 ) and minimum masses ( @xmath26sin@xmath27 ) . in addition we take the opportunity to update the orbit solutions for known planet - hosting stars in our sample using new radial velocity measurements . to address the aforementioned questions we make use of a uniform sample of 31 i m subgiants taken from an ongoing radial velocity survey at lick observatory ( @xcite ; @xcite ) . our observations span @xmath0 5 years and sample semimajor axes out to several au , enabling detailed comparisons with previous surveys targeting solar - type stars . in @xmath282 we describe our radial velocity measurements and define our sample selection . updated keplerian orbits for five previously - known planetary systems are presented in @xmath283 and in @xmath284 we describe time - series photometric observations of these systems . in @xmath285 we derive detection limits for stars in our sample . we discuss the frequency of jovian - mass planets in @xmath286 , and in @xmath287 we compare the mass - period distribution for solar - type stars to the results from our sample of i m subgiants . finally , we discuss the implications of our work in @xmath288 .

we provide updated orbital solutions incorporating new radial velocity measurements for five known planet - hosting stars in our sample ; uncertainties in the fitted parameters are assessed using a markov chain monte carlo method . we find that the values of and for planets around solar - type stars from cumming et al .

we present an analysis of years of lick observatory radial velocity measurements targeting a uniform sample of 31 intermediate - mass subgiants ( 1.5 2.0 ) with the goal of measuring the occurrence rate of jovian planets around ( evolved ) a - type stars and comparing the distributions of their orbital and physical characteristics to those of planets around sun - like stars . we provide updated orbital solutions incorporating new radial velocity measurements for five known planet - hosting stars in our sample ; uncertainties in the fitted parameters are assessed using a markov chain monte carlo method . the frequency of jovian planets interior to 3 au is 26% , which is significantly higher than the 5 - 10% frequency observed around solar - mass stars . the median detection threshold for our sample includes minimum masses down to \{0.2 , 0.3 , 0.5 , 0.6 , 1.3 } within \{0.1 , 0.3 , 0.6 , 1.0 , 3.0 } au . to compare the properties of planets around intermediate - mass stars to those around solar - mass stars we synthesize a population of planets based on the parametric relationshiplnln , the observed planet frequency , and the detection limits we derived . we find that the values of and for planets around solar - type stars from cumming et al . fail to reproduce the observed properties of planets in our sample at the 4 level , even when accounting for the different planet occurrence rates . thus , the properties of planets around a stars are markedly different than those around sun - like stars , suggesting that only a small ( 50% ) increase in stellar mass has a large influence on the formation and orbital evolution of planets .

0912.0518

c

little is known about the saturn- or neptune - mass population of planets around i m stars . most planets orbiting i m stars discovered to date have masses @xmath25 2 @xmath4 ( table [ evolvedtab ] ) , leading to suggestions that more massive stars tend to produce more massive planets ( @xcite ) . it is unclear , however , whether this is a _ bona fide _ property or a result of an observational bias caused by higher jitter levels in i m stars which might mask the signals of lower - mass planets . moreover , few authors have assessed the limiting planet masses attainable by doppler surveys of evolved i m stars . despite the dearth of jovian planets at small semimajor axes , could a population of saturn - mass planets exist interior to 1 au around i m stars ? would the higher jitter levels of evolved i m stars prevent the discovery of neptune - mass planets ? we address these questions in this study by deriving detection limits for our sample of 31 i m ( 1.5 @xmath19 @xmath2 @xmath19 2.0 ) subgiants . typical detection limits for our stellar sample include planet masses down to @xmath0 \{0.21 , 0.34 , 0.50 , 0.64 , 1.3 } @xmath4 within \{0.1 , 0.3 , 0.6 , 1.0 , 3.0 } au at the 95.4% confidence level , excluding targets with large radial velocity scatter . we can therefore rule out the existence of hot saturns within 0.1 au and jovian planets out to 1 au for most stars in our sample . these detection limits suggest that the notably high masses of planets from our sample ( @xmath25 2 @xmath4 ) compared to planet masses around solar - type stars may be caused by a real difference in planet population characteristics . for example , if a population of planets with random masses existed at 1 au then we would expect an observational bias to result in an observed mass distribution that was truncated near the typical mass detection limit . as jovian planets would have been detected out to @xmath0 1 au , the higher planet masses uncovered so far may be indicative of a real trend . we test this idea quantitatively by comparing the mass - period distribution of planets around sun - like stars to the observed number and properties of planets in our sample . even when correcting for the higher planet occurrence rate found in our sample , the values of @xmath11 and @xmath12 in equation [ eqn : mp ] fail to reproduce the number ( 7/28 ) , masses ( @xmath14 1.5 @xmath4 ) , and semimajor axes ( @xmath14 1 au ) of planets from our sample at a confidence level of @xmath14 4 @xmath13 . we conclude that the frequency and mass - period distribution of planets around i m stars is different from those around solar - type stars . increasing the mass of the host star by a mere factor of 1.5 - 2 results in an entirely new planet population which is characterized by a high frequency ( @xmath0 26% ) of high - mass planets ( @xmath26sin@xmath27 @xmath14 1.5 @xmath4 ) at large semimajor axes ( @xmath15 @xmath14 1 au ) . the detection limits of the residuals of the planet - hosting stars in our sample show the strength of subgiant jitter levels and therefore trace the sensitivity levels attainable to doppler surveys targeting subgiants . the residual rms velocities range from @xmath06 - 10 m s@xmath37 . the detection limits indicate that planetary companions with minimum masses above \{0.2 , 0.4 , 0.5 , 0.7 , 1.4 } @xmath4 within \{0.1 , 0.3 , 0.6 , 1.0 , 3.0 } au can not exist in these systems . if these detection limits are representative of the typical jitter levels of subgiants then the higher rms velocity values observed in other subgiants from our sample may suggest as - yet - unrecognized low - mass companions . given our jitter - dominated detection limits , the prospects of discovering neptune - mass planets ( @xmath0 0.053 @xmath4 ) in circular orbits around i m stars using the doppler technique is not encouraging . if the dominant source of jitter in subgiants is from @xmath92-mode oscillations , observing strategies that include longer integration times or repeated exposures over hour - long timescales may help to partially overcome this hurtle ( see @xcite ) . our ongoing survey of intermediate - mass subgiants at keck observatory will address this issue by using the high rv precision achievable with the hires spectrometer and larger telescope aperture of keck compared to the lick 3 m . we derive updated orbit solutions using new observations for five of the known planet - hosting i m subgiants in our sample , which were originally announced by @xcite , @xcite , and @xcite . our results are in excellent agreement with those previously reported in the literature . our parameter uncertainties are typically a factor of @xmath0 2 smaller than the published values as a result of longer baselines and more radial velocity measurements . we also note that there is no evidence for periodicity in the residuals of the previously - known planet - hosting stars . we acquired time - series photometric observations of the five known planet - hosting stars with the automatic photometric telescopes at fairborn observatory . we find no evidence for brightness variation levels in any of the five stars that could call the existence of their planetary companions into question . the eccentricities of three of the five planets in our sample with accurate orbital solutions are consistent with zero and emphasize a low - eccentricity trend for planets around i m subgiants , all but two of which have eccentricities below 0.3 ( table [ evolvedtab ] ) . this is in contrast to planets around solar - type stars , which have approximately uniform eccentricity distributions between 0.0 and 0.8 for semimajor axes @xmath25 0.3 au ( @xcite ; @xcite ) . interestingly , @xcite find that the eccentricity distributions for planets with masses @xmath19 1 @xmath4 peaks at @xmath44 @xmath19 0.2 , while the planets with masses @xmath14 1 @xmath4 have more uniformly distributed eccentricities between 0.0 @xmath19 @xmath44 @xmath19 0.6 . planets around i m stars show the opposite trend : high - mass planets tend to have circular orbits . we will explore this effect in detail in a future publication in this series . information about planets orbiting i m stars has been driven by observations rather than theory . there is a growing need for stellar mass - dependent theoretical models of planet formation that make testable predictions about the physical and orbital characteristics of planets in this stellar mass regime . specifically , the abundance of low - mass planets , the eccentricity distribution , and the fraction of multiple planetary systems are but a few of the many outstanding questions to be addressed in this young field . we also encourage high - contrast imaging campaigns to include more a - type stars in their surveys . five planets have already been directly imaged orbiting a stars : hr 8799 b , c , and d ( @xcite ) , formalhaut b ( @xcite ) , and @xmath12 pic b ( @xcite ) . moreover , @xcite made their discovery after observing only a few early - type stars , in contrast to the many hundreds of late - type stars that have yielded null detections . these results , combined with the higher inner planet occurrence rate we measure , suggest that more planet - hunting imaging surveys in this mass regime will yield fruitful results . we extend our gratitude to the many cat observers who have helped with this project over the years , including chris mccarthy , raj sareen , howard isaacson , joshua goldston , bernie walp , julia kregenow , jason wright , and shannon patel . we also gratefully acknowledge the efforts and dedication of the lick observatory staff , and the time assignment committee of the university of california for their generous allocations of observing time . b. p. b. thanks chris beaumont and eric ford for productive discussions about mcmc techniques . j. a. j. is an nsf astronomy and astrophysics postdoctoral fellow and acknowledges support from the nsf grant ast-0757887 . we appreciate funding from nasa grant nng05gk92 g ( to g. w. m. ) . g. w. h. acknowledges long - term support from nasa , nsf , tennessee state university , and the state of tennessee through its centers of excellence program . d. a. f. is a cottrell science scholar of research corporation and acknowledges support from nasa grant nng05g164 g that made this work possible . this research made use of the simbad database operated at csd , strasbourg france , and the nasa ads database .

the median detection threshold for our sample includes minimum masses down to \{0.2 , 0.3 , 0.5 , 0.6 , 1.3 } within \{0.1 , 0.3 , 0.6 , 1.0 , 3.0 } au . to compare the properties of planets around intermediate - mass stars to those around solar - mass stars we synthesize a population of planets based on the parametric relationshiplnln , the observed planet frequency , and the detection limits we derived . fail to reproduce the observed properties of planets in our sample at the 4 level , even when accounting for the different planet occurrence rates . thus , the properties of planets around a stars are markedly different than those around sun - like stars , suggesting that only a small ( 50% ) increase in stellar mass has a large influence on the formation and orbital evolution of planets .

we present an analysis of years of lick observatory radial velocity measurements targeting a uniform sample of 31 intermediate - mass subgiants ( 1.5 2.0 ) with the goal of measuring the occurrence rate of jovian planets around ( evolved ) a - type stars and comparing the distributions of their orbital and physical characteristics to those of planets around sun - like stars . we provide updated orbital solutions incorporating new radial velocity measurements for five known planet - hosting stars in our sample ; uncertainties in the fitted parameters are assessed using a markov chain monte carlo method . the frequency of jovian planets interior to 3 au is 26% , which is significantly higher than the 5 - 10% frequency observed around solar - mass stars . the median detection threshold for our sample includes minimum masses down to \{0.2 , 0.3 , 0.5 , 0.6 , 1.3 } within \{0.1 , 0.3 , 0.6 , 1.0 , 3.0 } au . to compare the properties of planets around intermediate - mass stars to those around solar - mass stars we synthesize a population of planets based on the parametric relationshiplnln , the observed planet frequency , and the detection limits we derived . we find that the values of and for planets around solar - type stars from cumming et al . fail to reproduce the observed properties of planets in our sample at the 4 level , even when accounting for the different planet occurrence rates . thus , the properties of planets around a stars are markedly different than those around sun - like stars , suggesting that only a small ( 50% ) increase in stellar mass has a large influence on the formation and orbital evolution of planets .

0906.3540

c

we have presented a simple extension of the mssm with an additional @xmath1 gauge symmetry that couples predominantly to higgs fields . while other sneutrino dark matter models have been proposed to explain the cosmic ray observations , the model presented here does so while also resolving the naturalness problems of the mssm . in this model , an electroweak scale @xmath2 term and appropriately suppressed dirac neutrino masses are generated upon @xmath1 breaking . the right - handed sneutrinos @xmath336 and @xmath11 are the lightest and next - to - lightest superpartners , allowing for a natural explanation of pamela and other experiments like atic and fermi - lat in the context of sneutrino dark matter . a complete study of the dm relic density in this model includes contributions from the lsp and the nlsp , which is essentially stable with respect to the lifetime of the universe . we also analysed the contributions coming from late decaying particles , _ i.e. _ , particles that decay after freeze - out . for the parameter set in ( [ inputs ] ) , we obtain @xmath337 for the total relic density of right - handed sneutrino , consistent with the current wmap value . we then discussed the pamela , atic and fermi - lat data , considering @xmath338 as the source decay for the observed positron excess . the possibility of producing a final positron through muon is also discussed separately . the suppression of the anti - proton flux compared to the positron flux suggests the model - building constraint that the flavor - changing entries of the neutrino yukawa coupling matrix are suppressed with respect to the flavor - conserving entries . the fitted lifetimes for the dm , of the order of @xmath339 sec , fit the pamela data well for positron energies greater than @xmath340 gev , as well as the atic and fermi - lat cases . the fit is better for the m1 and med models described in the text . it can be concluded from the values of the fitted lifetimes that it maybe possible to explain the pamela+atic and fermi - lat data simultaneously in the corresponding energy ranges , though the fermi - lat data requires a slightly larger lifetime values for the dm . in principle , it is foreseeable that a better scan of the model parameters as well as implementing an improved fitting procedure could offer an even closer simultaneous explanation of these three sets of experimental data .

we present an-parity conserving model of sneutrino dark matter within a higgs - philic extension of the minimal supersymmetric standard model . in this theory , the parameter and light dirac neutrino masses the leptonic and hadronic decays of another sneutrino , taken to be the next - to - lightest superpartner , allow for a natural fit to the recent results reported by the pamela experiment . we perform a detailed calculation of the dark matter relic density in this scenario , and show that the model is consistent with the atic and fermi - lat experiments .

we present an-parity conserving model of sneutrino dark matter within a higgs - philic extension of the minimal supersymmetric standard model . in this theory , the parameter and light dirac neutrino masses are generated naturally upon the breaking of the gauge symmetry . one of the right - handed senutrinos is the lsp . the leptonic and hadronic decays of another sneutrino , taken to be the next - to - lightest superpartner , allow for a natural fit to the recent results reported by the pamela experiment . we perform a detailed calculation of the dark matter relic density in this scenario , and show that the model is consistent with the atic and fermi - lat experiments .

1102.1309

c

the orbits of eight nearby pns are calculated with the as91 and fsc96 galactic models . the small number of pns in the present sample is limited by the available observation data for pns in the galaxy . in our present sample , only pns with direct parallax distances are considered . the errors of the derived orbital parameters are calculated with a monte carlo method . we also compared the orbital parameters derived with different galactic models . we find that the uncertainty of the derived orbital parameters is mainly from the observational errors in the input data . according to the kinematic criteria of @xcite for distinguishing different populations in the galaxy and using the @xmath49 diagram , we find that sh 2 - 216 , deht 5 , ngc 7293 , a21 , and ton 320 belong to the thin - disk population and pg 1034 + 001 and a31 belong to the thick - disk population . puwe 1 probably belongs to the thick - disk population , but with the large errors of its derived orbital parameters , its population classification becomes very uncertain . the present sample of pns is very small , hence we can not come to any conclusion about the population distribution of galactic pns in the disk . population classification for the eight pns in our sample indicates that most of the pns formed are closer to the galactic plane . the dramatic enlargement of the sample of pns with reliable parallaxes will only be expected when the data of the _ gaia _ mission are available . the primary objective of the _ gaia _ mission is to survey more than one billion stars between 6 and 20 mag . the expected accuracies for parallaxes , proper motions and positions are 7 25 @xmath64as down to 15 mag and a few hundred @xmath64as at 20 mag @xcite . the magnitudes of 96% cs in the catalog of @xcite are less than 20.0 ; the precise distances and proper motions for those stars obtained with the _ gaia _ mission can be used to study their kinematics and dynamics in the galaxy . we analyzed the interaction between the pns in our sample and their nearby ism . the pn - sim interaction are observed in the eight pns in our present sample . the p.a.s of the proper motions of the pns are also consistent with the directions of the pn - ism interaction regions . for all eight of the pns in our sample , their kinematic ages are much smaller than the time @xmath30 for them to cross the galactic plane , and the distances that they moved from their birthplaces are all smaller than their linear size . different orbits derived with different galactic models can not affect the pn - ism interaction for each pn . there are two main models to explain the pn - ism interaction . one is presented by bss and sbs . in their models , the pn interacts with the ism directly , and the pn - ism interaction can be observed only when the density of the pn drops below some critical value . the magnetic field is also important in the models of bss and sbs . the other one is the triple - wind " model presented by wzo . in their model , the slow agb wind formed in the early evolution phase of the agb star interacts with the ism , and then the pn interacts with the bow shock formed during the agb wind - ism interaction . so , in the model of wzo , the pn - ism interaction can be observed in the early evolution phase of the pn . the magnetic field is not considered in the model of wzo . for both models , the relative velocity of the pn and the density of the ism in the vicinity of the pn are very important parameters for studying the pn - ism interaction . we use the above - mentioned models to explain the observed pn - ism interaction in the eight pns in our sample . using the models of bss and sbs , the local densities of ism in the vicinity of puwe 1 and a31 are derived and are consistent with those derived from the model of @xcite . for ton 320 and deht 5 , no electron density data are available . using the local densities of ism for these two pns derived from the model of @xcite , the electron densities of these two pns are derived from the models of bss and sbs . compared with the observed electron densities of other pns which have evolved into their later stages , the derived electron densities of these two pns are reasonable . for the above four pns , the models of bss and sbs yield consistent results from the model of @xcite , but for sh 2 - 216 and a21 , the derived local densities of ism in the vicinity of these two pns with the models of bss and sbs are larger than those derived from the model of @xcite . for sh 2 - 216 , considering a magnetic field in the position of this pn in the models of bss and sbs can explain the observed pn - ism interaction . for a21 , an asymmetric region surrounding this pn can explain the predicted high ism density . for these two pns , the model of @xcite will underestimate the local densities of ism . the model of @xcite represents the large - scale and average ism distribution in the galaxy ; it can not predict the local density of ism very precisely . therefore , with the models of bss and sbs , the local ism densities in the vicinity of evolved pns can be derived with the observed pn - ism interaction @xcite . because pg 1034 + 001 and ngc 7293 are still in their early stage of evolution , the models of bss and sbs can not used to derive the ism densities for these two pns . on the other hand , according to the model of wzo , sh 2 - 216 , a21 , and ton 320 are in the wzo 3 stage , pg 1034 + 001 and ngc 7293 are in the wzo 1 stage , and puwe 1 is in the wzo 2 stage . lllllccccc sh 2 - 216 & 04 : 43 : 21.3&@xmath98 : 42 : 05.8&12.630&@xmath99 & @xmath100 & @xmath101&116&@xmath102&@xmath103 + puwe 1 & 06 : 19 : 34.3&@xmath104 : 36 : 42.3&15.534&@xmath105 & @xmath106&@xmath107&141&@xmath108&@xmath109 + a21 & 07 : 29 : 02.7&@xmath110 : 14 : 48.8&15.962&@xmath111 & @xmath112 & @xmath113&166&@xmath114&@xmath115 + ton 320 & 08 : 27 : 05.6&@xmath116 : 30 : 08.5&15.702&@xmath117 & @xmath118 & @xmath119&198&@xmath120&@xmath121 + a31 & 08 : 54 : 13.2&@xmath122 : 53 : 53.0&15.519&@xmath123&@xmath124&@xmath125&228&@xmath126&@xmath127 + pg 1034 + 001&10 : 37 : 03.8&@xmath128 : 08 : 19.2&13.211&@xmath129 & @xmath130&@xmath131&290&@xmath132&@xmath133 + ngc 7293 & 22 : 29 : 38.5&@xmath134 : 50 : 13.7&13.525&@xmath135&@xmath136 & @xmath137&101&@xmath138&@xmath115 + deht 5 & 22 : 19 : 33.7&@xmath139 : 56 : 03.3&15.474&@xmath140&@xmath141&@xmath142&221&@xmath143&@xmath144 + lccccccccc sh 2 - 216 & 100&3.7&128.9&8.0&0.10&0.02&4&0.45&5 + puwe 1 & 20&2.1&365.0&3.1&0.08&0.02&27&0.04&1 + a21 & 9&1.4&540.5&206.0&0.07&0.02&32&0.02&4 + ton 320 & 30&4.6&531.9&&0.05&0.02&&0.11 & + a31 & 16&2.9&621.1&11.4&0.04&0.02&11&0.13&2 + pg 1034 + 001&360&22.0&210.5&&0.07&0.02&&0.54 & + ngc 7293 & 18&1.1&215.5&630.0&0.06&0.02&21&0.03&3 + deht 5 & 9&0.9&344.8&&0.08&0.02&5&0.09&1 + llllccccc sh 2 - 216 & @xmath145&@xmath146&@xmath147&@xmath148&@xmath149&@xmath150&@xmath151 + puwe 1 & @xmath152&@xmath153&@xmath154&@xmath155&@xmath156&@xmath157&@xmath158 + a21 & @xmath159&@xmath160&@xmath161&@xmath162&@xmath163&@xmath164&@xmath165 + ton 320 & @xmath166&@xmath167&@xmath168&@xmath169&@xmath170&@xmath171&@xmath172 + a31 & @xmath173&@xmath174&@xmath175&@xmath176&@xmath177&@xmath178&@xmath179 + pg 1034 + 001&@xmath180&@xmath181&@xmath182&@xmath183&@xmath184&@xmath185&@xmath186 + ngc 7293 & @xmath187&@xmath188&@xmath189&@xmath190&@xmath191&@xmath192&@xmath193 + deht 5 & @xmath194&@xmath195&@xmath196&@xmath197&@xmath198&@xmath199&@xmath200 + llllllll sh 2 - 216 & @xmath201&@xmath202&@xmath202&@xmath203&@xmath204&33.9&44.4 + puwe 1 & @xmath205&@xmath206&@xmath207&@xmath208&@xmath209&35.1&46.5 + a21 & @xmath210&@xmath211&@xmath211&@xmath212&@xmath213&31.7&41.7 + ton 320 & @xmath214&@xmath215&@xmath215&@xmath216&@xmath217&35.1&44.4 + a31 & @xmath218&@xmath219&@xmath220&@xmath221&@xmath222&38.5&50.0 + pg 1034 + 001 & @xmath223&@xmath224&@xmath219&@xmath225&@xmath226&35.7&46.5 + ngc 7293 & @xmath227&@xmath228&@xmath228&@xmath229&@xmath230&34.5&44.4 + deht 5 & @xmath231&@xmath232&@xmath233&@xmath234&@xmath235&33.9&44.4 + the authors thank the referee for his / her comments . this work has been supported in part by the national natural science foundation of china , nos . 10633020 , 10778720 , 10873016 , and 10803007 and by the national basic research program of china ( 973 program ) , no . 2007cb815403 . w. is supported by the young researcher grant of the national astronomical observatories , chinese academy of sciences . this research has made use of the simbad database and vizier catalog access tool , operated at cds , strasbourg , france . allen , c. , & santilln , a. 1991 , , 22 , 255 ( as91 ) balick , b. , & frank , a. 2002 , , 40 , 439 barstow , m. a. , bannister , n. p. , holberg , j. b. , hubeny , i. , bruhweiler , f. c. , & napiwotzki , r. 2001 , , 325 , 1149 benedict , g. f. , et al . 2009 , , 138 , 1969 boffi , f. r. , & stanghellini , l. 1994 , , 284 , 248 borkowski , k. j. , sarazin , c. l. , & soker , n. 1990 , , 360 , 173 ( bss ) de marco , o. 2009 , , 121 , 316 dehnen , w. , & binney , j. 1998 , , 298 , 387 dickey , j. m. , & lockman , f. j. 1990 , , 28 , 215 drew , j. e. , et al . 2005 , , 362 , 753 burand , s. , acker , a. , & zijlstra , a. 1998 , , 132 , 13 esa , 1997 , the hipparcos and tycho catalogues , esa , sp-1200 flynn , c. , sommer - larsen , j. , & christensen , p. r. 1996 , , 281 , 1027 ( fsc96 ) frew , d. j. , madsen , g. j. , otoole , s. j. , & parker , q. a. 2010 , pasa , 27 , 203 gaustad , j. e. , mccullough , p. r. , rosing , w. , & van buren , d. 2001 , , 113 , 1326 gieseking , f. , hippelein , h. , & weinberger , r. 1986 , , 156 , 101 good , s. a. , barstow , m. a. , burleigh , m. r. , dobbie , p. d. , & holberg , j. b. 2005 , , 364 , 1082 gurzadyan , g. a. 1969 , planetary nebulae ( new york : gordon & breach ) harrs , h. c. , dahn , c. c. , monet , d. g. , & pier , j. r. 1997 , in proc . 180 , planetary nebulae , ed . j. habing & h. j. g. l. m lamers(dordrecht : kluwer ) , 40 harrs , h. c. , et al . 2007 , , 133 , 631 hewett , p. c. , irwin , m. j. , skillman , e. d. , foltz , c. b. , willis , j. p. , warren , s. j. , & walton , n. a. 2003 , , 599 , l37 hippelein , h. , & weinberger , r. 1990 , , 232 , 129 hg , e. , et al . 2000 , , 355 , l27 holberg , j. b. , barstow , m. a. & sion , e. m. 1998 , , 119 , 207 hua , c. t. , & kwok , s. 1999 , , 138 , 275 kalberla , p. m. w. , & kerp , j. 1998 , , 339 , 745 kerber , f. , mignani , r. p. , guglielmetti , f. , & wicenec , a. 2003 , , 408 , 1029 kerber , f. , mignani , r. p. , pauli , e. m. , wicenec , a. , & guglielmetti , f. 2004 , , 420 , 207 kerber , f. , mignani , r. p. , smart , r. l. , & wicenec , a. 2008 , , 479 , 155 kwitter , k. b. , jacoby , g. h. , & lawrie , d. g. 1983 , , 95 , 732 kwok , s. , purton , c. r. , & fitzgerald , p. m. 1978 , , 219 , l125 kwok , s. 1982 , , 258 , 280 lasker , b. m. , et al . 2008 , , 136 , 735 lindegren , l. 2010 , in iau symp . 261 , relativity in fundamental astronomy , ed . s. a. klioner , p. k. seidelman & m. h. soffel , 296 meaburn , j. , boumis , p. , lopez , j. a. , harman , d. j. , bryce , m. , redman , m. p. , & mavromatakis , f. 2005 , , 360 , 963 meaburn , j. , lpez , j. a. , & richer , m. g. 2008 , , 384 , 497 monet , d. g. , et al . 2003 , , 125 , 984 pauli , e. m. , napiwotzki , r. , altmann , m. , heber , u. , odenkirchen , m. , & kerber , f. 2003 , , 400 , 877 pauli , e. m. , napiwotzki , r. , heber , h. , altmann , m. , & odenkirchen , m. 2006 , , 447 , 173 phillips , j. p. 1998 , , 340 , 527 press , w. h. , teukolsky , s. a. , vetterling , w. t. , & flannery , b. p. 1992 , numerical recipes in fortran : the art of scientific computing , 2rd edn . cambridge univ . press , cambridge ramos - larios , g. , & phillips , j. p. 2009 , , 400 , 575 ransom , r. r. , uyaniker , b. , kothes , r. , & landecker , t. l. 2008 , , 684 , 1009 rauch , t. , kerber , f. , & pauli , e. m. 2004 , , 417 , 647 rauch , t. , ziegler , m. , werner , k. , kruk , j. w. , oliveira , c. m. , vande , p. d. , mignani , r. p. , & kerber , f. 2007 , , 470 , 317 recillas - cruz , e. , & pismis , p. 1981 , , 97 , 398 reynolds , r. j. 1985 , , 288 , 622 sabin , l. , zijlstra , a. a. , wareing , c. , corradi , r. l. m. , mampaso , a. , viironen , k. , wright , n. j. , & parker , q. a. 2010 , pasa , 27 , 166 schnrich , r. , binney , j. , & dehnen , w. 2010 , , 403 , 1829 smith , h. 1976 , , 175 , 419 soker , n. , borkowski , k. j. , & sarazin , c. l. 1991 , , 102 , 1381 ( sbs ) soker , n. , & dgani , r. 1997 , , 484 , 277 tweedy , r. w. , & napiwotzki , r. 1992 , , 259 , 315 tweedy , r. w. , & kwitter , k. b. 1994 , , 433 , l93 tweedy , r. w. , martos , m. a. , & noriega - crespo , a. 1995 , , 447 , 257 tweedy , r. w. , & kwitter , k. b. 1996 , , 107 , 255 villaver , e. , garca - segura , g. , & manchado , a. 2003 , , 585 , l49 wareing , c. j. , zijlstra , a. a. , & obrien , t. j. 2007 , , 382 , 1233 ( wzo ) weinberger , r. 1989 , , 78 , 301 werner , k. , dreizler , s. , & wolff , b. 1995 , , 298 , 567 wu , z. y. , zhou , x. , ma , j. , & du , c. h. 2009 , , 399 , 2146 xilouris , k. m. , papamastorakis , j. , paleologou , e. , & terzian , y. 1996 , , 310 , 603 york , d. g. , et al . 2000 , , 120 , 1579 zacharias , n. , urban , s. e. , zacharias , m. i. , wycoff , g. l. , hall , d. m. , monet , d. g. , & rafferty , t. j. 2004 , , 127 , 3043 zacharias , n. , et al . 2009 , vizier on - line data catalog : i/315

the errors of the derived orbital parameters are determined with a monte carlo method . based on the derived orbital parameters , we find that sh 2 - 216 , deht 5 , ngc 7293 , a21 , and ton 320 belong to the thin - disk population , and pg 1034 + 001 and a31 belong to the thick - disk population . puwe 1 probably belongs to the thick - disk population , but its population classification is very uncertain due to the large errors of its derived orbital parameters . the position angles of the proper motions of the pns are consistent with the directions of the pn - ism interaction regions . ( wzo ) , sh 2 - 216 , a21 , and ton 320 are in the wzo 3 stage , pg 1034 + 001 and ngc 7293 are in the wzo 1 stage , and puwe 1 is in the wzo 2 stage .

we present and analyze the orbits of eight nearby planetary nebulae ( pns ) using two different galactic models . the errors of the derived orbital parameters are determined with a monte carlo method . based on the derived orbital parameters , we find that sh 2 - 216 , deht 5 , ngc 7293 , a21 , and ton 320 belong to the thin - disk population , and pg 1034 + 001 and a31 belong to the thick - disk population . puwe 1 probably belongs to the thick - disk population , but its population classification is very uncertain due to the large errors of its derived orbital parameters . the pn - ism interactions are observed for the eight pns in our sample . the position angles of the proper motions of the pns are consistent with the directions of the pn - ism interaction regions . the kinematic ages of pns are much smaller than the time for them to cross the galactic plane . using the models of borkowski et al . and soker et al . , the pn - ism interaction can be used to derive the local density of ism in the vicinity of evolved pns . according to the three - dimensional hydrodynamic simulations of wareing et al . ( wzo ) , sh 2 - 216 , a21 , and ton 320 are in the wzo 3 stage , pg 1034 + 001 and ngc 7293 are in the wzo 1 stage , and puwe 1 is in the wzo 2 stage .

astro-ph0408391

i

we present a photometric study of the resolved stellar populations in i zw 18 , the most metal - deficient blue compact dwarf ( bcd ) galaxy known . the analysis of the color - magnitude diagram ( cmd ) of i zw 18 , based on _ hubble space telescope_/advanced camera for surveys @xmath0 and @xmath1 images , the deepest ever obtained for the bcd , have led us to the following conclusions : \1 . the cmd of i zw 18 is populated by stars with different ages including the youngest hydrogen core burning main - sequence ( ms ) stars ( age @xmath4 30 myr ) , evolved massive stars with helium core burning [ blue loop ( bl ) stars and red supergiants ( rsg ) ] with ages between 10 myr and 100 myr , and asymptotic giant branch ( agb ) helium shell burning stars with ages between 100 myr and 500 myr . however , _ i zw 18 is the first galaxy with resolved stellar populations where no red giant branch ( rgb ) stars are seen _ , although our data go 1 2 mag deeper than the tip of the rgb for a distance of i zw 18 in the range 12.6 mpc 15 mpc ( see conclusion 2 ) . the oldest stars located mainly in the southeastern part of the main body and the northwestern part of the c component have an age not exceeding @xmath6 500 myr . thus _ i zw 18 is a bona fide young galaxy_. \2 . since no rgb stars are seen , we can not use the brightness of the tip of the rgb to derive the distance to i zw 18 . instead , we compare the brightness of the agb stars in i zw 18 with those in the very metal - deficient bcd ugc 4483 with a heavy element abundance of @xmath2/23 to derive a distance in the range 12.6 mpc 15 mpc , with the most likely value in the upper range . \3 . several star formation episodes in i zw 18 can be inferred from its cmd . however star formation proceeds differently in the main body and in the c component . in the main body , three star formation episodes are indicated , separated by periods of @xmath6 100 200 myr . examination of the spatial distribution of the stellar populations suggests that the star formation process is still gradually building up the main body from the inside out as the young ms and bl+rsg stars occupy larger areas as compared to the older agb stars . in the c component , two star formation episodes are inferred separated by a period of @xmath6 200 myr . these separate star formation episodes occurred in spatially different regions , reflecting the stochastic mode of star formation in bcds . the southeastern region of the c component is a few hundred myr younger than the northwestern region . both in the main body and in the c component , the spatial distributions of the stellar populations in i zw 18 strongly suggest that the galaxy is still in the process of forming . t.x.t . has been partially supported by grant hst - go-08769.01-a . the research described in this publication was made possible in part by award no . up1 - 2551-kv-03 of the u.s . civilian research & development foundation for the independent states of the former soviet union ( crdf ) and a grant no . m/85 - 2004 of the ministry of education and science of ukraine . we are also grateful for the partial financial support of nsf grant ast-02 - 05785 . thanks the hospitality of the astronomy department of the university of virginia . dufour , r. j. , garnett , d. r. , skillman , e. d. , & shields , g. a. 1996b , in asp conference series 98 , from stars to galaxies , ed . c. leitherer , u. fritze-v.alvensleben , & j. huchra ( san francisco : asp ) , 358 crrcrr 22 23&100.0&100.0 & & 100.0&100.0 + 23 24 & 97.0 @xmath25 4.9 & 99.9 @xmath25 1.7 & & 100.0&100.0 + 24 25 & 91.7 @xmath25 5.3 & 96.1 @xmath25 3.1 & & 100.0 & 98.2 @xmath25 1.7 + 25 26 & 90.6 @xmath25 7.7 & 89.7 @xmath25 2.3 & & 97.4 @xmath25 3.0 & 98.2 @xmath25 1.7 + 26 27 & 85.1 @xmath25 8.7 & 85.7 @xmath25 6.5 & & 95.4 @xmath25 4.4 & 94.5 @xmath25 2.8 + 27 28 & 78.9 @xmath25 8.5 & 70.7 @xmath25 10.4 & & 92.9 @xmath25 9.2 & 80.4 @xmath25 4.2 + 28 29 & 55.3 @xmath25 15.7 & 39.0 @xmath25 6.3 & & 69.4 @xmath25 9.9 & 44.2 @xmath25 10.1 + 29 30 & 10.4 @xmath25 7.7 & 5.4 @xmath25 7.1 & & 16.5 @xmath25 9.4 & 9.8 @xmath25 8.4 + 30 31 & 0.6 @xmath25 2.5 & & & 0.6 @xmath25 3.0 & +

we present and photometry of the resolved stars in the most metal - deficient blue compact dwarf galaxy known , i zw 18 (/50 ) , using _ hubble space telescope_/advanced camera for surveys ( acs ) images , the deepest ones ever obtained for this galaxy . it reveals a young stellar population of blue main - sequence ( ms ) stars ( age 30 myr ) and blue and red supergiants ( 10 myr age 100 myr ) , but also an older evolved population of asymptotic giant branch ( agb ) stars ( 100 myr age 500 myr ) . we derive a distance to i zw 18 in the range 12.6 mpc 15 mpc from the brightness of its agb stars , with preferred values in the higher range . the red giant branch ( rgb ) stars are conspicuous by their absence , although , for a distance of i zw 18 15 mpc , our imaging data go 1 2 mag below the tip of the rgb . there have been respectively three and two episodes in these two parts , separated by periods of 100 200 myr . in the main body , the younger ms and massive post - ms stars are distributed over a larger area than the older agb stars , suggesting that i zw 18 is still forming from the inside out . in the c component , different star formation episodes are spatially distinct , with stellar population ages decreasing from the northwest to the southeast , also suggesting the ongoing build - up of a young galaxy .

we present and photometry of the resolved stars in the most metal - deficient blue compact dwarf galaxy known , i zw 18 (/50 ) , using _ hubble space telescope_/advanced camera for surveys ( acs ) images , the deepest ones ever obtained for this galaxy . the resulting vs. color - magnitude diagram ( cmd ) reaches limiting magnitudes = = 29 mag . it reveals a young stellar population of blue main - sequence ( ms ) stars ( age 30 myr ) and blue and red supergiants ( 10 myr age 100 myr ) , but also an older evolved population of asymptotic giant branch ( agb ) stars ( 100 myr age 500 myr ) . we derive a distance to i zw 18 in the range 12.6 mpc 15 mpc from the brightness of its agb stars , with preferred values in the higher range . the red giant branch ( rgb ) stars are conspicuous by their absence , although , for a distance of i zw 18 15 mpc , our imaging data go 1 2 mag below the tip of the rgb . thus , the most evolved stars in the galaxy are not older than 500 myr and _ i zw 18 is a bona fide young galaxy_. several star formation episodes can be inferred from the cmds of the main body and the c component . there have been respectively three and two episodes in these two parts , separated by periods of 100 200 myr . in the main body , the younger ms and massive post - ms stars are distributed over a larger area than the older agb stars , suggesting that i zw 18 is still forming from the inside out . in the c component , different star formation episodes are spatially distinct , with stellar population ages decreasing from the northwest to the southeast , also suggesting the ongoing build - up of a young galaxy .

1502.06617

i

virtually every massive galaxy hosts a supermassive black hole in its core . these central black holes exhibit tight correlations with properties of their host galaxies bulges @xcite : bulge mass @xcite , bulge luminosity @xcite , and bulge stellar velocity dispersion @xcite . recently these correlations were re - explored using the wealth of new black hole mass measurements ( @xmath3 ) and galaxy parameters by @xcite and @xcite . however , the discovery that the @xmath4 relation may evolve with redshift ( e.g. * ? ? ? * ) has led to the suggestion that the most basic scaling relation may instead be with total stellar mass @xcite ; in this case , the evolution of the @xmath4 relation with redshift indicates the changing fractions of mass in galaxy bulges ( which contribute to @xmath5 ) versus disks ( which do not ) . see @xcite for a detailed review of our current understanding of black hole scaling relations . the mechanism through which black hole masses correlate with galaxy properties has been canonically associated with gas - rich galaxy mergers ( e.g. * ? ? ? gravitational torques funnel the gas into their centers , triggering two phenomena : an intense burst of star formation to feed the bulge , and accretion of gas on to the black holes in the centers of each galaxy . it has been postulated that black hole growth can regulate this process through agn feedback @xcite via massive winds that evacuate the gas from the galaxy on short timescales , cutting off star formation and future black hole growth . this sense of self - regulation has been confirmed observationally by @xcite , who find that the eddington ratio of a sample of agns depends on the supply of cold gas in the galaxy . if there is plenty of cold gas , the accretion rate does not depend on the quantity of gas available ; if the supply of cold gas is limited , the accretion rate depends on the rate at which stellar winds provide fuel for the agn . though the detailed mechanisms causing these correlations are still unconfirmed , star formation and black hole growth are fed by the same reservoir of inflowing gas ; their growth histories are intertwined . it is likely that these two processes compete for fuel in a predictable fashion . to understand this interplay , it is critical to look at systems in the midst of this increased fueling . one set of such galaxies are gas - rich mergers , which tend to have extreme bursts of star formation and a higher incidence of agn activity ( e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? during such a merger , does the black hole grow first , leaving the stars to slowly consume the remaining gas ? or is star formation quenched once the black hole reaches a bright quasar phase of extreme growth ? the position of a merger on black hole scaling relations would indicate the relative growth timescales , and confirm whether the putative quasar - mode feedback occurs at the end of a merger ( see figure [ scalingrelationtracks ] for the schematic example for the @xmath4 relation . ) . as star formation happens on few - kiloparsec spatial scales , accreting gas must lose less angular momentum to fuel a starburst than to feed a black hole . subsequent models therefore suggest that a black hole would grow substantially only after star formation has quenched itself and the galaxy bulge is in place @xcite , or at least that the peak black hole accretion time occurs later in a merger relative to peak star formation @xcite . this scenario would predict that gas - rich mergers would fall below black hole scaling relations . relation for isolated galaxies from @xcite ( black ) with three possible evolutionary tracks for merging galaxies overlaid . if the black hole grows first or more quickly than the galaxy bulge , mergers would lie above the relation ( as shown by the gold arrows ) . if the black hole growth lags the bulge growth and is responsible for curtailing evolution ( e.g. quenching through agn feedback ) , mergers would lie below the relation ( as shown by the purple arrows ) . if instead the black hole and the bulge grow in lockstep , the mergers would remain on the relation ( as shown by the blue arrow ) . ] merger - driven galaxy evolution is not a complete explanation for all black hole growth , however . though some agn studies find a correlation with major mergers @xcite , agns found with other selection techniques and at different redshift ranges do not show a higher rate of merging than field galaxies @xcite . instead of mergers bringing in gas , some systems probably are undergoing secular evolution , accreting their gas directly from the cold intergalactic medium . bar and spiral disk instabilities are capable of dissipating sufficient angular momentum from this gas to fuel black hole growth @xcite . the dividing line between these two processes is not yet well understood ; here we focus on understanding the black hole growth due to major mergers . nearby ( ultra-)luminous infrared galaxies ( ( u)lirgs ; * ? ? ? * ) are an excellent sample with which to study such gas - rich mergers . these galaxies have infrared luminosities upwards of @xmath6 ( @xmath7 for ulirgs ) , generally caused by a starburst and/or an agn heating up dust . their infrared luminosities correlate with merger rate , star formation rate , and agn fraction @xcite . in fact , in the local universe , such strong infrared activity is almost exclusively triggered by major mergers : @xcite showed that in a complete sample of iras ulirgs , 117 out of 118 galaxies are in the midst of strong tidal interactions . in a companion paper @xcite , we have studied the kinematics of both gas and stars in the inner kiloparsecs of a sample of ( u)lirgs , finding that nuclear disks on scales of a few tens to hundreds of parsecs are common . in two other papers @xcite , we demonstrated a technique that uses high spatial resolution integral field spectroscopy to measure black hole masses . with kinematic maps that resolve inside the sphere of influence of a black hole , the complex and unrelaxed large - scale dynamics are less important , and black hole masses can be measured to within a factor of a few . we note that this technique measures the unresolved central mass , which includes both the black hole and its accretion disk , and in some cases may also include a reservoir of gas feeding the accretion disk . in @xcite , the black hole mass in mrk273 n measured with this technique was consistent with the measurement made by oh maser kinematics @xcite . using a robust technique such as this to measure black hole masses in these gas - rich mergers is important because more traditional methods of black hole mass measurements rely on assumptions that are nt valid in the case of galaxy mergers . three - integral orbital superposition models ( as in * ? ? ? * ; * ? ? ? * ) are able to use large - field kinematics to separate different components to the mass profile of the galaxy ; however , this approach requires a dynamically relaxed system and is used therefore in isolated galaxies . another successful black hole mass measurement technique is reverberation mapping ( e.g. * ? ? ? * and references therein ) , which measures the time lag between flux variations of the continuum and the lines in the broad line region . since the cores of ( u)lirgs are so dusty , the broad line regions are too obscured to view . obtaining data at spatial resolutions sufficiently high to resolve inside the sphere of influence of a supermassive black hole at the typical redshifts of local ( u)lirgs ( @xmath8 ) requires adaptive optics systems , which are becoming available at an increasing number of ground - based observatories . though the hubble space telescope has excellent resolution in the visible bands , its relatively small mirror size limits the resolution at the longer wavelengths ( @xmath9 m ) necessary to look through the dust in these galactic nuclei ; even at the longest wavelength available to the wide field camera 3 ( @xmath10-band ) , these nuclei are still sometimes obscured . in order to achieve high spatial resolution in @xmath11-band , large ground - based telescopes have employed adaptive optics systems which measure turbulence in the earth s atmosphere and use a deformable mirror to correct for the resulting distortions . these distortion measurements require references , either a natural guide star ( ngs ao ) or a laser guide star plus a fainter natural `` tip - tilt '' star ( lgs ao ) . the addition of laser guide star adaptive optics has increased the area of the sky observable with this technique . throughout this paper we have adopted a cosmology of @xmath12kms@xmath13mpc@xmath13 , @xmath14 = 0.28 , and @xmath15 = 0.72 @xcite . in [ obs ] we present our data and reduction techniques . in [ kinematicfitting ] we briefly describe the kinematic fitting techniques demonstrated in @xcite and @xcite . in [ results ] we present the black hole masses measured from several tracers and in [ scalingrelations ] compare them to black hole scaling relations . [ conclusions ] contains our conclusions .

we present black hole mass measurements from kinematic modeling of high - spatial resolution integral field spectroscopy of the inner regions of 9 nearby ( ultra-)luminous infrared galaxies in a variety of merger stages . these observations were taken with osiris and laser guide star adaptive optics on the keck i and keck ii telescopes , and reveal gas and stellar kinematics inside the spheres of influence of these supermassive black holes . we find that this sample of black holes are overmassive ( m ) compared to the expected values based on black hole scaling relations , and suggest that the major epoch of black hole growth occurs in early stages of a merger , as opposed to during a final episode of quasar - mode feedback .

we present black hole mass measurements from kinematic modeling of high - spatial resolution integral field spectroscopy of the inner regions of 9 nearby ( ultra-)luminous infrared galaxies in a variety of merger stages . these observations were taken with osiris and laser guide star adaptive optics on the keck i and keck ii telescopes , and reveal gas and stellar kinematics inside the spheres of influence of these supermassive black holes . we find that this sample of black holes are overmassive ( m ) compared to the expected values based on black hole scaling relations , and suggest that the major epoch of black hole growth occurs in early stages of a merger , as opposed to during a final episode of quasar - mode feedback . the black hole masses presented are the dynamical masses enclosed inpc , and could include gas which is gravitationally bound to the black hole but has not yet lost sufficient angular momentum to be accreted . if present , this gas could in principle eventually fuel agn feedback or be itself blown out from the system .

astro-ph0204465

i

gg tau a is one of the few t tauri systems in which a disk has been spatially resolved at both millimeter and near - infrared wavelengths and is therefore an ideal system for detailed studies of proto - planetary disk geometry and composition . as the second brightest millimeter object in the survey of beckwith et al . ( 1990 ) , gg tau was an early target for millimeter wave interferometry studies ( simon & guilloteau 1992 ; kawabe et al . 1993 ; dutrey , guilloteau & simon 1994 ; guilloteau , dutrey & simon 1999 , hereafter g99 ) . these observations showed the emission to be from a massive ( @xmath6 ) disk surrounding gg tau a , the closest pair of stars in the gg tau quadruple stellar system , with the bulk of the emission arising from a distinct ring structure extending from 180 to 260 au ( assuming a distance of 139 pc ; bertout , robichon & arenou , 1999 ) . the circumbinary disk was subsequently detected via near - infrared scattered light in multi - wavelength , ground - based adaptive optics ( ao ) images ( roddier et al . 1996 , hereafter known as r96 ) and in space - based hubble space telescope ( hst ) 1 polarimetric images ( silber et al . 2000 ) and wfpc2 optical images ( krist , stapelfeldt & watson 2002 ) . analysis of the ground - based near - infrared images resulted in disk colors that appear to be redder than the central stars ( r96 ) . such a red color excess could either indicate that the circumbinary disk has a substantial population of large dust grains , or that circumstellar disks , which are coplanar with the circumbinary disk , redden the stellar light before it scatters off the circumbinary disk . comparing the variation of disk magnitude with color around the disk , roddier et al . find a trend for fainter regions of the disk to be redder , leading them to suggest that circumstellar disks are the cause of the observed red color excess . the existence of circumstellar disks around the individual components in gg tau a is supported by observations of near - infrared excesses and strong hydrogen emission lines in each component ( white et al . no information , however , is currently available regarding their orientation and in fact many disks in binary systems show evidence of non - coplanarity ( e.g. , stapelfeldt et al . 1998 ; monin , mnard & duchne , 1998 ; jensen et al . 2000 ; wood et al . 2001 ) . to test the circumstellar disk hypothesis , wood , crosas & ghez ( 1999 ) ran monte carlo scattering simulations of the gg tau circumbinary ring with and without circumstellar disks being present . using the kim , martin & hendry ( 1994 ) interstellar medium ( ism ) grain properties and the disk geometry derived by dutrey et al . ( 1994 ) , they find that the circumstellar disks are required to match the disk to star flux ratios and near side to far side flux ratios observed in the ground - based ao images . while these simulations roughly reproduce the estimated quantities due to the large observational uncertainties , they predict blue rather than red disk color excesses . in order to make further progress in understanding the role of circumstellar disks and the possibility of large particles , much higher signal to noise measurements of the circumbinary disk are required at multiple wavelengths . in this paper we present new high angular resolution , multi - wavelength observations of the gg tau system taken with nicmos aboard hst . these deep , space - based observations offer a more stable point spread function ( psf ) than that obtainable with ground - based ao systems , allowing a more accurate determination of the disk properties . the observations are outlined in [ obs ] and the data reduction and psf subtraction method used are explained in [ reduc ] . newly derived stellar and circumbinary disk properties are presented in [ res ] and are discussed in sections [ discus ] and [ implications ] in light of additional monte carlo simulations .

we present deep , near - infrared images of the circumbinary disk surrounding the pre main - sequence binary star , a , obtained with nicmos aboard the hubble space telescope . our analysis , in comparison to previous simulations , shows that the major limitation to the study of grain growth in t tauri disk systems through scattered light lies in the uncertain ism dust grain properties . without explicit determination of the scattering properties it is not possible to differentiate between geometric , scattering and evolutionary effects .

we present deep , near - infrared images of the circumbinary disk surrounding the pre main - sequence binary star , a , obtained with nicmos aboard the hubble space telescope . the spatially resolved proto - planetary disk scatters.5% of the stellar flux , with a near - to - far side flux ratio of.4 , independent of wavelength , and colors that are comparable to the central source ( , ) ; all of these properties are significantly different from the earlier ground - based observations . new monte carlo scattering simulations of the disk emphasize that the general properties of the disk , such as disk flux , near side to far side flux ratio and integrated colors , can be approximately reproduced using ism - like dust grains , without the presence of either circumstellar disks or large dust grains , as had previously been suggested . a single parameter phase function is fitted to the observed azimuthal variation in disk flux , providing a lower limit on the median grain size of . our analysis , in comparison to previous simulations , shows that the major limitation to the study of grain growth in t tauri disk systems through scattered light lies in the uncertain ism dust grain properties . without explicit determination of the scattering properties it is not possible to differentiate between geometric , scattering and evolutionary effects . finally , we use the 9 year baseline of astrometric measurements of the binary to solve the complete orbit , assuming that the binary is coplanar with the circumbinary ring . we find that the estimated 1 range on disk inner edge to semi - major axis ratio , , is larger than that estimated by previous sph simulations of binary - disk interactions .

astro-ph0204465

i

the gg tau disk is clearly detected ( @xmath104 ) in all three nicmos filters between radii of 10 to 22 , scattering approximately 1.5% of the stellar light . no discernible wavelength dependence of scattered light is observed , although azimuthal variations in both width and intensity are seen and modeled . we confirm the observation of a kink in the disk by silber et al . ( 2000 ) . observed as a sharp elbow in the disk on the south - east edge , followed by a flattening of the isophotes along the southern edge of a disk , this feature is seen in all three filters . the projected distance of the northern edge from the center of mass , related to the total height of the ring , provides the first hint that the ring may not be as thick as previously estimated , with a total height of 35au at the inner edge of the disk ( 180au ) . the presence of such a well - observed circumbinary ring around this system , combined with the 9 year baseline of binary observations has allowed us to constrain the orbital parameters of the binary . we find a slightly elliptical orbit @xmath105 , with a semi - major axis @xmath44au and a corresponding orbital period of @xmath45yr . the 1@xmath4 range of estimated orbital semi - major axis is such that the ratio of semi - major axis to inner disk radius is larger than expected from previous sph simulations ( artymowicz & lubow , 1994 ) . this suggests that the dynamical evolution of the circumbinary ring may be more complex than previously thought . further astrometric observations of this close binary are needed to constrain the binary orbit further . the monte carlo simulations summarized in [ mcmodel ] show the wide range of colors one can ` predict ' from the gg tau disk , from blue to red , using different dust size distributions and grain properties ( @xmath36 , @xmath84 ) . specifically , our monte carlo simulations show that the observed neutral disk colors , ratio of disk to star light , and near side to far side flux ratio can probably be reproduced with some combination of an ism - like grain size distribution and dust properties and does not necessarily require either the presence of large dust grains or prior extinction by circumstellar disks . however , this does not rule out that either is present . because the disk is optically thick in the near - infrared , studies of scattered light are only sensitive to those grains that are located near the surface of the ring . any conclusion about grain growth only applies to those regions and does not provide any information the size of grains deep in the ring . for instance , it has been shown that grains larger than @xmath106 tend to segregate in the disk midplane because of their larger mass ( e.g. , suttner & yorke 2001 ) and possibly as the result of the enhanced grain - grain collision rate in higher density regions . the presence of such large grains in the midplane can not be determined in our near - infrared observations . circumstellar disks are known to surround both components of gg tau a , however , the possible effects they have on the integrated circumbinary disk colors have been shown to be subtle and somewhat surprising . while krist et al . ( 2002 ) suggest that the red disk colors observed in the optical could be caused by an @xmath107 1.2 mag of extinction , possibly in the form of circumstellar disks , wood et al . ( 1999 ) find that the inclusion of small circumstellar disks can actually cause the integrated disk colors to become _ bluer _ rather than redder . analysis of the disk colors at both optical and near - infrared wavelengths is planned for future work . while the color of scattered light in optically thick disks can not currently be used to constrain grain properties , the azimuthal intensity variations can be used to provide a lower limit on the median grain size , independent of grain model . this lower limit ( @xmath108 at 1 ) corresponds to a median grain size of @xmath3 . given that the ism dust models produce a wide range of median grain sizes ranging from @xmath00.16 ( mathis , rumpl & nordsieck 1977 ; kmh ) to 0.56 ( mw ) , this lower limit does not suggest that grain growth has occured in the surface layers of the disk in this young ( @xmath01 myr old ; white et al . 1999 ) system . there is still considerable uncertainty regarding the ism dust properties ( e.g. , witt 2000 ) , a point which is well illustrated here by the comparison of monte carlo scattering results using two of the more well known dust grain models . both the kmh and mw grain models , like most of the ism dust models to date , have been constrained using the ism extinction curve , which they reproduce equally well . the results presented here suggest that using the extinction curve _ alone _ to constrain the dust properties introduces a significant level of uncertainty in the scattering properties of the grains . as an example , kmh and mw grain models predict v band @xmath84 s of @xmath109 and @xmath110 respectively . observations of reflection nebulae in the same bandpass infer @xmath111 , significantly different from either of these models ( witt , oliveri & schild , 1990 ) . additionally , models of t tauri disks seen in scattered light with wfpc2 find that the observations are best fit by @xmath112 ( burrows et al . 1996 ; stapelfeldt et al . 1998 ; krist et al . 2002 ) , although these values may be affected by grain growth . combining additional sources of information , such as observations of dust scattering ( e.g. , witt , et al . 1990 ) , polarization ( e.g. , zubko & laor 2000 ) , and dust thermal emission ( e.g. , li & draine 2001 ) will provide additional constraints . without a more detailed knowledge of the ism dust grain properties it is unlikely that we will be able to unambiguously determine whether grain growth is occuring in t tauri disks through scattered light imaging . although dust properties in the disk can not currently be constrained from either colors or dust asymmetry alone , this work provides an outline for future analysis and modeling . observationally , further resolved intensity and polarization maps at other wavelengths are key in sampling a large enough grain size parameter ( @xmath100 ) range to constrain the dust grain properties . for instance , at 3 to 5 the dust asymmetry is expected to be much more isotropic , allowing significant color variations ( e.g. , @xmath113 ) between the front and back sides , unless significant grain growth has already occurred . such observations should be carried out in parallel with a full exploration of the parameter space ( grain size distribution , grain properties , ring geometry ) through monte carlo scattering simulations . the authors thank mike jura , alycia weinberger , franois mnard , kenny woods , lisa prato , and angelle tanner for enlightening discussions . we also thank the anonymous referee for their constructive comments . support for this work was provided by nasa through grant number go-06735.01 - 95a from the space telescope institute , the nasa astrobiology institute and the packard foundation . this research was based on observations made with the nasa / esa hubble space telescope , obtained at the space telescope science institute , which is operated by the association of universities for research in astronomy , inc , under nasa contract nas5 - 26555 . this research has made use of the simbad database , operated at cds , strasbourg , france .

the spatially resolved proto - planetary disk scatters.5% of the stellar flux , with a near - to - far side flux ratio of.4 , independent of wavelength , and colors that are comparable to the central source ( , ) ; all of these properties are significantly different from the earlier ground - based observations . new monte carlo scattering simulations of the disk emphasize that the general properties of the disk , such as disk flux , near side to far side flux ratio and integrated colors , can be approximately reproduced using ism - like dust grains , without the presence of either circumstellar disks or large dust grains , as had previously been suggested . a single parameter phase function is fitted to the observed azimuthal variation in disk flux , providing a lower limit on the median grain size of . we find that the estimated 1 range on disk inner edge to semi - major axis ratio , , is larger than that estimated by previous sph simulations of binary - disk interactions .

we present deep , near - infrared images of the circumbinary disk surrounding the pre main - sequence binary star , a , obtained with nicmos aboard the hubble space telescope . the spatially resolved proto - planetary disk scatters.5% of the stellar flux , with a near - to - far side flux ratio of.4 , independent of wavelength , and colors that are comparable to the central source ( , ) ; all of these properties are significantly different from the earlier ground - based observations . new monte carlo scattering simulations of the disk emphasize that the general properties of the disk , such as disk flux , near side to far side flux ratio and integrated colors , can be approximately reproduced using ism - like dust grains , without the presence of either circumstellar disks or large dust grains , as had previously been suggested . a single parameter phase function is fitted to the observed azimuthal variation in disk flux , providing a lower limit on the median grain size of . our analysis , in comparison to previous simulations , shows that the major limitation to the study of grain growth in t tauri disk systems through scattered light lies in the uncertain ism dust grain properties . without explicit determination of the scattering properties it is not possible to differentiate between geometric , scattering and evolutionary effects . finally , we use the 9 year baseline of astrometric measurements of the binary to solve the complete orbit , assuming that the binary is coplanar with the circumbinary ring . we find that the estimated 1 range on disk inner edge to semi - major axis ratio , , is larger than that estimated by previous sph simulations of binary - disk interactions .

astro-ph0403420

i

theoretical isochrones are commonly fit to the major observational sequences of star clusters in order to both better understand the underlying physics of stellar evolution and to determine properties of the clusters , i.e. , the age . if the metallicity , reddening and distance to the cluster are well constrained from independent techniques , the comparisons typically involve matching the morphology of the turn - off and location of the red giant stars to predictions . recently , the newer method of using synthetic colour - magnitude diagrams to compare with observational data has proven to be much more informative and rewarding @xcite . these montecarlo simulations allow modelling of several additional parameters which dictate the distribution of points in the cmd , such as stochastic star formation ( sf ) processes , binary fraction , photometric spread , main - sequence thickness , data incompleteness and small number statistics . consequently , the results not only provide a measure of the properties of the cluster , but can also constrain the star formation history ( sfh ) and the initial mass function ( imf ) . furthermore , by comparing the simulations based on several different sets of evolutionary tracks , we can constrain which models use the best prescription of parameters ( such as treatment of overshooting , mixing length , etc ... ) . confronting the simulations with observations requires a large data set with accurate photometry . for this , we use the deep @xmath0 photometry presented in the cfht open star cluster survey ( @xcite , hereafter jski ) . jski observed 19 open star clusters in our galaxy and have yet published results on the four richest clusters , ngc 6819 ( @xcite , hereafter jskii ) , ngc 2099 ( @xcite , hereafter jskiii ) , and ngc 2168 and ngc 2323 ( @xcite , hereafter jskiv ) . these data were reduced and calibrated in a homogenous manner as described in jski . the resulting cmds exhibit very tight main sequences showing several ` kinks ' and slope changes which are predicted by theory . more importantly , the combination of very short and deep exposures , and the large aerial coverage of the detector ( 42@xmath1 28@xmath2 ) has allowed the measurement of stars from the brightest asymptotic giant branch ( agb ) and red giant branch ( rgb ) phases down to very low - mass main - sequence phases ( @xmath30.2 m@xmath4 ) . this allows our comparisons to yield evolutionary information over a wide mass range . the reduced data set in the cfht open star cluster survey has been requested by , and made available to , several investigators for additional science rewards outside our goals ( e.g. , astrometric studies , proper motions , variable stars , radial velocities , brown dwarfs , blue stragglers and galactic disk star distributions ) . the present study complements these efforts and analyses the four published clusters in a way that allows us to include them in a large homogeneous sample of open clusters aimed at studying the formation and evolution of the galactic disk ( bragaglia 2003 , and references therein ) . galactic open clusters are indeed particularly well suited to this purpose , since they span a range of ages from a few million to several billion years and can be observed in various regions of the galactic disk characterised by different star formation histories . they can be used to study both the present day disk structure and its temporal evolution ( janes & phelps 1994 , friel 1995 , tosi 2000 , bellazzini et al . old open clusters offer a unique opportunity to trace the whole kinematical and chemical history of our disk , if collected in populous and representative samples and accurately and homogeneously analysed ( see e.g. , twarog , ashman , & anthony - twarog 1997 ; carraro , ng , & portinari 1998 ) . here we apply the synthetic cmd method to ngc 6819 , ngc 2099 , ngc 2168 and ngc 2323 to derive their age , reddening , distance modulus and ( approximate ) metallicity homogeneously to the bragaglia ( 2003 ) cluster sample . the method also allows us to determine other features of these clusters , such as the existence ( or lack thereof ) of a significant fraction of unresolved binary systems , the original total mass of formed stars and the possible evaporation of some of the lower mass stars . the organisation of the paper is as follows , [ observations ] briefly summarises the data and the reduction procedures . further details are given in jski . in [ firstresults ] we present a summary of our main results which relate to this work from the published papers in the cfht open star cluster survey . [ synthetic ] sets up the numerical simulations and presents details on how the synthetic cmds were created . next , we compare the cmds and the corresponding luminosity functions from the observations with the simulations on a cluster - by - cluster basis ( [ vs ] ) . finally , we discuss the results in [ discussion ] and conclude the study in [ conclusions ] .

we present detailed comparisons between high quality observational colour - magnitude diagrams ( cmds ) of open star clusters and synthetic cmds based on montecarlo numerical simulations . the comparisons account for all of the main parameters which determine the shape of the cmd for a stellar population . for the four clusters studied , ngc 6819 , ngc 2099 ( m37 ) , ngc 2168 ( m35 ) and ngc 2323 ( m50 ) , we derive reddening , distance , age , binary fraction , star formation rate and indicative metallicity by comparing the locations and density of points in the observed cmds to the simulated cmds . open clusters and associations : general open cluster and associations : individual : ngc 2099 , ngc 2168 , ngc 2323 , ngc 6819

we present detailed comparisons between high quality observational colour - magnitude diagrams ( cmds ) of open star clusters and synthetic cmds based on montecarlo numerical simulations . the comparisons account for all of the main parameters which determine the shape of the cmd for a stellar population . for the four clusters studied , ngc 6819 , ngc 2099 ( m37 ) , ngc 2168 ( m35 ) and ngc 2323 ( m50 ) , we derive reddening , distance , age , binary fraction , star formation rate and indicative metallicity by comparing the locations and density of points in the observed cmds to the simulated cmds . we estimate the uncertainties related to stellar evolution theories by adopting various sets of stellar models for all of the synthetic cmds and discuss which stellar models provide the theoretical cmds that best reproduce the observations . [ firstpage ] colour - magnitude diagrams methods : n - body simulations open clusters and associations : general open cluster and associations : individual : ngc 2099 , ngc 2168 , ngc 2323 , ngc 6819

astro-ph0605674

c

we have presented a global study of the neon @xmath0-shell and iron @xmath1-shell absorption in the ism . combined with our previous study of oxygen absorption ( paper i ) , we have determined the neutral abundances ratios between oxygen , iron , and neon . we find o / [email protected]@xmath51.6 , in line with current ism abundances . our fe / ne abundance of [email protected] is lower than the expected ism value of 0.309 , suggesting that iron is depleted in the ism . we note that unless depletion is taken into account in x - ray absorption models , a subsolar iron abundance may be found . this subsolar iron abundance can be due only to the ism and does not _ a priori _ signify an astrophysically interesting result related to the source properties . we also detected absorption lines from , , and in a number of the sources . we attribute these lines to the ism . a curve of growth analysis found that the large - scale ionization of neon in the ism is /@xmath20.3 and /@xmath20.07 . the implied column densities in the lines are consistent with the model of @xcite for all sources except the black hole lmxb gx 339@xmath154 . the ism of the galaxy is typically modeled as a multiphase medium ( see e.g. , * ? ? ? the phases have different temperatures , densities , and ionizations . the following discussion focuses on two of the phases , the warm neutral and warm ionized mediums ( wnm and wim , respectively ) . these two phases have similar temperatures ( @xmath96k ) but different hydrogen ionization fractions . in the wnm , the ionized hydrogen fraction /h@xmath97 , while in the wim , /h@xmath98 ( see * ? ? ? * and references therein ) . our implied ionization fractions for and are greater than we found for oxygen , /@xmath20.1 and /@xmath20.05 ( paper i ) . with higher first ionization potentials , we would expect the ionization of neon to track that of helium in the ism . measurements of the @xmath995876/h@xmath100 line intensity ratio suggest a helium ionization fraction @xmath101@xmath102he@xmath103 in regions where the hydrogen is primarily ionized ( i.e. in the wim ; * ? ? ? this has been taken to imply that the helium is primarily neutral in the wim , since the alternative explanation , that helium is primarily fully ionized , appears inconsistent with the low ionization of other elements , particularly sulfur and nitrogen . our measured neon ionization ratios include the contributions from all phases of the ism . in the following , we attribute the neutral and low - ionization features to the wnm and wim only . these phases should be the dominant contributors . we would like to estimate the /ne@xmath104 ratio in the wim to compare with the helium result . to do this , we assume that the and lines are produced in the wim only , while the neutral neon absorption includes contributions from both the wnm and wim . given the higher ionization potential of neon compared to hydrogen , we believe this is valid based on the hydrogen ionization in each phase . we must make two other assumptions : first , the , , and are the dominant contributors to the total interstellar neon budget , and second , that a significant fraction ( @xmath105% ) of the neutral neon is found in the wnm , as opposed to the wim . combining these assumptions , we find @xmath106 this work directly measures ( /)@xmath104 and ( /)@xmath104 , and we are assuming @xmath107/@xmath108 . our results then yield /ne@xmath109 in the wim . this is different from the helium results , although we note that the exact values of the ionization fraction of and are dependent on the assumed thermal velocity of the ism , which may make the difference between the measured ionizations of helium and neon less significant . in addition , our measurement of the / ratio seems incompatible with standard ob star models for the ionization of the wim ( see e.g. , * ? ? ? extra heating has been studied to explain the properties of optical emission and absorption lines ( e.g. , * ? ? ? * ; * ? ? ? * ) , but these results concentrate on the elements of interest in the optical . therefore , neon ionization fractions are not given . one possible explanation for our neon ionization results is that the lines of sight probed by the x - ray studies contain a larger wim fraction relative to the wnm . x - ray studies probe different lines of sight than traditional optical and ultraviolet work . many of our sight lines are towards the center of the galaxy and the galactic bulge . optical and ultraviolet studies concentrate on the perseus arm of the galaxy which is roughly anti - galactic center ( @xmath110 ) . while x - ray allows us to probe larger distances and cover a greater extent of the galaxy , this also makes it difficult to reconcile x - ray results with other ism studies . future work will use multiwavelength studies of x - ray binaries to compare x - ray ism results with optical and ultraviolet studies . @xcite identified the , , and lines in the spectrum of gx 339@xmath154 and attributed them to an agn - like warm absorber . our results show that the line shows a clear excess column density over the expected interstellar component . the measured column density for gx 339@xmath154 is @xmath2@xmath111 @xmath19 . for galactic latitude of gx 339@xmath154 and a distance of 6 kpc , the ism model predicts a column density of @xmath112 @xmath19 . while the exact distance to gx 339@xmath154 is unknown , the model column density as a function of galactic scale height reaches a maximum value of @xmath113 @xmath19 . from these values , we estimate that only @xmath226% of the measured column density to gx 339@xmath154 is due to the hot ism . this seems reasonable given the detection of other highly ionized lines in the spectrum of the source . the properties of the and lines however , are completely consistent with the other lmxbs in our sample . the measured line widths are all @xmath220 m off from the theoretical calculations of @xcite , within the quoted errors for the calculations . similar wavelength shifts were also required in our study of the oxygen edge ( paper i ) . the line widths are also consistent with the other sources in our sample , and are more likely indicative of the resolution of the instrument rather than an astrophysical origin . finally , the implied ionized abundances of and from the gx 339@xmath154 data are consistent with the ns lmxbs . if these lines had a local component , we should see deviations from these relationships . we note that variations in the ew of these lines were claimed by @xcite but we caution that comparisons between _ chandra_/hetg and _ xmm_/rgs spectra are suspect for narrow absorption features due to the factor of two difference in the spectral resolution between the instruments . narrow features easily detectable by _ chandra _ can be substantially washed out by the rgs resolution . we therefore claim that the low - ionization neon features in gx 339@xmath154 are completely consistent with an interstellar origin . 53 natexlab#1#1 , e. , & grevesse , n. 1989 , , 53 , 197 , m. , grevesse , n. , guedel , m. , & sauval , a. j. 2005 , , submitted as brief communications , ( astro - ph/0510377 ) , m. , grevesse , n. , & sauval , a. j. 2005 , in asp conf . ser . 336 : cosmic abundances as records of stellar evolution and nucleosynthesis , 2538 , j. n. , basu , s. , & serenelli , a. m. 2005 , , 631 , 1281 , e. , & netzer , h. 2002 , , 570 , 165 , a. c. , mewe , r. , langerwerf , t. , heise , j. , & peacock , a. 1985 , space science reviews , 40 , 201 , c. r. , et al . 2005 , , 117 , 1144 , c. t. 1995 , journal of physical and chemical reference data , 24 , 71 , m. , avaldi , l. , camilloni , r. , prince , k. c. , de simone , m. , karvonen , j. , colle , r. , & simonucci , s. 1999 , , 59 , 2494 , c. p. , den herder , j. w. , kaastra , j. s. , paerels , f. b. , den boggende , a. j. , & rasmussen , a. p. 2003 , , 404 , 959 , b. t. 2003 , , 41 , 241 , j. j. , & testa , p. 2005 , , 436 , 525 , t. , & dettmar , r .- j . 2005 , , 632 , 277 , y. x. , tennant , a. f. , & zhang , s. n. 2003 , , 597 , 1017 , k. , mitsuda , k. , takei , y. , fujimoto , r. , & yamasaki , n. y. 2004 , , 605 , 793 , m. , zdziarski , a. a. , poutanen , j. , coppi , p. s. , ebisawa , k. , & johnson , w. n. 1999 , , 309 , 496 , t. w. 2000 , , 61 , 024702 gorczyca , t. w. & mclaughlin , b. m. 2005 , bull . soc . , 50 , 39 , c. , & kulkarni , s. r. 1987 , in nato asic proc . 210 : physical processes in interstellar clouds , 1333 , b. l. , gullikson , e. m. , & davis , j. c. 1993 , atomic data and nuclear data tables , 54 , 181 , j. c. , & savage , b. d. 1999 , , 517 , 746 , j. c. , sembach , k. r. , & savage , b. d. 2003 , , 586 , 249 , p. g. , & nelemans , g. 2004 , , 354 , 355 , a. m. , & chakrabarty , d. 2003 , , 599 , 498 , a. m. , psaltis , d. , & chakrabarty , d. 2001 , , 560 , l59 , a. m. , schulz , n. s. , & chakrabarty , d. 2004 , , 612 , 308 ( paper i ) , s. m. , seward , f. d. , & chlebowski , t. 1984 , , 283 , 286 , j. b. , & kim , s. 2000 , , 62 , 12216 , e. , den hartog , p. r. , int zand , j. j. m. , verbunt , f. w. m. , harris , w. e. , & cocchi , m. 2003 , , 399 , 663 , j. c. , ogle , p. m. , canizares , c. r. , marshall , h. l. , schulz , n. s. , morales , r. , fabian , a. c. , & iwasawa , k. 2001 , , 554 , l13 , j. c. , reynolds , c. s. , remillard , r. , schulz , n. s. , blackman , e. g. , & fabian , a. c. 2002 , , 567 , 1102 , k. 2003 , , 591 , 1220 , p. g. 1970 , , 149 , 221 , j. s. , rumpl , w. , & nordsieck , k. h. 1977 , , 217 , 425 , c. f. , & ostriker , j. p. 1977 , , 218 , 148 , j. m. , et al . 2004 , , 601 , 450 , j. m. , raymond , j. , fabian , a. c. , wijnands , r. , van der klis , m. , & lewin , w. h. g. 2004 , the astronomer s telegram , 221 , 1 miller , j. m. , wojdowski , p. , schulz , n. s. , marshall , h. l. , fabian , a. c. , remillard , r. a. , wijnands , r. , & lewin , w. h. g. 2005 , 620 , 398 , f. , et al . 2003 , , 421 , 719 , f. , et al . 2001 , , 546 , 338 , r. j. , & tufte , s. l. 1995 , , 439 , l17 , r. j. , tufte , s. l. , kung , d. t. , mccullough , p. r. , & heiles , c. 1995 , , 448 , 715 , b. d. , & sembach , k. r. 1996 , , 34 , 279 , m. l. , & canizares , c. r. 1986 , , 301 , 759 , j. t. , nasraoui , k. , roames , j. k. , lippner , l. a. , & garst , j. w. 2005 , , 634 , l197 , n. s. , cui , w. , canizares , c. r. , marshall , h. l. , lee , j. c. , miller , j. m. , & lewin , w. h. g. 2002 , , 565 , 1141 , k. r. , howk , j. c. , ryans , r. s. i. , & keenan , f. p. 2000 , , 528 , 310 , k. r. , et al . 2003 , , 146 , 165 , j. d. , mckee , c. f. , & hollenbach , d. j. 2000 , , 541 , 218 , l. j. , & fitzpatrick , e. l. 1993 , , 409 , 299 , y. , fujimoto , r. , mitsuda , k. , & onaka , t. 2002 , , 581 , 307 , y. , mitsuda , k. , murakami , h. , & matsushita , k. 2005 , , 620 , 274 , p. a. , & liebscher , b. 2002 , physics and chemistry of minerals , 29 , 188 , d. a. , yakovlev , d. g. , band , i. m. , & trzhaskovskaya , m. b. 1993 , atomic data and nuclear data tables , 55 , 233 , j. c. , & draine , b. t. 2001 , , 548 , 296 , m. c. , odell , s. l. , paerels , f. , elsner , r. f. , becker , w. , tennant , a. f. , & swartz , d. a. 2004 , , 601 , 1050 , j. , allen , a. , & mccray , r. 2000 , , 542 , 914 , j. w. 1995 , , 447 , l129 , y. , & wang , q. d. 2005 , , 624 , 751

we present high - resolution spectroscopy of the neon-shell and iron-shell interstellar absorption edges in nine x - ray binaries using the high energy transmission grating spectrometer ( hetgs ) onboard the _ chandra x - ray observatory_. we found that the iron absorption is well fit by an experimental determination of the cross - section for metallic iron , although with a slight wavelength shift of m . combined with our earlier oxygen edge study , we find that a best fit o / ne ratio of 5.4.6 , consistent with standard interstellar abundances . our best fit fe / ne ratio of 0.20.03 is significantly lower than the interstellar value . we make the first measurement of the neon ionization fraction in the ism . we find /.3 and /.07 . these values are larger than is expected given the measured ionization of interstellar helium . for , our results confirm the detection of the hot ionized interstellar medium of the galaxy .

we present high - resolution spectroscopy of the neon-shell and iron-shell interstellar absorption edges in nine x - ray binaries using the high energy transmission grating spectrometer ( hetgs ) onboard the _ chandra x - ray observatory_. we found that the iron absorption is well fit by an experimental determination of the cross - section for metallic iron , although with a slight wavelength shift of m . the neon edge region is best fit by a model that includes the neutral neon edge and three gaussian absorption lines . we identify these lines as due to the- transitions from , , and . as we found in our oxygen edge study , the theoretical predictions for neutral and low - ionization lines all require shifts of m to match our data . combined with our earlier oxygen edge study , we find that a best fit o / ne ratio of 5.4.6 , consistent with standard interstellar abundances . our best fit fe / ne ratio of 0.20.03 is significantly lower than the interstellar value . we attribute this difference to iron depletion into dust grains in the interstellar medium . we make the first measurement of the neon ionization fraction in the ism . we find /.3 and /.07 . these values are larger than is expected given the measured ionization of interstellar helium . for , our results confirm the detection of the hot ionized interstellar medium of the galaxy .

astro-ph0408136

i

studying radio recombination lines ( rrls ) is one of the most direct ways of probing ionized gas such as hii regions . ionized gas properties such as kinematics , electron temperatures , and the geometrical filling factor can be directly constrained by the recombination line flux density , line width , free - free continuum flux density , and size of the line - emitting regions . at centimeter ( cm ) wavelengths , rrls are primarily stimulated emission amplifying extended non - thermal synchrotron emission . therefore , distinguishing emission arising from diffuse , low density gas from that from clumpy , high density gas is difficult . also , pressure broadening of the line width can complicate the interpretation of the cm rrl observations . for instance , cm rrl emission from luminous starburst systems such as arp 220 may be dominated by internally stimulated emission from diffuse ionized gas @xcite while spontaneous emission process is important at higher frequencies ( e.g. * ? ? ? * ; * ? ? ? * ) . interpretation of recombination lines at millimeter ( mm ) wavelengths is more straightforward since stimulated emission and pressure broadening become negligible in most cases . recent studies of mm rrls in galactic h ii regions @xcite and starburst galaxies @xcite found higher line fluxes than expected from the lower frequency measurements . a steep rise in line flux density with frequency , characteristic of optically thin spontaneous emission , is seen in nearby starburst galaxies m82 and ngc 253 @xcite . the central 1 parsec region surrounding the putative central source in our galactic center , sgr a@xmath2 , is a frequent target of multi - wavelength investigations primarily because it is the nearest and the best laboratory for studying the active galactic nucleus ( agn ) phenomenon and its fueling process . currently this region appears to be relatively gas free . however , immediately surrounding sgr a@xmath2 is an array of ionized gas streamers ( sgr a west ; see review by * ? ? ? these streamers have been previously studied in the 12.8 @xmath11 m [ ne ii ] @xcite , p@xmath0 @xcite , and in cm rrl @xcite , and they consist of several distinct kinematic features . the total mass of the ionized streamers is estimated to be less than 100 m@xmath12 in total . recent ir and radio observations found evidence for _ neutral _ gas within this central `` cavity '' @xcite , suggesting a more substantial presence of gas in the central parsec region . surrounding and closely interacting with the ionized streamers is the dense and clumpy molecular ring commonly referred to as the circumnuclear disk ( cnd ) . the cnd is asymmetric about sgr a@xmath2 , indicating its possible origin related to a gravitational capture of a passing cloud or energetic disruption of a stable ring @xcite . this ring is believed to represent a circumnuclear accretion disk feeding the inner parsec although some have argued that the cnd is not a complete ring ( see * ? ? ? * ; * ? ? ? the ionized streamers in sgr a west are explained as cloudlets from the clumpy ring that after losing momentum have fallen toward the center and thereby have stretched and have been ionized by photo - dissociation within the inner parsec ( see * ? ? ? sensitive imaging studies in cm rrl @xcite suggest high temperature ( @xmath13 k ) , with a possible radial temperature gradient increasing toward sgr a@xmath2 . the large proper motions of the stars very close to sgr a@xmath2 suggest central dark mass of 2.5 - 4.1 @xmath14 m@xmath12 @xcite . motivated by the detection of extragalactic mm rrls and recent new observations of the galactic center region , we have imaged the h@xmath15 line at high angular resolution toward sgr a@xmath2 in order to study the nature of the ionized streamers and their relation to the dense neutral gas in and around the cnd . at high frequencies , most of the rrl and continuum emission comes from the densest ionized gas ( see * ? ? ? * ; * ? ? ? one of the primary goals of this study is to examine the existence of ionized gas denser than that traced by cm - wavelength rrls in this region . the nature of the radiation mechanism is investigated by analyzing the new h31@xmath0 , h35@xmath0 , h41@xmath0 , and h44@xmath0 line observations obtained at the nrao 12-m telescope at kitt peak , arizona . we further examine whether any dense _ neutral _ gas is directly associated with the ionized streamers using our sensitive , high resolution hco@xmath10 ( 10 ) images . our hco@xmath10 ( 10 ) data have superior sensitivity and angular resolution over the previously published observations of similar molecular species @xcite . in addition , a detailed analysis of the spatial distribution and kinematics of the dense molecular gas and ionized gas in the cnd is offered using a simple kinematical model .

new observations of h31 , h35 , h41 and h44 lines were obtained using the nrao 12-m telescope , and their relative line strengths are interpreted in terms of various possible emission mechanisms . these nrao 12-m measurements are the most extensive recombination line survey of this region to date . observations of hco transition at 89 ghz are obtained simultaneously with a 40% improved angular resolution and 4 - 15 times improved sensitivity over the previously published results , and the distribution and kinematics of the dense molecular gas in the circumnuclear disk ( cnd ) are mapped and compared with those of the ionized gas .

we present high resolution h41 hydrogen recombination line observations of the ( 3 pc ) region surrounding sagittarius a ( sgr a ) at 92 ghz using the millimeter array at the owens valley radio observatory ( ovro ) with an angular resolution of and velocity resolution of 13 . new observations of h31 , h35 , h41 and h44 lines were obtained using the nrao 12-m telescope , and their relative line strengths are interpreted in terms of various possible emission mechanisms . these nrao 12-m measurements are the most extensive recombination line survey of this region to date . these ovro data also represent the highest angular resolution and the highest sensitivity observations of sgr a west in hydrogen recombination line and continuum emission at the millimeter ( mm ) wavelengths . observations of hco transition at 89 ghz are obtained simultaneously with a 40% improved angular resolution and 4 - 15 times improved sensitivity over the previously published results , and the distribution and kinematics of the dense molecular gas in the circumnuclear disk ( cnd ) are mapped and compared with those of the ionized gas . the line brightness ratios of the hydrogen recombination lines are consistent with purely spontaneous emission from k gas with near lte condition . a virial analysis suggests that the most prominent molecular gas clumps in the cnd have mean densities of order , sufficient to withstand the tidal shear in the galactic center region . therefore , these clumps may survive over several dynamical times , and the cnd may be a dynamically stable structure . we estimate a total gas mass of about for the cnd . our combined analysis of the new high resolution h41 and hco images and our kinematic model demonstrates a widely spread physical and dynamical link between the molecular gas in the cnd and the ionized gas , including along the eastern rim of the cnd where a gap was previously suggested .

astro-ph0408136

i

the ovro millimeter array observations of the h41@xmath0 and 92 ghz continuum emission from the ionized streamers around sgr a@xmath2 ( sgr a west ) and the hco@xmath10 ( 10 ) emission from the circumnuclear disk ( cnd ) are presented along with a new survey of the hydrogen recombination lines at millimeter wavelengths ( h31@xmath0 , h41@xmath0 , and h44@xmath0 ) obtained using the nrao 12-m telescope . these observations are compared with the vla h92@xmath0 and the 8.3 ghz continuum data by roberts & goss ( 1993 ) . we summarize our results as following : \1 . the 92 ghz continuum image is essentially identical to the vla continuum image at 8.3 ghz in morphology . the total continuum flux detected inside the 85 diameter is about 12 jy , but some extended flux associated with structure larger than about 30 is missed . the brightest feature , sgr a@xmath2 , is unresolved at 3 resolution of our observations and has a peak flux density of @xmath28 jy beam@xmath21 . assuming the 7000 k electron gas fills our 0.005 pc ( 1000 au ) beam , we infer average continuum optical depth of @xmath105 and electron density @xmath6 @xmath7 . the kinematics and the morphology of h41@xmath0 emission are very similar to those observed in h92@xmath0 and 12.8 @xmath11 m [ ne ii ] lines . the brightest emission occurs along the north arm with a peak line brightness temperature of less than 10 k. this suggests a h41@xmath0 optical depth of @xmath150 averaged over the 13 channel width . the emission along the central bar displays a line - of - sight velocity ranging over 300 , and this gas may be located in the deepest part of the gravitational potential within the cnd region . the molecular cnd is imaged in hco@xmath10 with a 40% improvement in resolution and 4 - 15 times better sensitivity over the previous bima observations made in hcn and hco@xmath10 . the cnd consists of several discrete concentrations , and their peak brightness ranging between 10 and 30 k averaged over the 0.1 pc synthesized beam suggests that they originate from the warm ( 60 - 100 k ) gas responsible for nh@xmath67 and dust continuum emission in the cnd . a virial analysis suggests that these clouds have mean density of @xmath151 @xmath7 , sufficient to withstand the tidal shear in the region , and the cnd may be a long lived structure . we estimate a total gas mass of about @xmath9 for the cnd . our non - detection of hco@xmath10 absorption along the sgr a west places an upper limit to the gas column density of @xmath152 @xmath40 , or the neutral gas within the cnd is depleted of molecules . \4 . a line - to - continuum ratio analysis under the lte assumption yields a fairly uniform electron temperature of about 7000 k along the ionized streamers in the sgr a west complex , in an excellent agreement with the electron temperature calculated at 8.3 ghz using the h92@xmath0 observations @xcite . evidence for increased @xmath92 ( or an unusually low l / c ratio ) along the central bar just southwest of sgr a@xmath2 is found in our data as well even though our data include all line emission within @xmath153 . the low l / c ratio we find at 92 ghz challenges the optically thick continuum sources irs 2 and irs 13 as additional sources of continuum emission as suggested by @xcite . therefore , the elevated @xmath92 ( a lower l / c ratio ) seen near the location of irs 2 and irs 13 is still not fully understood . \5 . a comparison of the velocity integrated line flux densities for h31@xmath0 , h41@xmath0 , h44@xmath0 , and h92@xmath0 emission from the sgr a west complex shows line ratios characteristic of spontaneous emission from optically thin gas near lte . a detailed analysis reveals that observed recombination line brightness is reduced by 10 - 30% ( i.e. , @xmath154 ) from the lte value . \6 . a combined analysis of the new high resolution h41@xmath0 and hco@xmath10 images and a kinematic model clearly demonstrates a widely spread , close physical and dynamical link between the molecular gas in the cnd and the ionized gas , including along the eastern rim where a gap in the cnd was previously reported . the same analysis also clearly identifies several features that do not follow the disk rotation . we conclude that the `` + 50 streamer '' is not directly associated with the cnd . the morphology of `` + 70 streamer '' is suggestive of its association with the cnd , but its kinematics and absence of any ionized gas challenge the idea of their close association . we are grateful to d. roberts for providing us with the h92@xmath0 and 8.4 ghz continuum data from the vla for comparison . we are indebted to c. lang for her expert advice and help with the gipsy data reduction package and for many helpful suggestions as the referee of this article . in addition , we would like to acknowledge the direction gained from insightful discussions with w. m. goss and late k. r. anantharamaiah . we would like to thank the ovro and the nrao 12-m telescope staff for the support and help without which this project would not have been possible . the national radio astronomy observatory is a facility of the national science foundation operated under cooperative agreement by associated universities , inc . lc rest frequency of h41@xmath0 line & 92.034 ghz + rest frequency of hco@xmath4 line & 89.188 ghz + primary beam ( hpbw ) & 85@xmath155 + phase center & @xmath156 + & @xmath157 + center lsr velocity & 0.0 + synthesized beam ( hpbw ) & @xmath19 ( pa@xmath141 ) + spectrometer settings & @xmath158 mhz ( 13 ) + rms noise & 0.13 jy beam@xmath21 ( 0.21 k ) + llllcccc northern arm & 0.9 & @xmath159 & @xmath160 & @xmath161 + sgr a@xmath2 & 0.1 & @xmath162 & @xmath163 & @xmath164 + bar & 1.1 & @xmath165 & @xmath166 & @xmath167 + western arc & 1.5 & @xmath168 & @xmath169 & @xmath170 + eastern arm & 0.4 & @xmath171 & @xmath172 & @xmath173 + llllcccc northern arm & 0.9 & @xmath174 & @xmath175 & @xmath176 + bar & 1.1 & @xmath177 & @xmath178 & @xmath179 + western arc & 1.5 & @xmath180 & @xmath181 & @xmath182 + eastern arm & 0.4 & @xmath183 & @xmath184 & @xmath185 + ccccccc 1 & @xmath186 & @xmath187 & 78 @xmath144 5 & 0.50 @xmath144 0.04 & 6394@xmath144608 + 2 & @xmath188 & @xmath189 & 213 @xmath144 18 & 0.18 @xmath144 0.02 & 6473@xmath144891 + 3 & @xmath190 & @xmath191 & 43 @xmath144 5 & 0.80 @xmath144 0.13 & 7470@xmath1441372 + 4 & @xmath192 & @xmath193 & 347 @xmath144 48 & 0.03 @xmath144 0.01 & 18806@xmath1444770 + 5 & @xmath194 & @xmath195 & 70 @xmath144 5 & 0.66 @xmath144 0.07 & 5528@xmath144623 + 6 & @xmath196 & @xmath197 & 101 @xmath144 6 & 0.26 @xmath144 0.02 & 9057@xmath144825 + cccccccc a & 0.4 & @xmath198 & @xmath199 & 20.7 & 2.1 @xmath200 & @xmath201 + b & 0.3 & @xmath202 & @xmath203 & 17.3 & 1.1 @xmath200 & @xmath204 + c & 0.3 & @xmath205 & @xmath206 & 12.0 & 0.5 @xmath200 & @xmath207 + d & 0.4 & @xmath208 & @xmath209 & 29.9 & 4.5 @xmath200 & @xmath210 + e & 0.2 & @xmath211 & @xmath212 & 11.6 & 0.3 @xmath200 & @xmath204 + f & 0.3 & @xmath213 & @xmath214 & 19.4 & 1.4 @xmath200 & @xmath215 + g & 0.6 & @xmath216 & @xmath217 & 16.1 & 1.9 @xmath200 & @xmath218 + h & 0.4 & @xmath219 & @xmath220 & 19.0 & 1.8 @xmath200 & @xmath221 + i & 0.2 & @xmath222 & @xmath223 & 13.0 & 0.4 @xmath200 & @xmath224 +

these ovro data also represent the highest angular resolution and the highest sensitivity observations of sgr a west in hydrogen recombination line and continuum emission at the millimeter ( mm ) wavelengths . the line brightness ratios of the hydrogen recombination lines are consistent with purely spontaneous emission from k gas with near lte condition . a virial analysis suggests that the most prominent molecular gas clumps in the cnd have mean densities of order , sufficient to withstand the tidal shear in the galactic center region . therefore , these clumps may survive over several dynamical times , and the cnd may be a dynamically stable structure . we estimate a total gas mass of about for the cnd . our combined analysis of the new high resolution h41 and hco images and our kinematic model demonstrates a widely spread physical and dynamical link between the molecular gas in the cnd and the ionized gas , including along the eastern rim of the cnd where a gap was previously suggested .

we present high resolution h41 hydrogen recombination line observations of the ( 3 pc ) region surrounding sagittarius a ( sgr a ) at 92 ghz using the millimeter array at the owens valley radio observatory ( ovro ) with an angular resolution of and velocity resolution of 13 . new observations of h31 , h35 , h41 and h44 lines were obtained using the nrao 12-m telescope , and their relative line strengths are interpreted in terms of various possible emission mechanisms . these nrao 12-m measurements are the most extensive recombination line survey of this region to date . these ovro data also represent the highest angular resolution and the highest sensitivity observations of sgr a west in hydrogen recombination line and continuum emission at the millimeter ( mm ) wavelengths . observations of hco transition at 89 ghz are obtained simultaneously with a 40% improved angular resolution and 4 - 15 times improved sensitivity over the previously published results , and the distribution and kinematics of the dense molecular gas in the circumnuclear disk ( cnd ) are mapped and compared with those of the ionized gas . the line brightness ratios of the hydrogen recombination lines are consistent with purely spontaneous emission from k gas with near lte condition . a virial analysis suggests that the most prominent molecular gas clumps in the cnd have mean densities of order , sufficient to withstand the tidal shear in the galactic center region . therefore , these clumps may survive over several dynamical times , and the cnd may be a dynamically stable structure . we estimate a total gas mass of about for the cnd . our combined analysis of the new high resolution h41 and hco images and our kinematic model demonstrates a widely spread physical and dynamical link between the molecular gas in the cnd and the ionized gas , including along the eastern rim of the cnd where a gap was previously suggested .

0801.1842

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the redshifts of our sample have a remarkably tight distribution . all of the sample lie in the range @xmath28 , with all but three lying within @xmath29 . if we exclude these three outliers , then the mean redshift for our sample is @xmath2 ( assuming fwhm@xmath44 ) . this is significantly tighter than the redshift distribution of sub - mm selected galaxies , which have @xmath45 @xcite , and the redshift distribution for lyman break galaxies , which have @xmath46 @xcite , though a larger sample would be needed to confrm this . our redshift distribution is much tighter than that of sources found by selecting on 24@xmath0m/0.7@xmath0 m flux ratio @xcite , which span @xmath47 . combined with the constraint that the ir luminosities of our sample must ( for any reasonable sed shape ) be in excess of 10@xmath48l@xmath5 , we conclude that our selection method is an excellent way of finding distant ulirgs in specific , narrow redshift intervals . this narrow redshift range likely arises due to a combination of two factors ; the demand of an excess flux at observed frame 4.5@xmath0 m favors sources with a rest - frame 1.6@xmath0 m opacity feature at @xmath49 , and the demand that sources be bright at observed - frame 24@xmath0 m biases towards sources whose redshifts place the 7.7@xmath0 m and 8.6@xmath0 m pah features within the mips 24@xmath0 m band . this method offers many advantages over other methods for finding high redshift ulirgs . for example , it avoids all of the observational difficulties in assigning optical counterparts to sub - mm selected ulirgs ( see for example @xcite ) . remarkably , we have arrived at this redshift distribution without demanding that the ` bump ' be detected with any statistical robustness , and it is notable that none of the seven sources that ` lost ' their bump in the 4.5@xmath0 m channel due to reprocessing ( table [ measurements ] ) are unusual in redshift or spectral shape . given the difficulties in obtaining accurate redshifts for distant ulirgs @xcite , we examine the accuracy of photometric redshifts for our sample obtained by @xcite and listed in table [ measurements ] . given the high redshifts and limited optical photometry , the photometric redshifts are surprisingly good . ` reliable ' solutions ( those with @xmath50 and detected in at least three of the @xmath51 bands ) are obtained for 14/32 objects ; these are plotted in the right panel of figure [ zphotzspec ] . of those 14 , four are classified as ` catastrophic ' failures , i.e. those where the photometric redshift deviates from the spectroscopic redshift by more than @xmath52 in log(1+z ) ( although two of these four are sources 11 and 15 , which have uncertain spectroscopic redshifts ) , while ten are classified as successes . we conclude that the @xcite photometric redshift method remains effective even for faint , high redshift sources . finally , we note that , of the seven objects in table [ measurements ] with ambiguous bump classifications , six have photometric and spectroscopic redshifts that agree very well . it seems therefore that , for the sources with an ambiguous bump classification , most are indeed ` bump 2 ' sources . the irs spectra provide the best diagnostics of the power source behind the ir emission . the presence of prominent pah features in 29/32 objects is strong evidence that @xmath53 of our sample harbor powerful starbursts . the star formation rates computed using equation [ pahstarconc ] and listed in table [ pahsils ] are all extremely high . if we extrapolate these star formation rates to ir luminosities via the relation given by @xcitem luminosity rather than 1 - 1000@xmath0 m luminosity , but the difference in wavelength range is unlikely to be significant ] , then these luminosities lie in the same range as those determined in [ takeaguess ] . we infer that dust heated by star formation can account for all of the ir emission from the sources that show strong pahs , and therefore that most of our sample are consistent with being pure starbursts . interestingly , the strong pahs and high degree of homogeneity of our sample make them similar to sub - mm selected ulirgs @xcite , suggesting that we may be drawing from the same parent population . we can not , however , rule out the presence of an agn in any of our sample . it is unlikely that an agn contributes significantly in the rest - frame near - ir , as we see no power law continua in the irac bands ( see e.g. @xcite ) , but it is possible that some of our sample contain mid - ir luminous agn , even in those objects with prominent pahs . an example of such an object at low redshift is ngc 6240 , which shows strong pahs accompanied by an agn continuum and the [ nev]@xmath2514.322 fine - structure [email protected] has @xmath54 ev , and models indicate that it is unlikely to be strong in galaxies without an agn @xcite . observationally , [ nev]@xmath2514.32 is occasionally seen in planetary nebulae and young supernova remnants @xcite , but is not seen in the integrated spectra of starburst galaxies . it is however strong in the spectra of agn @xcite ] @xcite . furthermore , previous authors have noted correlations between shallow ( @xmath55 ) or deep ( @xmath56 ) silicate features , and the presence of agn ; @xcite show that ulirgs with shallow silicate features usually also show the [ nev]@xmath2514.322 line , @xcite find that qsos and seyfert 1 galaxies often show the silicate feature in emission , and @xcite find that many high redshift ulirgs with deep silicate absorption features also show powerful radio jets . the shallow silicate features of our sample are therefore consistent with ( though not supportive of ) the presence of an agn . finally , we examine the irac colors as a diagnostic of the ir emission . in figure [ colcol ] we plot 5.8@xmath0m/3.6@xmath0 m color against 8.0@xmath0m/4.5@xmath0 m color , together with the selection ` wedge ' for agn from @xcite , defined empirically using the spitzer colors of sdss qsos . this diagnostic is not , on its own , particularly useful , as our 4.5@xmath0 m ` bump ' selection already excludes much of the agn selection region , but it serves as a useful check . nearly all of our sample lie outside the agn selection region , and are consistent with the positions of the bulk of the galaxies in the main spitzer first look survey ( fls ) dataset . our sample lies some distance from the sdss qsos and sy1 galaxies in figure 1 of @xcite . based solely on the irac colors , the rest - frame near - ir emission from our sample is consistent with arising from starlight . the prevalence of starbursts in our sample means we can investigate the nature of star formation in high redshift ulirgs . we start by considering diagnostics based solely on the pah features . in figure [ pahlumratio ] we plot pah luminosities against pah flux ratios . the 6.2@xmath0 m and 7.7@xmath0 m pah features are extraordinarily luminous , lending further weight to the conclusion that the starbursts in our sample are more intense than seen in any local ( @xmath9 ) ulirg . the dispersion in pah luminosity is perhaps slightly greater for our sample , but not significantly so given the sizes of the error bars . we see a more interesting picture if we consider pah color - color plots ( figure [ pahfluxratio ] ) . considering first only the low redshift sources ; local ir - luminous galaxies show a distinct ` environmental segregation ' with ir luminosity , corresponding to elevated 6.2@xmath0m/11.2@xmath0 m and 7.7@xmath0m/11.2@xmath0 m pah ratios in ulirgs compared to lower luminosity starbursts and agn . such a segregation is also seen in hii regions and photo - dissociation regions , and the reasons for it are not clear @xcite . the two most likely reasons are pah ionization and pah molecular structure . a higher fraction of ionized pahs gives rise to stronger pah features at shorter wavelengths , as does a higher fraction of open , uneven pah molecules compared to smooth , compact pah molecules ( see figure 9 of @xcite for diagrams of these pah features ) . the drivers behind pah molecular structure are unknown , but pah ionization fractions can be affected in two ways ; ( 1 ) a harder interstellar radiation field ( isrf ) would ionize more pahsm range ] , and ( 2 ) decreasing the electron density would decrease the recombination rate , leading to a higher fraction of ionized pahs . it is therefore likely that local ulirgs have either a harder isrf , a lower electron density , or a higher fraction of open , uneven pah molecules than do lower luminosity systems . turning now to the bump sources ; our sample appears to lie preferentially toward one ` edge ' of the local ulirg distribution , corresponding to even further elevated 6.2@xmath0 m pah emission compared to the 7.7@xmath0 m and 11.2@xmath0 m features , though the error bars are large even for the average bump point . these two diagrams alone suggest that the star formation in our sample _ may _ differ in some way from that seen in local ulirgs , although it is difficult to say what the physical origin of those differences could be . one possibility is a lower extinction level in our sample compared to the mean for low redshift ulirgs . we move on to consider diagnostics based on both the pah emission features and the 9.7@xmath0 m silicate absorption feature . in figure [ fork ] we plot our sample on the ` fork ' diagram of @xcite . our sources occupy a small region on the lower right of this plot , corresponding almost entirely to class 1c , with a small number in classes 2c and 2b , though the large error bars on the pah ews mean our sources are in many cases also consistent with class 1a/1b . these classes label our sources as pah dominated , with relatively weak apparent silicate absorption . to check whether this is just a chance similarity between these specific spectral features , we plot in figure [ comp_fork ] the averaged spectrum from figure [ composite_all ] against the averaged spectra for the classes in the fork diagram . clearly , our averaged spectrum closely resembles the average spectrum for the class 1c sources . figure [ fork ] raises interesting questions on the nature of starburst activity in our sample . as described in [ select ] , our selection method biases towards ulirgs harboring ongoing star formation , and selects against those ulirgs containing a rest - frame near - ir luminous agn . our sample should therefore resemble the majority of local ulirgs , as most low redshift ulirg are powered mainly by star formation ( e.g. @xcite ) . furthermore , our demand for an excess flux in one of the irac channels should not remove many ` local type ' ulirgs from the sample , as many local ulirgs have a rest - frame sed that either has a near - ir excess , or is not obviously a power law . moreover , previous studies of high redshift , l@xmath57l@xmath5 ulirgs selected using _ spitzer _ data have shown that they seem to resemble local ulirgs ; for example , @xcite find that @xmath10 ulirgs selected on the basis of red 24@xmath0m/8@xmath0 m and 24@xmath0m/0.7@xmath0 m color often show pahs accompanied by an agn continuum and in some ( @xmath58 ) cases strong silicate absorption , and their figure 13 appears to place the bulk of their sample in the upper branch of figure [ fork ] . we might therefore expect that our sources should be distributed mainly along the upper branch in figure [ fork ] , along with the majority of local ulirgs , and previous small samples of spitzer selected high redshift ulirgs . this however is not the case ; our sources are located in a specific region , classifying them as starbursts with ( relatively ) weak apparent silicate absorption , and almost completely avoid the upper branch in figure [ fork ] , where most local ulirgs reside . there is no _ a priori _ reason why our relatively crude selection method should select against ulirgs with strong silicate absorption , and the almost complete absence of such absorption in our sample is peculiar , for two reasons . first , many local ulirgs have a near - ir excess coupled with strong silicate absorption @xcite . second , the 24@xmath0 m flux cut ( in combination with the demand for a rest - frame 1.6@xmath0 m ` bump ' ) selects in favor of sources with strong pahs , but among local ulirgs , systems with strong pahs but weak silicate absorption are rare - e.g. @xcite examine ulirg local spectra medianed by optical spectra type , and find strong pahs and prominent silicate absorption in the hii and liner composites , and weak pahs and weak silicate absorption in the seyfert composite . if our sample do not resemble local ulirgs , then what do they look like ? we compare in figure [ comp_brandl ] our average spectrum with three different starburst templates ; arp 220 @xcite , the nucleus of m82 @xcite , and the average spectrum of the local starburst galaxies from @xcite ( which have ir luminosities between 10@xmath59l@xmath5 and 10@xmath60l@xmath5 ) . clearly , the brandl et al spectrum is the closest match to our spectrum , even though the parent samples differ in ir luminosity by over two orders of magnitude . both show strong pahs with an asymmetric 12.7@xmath0 m pah profile , and negligible silicate absorption . interestingly , another class of high redshift galaxy that tends to show strong pahs but weak silicate absorption are the sub - mm galaxies @xcite . the m82 nuclear spectrum is also a good match , except for slightly stronger silicate absorption . the arp 220 spectrum on the other hand is a poor match , with much stronger silicate absorption . the similarity of our composite spectrum to that of local starburst galaxies allows us to estimate the ir luminosities for our sample using the relation between ir luminosity and 6.2@xmath0 m pah luminosity in @xcite : @xmath61 where @xmath62 is the flux of the pah 6.2@xmath0 m feature in units of @xmath63 w @xmath64 , @xmath65 is the luminosity distance in kpc , and @xmath66 is in units of solar luminosities . the ir luminosities for our sample computed using equation [ pahlirs ] are presented in table [ pahsils ] , and are in good agreement with the ir luminosities estimated in [ takeaguess ] . we explore the robustness of the conclusion that our sample have systematically weaker apparent silicate absorption than is seen in local ulirgs using a different approach ; fitting their broad band optical through ir seds ( i.e. the @xmath51 , irac and mips data ) with the code of @xcite , with the redshifts fixed at the spectroscopic values , and comparing the results from these fits with the irs spectra . we consider only those objects ( 4 , 12 , 13 , 15 , 17 , 21 , 29 , 31 ) with detections in at least six optical through mips bands , and specifically do _ not _ fit to the irs spectra , as we wish to test the conclusions independently . the limited available photometry ( less than nine points in all cases ) renders this approach crude compared to the analysis of the irs spectra , but it serves as a useful check . the results from this fitting are shown in figure [ mrrdiag ] . in four cases ( 4 , 13 , 21 29 ) , an m82 template gives an excellent fit to the photometry , and is well matched to the irs spectrum . in two cases ( 12 and 17 ) an m82 template gives a good fit to the photometry , but predicts a higher flux at rest - frame 6@xmath0 m than is seen in the irs spectrum , which may indicate a steeper mid - ir continuum . in the final two cases ( 15 and 31 ) there is marginal evidence for strong silicate absorption , consistent with an arp 220 template , though the low s / n of the irs spectra means we can not rule out an m82 template either . overall , the results from the template fitting agree with the results from the individual irs spectra , and from the comparison between our average spectrum and arp 220 , m82 , and the @xcite composite in figure [ comp_brandl ] . all of the evidence points towards an unexpected result ; despite the fact that our sample are ultraluminous in the ir , their mid - ir spectra have systematically lower silicate absorption than low - redshift ulirgs , and instead resemble the mid - ir spectra of local starbursts that are over two orders of magnitude less luminous in the ir . what makes this even more puzzling is that high redshift ulirgs appear to be physically similar to local ulirgs in many ways ; they show evidence for being mergers ( @xcite , though see also @xcite ) between massive , gas rich systems @xcite . we can think of six possible reasons to explain this difference : 1 - _ ir luminosity dependent silicate strength : _ our sample is significantly more ir - luminous than most local ulirgs , so we would see weak apparent silicate absorption if compact , dusty starbursts and agn exhibit weaker silicate absorption as they increase in ir luminosity , but remain otherwise identical . while we can not rule this possibility out , we can think of no plausible physical reason why this should be the case . 2 - _ a specific evolutionary stage : _ we may be selecting high redshift ulirgs at a specific evolutionary stage , when a compact but relatively old starburst ( @xmath67myr if we assume an exponentially decaying burst ) becomes less obscured as supernova winds clear dust from the star - forming regions . while this is in principle plausible , our selection method is relatively crude compared to others cited as selecting distant ulirgs at specific evolutionary stages , which rely on the presence of specific fine - structure absorption lines @xcite . it seems unlikely that our method should find all 32 of our sample at this specific stage . 3 - _ silicate poor dust : _ weak apparent silicate absorption could arise from dust that is unusually poor in silicates . if the dust is made mainly in asymptotic giant branch ( agb ) stars @xcite , then silicate poor dust could be made in two ways ; a low metallicity ( z@xmath68 ) would suppress the formation of silicate dust , and a steep or ` top - heavy ' stellar imf may shift more agb stars into the carbon dust producing mass range , thereby reducing the production of silicate dust @xcite . the metallicities of distant ulirgs are not well constrained @xcite , but it seems unlikely that the metallicities of our sample could be lowered to the extent required , as low metallicities also suppress pah features @xcite . a top heavy imf is more plausible , and is consistent with the demands from structure formation models ( e.g. @xcite ) . interestingly , if the imf were top heavy , it would result in a harsher radiation field , which ( as described in [ pahfluxsect ] ) may result in enhanced 6.2@xmath0 m pah emission compared to the longer wavelength pah features , a result hinted at in figures [ pahfluxratio ] and [ comp_brandl ] . there is however no direct evidence for a top - heavy imf in distant ulirgs . moreover , some authors have suggested there is no evidence for evolution in dust properties with redshift , at least up to @xmath69 ( e.g. @xcite ) . 4 - _ an intrinsically weak underlying continuum : _ if the underlying near / mid - ir continua in our sample are weak , then we would see three effects ; the rest - frame 1.6@xmath0 m feature would be prominent , the pah ews would be higher , and we would see weak silicate absorption as there would be no background continuum upon which to make such absorption apparent . a weak continuum would arise if our sample harbored lower luminosity agn than those seen in local ulirgs . in this scenario the absence of silicate absorption , and the differences between our sample and that of @xcite , arises due to selection bias , as our selection method favors systems harboring active star formation . it is also possible that the differences between our sample and that of @xcite arise because our sample is fainter at observed - frame 24@xmath0 m ( most of our sample fall below the 24@xmath0 m flux cut of 0.9mjy used by @xcite ) which , if true , would imply a ` transition ' in the mid - ir properties of high redshift ulirgs at @xmath70mjy . this possibility is simple , but does suffer from three drawbacks . first , as described in [ select ] , we do not demand that the 1.6@xmath0 m bump is detected with any statistical significance , and many of our sources have a weak 1.6@xmath0 m bump . our selection method therefore does not demand that the underlying continuum in the rest - frame near - ir is negligible , and therefore by extension does not demand that the rest - frame mid - ir continuum is absent either . second , as can be seen in figures [ spectraa ] and [ spectrab ] , several of our sample have significant mid - ir continua . third , several local ulirgs with strong mid - ir continua , in some cases accompanied by silicate absorption , also show a near - ir ` bump ' ( e.g. arp 220 , ngc6240 , @xcite ) , hence the presence of a bump does not necessarily select against objects in the upper branch of figure [ fork ] . 5 - _ gas - rich mergers : _ a simple way to reduce the apparent silicate strength is to lower the total extinction , which can be achieved by reducing the amount of dust in the starburst regions , or equivalently by increasing the amount of gas so that the same level of star formation can be sustained for a smaller dust mass . this scenario is compatible with the presence of strong pah emission , as changing the dust - to - gas ratio mainly affects the total dust column to the central ionizing source , whereas pah emission is thought to originate from the surface layers of star - forming regions . there is some support for this possibility from millimeter interferometry of sub - mm selected ulirgs at high redshift , which shows that they may be unusually gas - rich compared to local examples @xcite , and also from models for the star formation history of the universe , which suggest a lower mean @xmath71 at @xmath72 compared to locally ( e.g. @xcite , their figure 20 ) . 6 - _ starburst geometry : _ the final possibility is a different star - forming region geometry , such that the total dust column is reduced . this can be achieved in two ways ; either make the star formation diffuse and extended over several kpc instead of the sub - kpc scale starbursts seen in local ulirgs , or by distributing the star formation in multiple compact dusty star forming regions spread over a few kpc , instead of a single sub - kpc nuclear starburst . there is observational evidence for both these ` modes ' of star formation in distant starburst galaxies ; there is evidence for extended star formation from high resolution radio observations @xcite and ly@xmath73 imaging @xcite , while other authors have found evidence for star formation in multiple small regions distributed across a few kpc in forming massive galaxies at high redshift @xcite . furthermore , @xcite have recently suggested that disklike , ` inefficient ' star formation may be prevalent among distant massive galaxies . there is however an observational limit on the spatial extents of these starbursts ; high resolution millimeter imaging of small samples of sub - mm selected ulirgs at high redshift have shown that the starbursts in these systems can not be much more than 4kpc in diameter @xcite . it is difficult to discriminate reliably between these six possibilities , as the irs spectra can not formally rule any of them out . the first two possibilities however do not seem likely ; one would require some as - yet unknown dependence on luminosity for the silicate feature , while the other would require an extraordinary level of serendipity to find nearly all of the sample in the same evolutionary stage . the third possibility is more plausible , but would require a ` top - heavy ' imf , for which there is currently no direct evidence . the fourth possibility is also plausble , and some level of selection bias is undoubtedly present in our sample as we are not selecting solely on the basis of ir luminosity , but selection bias likely plays only a minor role , for the reasons given above . we tentatively propose therefore that some combination of the final two possibilities is the most likely origin for most ( but not all ) of this effect . it is worth noting that these conclusions may also apply to sub - mm selected ulirgs , given the similarity between their respective irs spectra .

we present mid - infrared spectra of thirty two high redshift ultraluminous infrared galaxies , selected via the stellar photospheric feature at rest - frame 1.6 m , and an observed - frame 24 m flux ofjy . most of the spectra exhibit prominent polycyclic aromatic hydrocarbon emission features , and weak silicate absorption , consistent with a starburst origin for the ir emission .

we present mid - infrared spectra of thirty two high redshift ultraluminous infrared galaxies , selected via the stellar photospheric feature at rest - frame 1.6 m , and an observed - frame 24 m flux ofjy . nearly all the sample reside in a redshift range of , and have rest - frame 1 - 1000 m luminosities of 10 - 10l . most of the spectra exhibit prominent polycyclic aromatic hydrocarbon emission features , and weak silicate absorption , consistent with a starburst origin for the ir emission . our selection method appears to be a straightforward and efficient way of finding distant , ir - luminous , star - forming galaxies in narrow redshift ranges . there is however evidence that the mid - ir spectra of our sample differ systematically from those of local ulirgs ; our sample have comparable pah equivalent widths but weaker apparent silicate absorption , and ( possibly ) enhanced pah 6.2m/7.7 m and 6.2m/11.2 m flux ratios . furthermore , the composite mid - ir spectrum of our sample is almost identical to that of local starbursts with ir luminosities ofl rather than that of local ulirgs . these differences are consistent with a reduced dust column , which can plausibly be obtained via some combination of ( 1 ) star formation that is extended over spatial scales of 1 - 4kpc , and ( 2 ) star formation in unusually gas - rich regions .

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we have presented mid - infrared spectra , taken using the irs onboard spitzer , of 32 objects selected on ( 1 ) an optical band magnitude fainter than @xmath19 , ( 2 ) excess flux in the irac 4.5@xmath0 m passband compared to the other three irac channels , and ( 3 ) a 24@xmath0 m flux in excess of 0.5mjy . our conclusions are : 1 - all of the sample lie within @xmath28 , with more than 90% lying in a much tighter redshift range , characterized by @xmath2 . the rest - frame ir luminosities are consistent with the range @xmath74l@xmath5 . our selection method is therefore a straightforward and efficient way of finding large samples of distant ulirgs confined to narrow redshift ranges . it avoids all of the observational challenges inherent in finding distant ulirgs via their far - ir emission , and produces samples with redshift distributions akin to those of optically selected samples such as lyman - break galaxies . 2 - nearly all of the sample show two or more strong pah emission features in their mid - ir spectra , and systematically lack strong silicate absorption . the individual spectra closely resemble the irs spectra of high - redshift sub - mm selected ulirgs . the star formation rates computed from the pah luminosities are all extremely high , of order @xmath75m@xmath5yr@xmath14 , sufficient to power all of the ir emission . coupled with the lack of a power law continuum in the irac channels , we infer that star formation is likely to be the dominant power source in most of the sample , though it is possible that some also contain a luminous agn . 3 - our sample occupy a different region on the pah 6.2@xmath0 m ew vs silicate strength plane to most local ulirgs , and there is marginal evidence for enhanced pah 6.2@xmath0m/7.7@xmath0 m and 6.2@xmath0m/11.2@xmath0 m ratios . furthermore , the composite mid - ir spectrum of our sample resembles that of local starburst galaxies with ir luminosities of @xmath76l@xmath5 , rather than that of local ulirgs . though selection bias likely plays a role , we propose that the most likely reasons for this are that the star formation in distant ulirgs is extended over scales of a few kpc rather than the sub - kpc starbursts seen in local ulirgs , and/or occurs in unusually gas - rich environments . we thank the referee for a very helpful report . this work is based on observations made with the spitzer space telescope , which is operated by the jet propulsion laboratory , california institute of technology under a contract with nasa . support for this work by the irs gto team at cornell university was provided by nasa through contract number 1257184 issued by jpl / caltech . support for this work was provided by nasa . this research has made extensive use of the nasa / ipac extragalactic database ( ned ) which is operated by the jet propulsion laboratory , california institute of technology , under contract with nasa . mp acknowledges financial support from the marie - curie fellowship grant meif - ct-2007 - 042111 ccclcccccccccc 1 & swire3 j103205.16 + 574817.5 & 17420288 & 158.02150 & 57.804861 & 68 & 87 & 74 & 75 & 699 + 2 & swire3 j103707.79 + 591204.5 & 17422080 & 159.28250 & 59.201250 & 42 & 50 & 50 & 37 & 625 + 3 & swire3 j104011.60 + 580542.6 & 17416704 & 160.04837 & 58.095194 & 63 & 76 & 65 & & 751 + 4 & swire3 j104012.86 + 592712.4 & 17414912 & 160.05358 & 59.453472 & 150 & 150 & 116 & 101 & 838 + 5 & swire3 j104034.35 + 582314.5 & 17417472 & 160.14312 & 58.387389 & 42 & 49 & 54 & & 680 + 6 & swire3 j104129.25 + 581712.2 & 17421824 & 160.37192 & 58.286750 & 43 & 62 & 46 & & 561 + 7 & swire3 j104139.78 + 573723.8 & 17421056 & 160.41575 & 57.623306 & 40 & 52 & 48 & & 601 + 8 & swire3 j104232.04 + 575439.4 & 17418240 & 160.63350 & 57.910972 & 37 & 49 & & & 704 + 9 & swire3 j104343.93 + 571322.5 & 17414656 & 160.93304 & 57.222917 & 97 & 116 & 112 & 69 & 1009 + 10 & swire3 j104349.41 + 575438.7 & 17419776 & 160.95592 & 57.910750 & 78 & 102 & 72 & 62 & 700 + 11 & swire3 j104402.55 + 593204.6 & 17421568 & 161.01067 & 59.534639 & 63 & 73 & 77 & & 615 + 12 & swire3 j104427.54 + 593811.7 & 17418752 & 161.11475 & 59.636611 & 62 & 75 & 76 & 57 & 686 + 13 & swire3 j104436.55 + 593252.4 & 17416448 & 161.15233 & 59.547889 & 51 & 64 & 58 & 55 & 644 + 14 & swire3 j104514.38 + 575708.8 & 17415424 & 161.30996 & 57.952472 & 65 & 78 & 70 & & 874 + 15 & swire3 j104551.62 + 594234.8 & 17416192 & 161.46513 & 59.709694 & 49 & 55 & 49 & & 703 + 16 & swire3 j104614.90 + 594134.3 & 17420800 & 161.56208 & 59.692861 & 42 & 52 & & & 715 + 17 & swire3 j104627.82 + 592843.4 & 17420544 & 161.61596 & 59.478722 & 56 & 67 & 69 & & 607 + 18 & swire3 j104632.93 + 563530.2 & 17416960 & 161.63721 & 56.591750 & 76 & 91 & 68 & & 761 + 19 & swire3 j104643.29 + 575851.0 & 17415936 & 161.68037 & 57.980833 & 82 & 98 & 66 & 64 & 772 + 20 & swire3 j104653.07 + 592652.1 & 17421312 & 161.72117 & 59.447833 & 86 & 100 & 87 & & 637 + 21 & swire3 j104656.23 + 594008.0 & 17419264 & 161.73433 & 59.668889 & 50 & 67 & 57 & & 632 + 22 & swire3 j104754.66 + 583905.9 & 17418496 & 161.97775 & 58.651667 & 48 & 60 & 38 & & 688 + 23 & swire3 j104843.21 + 584537.8 & 17417728 & 162.18008 & 58.760500 & 48 & 62 & 48 & & 687 + 24 & swire3 j104845.19 + 561055.8 & 17419008 & 162.18833 & 56.182194 & 69 & 75 & & & 674 + 25 & swire3 j104922.64 + 564032.5 & 17417984 & 162.34438 & 56.675694 & 93 & 110 & 103 & 71 & 645 + 26 & swire3 j105056.08 + 562823.0 & 17419520 & 162.73371 & 56.473056 & 69 & 80 & 67 & 52 & 621 + 27 & swire3 j105152.73 + 564719.2 & 17417216 & 162.96975 & 56.788667 & 65 & 76 & 59 & & 590 + 28 & swire3 j105308.24 + 591447.5 & 17415680 & 163.28433 & 59.246528 & 75 & 88 & 79 & & 793 + 29 & swire3 j105334.59 + 574242.3 & 17414400 & 163.39417 & 57.711750 & 71 & 128 & 91 & 69 & 1108 + 30 & swire3 j105539.92 + 571711.8 & 17415168 & 163.91637 & 57.286639 & 74 & 100 & 85 & 66 & 863 + 31 & swire3 j105908.46 + 574511.4 & 17420032 & 164.78525 & 57.753167 & 60 & 74 & 71 & 56 & 688 + 32 & swire2 j161744.64 + 540031.4 & 16161792 & 244.43583 & 54.008722 & 62 & 88 & 68 & 69 & 1074 + clcc 1 & 2 & & 1.63 + 2 & 2/3 & 1.88 ? & 1.84 + 3 & 2 & & 1.83 + 4 & 1/2 & 1.18 & 1.43 + 5 & 2/3 & 1.73 & 1.89 + 6 & 2 & & 1.61 + 7 & 2 & & 1.69 + 8 & 2 & & 1.93 + 9 & 2 & & 1.71 + 10 & 2 & & 1.77 + 11 & 2/3 & 1.00 ? & 1.74 ? + 12 & 2/3 & 2.03 & 1.83 + 13 & 2 & 1.61 & 1.49 + 14 & 2 & & 1.78 + 15 & 2 & 1.30 & 0.76 ? + 16 & 2 & 0.58 & 2.11 + 17 & 2/3 & 1.63 & 1.80 + 18 & 2 & & 1.76 + 19 & 2 & 2.36 ? & 1.60 + 20 & 2 & & 1.69 + 21 & 2 & 1.61 & 1.66 + 22 & 2 & & 1.63 + 23 & 2 & & 2.23 + 24 & 2 & & 1.25 + 25 & 2 & & 1.70 + 26 & 2 & & 1.54 + 27 & 2 & & 1.88 ? + 28 & 2 & & 1.47 + 29 & 2 & 1.55 & 1.65 + 30 & 2 & & 1.68 + 31 & 2/3 & 1.42 & 1.65 + 32 & 2 & 1.81 ? & 1.80 + cccccccccc 1 & 3.88 @xmath78 1.13 & 1.01 @xmath78 1.14 & 5.67 @xmath78 1.53 & 0.53 @xmath78 0.26 & 2.68 @xmath78 0.58 & 0.63 @xmath78 0.20 & 0.00 @xmath78 0.45 & 1352 & 13.28 + 2 & @xmath794.13 & @xmath790.70 & @xmath795.82 & 0.43 @xmath78 0.31 & 2.53 @xmath78 0.70 & 0.48 @xmath78 0.19 & 0.35 @xmath78 0.53 & @xmath791850 & @xmath7913.46 + 3 & @xmath794.49 & @xmath795.39 & 8.62 @xmath78 1.97 & 0.77 @xmath78 0.28 & 3.99 @xmath78 0.95 & 1.44 @xmath78 1.01 & 1.07 @xmath78 1.00 & 2324 & 13.49 + 4 & 8.82 @xmath78 0.99 & 0.64 @xmath78 0.21 & 17.79 @xmath78 1.40 & 0.61 @xmath78 0.10 & 5.03 @xmath78 0.45 & 0.51 @xmath78 0.07 & 0.17 @xmath78 0.15 & 2067 & 13.53 + 5 & 2.47 @xmath78 0.95 & 2.66 @xmath78 14.15 & 5.27 @xmath78 1.35 & 0.58 @xmath78 0.23 & 1.55 @xmath78 0.77 & 0.37 @xmath78 0.32 & 0.24 @xmath78 0.62 & 1194 & 13.24 + 6 & 3.15 @xmath78 1.12 & 0.52 @xmath78 0.43 & 9.22 @xmath78 1.82 & 0.80 @xmath78 0.47 & 2.39 @xmath78 0.44 & 0.50 @xmath78 0.16 & 0.68 @xmath78 0.37 & 1108 & 13.16 + 7 & @xmath794.40 & @xmath793.16 & 5.96 @xmath78 1.46 & 0.69 @xmath78 0.36 & 1.72 @xmath78 0.46 & 0.39 @xmath78 0.14 & 0.06 @xmath78 0.43 & @xmath791378 & @xmath7913.39 + 8 & 4.18 @xmath78 1.36 & 0.91 @xmath78 1.04 & 3.98 @xmath78 0.79 & 0.34 @xmath78 0.09 & 2.65 @xmath78 0.70 & 0.52 @xmath78 0.20 & 0.87 @xmath78 0.39 & 2133 & 13.52 + 9 & 7.49 @xmath78 0.95 & 1.88 @xmath78 2.14 & 11.82 @xmath78 1.71 & 0.79 @xmath78 0.19 & 4.86 @xmath78 0.63 & 0.62 @xmath78 0.13 & 0.55 @xmath78 0.25 & 1160 & 13.27 + 10 & @xmath794.35 & @xmath790.64 & 7.52 @xmath78 1.85 & 0.77 @xmath78 0.32 & 2.95 @xmath78 0.61 & 1.38 @xmath78 1.24 & 1.19 @xmath78 0.80 & @xmath791844 & @xmath7913.44 + 11 & @xmath794.03 & @xmath790.83 & @xmath796.0 & @xmath794.00 & @xmath791.79 & @xmath790.34 & 0.02 @xmath78 0.40 & @xmath791410 & @xmath7913.38 + 12 & 3.46 @xmath78 1.05 & 1.02 @xmath78 1.39 & 4.48 @xmath78 0.84 & 0.38 @xmath78 0.10 & @xmath791.86 & @xmath790.41 & 0.67 @xmath78 0.43 & @xmath791458 & 13.37 + 13 & 4.72 @xmath78 1.38 & 0.63 @xmath78 0.59 & 4.62 @xmath78 1.53 & 0.22 @xmath78 0.08 & 2.30 @xmath78 0.42 & 0.25 @xmath78 0.06 & 0.20 @xmath78 0.26 & 1160 & 13.27 + 14 & 4.91 @xmath78 0.96 & 1.26 @xmath78 1.52 & 6.84 @xmath78 1.51 & 0.50 @xmath78 0.17 & 2.87 @xmath78 0.62 & 0.66 @xmath78 0.29 & 0.67 @xmath78 0.62 & 1991 & 13.50 + 15 & & & & & @xmath794.37 & @xmath791.49 & 1.89 @xmath78 0.43 & & + 16 & @xmath795.07 & @xmath791.23 & 2.80 @xmath78 0.93 & 0.22 @xmath78 0.08 & & & & & @xmath7913.72 + 17 & 1.53 @xmath78 0.54 & 0.63 @xmath78 1.09 & 3.94 @xmath78 1.84 & 0.57 @xmath78 0.33 & 2.33 @xmath78 0.00 & 0.59 @xmath78 0.00 & 0.01 @xmath78 0.44 & 1014 & 12.94 + 18 & 3.96 @xmath78 1.49 & 0.98 @xmath78 1.01 & 4.25 @xmath78 1.36 & 0.26 @xmath78 0.09 & 2.89 @xmath78 0.69 & 0.53 @xmath78 0.19 & 0.45 @xmath78 0.43 & 1706 & 13.38 + 19 & 4.94 @xmath78 1.06 & 0.95 @xmath78 0.75 & 9.65 @xmath78 1.98 & 0.59 @xmath78 0.18 & 2.99 @xmath78 0.65 & 0.44 @xmath78 0.14 & 0.27 @xmath78 0.51 & 1562 & 13.38 + 20 & @xmath794.16 & @xmath790.81 & @xmath796.00 & @xmath791.50 & 4.23 @xmath78 0.52 & 0.93 @xmath78 0.24 & 0.40 @xmath78 0.45 & @xmath793008 & @xmath7913.74 + 21 & 4.35 @xmath78 0.98 & 0.56 @xmath78 0.35 & 7.64 @xmath78 1.42 & 0.54 @xmath78 0.18 & 1.45 @xmath78 0.38 & 0.24 @xmath78 0.08 & 0.58 @xmath78 0.31 & 1423 & 13.42 + 22 & 5.85 @xmath78 1.10 & 7.34 @xmath78 40.91 & 8.28 @xmath78 1.59 & 0.58 @xmath78 0.21 & 3.89 @xmath78 0.66 & 0.71 @xmath78 0.23 & 0.54 @xmath78 0.52 & 2009 & 13.48 + 23 & @xmath794.86 & @xmath790.49 & 4.68 @xmath78 0.76 & 0.51 @xmath78 0.15 & & & & & @xmath7913.77 + 24 & & & 8.16 @xmath78 1.43 & 0.31 @xmath78 0.07 & 8.83 @xmath78 1.29 & 3.32 @xmath78 3.05 & 0.83 @xmath78 0.64 & & + 25 & @xmath793.10 & @xmath790.28 & @xmath795.00 & 0.25 @xmath78 0.11 & 2.39 @xmath78 0.68 & 1.06 @xmath78 0.66 & 1.34 @xmath78 1.34 & @xmath791253 & @xmath7913.22 + 26 & 8.39 @xmath78 1.21 & 0.65 @xmath78 0.22 & 7.22 @xmath78 1.47 & 0.28 @xmath78 0.07 & 5.13 @xmath78 0.75 & 0.66 @xmath78 0.15 & 0.51 @xmath78 0.35 & 2424 & 13.59 + 27 & @xmath793.31 & @xmath790.65 & @xmath794.80 & 0.41 @xmath78 0.22 & @xmath791.30 & @xmath790.26 & 0.01 @xmath78 0.43 & @xmath791281 & @xmath7913.35 + 28 & 3.49 @xmath78 1.19 & 0.47 @xmath78 0.45 & 5.97 @xmath78 1.23 & 0.31 @xmath78 0.09 & 2.96 @xmath78 0.40 & 0.35 @xmath78 0.06 & 0.00 @xmath78 0.24 & 1030 & 13.10 + 29 & 6.22 @xmath78 1.10 & 0.59 @xmath78 0.25 & 10.56 @xmath78 1.57 & 0.45 @xmath78 0.09 & 2.86 @xmath78 0.55 & 0.24 @xmath78 0.05 & 0.73 @xmath78 0.27 & 1929 & 13.53 + 30 & 4.50 @xmath78 1.12 & 1.08 @xmath78 1.06 & 5.77 @xmath78 1.62 & 0.33 @xmath78 0.11 & 2.40 @xmath78 0.50 & 0.33 @xmath78 0.09 & 0.37 @xmath78 0.32 & 1533 & 13.39 + 31 & 4.81 @xmath78 0.93 & 2.62 @xmath78 5.95 & 9.36 @xmath78 1.18 & 0.77 @xmath78 0.31 & 1.64 @xmath78 0.49 & 0.20 @xmath78 0.07 & 0.85 @xmath78 0.47 & 1370 & 13.40 + 32 & 5.80 @xmath78 0.90 & 0.36 @xmath78 0.10 & 4.40 @xmath78 0.96 & 0.26 @xmath78 0.07 & @xmath791.85 & @xmath790.19 & 0.02 @xmath78 0.50 & @xmath792017 & 13.60 + . the number in the top left of each panel corresponds to the i d number in the tables . the vertical dotted lines mark the wavelengths of the 6.2@xmath0 m , 7.7@xmath0 m , 8.8@xmath0 m , 11.2@xmath0 m and 12.7@xmath0 m pah features . [ spectraa],width=642 ] . _ right panel : _ comparison between the irs redshifts , and the photometric redshifts from @xcite , listed in table [ measurements ] . the dotted lines denote a deviation of 0.06 in log(1+z ) , the boundary defined as a ` catastrophic failure ' by @xcite . sources plotted as triangles have an uncertain irs redshift . sources plotted in grey have a photometric redshift derived from three bands . [ zphotzspec],title="fig:",width=321 ] . _ right panel : _ comparison between the irs redshifts , and the photometric redshifts from @xcite , listed in table [ measurements ] . the dotted lines denote a deviation of 0.06 in log(1+z ) , the boundary defined as a ` catastrophic failure ' by @xcite . sources plotted as triangles have an uncertain irs redshift . sources plotted in grey have a photometric redshift derived from three bands . [ zphotzspec],title="fig:",width=321 ] dispersion . the average of the ten objects with the largest pah 6.2@xmath0 m ews is plotted in red , and the average of the ten objects with the largest silicate strengths is plotted in blue . a ` p ' denotes the wavelength of a pah feature . [ composite_all],width=642 ] l@xmath5 - 10@xmath60l@xmath5 are plotted in red and blue , respectively . the large orange point is the mean value for our sample . [ pahfluxratio],title="fig:",width=321 ] l@xmath5 - 10@xmath60l@xmath5 are plotted in red and blue , respectively . the large orange point is the mean value for our sample . [ pahfluxratio],title="fig:",width=321 ] l@xmath5 are plotted in blue and red respectively . the large orange point is the average for all the bump sources . our sources occupy a small region , mostly the 1c class . this contrasts with local ulirgs , which are found in nearly all classes . [ fork],width=642 ] errors denoted by the grey region ) and averaged spectra for classes in the ` fork ' diagram of @xcite , normalized at 14@xmath0 m ; class 1a ( green ) , class 1b ( cyan ) , class 1c ( blue ) , class 2a ( yellow ) , class 2b ( magenta ) , class 2c ( purple ) , class 3a(red ) , and class 3b ( orange ) . [ comp_fork],width=642 ] 10@xmath3 - 10@xmath4l@xmath5 ) and three different starburst galaxy templates , all normalized at 6@xmath0 m ; the averaged spectrum of the starburst galaxies in @xcite ( blue , l@xmath8010@xmath59 - 10@xmath60l@xmath5 ) , arp 220 ( @xcite , green , l@xmath8110@xmath82l@xmath5 ) , and m82 ( @xcite , orange , l@xmath8110@xmath59l@xmath5 , this spectrum was taken with the iso - sws and hence is of higher spectral resolution than the other spectra ) . despite being approximately two orders of magnitude less luminous , the brandl et al spectrum is an excellent match to our average spectrum . m82 is also a reasonable match , except for slightly stronger apparent silicate absorption . arp 220 on the other hand is a very poor match , with much stronger absorption . [ comp_brandl],width=642 ]

nearly all the sample reside in a redshift range of , and have rest - frame 1 - 1000 m luminosities of 10 - 10l . our selection method appears to be a straightforward and efficient way of finding distant , ir - luminous , star - forming galaxies in narrow redshift ranges . there is however evidence that the mid - ir spectra of our sample differ systematically from those of local ulirgs ; our sample have comparable pah equivalent widths but weaker apparent silicate absorption , and ( possibly ) enhanced pah 6.2m/7.7 m and 6.2m/11.2 m flux ratios . furthermore , the composite mid - ir spectrum of our sample is almost identical to that of local starbursts with ir luminosities ofl rather than that of local ulirgs . these differences are consistent with a reduced dust column , which can plausibly be obtained via some combination of ( 1 ) star formation that is extended over spatial scales of 1 - 4kpc , and ( 2 ) star formation in unusually gas - rich regions .

we present mid - infrared spectra of thirty two high redshift ultraluminous infrared galaxies , selected via the stellar photospheric feature at rest - frame 1.6 m , and an observed - frame 24 m flux ofjy . nearly all the sample reside in a redshift range of , and have rest - frame 1 - 1000 m luminosities of 10 - 10l . most of the spectra exhibit prominent polycyclic aromatic hydrocarbon emission features , and weak silicate absorption , consistent with a starburst origin for the ir emission . our selection method appears to be a straightforward and efficient way of finding distant , ir - luminous , star - forming galaxies in narrow redshift ranges . there is however evidence that the mid - ir spectra of our sample differ systematically from those of local ulirgs ; our sample have comparable pah equivalent widths but weaker apparent silicate absorption , and ( possibly ) enhanced pah 6.2m/7.7 m and 6.2m/11.2 m flux ratios . furthermore , the composite mid - ir spectrum of our sample is almost identical to that of local starbursts with ir luminosities ofl rather than that of local ulirgs . these differences are consistent with a reduced dust column , which can plausibly be obtained via some combination of ( 1 ) star formation that is extended over spatial scales of 1 - 4kpc , and ( 2 ) star formation in unusually gas - rich regions .

1404.3760

i

a major stumbling block to understanding the accretion history of supermassive black holes ( bhs ) over cosmic time is determining the role of obscuration in the demographics of active galactic nuclei ( agn ) . optical surveys are quite successful at finding luminous blue ( unobscured type i ) quasars ( e.g. , * ? ? ? * ; * ? ? ? * ) , but are not sensitive to truly obscured ( or type ii ) quasars , where the quasar continuum and broad emission lines are completely hidden . sensitive 0.5 - 10 kev x - ray surveys can find modestly obscured systems , but typically cover a limited solid angle , and thus are not sensitive to rare luminous objects ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? similar caveats apply to mid - infrared ( mir ) selection using _ * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) , while _ wise _ can unambiguously select only the most luminous agn ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? many x - ray based studies indicate a decreasing obscured fraction as a function of luminosity over a broad redshift range ( e.g. , * ? ? ? * ; * ? ? ? * ) , but at low redshift ( @xmath11 ) , luminous optically selected samples suggest comparable numbers of obscured and unobscured systems @xcite . at high redshifts , at the peak of quasar activity ( @xmath12 ) , demographics are even more uncertain and a large - area survey of luminous obscured quasar activity is required to determine the obscured fraction . although unified theories state that type i and type ii quasars differ only in orientation ( e.g. , * ? ? * ; * ? ? ? * ; * ? ? ? * ) , there are many hints that type ii quasars may represent a special phase in the growth of black holes . there have been numerous suggestions , both observational ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) and theoretical ( e.g. , * ? ? ? * ) , that major galaxy mergers trigger an obscured phase of central bh growth . this obscured phase persists until the agn grows powerful enough to expel all remaining gas out of the surrounding galaxy , leading to an optically luminous quasar phase . samples of type i quasars with moderate extinction hosted by merging galaxies provide some support for this scenario ( e.g. , * ? ? ? again , larger homogeneous samples of obscured quasars , at the peak epoch of bh growth , are needed to statistically address the growth phase of these objects . finally , some obscuration may occur in a torus near the agn , while some may be due to galaxy - scale dust @xcite . the torus geometry or porosity may also depend on luminosity ( e.g. , * ? ? ? * ; * ? ? ? larger samples of luminous obscured quasars could address the full distribution of obscuration as a function of bolometric luminosity . to date , type ii samples at high redshift number in the tens , including targets selected in the radio ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) , x - ray @xcite , mid - infrared @xcite and optical @xcite . the operational definition of obscured quasar depends on the selection technique . the typical x - ray definition of column density @xmath13 @xmath14 ( e.g. , * ? ? ? * ) apparently corresponds to an @xmath15 in agn @xcite . in contrast , optically selected type ii seyfert galaxies typically have @xmath16 ( e.g. , * ? ? ? * ; * ? ? ? finally , near - infrared selection criteria yield moderately reddened quasars with broad h@xmath2 and typical @xmath17 ( e.g. , * ? ? ? * ; * ? ? ? * ) . in this paper , we focus on type ii candidates selected in the rest - frame uv , to explore the @xmath9 distribution of objects selected on the basis of narrow uv emission lines . low - redshift ( @xmath18 ) type ii quasars were successfully discovered in large numbers in the sloan digital sky survey ( sdss ; * ? ? ? * ) based on their strong and narrow [ ] @xmath5 emission @xcite , and subsequently shown to be bona fide obscured quasars @xcite . not until the baryon oscillation spectroscopic survey ( boss ; * ? ? ? * ; * ? ? ? * ) , which spectroscopically targeted quasars down to a magnitude limit of @xmath19 or @xmath20 @xcite , did it become possible to select type ii quasar candidates with @xmath21 with the sdss . in ( * ? ? ? * hereafter paper i ) and this work , high redshift type ii quasar candidates are identified based on the presence of strong and narrow high - ionization lines in their rest - frame uv spectra ( e.g. , ) . in paper i , we presented a sample of 145 type ii quasar candidates selected from the boss survey based on their narrow ( @xmath22 km s@xmath4 ) and ly @xmath2 emission . the narrow linewidths and high rest equivalent widths ( ews ) of the sample objects bear strong resemblance to those of other samples of type ii quasars . furthermore , in the two objects we observed with a spectropolarimeter , we detected continuum polarization of @xmath23 , inconsistent with typical unobscured quasars . on the other hand , our boss type ii quasar candidates are too luminous and blue in the uv continuum to be explained by galaxy light alone . they have typical rest - frame uv continuum luminosities of @xmath24 ab mag at 1450 , as compared to magnitudes of @xmath25 ab mag @xcite for the most luminous uv - selected galaxies at similar redshifts @xcite . the agn must contribute some uv light , whether it be directly transmitted or due to scattered light . furthermore , the uv line ratios are more akin to type i rather than type ii objects . finally , in one object with broad spectral energy distribution ( sed ) coverage , the optical / uv is weaker than seen in typical type i objects indicating some obscuration , but more prominent than in typical type ii objects . in the same sense , the optical / nir colors of our type ii candidates are similar to unobscured quasars . thus , based on the rest - frame uv spectra alone , it is difficult to determine the true nature of these sources . -0 mm [ tab : sample ] here , we present nir spectroscopy that probes the rest - frame optical spectra of 25 of the type ii quasar candidates presented in paper i. we use three nir echellettes , triplespec @xcite on the 3.5 m at apache point observatory ( apo ) , the folded - port infrared echellette ( fire ; * ? ? ? * ) at magellan , and gemini near infrared spectrograph ( gnirs ; * ? ? ? * ) on gemini north , all three of which afford us @xmath0 spectroscopy in a single observation . we simultaneously measure h@xmath26 , h@xmath2 , and the strong and ubiquitous [ ] @xmath5 line in the majority of our targets . the [ ] line luminosity is known to correlate with the intrinsic luminosity of the quasar @xcite , while the strength and width of the balmer lines provide new insight into the level and scale of the extinction . finally , the [ ] line shape unambiguously traces the low - density ( narrow - line region ) gas kinematics , and thus allows us to characterize any additional ( broader ) components in the permitted lines . in fact , we specifically targeted two galaxies with multiple velocity peaks in the and/or ly @xmath2 line ( paper i ) , to determine whether the peaks are caused by absorption or real kinematic structure in the gas . -0 mm the paper proceeds as follows . in [ sec : observations ] we present properties of the sample and details of the observations . in [ sec : reductions ] we discuss the data reduction , while in [ sec : fitting ] we outline our line - fitting technique . we present our results in [ sec : results ] , and discuss the implications for obscured quasars in [ sec : discussion ] . we assume a concordance cosmology with h@xmath27 km s@xmath4 mpc@xmath4 , @xmath28 , and @xmath29 @xcite .

we present near - infrared ( nir ) spectroscopy of 25 candidate type ii quasars selected from the sloan digital sky survey , using triplespec on the apache point observatory 3.5 m telescope , fire at the magellan / baade 6.5 m telescope , and gnirs on gemini . at redshifts of , our nir spectra probe the rest - frame optical region of these targets , which were initially selected to have strong lines of and ly , with fwhm km s from the sdss pipeline . we also describe one unusual object with three distinct velocity peaks in its [ ] spectrum .

we present near - infrared ( nir ) spectroscopy of 25 candidate type ii quasars selected from the sloan digital sky survey , using triplespec on the apache point observatory 3.5 m telescope , fire at the magellan / baade 6.5 m telescope , and gnirs on gemini . at redshifts of , our nir spectra probe the rest - frame optical region of these targets , which were initially selected to have strong lines of and ly , with fwhm km s from the sdss pipeline . we use the [ ] line shape as a model for the narrow line region emission , and find that h consistently requires a broad component with fwhms ranging from 1000 to 7500 km s . interestingly , the lines also require broad bases , but with considerably narrower widths of to km s . estimating the extinction using the balmer decrement and also the relationship in lower- quasars between rest equivalent width and luminosity in the [ ] line , we find typical values of mag , which naturally explains the attenuated lines relative to h . we propose that our targets are moderately obscured quasars . we also describe one unusual object with three distinct velocity peaks in its [ ] spectrum .

1404.3760

r

we now examine the rest - frame optical line widths and strengths in an attempt to understand in more detail the nature of our candidate type ii quasars . qualitatively , the rest - frame optical emission line properties appear as we expect . we find high ratios of [ ] to h@xmath26 in nearly all sources , in contrast to nls1 galaxies that are characterized by [ ] /h@xmath26@xmath92 ( e.g. , * ? ? ? we detect broad components in the h@xmath2 line that are systematically broader than those we see in , while on average in the quasar population as a whole , is broader , albeit with large scatter ( e.g. , * ? ? ? we only rarely detect broad h@xmath26 , and will use this fact to place limits on the extinction of the broad - line region in [ sec : extinction ] . -0 mm in what follows , we will investigate the incidence of broad permitted lines , the broad - band seds , and the relationship between [ ] rest - frame ew and luminosity as clues to the nature of our quasars . we start with the incidence and properties of the broad permitted lines . in all cases we measure line widths from the gaussian fits . for [ ] , we measure the fwhm from the total fit to the line . for h@xmath2 we quote the broad - line fwhm based on the gaussian fit . in the case of , we calculate both a _ total _ linewidth , measured nonparametrically on the combined narrow+broad line fit , for comparison with [ ] , and a _ broad _ linewidth using just the single broad gaussian , for comparison with h@xmath2 . recall that these targets were originally selected to have line widths @xmath22 km s@xmath4 based on a single gaussian fit with the width tied to other emission lines ( excluding ly @xmath2 ) performed by the sdss pipeline @xcite . the line widths that we present here make the physically motivated assumption that the [ ] linewidth traces the narrow - line region , while any additional component we find in the lines arises from the broad - line region . thus we are able to uncover weak broad emission not captured by the pipeline fit . narrow - line widths , as measured from the [ ] lines , range from 200 to 1000 km s@xmath4 , consistent with lower - redshift narrow - line regions in luminous targets ( fig . [ fig : fwcolor ] , e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? we detect significant broad h@xmath2 in all of the targets , ranging in width from 1000 to 7500 km s@xmath4 . likewise , we detect an additional component beyond the [ ] model in every line . the total linewidths span only @xmath6 to @xmath93 km s@xmath4(figures [ fig : nirfits ] & [ fig : nirfitsapo ] ) . the broad linewidths range from 1300 to 4500 km s@xmath4 , but nearly all have fwhm @xmath94 km s@xmath4 , and they are systematically lower than the broad component seen in h@xmath2 ( figure [ fig : fwcolorha ] , left ) . we seek correlations between the broad - line widths and broad - line fractions with continuum color . first , in figure [ fig : fwcolor ] , we compare the profile widths of [ ] ( the bona - fide narrow - line region ) and total linewidth of . the two are strongly correlated , but the line is @xmath95 times as broad as [ ] on average . we see no clear correlation between fwhm@xmath96}$]/fwhm@xmath97 and optical or mid - infrared color . we also search for a correlation in line shifts between [ ] and , but found no correlation ( spearman rank @xmath98 , probability of no correlation @xmath99 ) . to emphasize the narrowness of the broad component of , we compare it with the broad h@xmath2 ( figure [ fig : fwcolorha ] , left ) . with a couple of exceptions , the h@xmath2 lines are roughly twice as broad as . the ratio of to h@xmath2 in typical blue quasars is known to span a large range ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) , but on average the line is broader than h@xmath2 in unobscured quasars . we also examine the ratio of broad to total flux in h@xmath2 ( figure [ fig : fwcolorha ] ) and ( figure [ fig : brcolor ] ) . the broad component dominates the total line flux in both lines in most cases . there is no strong correlation between the broad - line fraction and mid - infrared color , perhaps because the latter spans such a narrow range . our targets were selected to have narrow , but with physically motivated decompositions , we can state that there is a broad component distinct from [ ] and that it is relatively narrow . while most of our targets have broad linewidths @xmath100 km s@xmath4(figure [ fig : fwcolorha ] ) , in the @xcite compilation of sdss quasars , only 1% of @xmath101 quasars have lines narrower than @xmath93 km s@xmath4 . the fraction rises to 10% when we match in luminosity ( @xmath102 mag , with no extinction correction applied to either sample ) . in contrast , comparing the distribution of h@xmath2 linewidths between our sample and the objects in the @xcite catalog with @xmath102 mag , we find comparable median fwhm in h@xmath2 of @xmath103 km s@xmath4 and 3300 km s@xmath4 , respectively . a kolmogorov - smirnov test suggests the two distributions are marginally consistent ( @xmath104 ) , with our objects having broader lines on average . thus , extinction is a natural culprit to explain the weakened broad emission lines at uv wavelengths , assuming a standard wavelength dependence for the reddening law . in the next section we will quantify the amount of extinction needed to explain our observations . we note that some of the absorption may arise from intervening @xcite or associated absorbers @xcite . -0 mm [ tab : line ] to summarize this section , we detect permitted line emission that is broader than the narrow - line model alone . the broad lines are relatively narrow ( with fwhm ranging from @xmath6 to @xmath7 km s@xmath4 , but most having fwhm@xmath105 km s@xmath4 ) . these relatively narrow linewidths are not surprising , given the initial sample selection . in contrast , the h@xmath2 lines span a more typical range of widths from @xmath6 to @xmath106 km s@xmath4 . let us now examine whether we can explain the difference between these two lines using extinction . another valuable clue to the nature of our sources comes from comparing the [ ] line rest - frame equivalent widths ( ews ) and luminosities . we assume that the [ ] is extended relative to the broad - line region . moving from unobscured to obscured sources , we would expect @xmath107}$ ] to stay constant at a given bolometric luminosity while the continuum is obscured and grows fainter . as a result , obscured sources should have much higher ews at a given line luminosity ( see figure [ fig : ewo3 ] ) . the observed range of the [ ] @xmath108 line ew is bracketed by obscured quasars at @xmath109 from @xcite and unobscured quasars at comparable redshift from @xcite . our targets lie between the obscured and unobscured sources . we can derive an estimate for the extinction using the ratio of the observed rest - frame ew to that expected for an unobscured quasar with the same @xmath107}$ ] . since we expect the [ ] flux to emerge from larger scales with lower extinction , the ratio of the observed and expected ew simply diagnoses the extinction level of the continuum at 5007 . assuming smc - like dust @xcite , which appears appropriate for quasars @xcite , we calculate the extinction in the @xmath110-band , @xmath111 , for the seven quasars with ew@xmath112ew@xmath113 and an h@xmath2 measurement . note that this estimate is independent of the absolute flux calibration . based on this calculation , we find values of @xmath111 ranging from @xmath114 to @xmath115 mags with a median of @xmath116 mag ( table 3 ; @xmath117 mag ; median @xmath118 mag ) . for reference , a value of @xmath116 mag corresponds to a transmitted uv flux at 1500 that is 14% of the intrinsic flux , assuming the smc reddening curve of @xcite . the two largest extinction values belong to sdss j1330 + 0146 and sdss j0958 + 0135 ( the latter is in cosmos ; * ? ? * paper i ) . given that in general we detect broad h@xmath2 but not broad h@xmath26 , we can derive a second estimate of the reddening @xmath111 if we make the assumption that all objects have the same intrinsic h@xmath26/h@xmath2 ratio . we derive @xmath119 limits to the broad h@xmath26 flux by integrating the h@xmath26 fit residuals over twice the fwhm of the h@xmath2 line . we then estimate a lower limit to the extinction , assuming an intrinsic case b@xmath120 h@xmath2/h@xmath26 ratio of 3:1 . this ratio is reasonable , since the typical observed h@xmath2/h@xmath26 ratio in lower redshift sdss quasars is @xmath121 @xcite . going a step further , we predict the broad flux based on the observed broad h@xmath2 flux and the calculated extinction . we assume that intrinsically the line is 35% brighter than the h@xmath2line , based on the compilation of @xcite of 60 sdss quasars with @xmath122 . we will use this single value although there is nearly an order of magnitude scatter in the ratio ratios range from 0.04 to 2 . we find no significant correlation between the observed line ratios and the reddening , but the total number of objects is small . ] . the expected broad flux is nearly always higher than what is observed by a factor of two to ten ( with measurement errors causing a factor of @xmath95 uncertainties on these ratios ) . the one exception is sdss j1330 + 0146 , where the expected flux is only 6% of what is observed , but the broad emission lines are both quite weak in this case . there are two possible interpretations . given that the broad component of is much narrower than that of h@xmath2 , one possibility is that we are not detecting the full broad line , and that the actual extinction is greater than what we estimate from the balmer decrement . alternatively , the extinction curve may be flatter in the uv than the smc curve ( e.g. , * ? ? ? * ) , in which case we would be overpredicting the intrinsic luminosity by factors of several . a third possibility is that the civ / h@xmath2 ratios are anomalous in these objects . we compare the ew estimate for @xmath111 with the limits derived from the flux ratio of h@xmath26/h@xmath2 in figure [ fig : civhbab ] ( left ) . a value of @xmath123 on the x - axis means that the [ ] ew is consistent with the unobscured quasars . the two estimates are correlated , which is encouraging , since both are estimates of the reddening to the continuum / broad - line region . in general , the h@xmath26-based absorption estimates are larger , perhaps because the underlying h@xmath26 to h@xmath2 ratios span a wide range , rather than having the case b@xmath120 recombination value ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? the other possibility is that the [ ] -derived values are too low , because we have ignored extinction of the [ ] line and/or scattered light boosting the continuum emission in the type ii quasars . as a sanity check , we can also calculate the minimum extinction needed to bring the @xmath124 color in line with the @xcite blue quasar sed . we find this minimum to be @xmath125 mag ( @xmath126 mag ) in all cases , consistent with the other estimates but less restrictive ( figure [ fig : civhbab ] , right ) . we do not calculate the extinction using the narrow h@xmath26 and h@xmath2 lines because of the low significance of the h@xmath26 detections . in summary , based on the ew of [ ] and limits on the balmer decrement in the broad emission lines , we find evidence for modest absorption ( @xmath127 mag or @xmath128 mag ) . we now investigate the seds and bolometric luminosities of these quasars . in a future paper we will present full seds , but for the moment we simply compare rest - frame uv and optical line luminosities with uv and mid - infrared continuum luminosities . in the case of unobscured sources , the rest - frame uv light traces the big blue bump directly , while the near to mid - infrared emission ( longward of @xmath129 ) traces hot dust sitting close to the accreting black hole . -0 mm the latter , therefore , is expected to be relatively isotropic ( although see also * ? ? ? * ; * ? ? ? line luminosities , in so far as they are photoionized by the central source , also correlate with the continuum luminosity ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? the narrow line luminosities should also be relatively isotropic ( although see also * ? ? ? we compare various intrinsic luminosity indicators with each other in figure [ fig : wiselum ] . in the case of h@xmath2 and , we plot total ( broad+narrow ) luminosities . we do this for consistency with other work @xcite , but since the narrow emission is such a small fraction of the total flux , removing it would make little difference to the final outcome . -0 mm -0 mm -0 mm [ tab : line ] if there is substantial extinction of the broad - line region specifically , then we expect the weakest correlation between the strength of the line and the uv continuum emission , while correlations with progressively redder diagnostics should be stronger . the tightest correlation is expected to be between the _ wise _ and [ ] luminosities , as the most isotropic . in fact , we do not find significant correlations between any of our luminosity probes ( figure [ fig : wiselum ] ) , based on spearman rank coefficients . we have also investigated @xmath130 and @xmath131}$ ] against the uv luminosity , and find no significant correlation . we also show the `` dereddened '' uv and fluxes , adopting the balmer decrement estimates of @xmath132 ; even with an extinction correction , we detect no correlation . in general the luminosity indicators all span a similar range of @xmath133 dex . the one exception is the observed uv luminosity , which spans a narrow range . considering that we selected the targets to be at the flux limit of the boss survey and to have high - ew emission lines , the narrow observed range in uv luminosity may be no more than a selection effect . there are two possible explanations for the lack of luminosity correlations . one is the limited range in observed luminosity of the sample . it may be that intrinsic sed differences , combined with extinction of the narrow - line region , wash out correlations over the narrow luminosity range we probe here . bona fide type ii quasars at @xmath134 are clearly redder in the mir than are unobscured quasars , possibly adding additional scatter to the _ wise _ luminosities ( e.g. , * ? ? ? the other major caveat here remains outstanding uncertainties in our flux calibration . we have tried splitting the data into apo and magellan subsamples to see if a strong correlation holds with one or the other , but the total number of objects is too small to seriously address this question . with rest - frame optical spectra , and detected broad emission lines , we can use scaling relations to estimate black hole ( bh ) masses for these luminous quasars ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? we assume that only gravity influences the motions of the broad - line region gas , so that the velocity dispersion of the gas relates directly to @xmath135 ; @xmath136 . we also need a size scale for the emitting gas , which we estimate from the agn luminosity using the `` radius - luminosity '' relation , calibrated using radius measurements from reverberation mapping ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? because we do not detect the optical agn continuum directly in our observations , we rely on the known correlation between continuum and line luminosity ( e.g. , * ? ? ? * ) to calculate the bh mass from observations of the h@xmath2 line alone ( uncorrected for extinction ) . the relationship between continuum luminosity and line luminosity , as well as the relation between h@xmath26 and h@xmath2 fwhm , are taken from @xcite , while the radius - luminosity relation is taken from @xcite . bh masses derived in this manner clearly carry a large number of systematic uncertainties that are difficult to quantify ( e.g. , * ? ? ? * ; * ? ? ? including these systematics , the bh mass uncertainties are estimated to be factors of a few ( e.g. , * ? ? ? * ; * ? ? ? eventually we hope two - dimensional reverberation mapping of nearby seyfert galaxies will mitigate these problems ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) , but in the meantime we must be careful not to overinterpret the bh mass estimates . taking the measurements at face value , the derived bh masses are typically @xmath137 @xmath138 . technically , these are lower - limits , since they rely on the h@xmath2 luminosity , which almost certainly suffers extinction . on the other hand , the inferred @xmath135 only depends on the square root of the h@xmath2 luminosity ; a factor of three error in broad h@xmath2 luminosity corresponds to only a @xmath139 dex change in @xmath135 . the line width may be underestimated due to extinction as well , but given that the distribution of h@xmath2 widths spans a similar range to other quasar samples ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) , it is hard to estimate how large that bias may be . for comparison , we show both the median source from the sdss sample in a matching redshift and magnitude range @xcite as well as the median object from a nir - selected sample presented in @xcite . we can ask whether these masses are reasonable given the total luminosities of the objects . in addition to factors of a few uncertainties in @xmath135 , there are also a number of uncertainties involved in calculating the bolometric luminosities . the composite sed of unobscured objects in @xcite shows that the bolometric luminosity is @xmath140 times @xmath141 . using this scaling , the majority of the sample has sensible eddington ratio estimates of @xmath142 , with all targets consistent with being below the eddington limit . considering the lack of correlation between _ wise _ and [ ] luminosities discussed above , these eddington ratios are no better than order - of - magnitude estimates . the largest uncertainty is in our choice of the broad emission line used to measure the gas velocity dispersion . if we used the linewidth instead of the h@xmath2 linewidth , our @xmath135values would be @xmath143 times smaller on average . however , there may be a component of the that is completely obscured . thus the h@xmath2 linewidth may be more representative of the broad - line region kinematics . -0 mm paper i highlighted an intriguing sub - sample of our targets that contained multiple velocity peaks in their spectra . we postulated that , since is a resonance line , absorption was the most likely explanation for the subcomponents , rather than physically distinct clumps of gas with differing kinematics . we specifically obtained nir spectra for two of these sources ( sdss j1339 + 0441 and sdss j1444@xmath770013 , the latter subsequently fell out of the main sample in paper i due to revised line width measurements ) . here we compare the and [ ] line profiles ( figure [ fig : onedclump ] ) . in figure [ fig : twodclump ] we show the two - dimensional , flat - fielded and sky - subtracted fire spectrum of sdss j1339 + 0441 , which clearly has a multi - peaked structure in both the 4959 and 5007 lines . we also see strong sky residuals directly to the red of [ ] @xmath5 . in sdss j1339 + 0441 the [ ] line has a complicated velocity structure with multiple kinematic components , although less distinct than that in . this profile could be due to outflow kinematics @xcite or to narrow line regions around distinct black holes ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) , as found in low - redshift objects . another intriguing possibility specific to high - redshift objects is that the quasar host galaxy is being formed from multiple components which are illuminated by the main quasar ( e.g. , * ? ? ? * ; * ? ? ? -0 mm we now directly compare the velocity structure in the and [ ] lines . since is a doublet , it is tricky to perform a direct comparison of the two lines @xcite . as throughout the paper , we assume that the [ ] provides a model for the narrow - line region . we then assume the same redshift for both the [ ] and lines , and construct a model profile as the superposition of two lines with the same line shape in velocity space as the [ ] line . we convert the fire spectra to vacuum wavelengths , place the two doublet components at their laboratory wavelengths , and impose a line ratio of 1:2 @xcite ( although we also tried 0.9:1 as above ; the results do not change ) . -0 mm much like all other targets studied in this paper , the line in both triple - peaked objects has a broad base that can not be explained by a simple superposition of the [ ] lines ( figure [ fig : onedclump ] ) . furthermore , some narrow absorption must be superposed on the emission profiles to fully explain their velocity structure . we indicate in dotted red lines the locations of these putative absorbers in each system . however , this additional absorption is only marginally broader than one pixel , making it quite suspect , and the doublet line ratios are not sensible . in summary , these multi - peaked objects have become more intriguing and more mysterious with our additional nir data . on the one hand , in one case we found velocity structure in the [ ] line , which , unlike in the , can not be due to blue - shifted absorption . on the other hand , we can not fully explain the observed kinematics with a simple superposition of the [ ] line profiles . we either must postulate absorption in addition to real velocity structure , or accept that the line shapes are unrelated . for instance , perhaps the arises from the broad - line region , or an intermediate - line region sitting between the classic narrow and broad - line regions @xcite .

we use the [ ] line shape as a model for the narrow line region emission , and find that h consistently requires a broad component with fwhms ranging from 1000 to 7500 km s . estimating the extinction using the balmer decrement and also the relationship in lower- quasars between rest equivalent width and luminosity in the [ ] line , we find typical values of mag , which naturally explains the attenuated lines relative to h .

we present near - infrared ( nir ) spectroscopy of 25 candidate type ii quasars selected from the sloan digital sky survey , using triplespec on the apache point observatory 3.5 m telescope , fire at the magellan / baade 6.5 m telescope , and gnirs on gemini . at redshifts of , our nir spectra probe the rest - frame optical region of these targets , which were initially selected to have strong lines of and ly , with fwhm km s from the sdss pipeline . we use the [ ] line shape as a model for the narrow line region emission , and find that h consistently requires a broad component with fwhms ranging from 1000 to 7500 km s . interestingly , the lines also require broad bases , but with considerably narrower widths of to km s . estimating the extinction using the balmer decrement and also the relationship in lower- quasars between rest equivalent width and luminosity in the [ ] line , we find typical values of mag , which naturally explains the attenuated lines relative to h . we propose that our targets are moderately obscured quasars . we also describe one unusual object with three distinct velocity peaks in its [ ] spectrum .

astro-ph0502591

c

our new observations hst / stis spectra of the elements ge , zr , os and pt , and keck i hires spectra of ir allow us to make @xmath4-capture abundance comparisons among the sample of metal - poor galactic halo stars . we have also incorporated these new detections with previously determined values for other elements to obtain detailed @xmath4-capture elemental abundance distributions for the well - studied and @xmath1-process rich stars 22 and 17 . in figure [ fig1 ] the entire abundance set is summarized by plotting relative abundance ratios [ el / fe ] versus [ fe / h ] metallicities . a rough progression of increasing abundance ratio with increasing atomic number is evident : large deficiencies of the light @xmath4-capture element ge in all program stars ; weak or no enhancements of the intermediate - mass element zr in all stars except the extreme @xmath1-process - rich star 22 ; and large overabundances of the heaviest elements os , ir , and pt in all stars except the @xmath1-process - poor star hd 122563 . a similar conclusion may be seen in figure [ fig2 ] , in which we show the observed spectra of three stars with contrasting @xmath1-process abundance levels : hd 122563 ( [ /h ] = 2.61 , [ eu / fe ] = 0.50 ; see tables [ tab1 ] and [ tab3 ] , and their literature references ) ; hd 115444 ( ( [ /h ] = 2.71 , [ eu / fe ] = + 0.58 ) ; and 22 ( ( [ /h ] = 3.09 , [ eu / fe ] = + 1.62 ) . while the relative absorption strengths of the lines of these three stars qualitatively track the [ eu / fe ] values ( top panel ) , no such correlation is seen in the line strengths ( bottom panel ) . in fact , 22 has the largest [ eu / fe ] value but clearly the weakest feature . in the following subsections we amplify and interpret these observational results . earlier work ( cowan 1996 ; sneden 1998 , 2003 ) used hst with stis and the goddard high resolution spectrograph to detect @xmath4-capture - peak ( _ e.g. _ , pt ) in a few individual metal - poor halo stars . our new abundance data for os , ir , and pt allow us to make the first moderate - sample systematic study of the heaviest stable @xmath4-capture elements , and to compare them with the @xmath4-capture element eu , which is synthesized almost entirely in the @xmath1-process . we make direct comparisons of os , ir , and pt abundances with eu in the three panels of figure [ fig3 ] . while the ratios [ el / fe ] shown in figure [ fig1 ] all indicate substantial overabundances of these three elements , the comparisons to eu in figure [ fig3 ] demonstrate the clearly correlated abundance behavior of eu , os , ir , and pt . the very small deviations from [ el / eu ] = 0.0 indicated by the solid horizontal lines of each panel ( @xmath18[os / eu]@xmath2 = + 0.15 , @xmath38 = 0.12 ; @xmath18[ir / eu]@xmath2 = + 0.13 , @xmath38 = 0.09 ; , and @xmath18[pt / eu]@xmath2 = + 0.13 , @xmath38 = 0.20 ) suggest that the solar - system @xmath1-process abundance distribution is mimicked in our sample ( and possibly all ) @xmath1-process - rich stars born in the early galactic halo . we regard the mean @xmath20 + 0.15 dex offset as observationally indistinguishable from [ el / eu ] = 0.0 ; see the uncertainty discussion of 3.3 . these very - heavy - element abundance comparisons strongly suggest a similar synthesis origin for eu , os , ir , and pt in the @xmath1-process sites that were the progenitors to the observed halo stars . we also want to note the la / eu ratios listed in table [ tab3 ] ( see also the discussion in 3.2 ) . in solar system material la ( dominantly an @xmath5-process element , see simmerer 2004 ) is more abundant than the @xmath1-process element eu . as is seen in the data compiled in table [ tab3 ] , however , @xmath18[la / eu]@xmath2 = 0.4 , clearly indicating that all of the stars in our sample are @xmath1-process - rich . ( see simmerer for further discussion of the synthesis of la in these stars . ) in figure [ fig4 ] we plot [ ge / h ] values with respect to the traditional metallicity indicators [ fe / h ] . it is easy to see that the ge abundances scale with metallicity but at a depressed ( with respect to solar ) level : @xmath18[ge / h]@xmath2 = [ fe / h ] [email protected] ( @xmath38 = 0.14 ) . further supporting this interpretation are abundance comparisons of ge with respect to the @xmath4-capture element eu that we illustrate in figure [ fig5 ] . if ge and eu were correlated , the abundances would fall along the straight ( diagonal ) line illustrated in the figure . obviously the abundances of ge seem to be uncorrelated with those of the @xmath1-process element eu . in fact , [ ge / fe ] for the @xmath1-process poor star hd 122563 is comparable to the values found for @xmath1-process ( _ i.e. _ , eu ) rich stars , including the upper limit for 22 . while @xmath4-capture processes are important for ge production in solar system material ( , simmerer 2004 ) , these abundance comparisons immediately suggest a different origin for this element early in the history of the galaxy . our abundance data appear to be more consistent with an explosive ( or charged - particle ) synthesis for ge . this might occur as a result of capture on iron - peak nuclei , perhaps during the so - called `` @xmath3-rich freeze - out '' in a supernova environment . however , calculations to date ( nakamura 1999 ; hoffman 2001 ; heger & woosley 2002 ; umeda & nomoto 2005 ; chieffi & limongi 2004 ) have difficulties explaining the observed trends in [ ge / fe ] . indeed , the trends in iron - peak nuclei revealed in cayrel 2004 ) strongly suggest the occurrence of a rather dramatic alpha - rich freeze associated with the earliest and most metal - deficient stellar populations , down to at least a metallicity level [ fe / h ] @xmath20 -4 ( truran 2005 ) . the strong temperature ( density ) dependence of this process indicates that fine tuning may be required to fit the observations . this may explain the fact that existing studies have not reproduced the trends . it is interesting to note , in this regard , that the trends seen in the two `` hyper''-iron - poor stars ( frebel 2004 ; christlieb 2004 ) do not appear to be consistent with the extrapolation of those reflected in the cayrel ( 2004 ) study below [ fe / h ] @xmath20 -4 . this contribution to ge synthesis appears to be the dominant production mechanism at low metallicities . of course , un - tracebly small contributions from @xmath5- and/or @xmath1-process production can not be ruled out ( but significant @xmath5-process production is not expected at [ fe / h ] @xmath41 2 ) . at higher metallicities and the onset of the @xmath5-process , it would be expected that the ge production would increase sharply and no longer be correlated with the iron production ( gallino , private communication ) . we make a similar abundance comparison of zr versus eu for our sample of stars in figure [ fig6 ] . as discussed in 3.3 , we note that the zr abundances obtained with hst / stis are well correlated with the ground - based abundances of this element . the abundance data , excluding 22 , show very little scatter and appear to be uncorrelated with eu this includes stars with [ eu / fe ] @xmath12 1.0 . the exception is 22 , for which [ zr / fe ] is substantially higher than in , for example , hd 122563 . the zr and eu abundances , however , do not follow a clearly linear correlation in the figure . this again would seem to indicate a different synthesis origin for these two elements , something recently discussed in more detail by travaglio ( 2004 ) . their more extensive abundance analysis suggests that known @xmath4-capture processes can explain some of the production of zr , but that the nucleosynthetic origin of this element is different than that for heavier @xmath4-capture elements such as ba and eu . furthermore , travaglio argue that an additional ( lighter element ) primary process is also responsible for some fraction of the synthesis of sr and y. we note finally that in addition to our abundance determination for 22 , the halo giant cs 31081001 ( the hill 2002 `` uranium '' star ) also has very enhanced [ eu / fe ] @xmath42 [ zr / fe ] . it may be that in these very @xmath1-process - enhanced stars , this kind of @xmath4-capture nucleosynthesis contribution overwhelms the light primary process proposed by travaglio perhaps as a result of fission recycling . we note that the relative constancy of [ zr / fe ] with both [ fe / h ] and [ eu / fe ] supports the conclusion of johnson and bolte ( 2002 ) - based on the constancy of the ratio [ y / zr ] with respect to [ zr / fe ] and [ ba / fe ] - that the source of zr in metal - poor stars must be the same for both the @xmath1-process - rich and @xmath1-process - poor stars . the heavy element abundance patterns presented here exhibit striking differences as a function of metallicity . the linear correlation ( with very small scatter ) of ge and fe abundances suggests that ge must have been produced rather commonly in stars even at early times in the galaxy over a wide range of metallicity . the zr abundances show much the same behavior as ge with ( perhaps ) somewhat more scatter , suggesting some variations in abundance with respect to fe . the pattern of the heavy @xmath4-capture elements eu , os , ir and pt is however very different than that of ge and zr . there is a very large star - to - star scatter in the abundance values with respect to iron , particularly at low metallicity a factor of @xmath2 100 at [ fe / h ] @xmath18 2.5 . ( we note that while there is only one star , hd 122563 , in our sample with a very low [ eu / fe ] ratio , observations ( see _ e.g. _ , burris et al . 2000 ) have indicated other such stars . at higher metallicities this scatter diminishes dramatically this general notion is of course not new , having been seen previously for eu ( see e.g. , gilroy 1988 ; burris 2000 ; sneden & cowan 2003 ) . this is the first clear indication that @xmath1-process peak elements also show the same scatter . these apparently conflicting trends can be explained by assuming that at early times ( and some low metallicities ) the galaxy was chemically inhomogeneous with some regions containing larger amounts of @xmath1-process ejecta than others . then at higher metallicities ( and later times ) these differences in the total abundance levels would be minimized this would be as a result of a higher number of events , which would produce an abundance average , and probably mixing throughout the galaxy . thus , from ge to zr to eu - os - ir - pt we might be witnessing decreasing event statistics , , a smaller number of ( supernova ) sites at very low metallicities , which create these elements ( cowan & thielemann 2004 and references therein ) . this might further indicate that not all supernovae , or at least those that make lighter @xmath4-capture elements like ge and zr , are responsible for synthesizing the heavier @xmath4-capture elements ( these @xmath1-process events would have been rare ) at very low metallicities early in the history of the galaxy . such abundance comparisons and scatter ( , [ eu / fe ] versus [ fe / h ] ) are also providing new clues into the earliest stars and the chemical evolution of the galaxy ( , wasserburg & qian 2000 ; fields , truran & cowan 2002 ) and the nature of and site for the @xmath1-process , particularly early in the galaxy ( argast 2004 ) . two of our sample stars are the very @xmath1-process rich stars 22 and 17 . employing our new observations and new , more reliable abundance determinations for nd ( den hartog 2003 ) and ho ( lawler , sneden , & cowan 2004 ) , we have updated and supplemented the ( ground - based and hst ) abundances previously obtained for 22 ( sneden 2003 ) and 17 ( cowan 2002 ) . we show in figure [ fig7 ] the detailed abundance distributions for both of these stars . the values for 17 have been arbitrarily displaced downward for display purposes . we also show for comparison the solar system @xmath1-process abundances ( solid lines ) , determined based upon the classical @xmath5-process model and utilizing the most recent @xmath1-/@xmath5-process deconvolution reported by simmerer ( 2004 ) . several points are worth noting in this figure . the agreement between the rare earth elements ( , ba and eu ) and the solar system @xmath1-process abundances is now seen to extend into , and includes , the @xmath1-process peak elements os pt in 22 and 17 . note that employing the new atomic experimental data of den hartog ( 2005 ) results in a shift downward of 0.1 dex with respect to the previously determined value in the abundance of pt . this element ( along with os and ir ) now falls on the same scaled solar system @xmath1-process curve that also matches the abundances of the rare - earth elements such as eu , strengthening the apparent synthesis connection between these heavier @xmath4-capture elements . our new , more reliable abundance determinations for the elements nd and ho are also consistent with the solar system @xmath1-process distribution . however , as shown in figure [ fig7 ] , the abundances of elements with z @xmath18 56 ( , below ba ) in general fall below the scaled solar @xmath1-process curve for 22 . there is very little data available for 17 in this region of 40 @xmath8 z @xmath8 50 , but its ag abundance , in particular , is much less than the scaled solar - system @xmath1-process curve . only upper limits on ge and ga were obtained with hst for 22 , but those abundances fall far below the solar curve , as does the ge abundance in 17 . this indicates that there may be two processes and may suggest two astrophysical sites for @xmath1-process nucleosynthesis with one for lighter and another for the heavier @xmath4-capture elements . this possibility was suggested earlier ( see wasserburg , busso , & gallino 1996 and wasserburg & qian 2000 ) with supernovae with different masses and frequencies responsible for the two ends of the @xmath4-capture abundance distribution . other models have suggested neutron - star binary mergers as one of the possible sites , particularly for the heavier @xmath4-capture elements where supernovae models have had difficulties in achieving the required high entropies ( freiburghaus 1999 ; rosswog , rosswog , & thielemann 1999 ; but see argast 2004 ) . in addition to a combination of supernovae and neutron - star mergers , it has been suggested that the light and heavy @xmath4-capture elements could also be synthesized in the same core - collapse supernova ( cameron 2001 ; see also recent reviews by cowan & sneden 2004 and cowan & thielemann 2004 for further discussion ) .

we present new abundance determinations of neutron - capture elements ge , zr , os , ir , and pt in a sample of 11 metal - poor ( 3.1 [ fe / h ] 1.6 ) galactic halo giant stars , based on hubble space telescope uv and keck i optical high - resolution spectroscopy . the stellar sample is dominated by-process - rich stars such as the well - studied cs 22892 - 052 and 17 , but also includes the-process - poor , bright giant hd 122563 . however , the large ( and correlated ) scatters of [ eu , os , ir , pt / fe ] suggests that the heaviest neutron - capture-process elements are not formed in _ all _ supernovae . in contrast , the ge abundances of all program stars track their fe abundances , very well . an explosive process on iron - peak nuclei ( _ e.g. _ , the-rich freeze - out in supernovae ) , rather than neutron capture , appears to have been the dominant synthesis mechanism for this element at low metallicities ge abundances seem completely uncorrelated with eu . the correlation ( with very small scatter ) of ge and fe abundances suggests that ge must have been produced rather commonly in stars even at early times in the galaxy over a wide range of metallicity . the zr abundances show much the same behavior as ge with ( perhaps ) somewhat more scatter , suggesting some variations in abundance with respect to fe . detailed abundance distributions , for 22 and 17 , combining the new elemental determinations for os - pt and recently published nd and ho measurements , show excellent agreement with the solar system-process curve from the elements ba to pb . the lighter-capture elements , including ge , in general fall below the same solar system-process curve that matches the heavier elements .

we present new abundance determinations of neutron - capture elements ge , zr , os , ir , and pt in a sample of 11 metal - poor ( 3.1 [ fe / h ] 1.6 ) galactic halo giant stars , based on hubble space telescope uv and keck i optical high - resolution spectroscopy . the stellar sample is dominated by-process - rich stars such as the well - studied cs 22892 - 052 and 17 , but also includes the-process - poor , bright giant hd 122563 . our results demonstrate that abundances of the -process peak elements os , ir and pt in these metal - poor halo stars are very well - correlated among themselves , and with the abundances of the canonical-process element eu ( determined in other studies ) , thus arguing for a common origin or site for-process nucleosynthesis of heavier ( z 56 ) elements . however , the large ( and correlated ) scatters of [ eu , os , ir , pt / fe ] suggests that the heaviest neutron - capture-process elements are not formed in _ all _ supernovae . in contrast , the ge abundances of all program stars track their fe abundances , very well . an explosive process on iron - peak nuclei ( _ e.g. _ , the-rich freeze - out in supernovae ) , rather than neutron capture , appears to have been the dominant synthesis mechanism for this element at low metallicities ge abundances seem completely uncorrelated with eu . the correlation ( with very small scatter ) of ge and fe abundances suggests that ge must have been produced rather commonly in stars even at early times in the galaxy over a wide range of metallicity . the zr abundances show much the same behavior as ge with ( perhaps ) somewhat more scatter , suggesting some variations in abundance with respect to fe . the zr abundances also do not vary cleanly with eu abundances , indicating a synthesis origin different than that of heavier neutron - capture elements . detailed abundance distributions , for 22 and 17 , combining the new elemental determinations for os - pt and recently published nd and ho measurements , show excellent agreement with the solar system-process curve from the elements ba to pb . the lighter-capture elements , including ge , in general fall below the same solar system-process curve that matches the heavier elements .

astro-ph0502591

c

we have made new detections of the elements ge , zr , os , and pt with hst ( stis ) , along with ir using keck i ( hires ) , in a sample of metal - poor galactic halo stars . these are the first large - sample abundance determinations of these elements in such stars . the abundances of the elements os , ir and pt , in the @xmath1-process peak appear to be correlated among themselves and with eu the extensively observed , rare - earth , @xmath1-process element indicating a similar nucleosynthesis origin and site . in contrast the ge abundance appears to scale with iron in the halo stars and is independent of the eu abundances in those stars . this suggests an explosive , rather than @xmath4-capture , synthesis for this element in stars at very low metallicities . perhaps this might be the result of some type of alpha - rich freeze out in sne early in the history of the galaxy at higher ( _ e.g. _ , near solar ) metallicities , and later times , it would be expected that @xmath1- and @xmath5-process production would dominate production . the zr abundances in the sample stars do not in general scale with metallicity , nor with the eu abundances , suggesting a different origin for this element than for the heavier @xmath4-capture elements . the one exception is for the very @xmath1-process rich ( high eu abundance ) star 22 , where there is a significant increase in the zr abundance . this element , however , has a complicated synthesis with perhaps several processes contributing ( see _ e.g. _ , travaglio et al . 2004 ) . the star - to - star abundance scatter among the elements is quite different , with the lighter element ge showing very little scatter over the range of metallicity studied . this suggests a common origin - most sne making this element - even at very low metallicities . zr like ge also shows little scatter with iron except for the case again of 22 . it has been shown previously that [ eu / fe ] exhibits a large star - to - star scatter as a function of metallicity ( see _ e.g. _ burris et al . our results are the first demonstration that the abundances of the @xmath1-process elements os - ir - pt to iron coincide with and exhibit a similar scatter to [ eu / fe ] , again suggesting a similar origin for these four elements . these new elemental abundance scatter data also appear to be consistent with the idea that not all supernovae will make eu ( and os - pt ) these appear to be rarer events than the synthesis of , for example , ge and zr and to point to a lack of chemical homogeneity early in the history of the galaxy . the new abundance determinations for os - ir - pt fall on the same solar system scaled @xmath1-process curves as the rare - earth elements in the @xmath1-process rich stars 22 and 17 . this agreement ( or consistency ) now extends from ba through the @xmath1-process peak for these stars , again indicating a similar synthesis origin for these elements . the observed abundances of the lighter @xmath4-capture elements ( ge and zr ) do not fall on the same solar curve that matches the heavier such elements , and may indicate two sites , or at least astrophysical conditions , for the synthesis of all of the @xmath4-capture elements . while the astrophysical site for the @xmath1-process has still not been precisely identified ( see _ e.g. _ , cowan & thielemann 2004 ) , the abundance determinations presented here are consistent with a supernova origin and suggest that not all supernovae may be responsible for synthesizing these @xmath4-capture elements . however , additional abundance determinations particularly over a range of mass number including both lighter and heavier @xmath4-capture elements in stars of very low metallicity will be needed to constrain models of @xmath1-process production , determine if there are multiple sites and to understand the history of element , and star , formation at very early times in the history of the galaxy . we thank roberto gallino , ken nomoto and an anonymous referee for useful discussions and comments that have helped us to improve the paper . this work has been supported in part by nsf grants ast 03 - 07279 ( j.j.c . ) , ast 03 - 07495 ( c.s . ) , ast 00 - 98508 , ast 00 - 98549 , ast 04 - 06784 ( t.c.b . ) and ast 02 - 05124 ( j.e.l . ) , and by stsci grants go-8111 and go-8342 . partial support was also provided by the nsf frontier center for nuclear astrophysics ( jina ) under grant phy 02 - 16783 ( j.w.t and t.c.b ) and the doe under grant de - fg 02 - 91er 40606 ( j.w.t . ) .

our results demonstrate that abundances of the -process peak elements os , ir and pt in these metal - poor halo stars are very well - correlated among themselves , and with the abundances of the canonical-process element eu ( determined in other studies ) , thus arguing for a common origin or site for-process nucleosynthesis of heavier ( z 56 ) elements . the zr abundances also do not vary cleanly with eu abundances , indicating a synthesis origin different than that of heavier neutron - capture elements .

we present new abundance determinations of neutron - capture elements ge , zr , os , ir , and pt in a sample of 11 metal - poor ( 3.1 [ fe / h ] 1.6 ) galactic halo giant stars , based on hubble space telescope uv and keck i optical high - resolution spectroscopy . the stellar sample is dominated by-process - rich stars such as the well - studied cs 22892 - 052 and 17 , but also includes the-process - poor , bright giant hd 122563 . our results demonstrate that abundances of the -process peak elements os , ir and pt in these metal - poor halo stars are very well - correlated among themselves , and with the abundances of the canonical-process element eu ( determined in other studies ) , thus arguing for a common origin or site for-process nucleosynthesis of heavier ( z 56 ) elements . however , the large ( and correlated ) scatters of [ eu , os , ir , pt / fe ] suggests that the heaviest neutron - capture-process elements are not formed in _ all _ supernovae . in contrast , the ge abundances of all program stars track their fe abundances , very well . an explosive process on iron - peak nuclei ( _ e.g. _ , the-rich freeze - out in supernovae ) , rather than neutron capture , appears to have been the dominant synthesis mechanism for this element at low metallicities ge abundances seem completely uncorrelated with eu . the correlation ( with very small scatter ) of ge and fe abundances suggests that ge must have been produced rather commonly in stars even at early times in the galaxy over a wide range of metallicity . the zr abundances show much the same behavior as ge with ( perhaps ) somewhat more scatter , suggesting some variations in abundance with respect to fe . the zr abundances also do not vary cleanly with eu abundances , indicating a synthesis origin different than that of heavier neutron - capture elements . detailed abundance distributions , for 22 and 17 , combining the new elemental determinations for os - pt and recently published nd and ho measurements , show excellent agreement with the solar system-process curve from the elements ba to pb . the lighter-capture elements , including ge , in general fall below the same solar system-process curve that matches the heavier elements .

astro-ph0303586

i

in this paper we have presented a survey of the oxygen gas - phase abundance using stis/_fuse _ data toward 19 stars with the purpose of probing the oxygen abundance far away in the disk . this work follows from previous surveys in the local ism and is possible due to the _ fuse _ detector s sensitivity , which permits measurements of the h@xmath0 content through long pathlengths . a summary of our results is as follow : 1 . we demonstrate that the oxygen abundance shows little variation in various environments and various locations in the disk . we find a mean ratio of = 408 ppm with an error in the mean of 13 ppm . this is 19% higher than the mean previously derived in the local ism by meyer et al . we argue that a recent local infall of metal - poor material is not excluded as an explanation for the difference . 2 . the oxygen abundance derived from our sample combined with previous surveys ( 37 sight lines ) is consistent with both the oxygen abundance of young g & f stars ( @xmath70 ppm ; sofia & meyer 2001 ) or the newly revised solar value ( @xmath71 ppm ; holweger 2001 , allende et al . 2001 ) once dust is taken into account . it is likely that the o i column density can be used as a surrogate tracer of the total neutral hydrogen column density , at least in a statistical sense , in diffuse ism abundance studies . although above we have emphasized the 19% difference between the mean found in this study and the lower value found for the lism by meyer et al . ( 1998 ) , the most striking result from both studies is the lack of large deviations from the mean . the standard deviation in the sample reported here is 15% . if the meyer et al . ( 1998 ) and the cartledge et al . ( 2001 ) data are included , the standard deviation increases to only 20% for a wide variety of diffuse ism conditions . the use of o i as a tracer of the total hydrogen column density could be of use in a variety of chemical abundance studies . as an example , consider the d / h studies , presently under way with the _ fuse _ satellite . in many cases , determining accurate h i column measurements requires using _ hst _ or _ euve _ data , which may not be available . in other cases , because the column densities of d i and h i differ by about five orders of magnitude , accurate measurements of both species may be precluded by special conditions associated with a particular sight line . preliminary studies of d / o ratios using _ fuse _ measurements of d i and o i are encouraging ( moos et al . 2002 , and references therein , hbrard et al . additional studies are also needed to determine the special cases in which there are large deviations in the and identify the special conditions under which such deviations might exist ( e.g hoopes et al . 2003 ) . we are grateful to paule sonnentrucker for sharing with us information on the lines of sight toward hd185418 and hd192639 . we also want to thank dr . ken sembach for fruitful advice . we are pleased to acknowledge comments by dr . stefan cartledge , dr . james lauroesch and dr . david meyer leading to several improvements on this paper . we thank also the referee for his thoughtful remarks . this work is based on data obtained for the guaranteed time team by the nasa - cnes - csa _ fuse _ mission operated by the johns hopkins university . financial support to u. s. participants has been provided in part by nasa contract nas5 - 32985 to johns hopkins university . support for french participation in this study has been provided by cnes . based on observations made with the nasa / esa hubble space telescope , obtained from the data archive at the space telescope science institute , which is operated by the association of universities for research in astronomy , inc . , under nasa contract nas5 - 26555 . these observations are associated with proposal 8241 . this work has been done using the profile fitting procedure owens.f developed by m. lemoine and the french _ fuse _ team . abgrall , h. , roueff , e. , launay , f. , roncin , j. y. , & subtil , j. l. 1993a , , 101 , 273 abgrall , h. , roueff , e. , launay , f. , roncin , j. y. , & subtil , j. l. 1993b , , 101 , 323 allende prieto , c. , lambert , d. l. , & asplund , m. 2001 , , 556 , l63 audouze , j. & tinsley , b. m. 1976 , , 14 , 43 biemont , e. & zeippen , c. j. 1992 , , 265 , 850 bohlin , r. c. 1975 , , 200 , 402 cardelli , j. a. , meyer , d. m. , jura , m. , & savage , b. d. 1996 , , 467 , 334 cartledge , s. i. b. , meyer , d. m. , lauroesch , j. t. , & sofia , u. j. 2001 , , 562 , 394 catanzaro , g. , leone , f. , andre , m. , & sonnentrucker , p. 2001 , american astronomical society meeting , 198 , comeron , f. & torra , j. 1994 , , 281 , 35 de boer , k. s. 1981 , , 244 , 848 deharveng , l. , pe~ na , m. , caplan , j. , & costero , r. 2000 , , 311 , 329 diplas , a. & savage , b. d. 1994 , , 93 , 211 dufour , r. j. , shields , g. a. , & talbot , r. j. 1982 , , 252 , 461 garc ' ia , b. & walborn , n. r. 2000 , , 112 , 1549 harris , a. w. & mas hesse , j. m. 1986 , , 308 , 240 h ' ebrard , g. et al . 2002a , , 140 , 103 hbrard , g. et al . 2002b , , 50 , 1169 henry , r. b. c. & worthey , g. 1999 , , 111 , 919 holweger , h. 2001 , aip conf . proc . 598 : joint soho / ace workshop `` solar and galactic composition '' , 23 hong , s. s. & greenberg , j. m. 1980 , , 88 , 194 hoopes , c. g. , sembach , k. r. , h ' ebrard , g. , & moos , h. w. 2003 , in press howk , j. c. , savage , b. d. , & fabian , d. 1999a , , 525 , 253 howk , j. c. & savage , b. d. 1999b , , 517 , 746 howk , j. c. & sembach , k. r. 2000a , , 119 , 2481 howk , j. c. , sembach , k. r. , & savage , b. d. 2000b , , 543 , 278 jenkins , e. b. & tripp , t. m. 2001 , , 137 , 297 johnson , c. e. 1972 , , 5 , 2688 kaltcheva , n. t. & hilditch , r. w. 2000 , , 312 , 753 keenan , f. p. , hibbert , a. , & dufton , p. l. 1985 , , 147 , 89 kimble , r. a. et al . 1998 , , 492 , l83 lemoine , m. et al . 2002 , , 140 , 67 lehner , n. , gry , c. , sembach , k. r. , h ' ebrard , g. , chayer , p. , moos , h. w. , howk , j. c. , & d ' esert , j .- m . 2002 , , 140 , 81 mason , j. j. 1990 , meas.sci.technol , 1 , 596 mckee , c. f. , hollenbach , d. j. , seab , g. c. , & tielens , a. g. g. m. 1987 , , 318 , 674 meyer , d. m. , cardelli , j. a. , & sofia , u. j. 1997 , , 490 , l103 meyer , d. m. , jura , m. , & cardelli , j. a. 1998 , , 493 , 222 meyer , d. m. 2001 , xviith iap colloquium , paris , edited by r. ferlet et al . , p. 135 moos , h. w. et al . 2000 , , 538 , l1 moos , h. w. et al . 2002 , , 140 , 3 morton , d. c. 1991 , , 77 , 119 nowak , g. , borst , w. l. , & fricke , j. 1978 , , 17 , 1921 primas , f. , rebull , l. m. , duncan , d. k. , hobbs , l. m. , truran , j. w. , & beers , t. c. 2001 , new astronomy review , 45 , 541 rachford , b. l. et al . 2002 , apj . , 5415 reed , b. c. 2000 , , 119 , 1855 richter , p. , sembach , k. r. , wakker , b. p. , savage , b. d. , tripp , t. m. , murphy , e. m. , kalberla , p. m. w. , & jenkins , e. b. 2001 , , 559 , 318 roy , j .- & kunth , d. 1995 , , 294 , 432 savage , b. d. , massa , d. , meade , m. , & wesselius , p. r. 1985 , , 59 , 397 savage , b. d. & sembach , k. r. 1991 , , 379 , 245 savage , b. d. , sembach , k. r. , & howk , j. c. 2001 , , 547 , 907 sahnow , d. j. et al . 2000 , , 538 , l7 sembach , k. r. & savage , b. d. 1992 , , 83 , 147 sembach , k. r. & savage , b. d. 1996 , , 457 , 211 shull , j. m. et al . 2000 , , 538 , l73 smartt , s. j. & rolleston , w. r. j. 1997 , , 481 , l47 snow , t. p. & witt , a. n. 1996 , , 468 , l65 sonnentrucker , p. , friedman , s. d. , welty , d. e. , york , d. g. , & snow , t. p. 2002 , , 576 , 241 tielens , a. g. g. m. , mckee , c. f. , seab , c. g. , & hollenbach , d. j. 1994 , , 431 , 321 tumlinson , j. et al . 2002 , , 566 , 857 vidal - madjar , a. & ferlet , r. 2002 , , 571 , l169 wells , w. c. & zipf , e. c. 1974 , , 9 , 568 welty , d. e. , hobbs , l. m. , lauroesch , j. t. , morton , d. c. , spitzer , l. , & york , d. g. 1999 , , 124 , 465 weselak , t. , fulara , j. , schmidt , m. r. , & kreowski , j. 2001 , , 377 , 677 wood , b. e. , linsky , j. l. , h ' ebrard , g. , vidal - madjar , a. , lemoine , m. , moos , h. w. , sembach , k. r. , & jenkins , e. b. 2002 , , 140 , 91 woodgate , b. e. et al . 1998 , , 110 , 1183 york , d. g. , spitzer , l. , jenkins , e. b. , bohlin , r. c. , hill , j. , savage , b. d. , & snow , t. p. 1983 , , 266 , l55 ccccccc name & d & z & l & b & @xmath72&spectral type + & [ pc ] & [ pc ] & & & + hd75309 & 2405 & 80 & 265.9 & -1.9 & 0.27&bi iip + hd88115 & 3654 & 350 & 285.3 & -5.5 & 0.16&b1 ib / ii + hd91824 & 2930 & 5 & 285.7 & + 0.1 & 0.27&o6 + hd93205 & 2630 & 32 & 287.6 & -0.7 & 0.45&o3 v + hd93222 & 2900 & 50 & 287.7 & -1.0 & 0.36&o7 iii + hd94493 & 3328 & 70 & 289.0 & -1.2 & 0.20&b0.5 iab / ib + hd99857 & 3070 & 267 & 294.8 & -5.0 & 0.33&b1 ib + hd104705 & 3900 & 20 & 297.4 & -0.3 & 0.26&b0 iii / iv + hd124314 & 1150 & 8 & 312.7 & -0.4 & 0.53&o7 + hd157857 & 2380 & 548 & 13.0 & + 13.3 & 0.49&o7 + hd177989 & 5010&1042 & 17.8 & -12.0 & 0.25&b2 ii + hd185418 & 950 & 33 & 53.6 & -2.0 & 0.43&b0.5 v + hd192639 & 1830 & 48 & 74.9 & + 1.5 & 0.64&o7 + hd202347 & 1300 & 45 & 88.2 & -2.0 & 0.17&b1 v + hd210809 & 3470 & 188 & 99.8 & -3.1 & 0.33&o9 ib + hd210839 & 840 & 38 & 103.8 & + 2.6 & 0.62&o6 iab + hd218915 & 3660 & 436 & 108.1 & -6.9 & 0.29&o9.5 iab + hd224151 & 1360 & 110 & 115.4 & -4.6 & 0.44&b0.5 iii + hd303308 & 2630 & 27 & 287.6 & -0.6 & 0.45&o3 v + lcccc hd75309 & o5c05b010 & 03 - 28 - 99 & 720 & @xmath18 + hd88115 & o54305010 & 04 - 19 - 99 & 1300 & @xmath14 + hd91824 & o5c095010 & 03 - 23 - 99 & 360 & @xmath18 + hd93205 & o4qx01010 & 04 - 20 - 99 & 1200 & @xmath17 + & o4qx01020 & 04 - 20 - 99 & 780 & @xmath17 + hd93222 & o4qx02010 & 12 - 28 - 98 & 1680 & @xmath17 + & o4qx02020 & 12 - 28 - 98 & 1140 & @xmath17 + hd94493 & o54306010 & 04 - 22 - 99 & 1466 & @xmath14 + hd99857 & o54301010 & 02 - 21 - 99 & 1307 & @xmath14 + hd104705 & o57r01010 & 12 - 24 - 98 & 2400 & @xmath17 + hd124314 & o54307010 & 04 - 11 - 99 & 1466 & @xmath14 + hd157857 & o5c04d010 & 06 - 03 - 99 & 720 & @xmath18 + hd177989 & o57r03020 & 05 - 28 - 99 & 2897 & @xmath17 + hd185418 & o5c01q010 & 11 - 12 - 98 & 720 & @xmath18 + hd192639 & o5c08t010 & 03 - 01 - 99 & 1440 & @xmath18 + hd202347 & o5g301010 & 10 - 09 - 99 & 830 & @xmath14 + hd210809 & o5c01v010 & 10 - 30 - 98 & 720 & @xmath18 + hd210839 & o54304010 & 04 - 21 - 99 & 1506 & @xmath14 + hd218915 & 057r05010 & 12 - 23 - 98 & 2018 & @xmath17 + hd224151 & o54308010 & 02 - 18 - 99 & 1496 & @xmath14 + hde303308 & o4qxo4010 & 03 - 19 - 98 & 2220 & @xmath17 + & o4qxo4020 & 03 - 19 - 98 & 1560 & @xmath17 + lcccccc hd75309 & p1022701 & 01 - 26 - 00 & lwrs & 4.7 & 8 & hist + hd88115 & p1012301 & 04 - 04 - 00 & lwrs & 4.5 & 8 & hist + hd91824 & a1180802 & 06 - 02 - 00 & lwrs & 4.6 & 6 & hist + hd93205 & p1023601 & 02 - 01 - 00 & lwrs & 4.7 & 7 & hist + hd93222 & p1023701 & 02 - 03 - 00 & lwrs & 3.9 & 4 & hist + hd94493 & p1024101 & 03 - 26 - 00 & lwrs & 4.4 & 7 & hist + hd99857 & p1024501 & 02 - 05 - 00 & lwrs & 4.3 & 7 & hist + hd104705 & p1025701 & 02 - 05 - 00 & lwrs & 4.5 & 6 & hist + hd124314 & p1026201 & 03 - 22 - 00 & lwrs & 4.4 & 6 & hist + hd157857 & p1027501 & 09 - 02 - 00 & lwrs & 4.0 & 8 & hist + hd177989 & p1017101 & 08 - 28 - 00 & lwrs & 10.3 & 20 & hist + hd185418 & p1162301 & 08 - 10 - 00 & lwrs & 4.4 & 3 & ttag + hd192639 & p1162401 & 06 - 12 - 00 & lwrs & 4.8 & 2 & ttag + hd202347 & p1028901 & 06 - 20 - 00 & lwrs & 0.1 & 1 & hist + hd210809 & p1223101 & 08 - 05 - 00 & lwrs & 5.5 & 10 & hist + hd210839 & p1163101 & 07 - 22 - 00 & lwrs & 6.1 & 10 & hist + hd218915 & p1018801 & 07 - 23 - 00 & lwrs & 5.4 & 10 & hist + hd224151 & p1224101 & 08 - 11 - 00 & lwrs & 6.0 & 12 & hist + hd303308 & p1222601 & 05 - 25 - 00 & lwrs & 6.1 & 9 & hist + & p1222602 & 05 - 27 - 00 & lwrs & 7.7 & 12 & hist + cccccc name & n(h i ) & n(h@xmath0 ) & n(h@xmath73 ) & f(h@xmath13 ) & t@xmath39 + & @xmath74 @xmath75 & @xmath74 @xmath75 & @xmath74 @xmath75 & & ( k ) + hd75309 & 11.2 ( 2.0 ) & 1.5 ( 0.2 ) & 14.2 ( 2.0 ) & 0.21 & 65 + hd88115 & 10.0 ( 2.0 ) & 0.2 ( 0.1 ) & 10.3 ( 2.0 ) & 0.03 & 145 + hd91824 & 11.7 ( 1.7 ) & 0.7 ( 0.2 ) & 13.1 ( 1.7 ) & 0.11 & 65 + hd93205 & 24.0 ( 2.3 ) & 0.6 ( 0.1 ) & 25.3 ( 2.3 ) & 0.05 & 75 + hd93222 & 25.1 ( 3.7 ) & 0.6 ( 0.1 ) & 26.4 ( 3.7 ) & 0.05 & 121 + hd94493 & 12.0 ( 1.2 ) & 1.4 ( 0.2 ) & 14.8 ( 1.3 ) & 0.19 & 53 + hd99857 & 17.4 ( 3.0 ) & 2.7 ( 0.4 ) & 22.8 ( 3.1 ) & 0.24 & 53 + hd104705 & 12.6 ( 2.5 ) & 1.2 ( 0.1 ) & 15.0 ( 2.6 ) & 0.16 & 137 + hd124314&25.7 ( 5.2 ) & 3.3 ( 0.4 ) & 32.3 ( 5.3 ) & 0.20 & 54 + hd157857 & 18.6 ( 2.3 ) & 4.5 ( 0.6 ) & 27.6 ( 2.6 ) & 0.33 & 49 + hd177989 & 9.1 ( 1.8 ) & 1.5 ( 0.2 ) & 12.1 ( 1.8 ) & 0.25 & 88 + hd185418 & 14.1 ( 2.5 ) & 5.1 ( 1.3 ) & 24.3 ( 3.6 ) & 0.42 & 101 + hd192639 & 19.5 ( 3.4 ) & 5.5 ( 1.5 ) & 30.5 ( 4.5 ) & 0.36 & 98 + hd202347 & 8.7 ( 1.8 ) & 0.9 ( 0.2 ) & 10.5 ( 1.8 ) & 0.17 & 116 + hd210809 & 17.8 ( 4.1 ) & 1.3 ( 0.3 ) & 20.4 ( 4.1 ) & 0.13 & 166 + hd210839 & 15.5 ( 1.9 ) & 6.5 ( 1.0 ) & 28.5 ( 2.8 ) & 0.46 & 92 + hd218915 & 14.8 ( 1.4 ) & 1.6 ( 0.2 ) & 18.0 ( 1.5 ) & 0.18 & 56 + hd224151 & 20.9 ( 3.6 ) & 4.1 ( 0.6 ) & 29.1 ( 3.8 ) & 0.28 & 42 + hd303308 & 25.7 ( 4.5 ) & 2.2 ( 0.4 ) & 30.1 ( 4.6 ) & 0.15 & 54 + ccccccc name & w@xmath76 ( 1355 ) & o i ( aod ) & o i ( fit ) & o i ( adopted ) & @xmath77 & @xmath78 + & m & @xmath79 @xmath75 & @xmath79 @xmath75 & @xmath79 @xmath75 & ppm & ppm + hd75309 & 9.0 ( 0.7 ) & 5.3 ( 0.4 ) & 5.2 ( 0.3 ) & 5.2 ( 0.4 ) & 366 ( 60 ) & 151 + hd88115 & 8.8 ( 1.1 ) & 5.1 ( 0.6 ) & 4.4 ( 0.6 ) & 4.7 ( 0.6 ) & 454 ( 117 ) & 62 + hd91824 & 11.0(1.4 ) & 6.2 ( 0.7 ) & 6.5 ( 0.4 ) & 6.4 ( 0.7 ) & 488 ( 84 ) & 29 + hd93205 & 19.5 ( 1.1 ) & 8.5 ( 0.6 ) & 9.4 ( 0.5 ) & 9.0 ( 0.6 ) & 356 ( 40 ) & 161 + hd93222 & 25.8 ( 1.2 ) & 13.0 ( 0.6 ) & 14.0 ( 0.4 ) & 13.5 ( 0.6 ) & 512 ( 75 ) & 5 + hd94493 & 12.2(0.7 ) & 6.6 ( 0.6 ) & 7.5 ( 0.6 ) & 7.0 ( 0.6 ) & 473 ( 57 ) & 44 + hd99857 & 14.1 ( 0.8 ) & 8.0 ( 0.5 ) & 7.6 ( 0.5 ) & 7.8 ( 0.5 ) & 342 ( 51 ) & 175 + hd104705 & 11.2 ( 0.7 ) & 6.4 ( 0.3 ) & 6.3 ( 0.3 ) & 6.4 ( 0.3 ) & 427 ( 74 ) & 90 + hd124314 & 25.3 ( 1.0 ) & 15.3 ( 0.6 ) & 15.4 ( 0.8 ) & 15.3 ( 0.8 ) & 474 ( 81 ) & 43 + hd157857 & 17.7 ( 0.8 ) & 11.6 ( 0.4 ) & 12.1 ( 0.4 ) & 11.9 ( 0.4 ) & 431 ( 43 ) & 86 + hd177989 & 10.5 ( 0.6 ) & 6.1 ( 0.3 ) & 6.0 ( 0.4 ) & 6.1 ( 0.4 ) & 504 ( 84 ) & 13 + hd185418 & 18.0 ( 0.7 ) & 11.4 ( 0.4 ) & 11.0 ( 0.3 ) & 11.2 ( 0.4 ) & 461 ( 70 ) & 56 + hd192639 & 22.1 ( 0.9 ) & 13.5 ( 0.3 ) & 13.5 ( 0.6 ) & 13.5 ( 0.6 ) & 443 ( 69 ) & 74 + hd202347 & 6.8 ( 1.1 ) & 3.8 ( 0.6 ) & 3.8 ( 0.4 ) & 3.8 ( 0.6 ) & 362 ( 85 ) & 155 + hd210809 & 12.5 ( 1.4 ) & 7.1 ( 0.7 ) & 5.6 ( 0.6 ) & 6.3 ( 0.7 ) & 309 ( 71 ) & 208 + hd210839 & 21.6 ( 0.9 ) & 13.4 ( 0.5 ) & 12.3 ( 0.6 ) & 13.0 ( 0.6 ) & 456 ( 49)&61 + hd218915 & 12.0 ( 0.8 ) & 6.8 ( 0.4 ) & 6.5 ( 0.2 ) & 6.6 ( 0.4 ) & 367 ( 37 ) & 150 + hd224151 & 18.5 ( 0.9 ) & 12.2 ( 0.8 ) & 10.7 ( 0.7 ) & 11.4 ( 0.8 ) & 392 ( 58 ) & 125 + hd303308 & 21.5 ( 1.1 ) & 12.7 ( 0.6 ) & 11.8 ( 0.4 ) & 12.2 ( 0.6 ) & 405 ( 65 ) & 112 + ccc stars & kr i & log o / kr + & 10@xmath80 @xmath75 & + hd75309 & 17.4 ( 2.8 ) & 5.47@xmath81 + hd99857 & 19.6 ( 4.1 ) & 5.62@xmath82 + hd104705 & 13.3 ( 4.9 ) & 5.50@xmath83 + hd185418 & 30.1 ( 2.5 ) & 5.57@xmath84 +

we present new measurements of the interstellar gas - phase oxygen abundance along the sight lines towards 19 early - type galactic stars at an average distance of 2.6 kpc . we derive total hydrogen column densities [ n(h i)+2n(h ) ] using _ hst_/stis observations of lyman- and _ fuse _ observations of molecular hydrogen . we see no evidence for decreasing gas - phase oxygen abundance with increasing molecular hydrogen fraction and the relative constancy of suggests that the component of dust containing the oxygen is not readily destroyed . we note that the smaller oxygen abundances derived for the interstellar gas within 500 pc or from nearby b star surveys are consistent with a local elemental deficit .

we present new measurements of the interstellar gas - phase oxygen abundance along the sight lines towards 19 early - type galactic stars at an average distance of 2.6 kpc . we derive o i column densities from _ hst_/stis observations of the weak 1355 intersystem transition . we derive total hydrogen column densities [ n(h i)+2n(h ) ] using _ hst_/stis observations of lyman- and _ fuse _ observations of molecular hydrogen . the molecular hydrogen content of these sight lines ranges from f(h ) = 2n(h)/[n(h i)+2n(h ) ] = 0.03 to 0.47 . the average of 6.3 mag with a standard deviation of 15% is consistent with previous surveys . the mean oxygen abundance along these sight lines , which probe a wide range of galactic environments in the distant ism , is 10 = ( 1 in the mean ) . we see no evidence for decreasing gas - phase oxygen abundance with increasing molecular hydrogen fraction and the relative constancy of suggests that the component of dust containing the oxygen is not readily destroyed . we estimate that , if 60% of the dust grains are resilient against destruction by shocks , the distant interstellar total oxygen abundance can be reconciliated with the solar value derived from the most recent measurements of 10 = 517 58 ( 1 ) . we note that the smaller oxygen abundances derived for the interstellar gas within 500 pc or from nearby b star surveys are consistent with a local elemental deficit .

1304.1253

i

reliable theoretical predictions for standard - model processes at the large hadron collider ( lhc ) are important to ongoing searches for new physics . they are also important to the increasingly precise studies of the newly discovered higgs - like boson @xcite , of the top quark , and of vector boson self - interactions . new - physics signals very typically lie beneath standard - model backgrounds in a broad range of search strategies . ferreting out the signals requires a good quantitative understanding of the backgrounds and their uncertainties . with the increasing jet multiplicities used in cutting - edge search strategies , this becomes more and more challenging . some of the uncertainty surrounding predictions of standard - model background rates can be alleviated through use of data - driven estimates , but this technique also requires theoretical input to predict the ratios of background processes in signal regions to those for control processes or in control regions . predictions for background rates at the lhc rely on perturbative qcd , which enters all aspects of short - distance collisions at a hadron collider . leading - order ( lo ) predictions in qcd suffer from a strong dependence on the unphysical renormalization and factorization scales . this dependence gets stronger with increasing jet multiplicity . next - to - leading ( nlo ) results generally reduce this dependence dramatically , typically to a 10 - 15% residual sensitivity . thus they offer the first quantitatively reliable order in perturbation theory . the production of a @xmath0 boson in association with jets has played a special role in collider physics . it was the dominant background to top - quark pair production at the tevatron . at the lhc it remains an important background for precision studies , including those of top quarks . it is important to many new physics searches involving missing energy , including those for supersymmetry . recent searches have made use of samples with high jet multiplicity , and proposed searches aim to push to higher multiplicities yet . precise quantitative control over the theoretical predictions leads to improved sensitivity to new phenomena . measurements of @xmath0 boson production in association with multiple jets have been made by the cdf @xcite and d0 @xcite collaborations at the tevatron , and by the atlas @xcite and cms @xcite collaborations at the lhc . such measurements also permit stringent tests of the predictions of the standard model . theoretical predictions for the production of vector bosons with a lower multiplicity of jets ( one or two jets ) have been available at nlo in qcd for many years @xcite . in recent years , the advent of new on - shell techniques @xcite for computing one - loop amplitudes at larger multiplicity has led to nlo results for three @xcite and four @xcite associated jets . other new results include those for the production of vector - boson pairs @xcite or top anti - top pairs @xcite in association with two jets . another recent approach @xcite has been demonstrated in the production of up to seven jets in @xmath1 collisions , and shows promise for lhc physics as well . there have also been important advances with more traditional methods , especially for the case of heavy quarks @xcite . in the present article , we take another step forward in multiplicity , presenting nlo results for inclusive -jet production at the lhc . these are the first nlo qcd results at a hadron collider with six or more electroweak bosons or jets in the final state . we incorporate the decay of the @xmath0 boson into leptons , so that there are seven final - state objects to track . in the present paper we use on - shell methods as implemented in numerical form in the blackhat software library @xcite . this library , together with the sherpa package @xcite , has previously been used to make nlo predictions for -jet production @xcite , for -jet production @xcite , and for four - jet production @xcite . it has also been used in investigations of high-@xmath2 @xmath0 polarization @xcite , and to compute -jet to -jet ratios for assessing theoretical uncertainties @xcite in the cms searches @xcite for supersymmetric particles . the atlas collaboration has also used results from blackhat computations with sherpa for standard - model studies of electroweak vector - boson production in association with three or more jets @xcite . other programs that use on - shell methods are described in refs . @xcite . sherpa is used to manage the numerous partonic subprocesses entering the calculation , to integrate over phase space , to construct physical distributions , and to output @xcite @xmath3-tuples . in contrast to earlier computations , we use the comix package @xcite to compute born and real - emission matrix elements , along with the catani seymour @xcite dipole subtraction terms . rather than repeating the entire computation for each scale and for each parton distribution function ( pdf ) set , we store intermediate results in @xmath3-tuple format , recording momenta for all partons in an event , along with the coefficients of various scale- or pdf - dependent functions in the event weight . the @xmath3-tuple storage makes it possible to evaluate cross sections and distributions for different scales and pdf error sets . we perform the basic calculation with loose cuts , also making it possible to choose different ( tighter ) cuts without recomputing the time - consuming matrix elements . in this paper , we compute the total cross sections at nlo for inclusive -jet and -jet production with @xmath4 and describe @xmath5 ratios and -jet/-jet ratios . such ratios can be sensitive probes of new physics . we also study two types of distributions : the differential cross section in the total hadronic transverse energy @xmath6 , and the complete set of differential cross sections in the jet transverse momenta . for four and five jets we make use of a leading - color approximation for the virtual contributions . this approximation has been shown to have subleading - color corrections of under 3% for processes with four or fewer associated jets @xcite . this paper is organized as follows . in we summarize the basic setup of the computation . in we present our results for cross sections , ratios and distributions . we give our summary and conclusions in .

we also present ratios of total cross sections , and use them to obtain an extrapolation formula to an even larger number of jets . we include the decay of the boson into leptons . this is the first such computation with six final - state vector bosons or jets .

we present next - to - leading order qcd predictions for the total cross section and for a comprehensive set of transverse - momentum distributions in -jet production at the large hadron collider . we neglect the small contributions from subleading - color virtual terms , top quarks and some terms containing four quark pairs . we also present ratios of total cross sections , and use them to obtain an extrapolation formula to an even larger number of jets . we include the decay of the boson into leptons . this is the first such computation with six final - state vector bosons or jets . we use blackhat together with sherpa to carry out the computation .

1605.07182

c

for very low - mass stars ( @xmath210.1 ) and high mass brown dwarfs , lithium is destroyed at a slow enough rate that it can be used to determine the ages of stellar associations up to at least @xmath12100myr . higher mass objects destroy their primordial lithium at a faster rate , so at older ages lithium disappears from the spectra of progressively lower mass objects . therefore , the brightest stars to display ( 6708 ) absorption in a given cluster define an empirical boundary that can be used as a relative age scale between different clusters , and evolutionary models can be used to infer absolute ages of individual clusters based on the location of this lithium depletion boundary ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? lspm j1314 + 1320ab allows us to test these model predictions with stars of known mass for the first time at ages comparable to that of nearby open clusters . @xcite measured a ( 6708 ) pseudo - equivalent width of @xmath110 from the integrated - light spectrum of lspm j1314 + 1320ab . they noted that this is consistent with measurements of comparable pleiades late - m dwarfs , e.g. , @xcite report three m7 dwarfs that all have @xmath1110.6 . given our mass and luminosity measurements for each component , bhac15 evolutionary models predict that the fraction of initial lithium remaining in the primary and secondary components is @xmath112 and @xmath113 , respectively . since the component masses are nearly equal , the predicted lithium depletion is correspondingly consistent within 1.2@xmath10 . the mean lithium fraction of the two components is predicted to be li / li@xmath114 . an equivalent width measurement can not be directly converted into lithium abundance . @xcite used a model dependent curve of growth approach to estimate the relationship between pseudo - equivalent widths and lithium abundance , defined by @xmath115 . if the lithium depletion level in the components of lspm j1314 + 1320ab is @xmath80.15 as predicted by evolutionary models , and the initial cosmic lithium abundance is @xmath116dex @xcite , then their present day abundance would be @xmath117dex . over a range of @xmath1183600k at @xmath90dex , @xcite found that @xmath119dex corresponds to ew = 0.410.51 , which is consistent with the lithium detection from @xcite . if this calibration from @xcite is accurate and applicable at the somewhat lower here ( @xmath83000k according to evolutionary models ; section [ sec : evol ] ) , then the detection of lithium absorption is fully consistent with the evolutionary model prediction that the components of lspm j1314 + 1320ab have depleted most of their initial lithium supply . as discussed in section [ sec : evol ] , models predict an age of @xmath5myr based on the mass and luminosity of the components of lspm j1314 + 1320ab . we can place this in the context of the relative age scale provided by nearby open clusters with well determined lithium depletion boundaries . for the pleiades , the boundary is at @xmath120mag @xcite using the vlbi parallax distance of @xcite . the components of lspm j1314 + 1320ab are 0.40.5mag brighter than this ( table [ tbl : props ] ) , implying that they must be significantly younger than the pleiades in order to still possess lithium . likewise for blanco 1 , @xcite found a lithium depletion boundary of @xmath121mag , @xmath80.7mag fainter than the components of lspm j1314 + 1320ab , so they must also be younger than blanco 1 . the younger cluster @xmath19 persei has a lithium depletion boundary of @xmath122mag @xcite , which is actually consistent within the errors for both components of lspm j1314 + 1320ab . therefore , we conclude that the age of lspm j1314 + 1320ab must be consistent with or younger than that of @xmath19 per . @xcite report an age of @xmath123myr for @xmath19 per , and recent age determinations for the pleiades and blanco 1 are , respectively , @xmath124myr @xcite and @xmath125myr @xcite . the age of lspm j1314 + 1320ab that we derived from models using mass and luminosity ( @xmath5myr ) is therefore consistent with the requirement from lithium for the system age to be equal to or younger than the age of @xmath19 per . finally , we compare the integrated - light color and resolved absolute magnitudes of lspm j1314 + 1320ab to the cluster sequences of @xmath19 per and the pleiades . using our observed spectrum , we compute integrated - light apparent magnitudes on the cousins system ( @xmath126mag ) and sdss system ( @xmath127mag ) . these give integrated - light colors of @xmath128mag and @xmath129mag . the @xmath19 per members from within 0.15mag of this color have apparent magnitudes of @xmath130mag , and assuming a distance of @xmath131pc gives an absolute magnitude of @xmath132mag . this is somewhat brighter than but consistent with the absolute magnitudes of the lspm j1314 + 1320ab components ( @xmath133mag and @xmath134mag ) . performing the same exercise for the dance sample of probable ( @xmath135 ) pleiades members from using our @xmath136 color gives @xmath137mag and thereby @xmath138mag assuming a pleiades distance of @xmath139pc @xcite . this is somewhat fainter than but consistent with the absolute magnitudes of the lspm j1314 + 1320ab components . the scatter in these cluster sequences on the color magnitude diagram ( @xmath80.3mag ) is relatively large compared to the change of @xmath80.6mag in absolute magnitude from @xmath19 per to the pleiades , which limits the discriminating power of this comparison . the components are somewhat fainter than expected for being as old or younger than @xmath19 per ( 0.40.5mag ) , but the effect is not significant . we therefore conclude that the location of the components of lspm j1314 + 1320ab on the color magnitude diagram is consistent with the more precise constraints on age from the lithium depletion boundary comparison , being comparable age to @xmath19 per and younger than the pleiades . combining our proper motion and parallax with the published radial velocity of the lspm j1314 + 1320ab system allows us to derive its space motion and thereby assess potential membership in known associations of young stars . @xcite reported spectrally resolved radial velocities of the two components of lspm j1314 + 1320ab from which they computed a system velocity of @xmath140 under the assumption that the two components are equal in mass . our astrometric mass ratio of @xmath141 now validates this assumption within their measurement uncertainty and thereby their reported system velocity . we derive a space motion of @xmath142 and plot this vector alongside various known young associations in figure [ fig : uvw ] . there are no clear visual associations , except perhaps with @xmath143 cha in @xmath144 , but lspm j1314 + 1320 is very far from @xmath143 cha in @xmath145 . using the banyan ii web tool ( v1.4 ; * ? ? ? * ; * ? ? ? * ) , we find a 99.98% membership probability in the young field population assuming the age of the system is @xmath1461gyr . therefore , according to banyan , lspm j1314 + 1320 is not likely a member of any of the seven young moving groups considered in their model ( ab dor , argus , @xmath147 pic , carina , columba , tuc - hor , and twa ) . we therefore conclude that the lspm j1314 + 1320ab does not belong to any known young association , despite being unambiguously pre main - sequence and located at only 17.25pc . it is possible that lspm j1314 + 1320ab belongs to an as yet unidentified @xmath146100 myr association in the solar neighborhood , and if so this should be testable with the upcoming release of _ gaia_astrometry . if no new associations are found that match lspm j1314 + 1320ab , then it will join the growing ranks of orphaned young objects in the solar neighborhood ( e.g. , liu et al.2016 , submitted ) . in principle , the rotation period ( @xmath148 ) and @xmath149 measurements from @xcite and @xcite provide an empirical constraint on the minimum stellar radius , @xmath150 . and @xmath151 here to indicate to the stellar rotation period and the inclination of the stellar rotation axis with respect to the plane of the sky , respectively , since we have already used @xmath47 and @xmath49 for the binary orbit s period and inclination . ] in practice , such a calculation is complicated by the fact that their measurements are made in integrated light , but for the sake of argument we will assume that they both correspond to one of the two components of lspm j1314 + 1320ab . @xcite reported a rotation period of @xmath152hr from multi - epoch vla observations and a @xmath153 from optical spectroscopy . in optical photometric monitoring , @xcite find two distinct rotation periods of @xmath154hr and @xmath155hr and conclude that the cause of the two very similar but distinct periods is not clear . assuming @xmath156 and 3.8hr gives @xmath157 . this is consistent with the model - derived average @xmath158 , which would correspond to @xmath159 . interestingly , this value is in good agreement with the measured orbital inclination @xmath160 , which would be consistent with a stellar spin axis aligned with the orbital plane . however , it is also possible that the true radius is smaller or larger than predicted by models , corresponding to @xmath161 or @xmath162 , respectively . the bhac15 evolutionary models that we have used to derive stellar parameters like radius and employ bt - settl model atmospheres as their boundary conditions for the surfaces of stars . therefore , we can test for consistency between the value of derived from bhac15 and an independent estimate based on the spectrum of lspm j1314 + 1320ab . direct fitting of our combined optical and nir spectrum with bt - settl models yields @xmath89k and @xmath90dex ( figure [ fig : btsettl ] ) , but these values necessarily lack in precision due to the somewhat coarse ( 100k , 0.5dex ) model grid steps . the spectral type scale of @xcite , which is based on bt - settl model atmospheres , gives @xmath163k for a spectral type of m7 , in good agreement with the direct fitting . therefore , we find the bt - settl models give @xmath8180k cooler values for than the average evolutionary model derived value of @xmath164k.k at m7 , in better agreement with the bhac15 . however , this could be due to the fact that the @xcite scale was designed to match evolutionary model isochrones of an earlier generation of the bhac15 models and thus does not provide a truly independent as needed for our consistency check . moreover , using a spectral type scale intended for higher gravity field dwarfs results in an even cooler , more inconsistent . ] in the absence of additional information , it is equally possible that this discrepancy could be caused by systematic errors in either or both of the evolutionary and atmosphere models . indeed , the bt - settl models do not fit the overall spectrum with high accuracy ( figure [ fig : btsettl ] ) , implying that any temperature based on these models will harbor some systematic error . observations of other pre main - sequence binaries at younger ages show discrepancies consistent with the 180k difference here . for example , @xcite found that for two unequal - mass m dwarf binary systems in the 10-myr - old upper scorpius subgroup , the evolutionary model - derived temperatures were 100300k higher than model atmospheres . if the discrepancy for lspm j1314 + 1320ab were due to evolutionary models , then at fixed luminosity this would imply model radii that are too small by 13% . interestingly , there are other cases of pre main - sequence m dwarfs for which such under - predicted model radii can explain observed discrepancies . @xcite found that for the 10myr old m5 eclipsing binary uscoctio 5 , multiple evolutionary models ( including bhac15 ) underpredicted the component radii by 10%15% while simultaneously overpredicting by @xmath8300k and thereby predicting consistent luminosities . in addition , evolutionary models of low - mass stars that include the effects of magnetic fields predict larger radii due a slowing down of their contraction ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? therefore , both observations and theory suggest that the dominant source of the discrepancy we observe for lspm j1314 + 1320ab is most likely due to evolutionary model radii , although we note that spectral type scale could still harbor systematic errors . lspm j1314 + 1320ab is much older than other pre main - sequence systems with dynamical mass measurements in nearby star - forming regions , implying that the same qualitative radius/ problem with evolutionary models extends to ages of at least @xmath1280myr . to our knowledge , this is the first mass measurement for an ultracool dwarf ( spectral type @xmath165m7 ) with spectral signatures of lower surface gravity than typical field objects . in section [ sec : spt ] , we classified the integrated - light spectrum as fld - g , but on the borderline of being int - g , and both @xcite and we note the presence of spectral features indicative of lower surface gravity relative to field dwarfs of similar spectral type . evolutionary models indicate that the surface gravities of the binary components are @xmath1664.87dex , which is 0.420.46dex lower than the predicted main sequence surface gravity of 5.29dex for a 0.09 star . if the model radii are too small by 13% as suggested above , then the model - derived gravities would be 0.1dex lower . overall , this implies that the borderline between fld - g and int - g designations for late - m dwarfs corresponds to a surface gravity @xmath80.5dex lower than field objects . while the lspm j1314 + 1320ab system itself does not belong to an association of independently determined age , numerous other ultracool dwarfs with gravity classifications do this allows us to check for consistency of spectral behavior between lspm j1314 + 1320ab and other young late - m dwarfs of known age . in the ab dor moving group ( 125myr ) , @xcite list 15 bona fide or strong candidate members . of these , all but one object have gravity classifications of int - g or vl - g , with only 2mass j03264225@xmath1672102057 ( l5 ) classified as fld - g ( but possessing some visual signs of youth , like lspm j1314 + 1320ab but at much later type ) . of 17 possible candidate members none are classified fld - g . moreover , @xcite report gravity classifications for eight ultracool dwarfs in the pleiades ; none were fld - g , and the two m7 dwarfs ppl 1 and teide 1 were int - g and vl - g , respectively . these comparisons imply that spectral signatures leading to int - gand vl - g classifications are typically still quite entrenched at ages significantly older than lspm j1314 + 1320ab . at even younger ages , e.g. , tuc - hor ( 50myr ) and @xmath147 pic ( 23myr ) , no known members are classified as fld - g either ( e.g. , see compilation of liu et al . 2016 , submitted ) . therefore , the fact that lspm j1314 + 1320ab has a gravity classification of fld - g is at odds with its model - derived age of @xmath5myr and that our lithium analysis that empirically places the system at a significantly younger age than the pleiades . we suggest a few possible explanations for the fact that lspm j1314 + 1320ab shows less distinct evidence for low gravity than older ultracool dwarfs . perhaps it is not that uncommon for late - m dwarfs to have more muted gravity signatures than l dwarfs , and the existing samples of ultracool dwarfs are too sparse to detect this yet . as noted by @xcite , the currently available infrared spectra of pleiades late - m dwarfs are of much lower s / n than was used to define the gravity classification system , so higher quality spectra may result in somewhat different , higher gravity , classifications . the classification of lspm j1314 + 1320ab is done in integrated light , so perhaps the gravity signatures are somehow obscured in combined light . @xcite tested such an idea , mostly using vl - gtemplates for components , and found that it is quite rare for two components to be classified as lower gravity in combined light . finally , maybe some third parameter is at work , e.g. , metallicity or rotation , causing the gravity classification to deviate slightly from other young ultracool dwarfs . our spectrum shows no signs of unusual metallicity , and it also seems unlikely that such a young object would different substantially in composition from other young associations in the solar neighborhood . pre main - sequence stellar models are commonly used to infer masses by placing objects on the h - r diagram ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) . to test the accuracy of masses derived from models in this way , we used the effective temperatures and luminosities of lspm j1314 + 1320ab to derive mass and age . given that the masses and luminosities of the components are nearly equal , we simply consider the average integrated - light properties for this test . as mentioned above , the spectral type scale for young objects from @xcite gives @xmath163k , and they estimate a systematic error of 100k for their scale , which we adopt here . the mean measured luminosity of lspm j1314 + 1320ab is @xmath168dex . figure [ fig : hrd ] shows these values of and compared to bhac15 evolutionary model tracks . for this test , we interpolated model tracks on a uniform grid of @xmath169 and @xmath170 in the same fashion as described above in section [ sec : evol ] . we found an h - r diagram derived average component mass of @xmath171 , age of @xmath172myr , and of @xmath173dex . this would imply that lspm j1314 + 1320ab is actually a pair of young brown dwarfs , due to the h - r diagram derived mass being @xmath9% ( 2.0@xmath10 ) smaller than our directly measured component masses of @xmath892 . the h - r diagram age is also much smaller ( @xmath174dex ) than the age derived from the same models using mass and . as expected , the mass and age posteriors derived from the h - r diagram are highly correlated , where lower masses correspond to younger ages . the discrepancy between the h - r diagram derived mass and our dynamically measured masses suggests either large errors in the spectral type relations , which are calibrated using bt - settl model atmospheres , systematic errors in the evolutionary models , or some combination of both things . as we discuss in section [ sec : teff ] , we suggest the dominant source of this discrepancy is that evolutionary model radii are underpredicted and is thereby overpredicted at a given luminosity . regardless of the cause of the discrepancy , this test case shows that masses derived from the h - r diagram can harbor large systematic errors . unfortunately , this method is often the only practical option when attempting to infer masses of stars and brown dwarfs in young associations where age can be uncertain due to potential underlying age spreads . therefore , the systematic error we have identified here will have significant implications for efforts to determine the low - mass end of the initial mass function , suggesting that young low - mass stars may be mistakenly identified as young brown dwarfs .

we suggest that the dominant source of this discrepancy is model radii being too small by% . in a test that mimics the typical application of evolutionary models by observers , we derive masses on the h - r diagram using the luminosity and bt - settl temperature . the estimated masses are% ( 2.0 ) lower than we measure dynamically and would imply that this is a system of brown dwarfs , highlighting the large systematic errors possible when inferring masses from the h - r diagram . based on features in the infrared , lspm j1314 + 1320ab appears higher gravity than typical pleiades and ab dor members , opposite the expectation given its younger age .

we present novel tests of pre main - sequence models based on individual dynamical masses for the m7 binary lspm j1314 + 1320ab . joint analysis of our keck adaptive optics astrometric monitoring along with very long baseline array radio data from a companion paper yield component masses of ( ) and ( ) and a parallactic distance ofpc . we also derive component luminosities that are consistent with the system being coeval at an age ofmyr , according to bhac15 evolutionary models . the presence of lithium is consistent with model predictions , marking the first time the theoretical lithium depletion boundary has been tested with ultracool dwarfs of known mass . however , we find that the average evolutionary model - derived effective temperature (k ) is 180k hotter than we derive from a spectral type relation based on bt - settl models (k ) . we suggest that the dominant source of this discrepancy is model radii being too small by% . in a test that mimics the typical application of evolutionary models by observers , we derive masses on the h - r diagram using the luminosity and bt - settl temperature . the estimated masses are% ( 2.0 ) lower than we measure dynamically and would imply that this is a system of brown dwarfs , highlighting the large systematic errors possible when inferring masses from the h - r diagram . this is first time masses have been measured for ultracool (m6 ) dwarfs displaying spectral signatures of low gravity . based on features in the infrared , lspm j1314 + 1320ab appears higher gravity than typical pleiades and ab dor members , opposite the expectation given its younger age . the components of lspm j1314 + 1320ab are now the nearest , lowest mass pre main - sequence stars with direct mass measurements .

1605.07182

c

we present here individual dynamical masses for the components of lspm j1314 + 1320ab , a pre main - sequence binary located at a distance of only @xmath4pc . these masses and parallactic distance are made possible by a joint analysis of our resolved relative astrometry of the primary and secondary from keck ao imaging and masking along with absolute astrometry from vlba radio interferometry of the secondary ( i.e. , the component that is fainter in the optical and infrared ) . we also derive component luminosities using integrated - light spectroscopy and photometry and our resolved infrared photometry . the measured component masses of @xmath0 ( @xmath1 ) and @xmath2 ( @xmath3 ) and luminosities of @xmath175dex and @xmath176dex , respectively , are consistent with being coeval at an age of @xmath5myr according to bhac15 evolutionary models . our precise masses and luminosities are largely thanks to a remarkably precise vlba parallax ( @xmath177 ; paper i ) . we determine that lspm j1314 + 1320ab is unambiguously in the pre main - sequence phase of its evolution based on having lithium absorption and luminosities @xmath84@xmath109 higher than predicted for the main sequence at our measured masses . this combination of precise distance , masses , luminosities , and the detection of lithium by @xcite enables novel tests of pre main - sequence models distinct from previous work on objects in star forming regions with more uncertain distances . 1 . evolutionary models self - consistently predict luminosity and lithium depletion in this binary thereby passing the first test of the theoretical lithium depletion boundary using ultracool dwarfs of known mass . models predict the components have lost @xmath178% and @xmath179% of their initial lithium , leaving enough remaining that they are still expected to display lithium absorption . on the empirically defined relative cluster age scale , the presence of lithium and the component absolute magnitudes of lspm j1314 + 1320ab imply an age consistent with or younger than @xmath19 persei and significantly younger than the pleiades and blanco 1 . we compare the effective temperature derived from evolutionary models given our mass and luminosity ( component average @xmath180k ) to that derived from spectral type relations based on bt - settl models ( @xmath7k ) . the 180k discrepancy in these values would correspond to a 13% radius error at fixed luminosity , which is similar to a problem observed for low mass stars in the much younger upper scorpius star - forming region . the eclipsing binary usco ctio 5 shows that model radii are likely the dominant source of the problem , while the radius and errors cancel so that model luminosities are accurate . we suggest that the same physical cause is responsible for the 180k discrepancy for lspm j1314 + 1320ab , showing that this radius problem can extend to much older pre main - sequence ages than previously recognized . 3 . in a test that mimics the typical application of evolutionary models by observers , we used the derived from spectral type and the average component luminosity to infer mass and age from evolutionary model tracks on the h - r diagram . the derived average component mass of @xmath171 is much lower ( @xmath9% , 2.0@xmath10 ) than we measure dynamically . this highlights the large systematic errors possible when inferring masses of low - mass stars and brown dwarfs at young ages and implies that some stars may be mistakenly identified as brown dwarfs when using the h - r diagram . the integrated - light spectrum of lspm j1314 + 1320ab displays signatures of low surface gravity , although we formally classify it as fld - g ( on the borderline of int - g ) on the infrared @xcite system . this is the first time dynamical masses have been measured for ultracool dwarfs with low - gravity spectral features . however , contrary to expectations , lspm j1314 + 1320ab shows less distinct spectral signs of low gravity than ultracool dwarfs at older ages ( pleiades , ab dor ) , which we are unable to explain . lspm j1314 + 1320ab provides a high - precision benchmark for pre main - sequence models at a distance @xmath1210@xmath109 closer than even the nearest star - forming regions . one major unresolved question is why only the secondary component is radio emitting , as discussed in detail in paper i. given that we have shown that the component masses are within 2% of each other for this coeval , co - compositional binary system , one likely explanation for the divergent behavior is a difference in the angular momentum evolution of the two components . projected rotational velocities ( @xmath181 ) of other very low - mass binaries have hinted at such differences in angular momentum evolution ( e.g. , * ? ? ? * ) , but such measurements have yet to be obtained for lspm j1314 + 1320ab . the components of lspm j1314 + 1320ab are now the nearest , lowest mass pre main - sequence stars with direct mass measurements . in the future , _ gaia _ parallaxes combined with ongoing ground - based orbit monitoring efforts will make many more such tests of models possible for more distant binaries in star forming regions . _ gaia _ data could even help identify previously unrecognized associations of young stars in the solar neighborhood to which lspm j1314 + 1320ab , currently not associated with any known group , may belong . this work was supported by a nasa keck pi data award , administered by the nasa exoplanet science institute . we thank will best for assistance with some keck / nirc2 observations . it is a pleasure to thank joel aycock , carolyn jordan , jason mcilroy , luca rizzi , terry stickel , hien tran , and the keck observatory staff for assistance with our keck ao observations . we also thank p. k. g. williams , michael ireland , katelyn allers , joshua schlieder , and mark reid for useful discussions . the anonymous referee provided a remarkably rapid and thoughtful review that helped refine our discussion . james r. a. davenport for distributing his idl implementation of the cubehelix color scheme @xcite . our research has employed the 2mass data products ; nasa s astrophysical data system ; data from the wide - field infrared survey explorer , which is a joint project of the university of california , los angeles , and the jet propulsion laboratory / california institute of technology , funded by nasa and curated by the nasa / ipac infrared science archive ; and the simbad database operated at cds , strasbourg , france . finally , the authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of maunakea has always had within the indigenous hawaiian community . we are most fortunate to have the opportunity to conduct observations from this mountain . aldering , g. , adam , g. , antilogus , p. , et al . 2002 , in society of photo - optical instrumentation engineers ( spie ) conference series , vol . 4836 , survey and other telescope technologies and discoveries , ed . j. a. tyson & s. wolff , 6172 allard , f. , homeier , d. , & freytag , b. 2011 , in astronomical society of the pacific conference series , vol . 448 , 16th cambridge workshop on cool stars , stellar systems , and the sun , ed . c. johns - krull , m. k. browning , & a. a. west , 91 cutri , r. m. , skrutskie , m. f. , van dyk , s. , et al . 2003 , 2mass all sky catalog of point sources . ( the irsa 2mass all - sky point source catalog , nasa / ipac infrared science archive . http://irsa.ipac.caltech.edu/applications/gator/ ) lantz , b. , aldering , g. , antilogus , p. , et al . 2004 , in society of photo - optical instrumentation engineers ( spie ) conference series , vol . 5249 , optical design and engineering , ed . l. mazuray , p. j. rogers , & r. wartmann , 146155 ) . contours are in logarithmic intervals from unity to 10% of the peak flux in each band . the image cutouts are all 05 across and interferogram cutouts are 1@xmath1822 across . in the interferograms , the binary can be seen by eye as an elongation or double peak in the center of the point - spread function . all cutouts have the same native pixel scale , and here we have rotated them so that north is up . [ fig : keck],title="fig:",height=144 ] 0.04 in ) . contours are in logarithmic intervals from unity to 10% of the peak flux in each band . the image cutouts are all 05 across and interferogram cutouts are 1@xmath1822 across . in the interferograms , the binary can be seen by eye as an elongation or double peak in the center of the point - spread function . all cutouts have the same native pixel scale , and here we have rotated them so that north is up . [ fig : keck],title="fig:",height=144 ] 0.04 in ) . contours are in logarithmic intervals from unity to 10% of the peak flux in each band . the image cutouts are all 05 across and interferogram cutouts are 1@xmath1822 across . in the interferograms , the binary can be seen by eye as an elongation or double peak in the center of the point - spread function . all cutouts have the same native pixel scale , and here we have rotated them so that north is up . [ fig : keck],title="fig:",height=144 ] 0.04 in ) . contours are in logarithmic intervals from unity to 10% of the peak flux in each band . the image cutouts are all 05 across and interferogram cutouts are 1@xmath1822 across . in the interferograms , the binary can be seen by eye as an elongation or double peak in the center of the point - spread function . all cutouts have the same native pixel scale , and here we have rotated them so that north is up . [ fig : keck],title="fig:",height=144 ] 0.04 in ) . contours are in logarithmic intervals from unity to 10% of the peak flux in each band . the image cutouts are all 05 across and interferogram cutouts are 1@xmath1822 across . in the interferograms , the binary can be seen by eye as an elongation or double peak in the center of the point - spread function . all cutouts have the same native pixel scale , and here we have rotated them so that north is up . [ fig : keck],title="fig:",height=144 ] 0.04 in ) . contours are in logarithmic intervals from unity to 10% of the peak flux in each band . the image cutouts are all 05 across and interferogram cutouts are 1@xmath1822 across . in the interferograms , the binary can be seen by eye as an elongation or double peak in the center of the point - spread function . all cutouts have the same native pixel scale , and here we have rotated them so that north is up . [ fig : keck],title="fig:",height=144 ] 0.04 in ) . contours are in logarithmic intervals from unity to 10% of the peak flux in each band . the image cutouts are all 05 across and interferogram cutouts are 1@xmath1822 across . in the interferograms , the binary can be seen by eye as an elongation or double peak in the center of the point - spread function . all cutouts have the same native pixel scale , and here we have rotated them so that north is up . [ fig : keck],title="fig:",height=144 ] 0.04 in band shown in comparison to m6 dwarfs with field gravity ( fld - g ) and very low gravity ( vl - g ) . although the alkali lines visually appear intermediate between field- and low - gravity m6 dwarfs , a full analysis of all gravity scores from @xcite yields a classification of fld - g . lspm j1314 + 1320ab is best described as having a spectrum on the borderline between fld - g and int - g classifications . _ bottom : _ the full spex spectrum with other indices ( feh , vo , and @xmath44-band continuum shape ) labeled . [ fig : ir - grav],height=336 ] band shown in comparison to m6 dwarfs with field gravity ( fld - g ) and very low gravity ( vl - g ) . although the alkali lines visually appear intermediate between field- and low - gravity m6 dwarfs , a full analysis of all gravity scores from @xcite yields a classification of fld - g . lspm j1314 + 1320ab is best described as having a spectrum on the borderline between fld - g and int - g classifications . _ bottom : _ the full spex spectrum with other indices ( feh , vo , and @xmath44-band continuum shape ) labeled . [ fig : ir - grav],height=336 ] 3% of both measured individual masses . isochrones from 1myr to 1gyr are indicated by dotted lines . the used for lspm j1314 + 1320ab here is calibrated off of the bt - settl model atmospheres , the same used for boundary conditions in the bhac15 evolutionary models . when we use this and luminosity to infer properties from bhac15 models , we find a mass @xmath9% ( 2.0@xmath10 ) lower than we measured dynamically . this discrepancy indicates either large errors in spectral type relations ( @xmath8180k ) or systematic errors in evolutionary models ( e.g. , 13% in radius ) . in either case , this result suggests that masses inferred for young stars from the h - r diagram will harbor large systematic errors , and young stars may be confused for young brown dwarfs . [ fig : hrd],width=480 ] lccccc 2013 jan 18 & @xmath23 & @xmath183 & @xmath184 & @xmath185 & masking + 2014 jan 22 & @xmath23 & @xmath186 & @xmath187 & @xmath188 & masking + 2014 may 9 & @xmath23 & @xmath189 & @xmath190 & @xmath191 & imaging + 2014 jun 15 & @xmath22 & @xmath192 & @xmath193 & @xmath194 & imaging + 2015 jan 14 & @xmath23 & @xmath195 & @xmath196 & @xmath197 & imaging + 2015 apr 10 & @xmath23 & @xmath198 & @xmath199 & @xmath200 & imaging + 2015 jun 28 & @xmath23 & @xmath201 & @xmath202 & @xmath203 & imaging + lcccc + + orbital period @xmath47 ( yr ) & @xmath204 & 9.58 & 9.45 , 9.74 & @xmath205 ( log - flat ) + semimajor axis @xmath56 ( mas ) & @xmath206 & 146.4 & 145.6 , 147.7 & @xmath207 ( log - flat ) + eccentricity @xmath48 & @xmath208 & 0.6014 & 0.5964 , 0.6060 & uniform , @xmath209 + inclination @xmath49 ( ) & @xmath210 & 49.19 & 48.77 , 49.82 & @xmath211 , @xmath212 + pa of the ascending node @xmath52 ( ) & @xmath213 & 60.2 & 59.6 , 61.3 & uniform + argument of periastron @xmath50 ( ) & @xmath214 & 205.8 & 204.1 , 207.1 & uniform + mean longitude at 2455197.5 jd @xmath51 ( ) & @xmath215 & 71.9 & 69.2 , 74.5 & uniform + @xmath216 ( mas ) & @xmath217 & 0.0 & @xmath1670.8 , 0.8 & uniform , @xmath218 + @xmath219 ( mas ) & @xmath220 & 0.0 & @xmath1671.7 , 1.7 & uniform , @xmath221 + proper motion in ra @xmath59 ( ) & @xmath222 & @xmath167248.01 & @xmath167248.19 , @xmath167247.78 & uniform + proper motion in dec @xmath60 ( ) & @xmath223 & @xmath167183.64 & @xmath167184.05 , @xmath167183.17 & uniform + parallax @xmath61 ( mas ) & @xmath224 & 57.988 & 57.856 , 58.082 & @xmath225 ( uniform volume density ) + semimajor axis of secondary @xmath55 ( mas ) & @xmath226 & 73.7 & 73.1 , 74.4 & uniform + ra vlbi error parameter @xmath227 [ deg@xmath228 & @xmath229 & @xmath16715.8 & @xmath16716.2 , @xmath16714.7 & uniform + dec vlbi error parameter @xmath230 [ deg@xmath228 & @xmath231 & @xmath16714.7 & @xmath16715.4 , @xmath16713.7 & uniform + + + + total mass @xmath232 ( ) & @xmath233 & 183.7 & 181.1 , 187.6 & + primary mass @xmath234 ( ) & @xmath0 & 92.5 & 91.5 , 94.0 & + secondary mass @xmath235 ( ) & @xmath2 & 91.2 & 89.6 , 93.8 & + mass ratio @xmath236 & @xmath237 & 0.986 & 0.975 , 1.002 & + distance @xmath238 ( pc ) & @xmath4 & 17.245 & 17.217 , 17.284 & + semimajor axis @xmath239 ( au ) & @xmath240 & 2.525 & 2.512 , 2.548 & + time of periastron @xmath241 ( jd ) & @xmath242 & 2456498.8 & 2456495.0 , 2456502.0 & + spectral type ( optical ) & & & m@xmath97 & + spectral type ( near - ir ) & & & m@xmath98 fld - g & + spectral type ( optical ) & & & m@xmath97 & + spectral type ( near - ir ) & & & m@xmath98 fld - g & + @xmath243 ( mag ) & @xmath244 & @xmath245 & @xmath246 & @xmath247 + @xmath248 ( mag ) & @xmath249 & @xmath250 & @xmath251 & @xmath252 + @xmath253 ( mag ) & @xmath254 & @xmath255 & @xmath256 & @xmath257 + @xmath258 ( mag ) & @xmath259 & @xmath260 & @xmath261 & @xmath247 + @xmath262 ( mag ) & @xmath263 & @xmath249 & @xmath264 & @xmath252 + @xmath265 ( mag ) & @xmath266 & @xmath267 & @xmath268 & @xmath257 + @xmath269 ( mag ) & @xmath270 & @xmath271 & @xmath246 & @xmath247 + @xmath272 ( mag ) & @xmath273 & @xmath274 & @xmath251 & @xmath252 + @xmath275 ( mag ) & @xmath276 & @xmath277 & @xmath256 & @xmath257 + @xmath278 ( mag ) & @xmath279 & @xmath280 & @xmath261 & @xmath247 + @xmath281 ( mag ) & @xmath282 & @xmath273 & @xmath264 & @xmath252 + @xmath283 ( mag ) & @xmath284 & @xmath285 & @xmath268 & @xmath257 + @xmath286 [ erg@xmath92s@xmath26 ] & @xmath288 & @xmath289 & @xmath290 & @xmath291 + @xmath292 ( mag ) & @xmath293 & @xmath294 & @xmath295 & @xmath296 + @xmath297 ( dex ) & @xmath298 & @xmath176 & @xmath299 & @xmath291 + + + age ( myr ) & @xmath300 & @xmath301 & @xmath5 & @xmath302 + ( k ) & @xmath303 & @xmath304 & @xmath164 & @xmath305 + radius ( ) & @xmath306 & @xmath307 & @xmath308 & @xmath309 + [ cms@xmath310 & @xmath311 & @xmath312 & @xmath313 & @xmath314 + li / li@xmath315 & @xmath112 & @xmath113 & @xmath316 & @xmath317 + lc feh@xmath318 & @xmath319 + feh@xmath320 & @xmath321 + vo@xmath318 & @xmath322 + @xmath320 & @xmath323 + @xmath44-cont & @xmath324 + & @xmath325 + ( 1.169 ) & @xmath326 + ( 1.177 ) & @xmath327 + ( 1.253 ) & @xmath328 + alkali score & 1000 + final score & 0n01 + gravity classification & fld - g +

we present novel tests of pre main - sequence models based on individual dynamical masses for the m7 binary lspm j1314 + 1320ab . we also derive component luminosities that are consistent with the system being coeval at an age ofmyr , according to bhac15 evolutionary models . the presence of lithium is consistent with model predictions , marking the first time the theoretical lithium depletion boundary has been tested with ultracool dwarfs of known mass . however , we find that the average evolutionary model - derived effective temperature (k ) is 180k hotter than we derive from a spectral type relation based on bt - settl models (k ) . this is first time masses have been measured for ultracool (m6 ) dwarfs displaying spectral signatures of low gravity . the components of lspm j1314 + 1320ab are now the nearest , lowest mass pre main - sequence stars with direct mass measurements .

we present novel tests of pre main - sequence models based on individual dynamical masses for the m7 binary lspm j1314 + 1320ab . joint analysis of our keck adaptive optics astrometric monitoring along with very long baseline array radio data from a companion paper yield component masses of ( ) and ( ) and a parallactic distance ofpc . we also derive component luminosities that are consistent with the system being coeval at an age ofmyr , according to bhac15 evolutionary models . the presence of lithium is consistent with model predictions , marking the first time the theoretical lithium depletion boundary has been tested with ultracool dwarfs of known mass . however , we find that the average evolutionary model - derived effective temperature (k ) is 180k hotter than we derive from a spectral type relation based on bt - settl models (k ) . we suggest that the dominant source of this discrepancy is model radii being too small by% . in a test that mimics the typical application of evolutionary models by observers , we derive masses on the h - r diagram using the luminosity and bt - settl temperature . the estimated masses are% ( 2.0 ) lower than we measure dynamically and would imply that this is a system of brown dwarfs , highlighting the large systematic errors possible when inferring masses from the h - r diagram . this is first time masses have been measured for ultracool (m6 ) dwarfs displaying spectral signatures of low gravity . based on features in the infrared , lspm j1314 + 1320ab appears higher gravity than typical pleiades and ab dor members , opposite the expectation given its younger age . the components of lspm j1314 + 1320ab are now the nearest , lowest mass pre main - sequence stars with direct mass measurements .

astro-ph9811344

c

we present optical identifications , finding charts , and spectra for seventeen new high redshift radio sources selected from the mg 5 ghz survey . we select targets of moderately steep spectral index to preferentially observe radio galaxies , and , indeed , fifteen of the seventeen sources discussed herein are radio galaxies . the remaining two sources are moderately steep spectrum , radio loud quasars which may be important in terms of unified models of extragalactic radio sources . the spectra were all taken at the w.m . keck telescopes and are representative of the fainter mg identifications attempted thus far , with typical @xmath16 magnitudes of @xmath17 we construct a composite mg radio galaxy spectrum and compare it with the higher radio power composite 3c / mrc radio galaxy spectrum of mcl98 . we find that the mg radio galaxies typically exhibit lower ionization state spectra than the 3c / mrc radio galaxies . the 2 emission line is extremely strong in the mg composite relative to the other rest frame uv emission lines , with 2 / 3 @xmath95 and 2 / @xmath96 . extensive modeling with single zone photoionization models are incapable of reproducing the high 2 / 3 ratio , indicating that shocks and/or more complicated photoionization scenarios are producing the emission line spectra of these distant radio galaxies . we have amassed a large sample of high redshift radio galaxies with published 4 and 3 line strengths . comparing the 4 / 3 ratio to the rest frame 1.4 ghz radio power , we find evidence for a correlation between ionization state and radio power . a likely interpretation is that the more powerful radio sources are in an active phase when the central engine is emitting more flux across the electromagnetic spectrum with the augmented uv flux leading to higher ionization state spectra . as we progress from the strongest radio sources to weaker sources , we find the emission line strengths attenuate , the ionization state of the emission line region diminishes , and the stellar populations apparently become more dominant . this last effect is seen both in the diminished alignment affect for weak radio sources and the discovery of several weak radio sources at moderate redshift whose spectra are devoid of the uv emission lines that dominate most radio galaxy spectra ( spinrad 1997 ) . an alternative explanation is to invoke multiple emission line regions whose relative contributions vary with radio power . the high redshift radio galaxies discussed herein are faint , and the radio power line strength correlation implies that long integrations with the new generation of large aperture telescopes is necessary to measure the emission line strengths and redshifts of these sources . redshift radio galaxies from a range of radio flux density will be the key to further investigations of the ionization state radio power relation . we are very grateful to b. burke and sam conner at mit for introducing us to the mg sample and for supplying much of the astrometry for our candidate subset . we thank aaron barth , wil van breugel , and pat mccarthy for valuable discussion and useful comments on the manuscript . we acknowledge chuck steidel for graciously obtaining the mdm images , marc davis and steve zepf for obtaining the spectra of mg 0422 + 0816 and mg 0511 + 0143 , marc davis and jeffrey newman for obtaining the spectra of mg 0148 + 1028 and mg 0308 + 0720 , and pat mccarthy for providing the composite 3c / mrc radio galaxy spectrum . we thank brian mcleod who has imaged a subset of the mg sample in the k band and t. bida , w. wack and j. aycock for invaluable help during our keck runs . the authors also gratefully acknowledge the referee , rogier windhorst , for useful comments . ds acknowledges support from igpp grant 99ap026 , ad acknowledges the support of nasa grant hf01089.0197a and partial support from a postdoctoral research fellowship at noao , hs acknowledges support from nsf grant ast 9528536 . ds 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dey , a. , stern , d. , dunlop , j. , peacock , j. , jimenez , r. , & windhorst , r. 1997 , , 484 , 581 spinrad , h. , dey , a. , stern , & bunker , a. 1998 , in proc . knaw colloq . , ed . h. rttgering , in press steidel , c.c . , giavalisco , m. , pettini , m. , dickinson , m. , & adelberger k.l . 1996 , , 462 , l17 stern , d. , spinrad , h. , dickinson , m. 1996 , , 111 , 102 stern , d. , spinrad , h. , dey , a. , dickinson , m. , & schlegel , d. 1997 , in the hst and the high redshift universe , ed . n. tanvir , a. aragon salamanca , & j. wall ( 37th herstmonceux ) , 413 . tadhunter , c.n . , morganti , r. , robinson , a. , dickson , r. , villar martin , m. , & fosbury , r.a.e . 1998 , , in press thompson , d. , djorgovski , s. , vigotti , m. , & grueff , g. 1994 , 108 , 828 van breugel , w. , stanford , s. , spinrad , h. , stern , d. , & graham , j.r . 1998 , , 502 , 614 van ojik , r. 1995 , phd thesis , rijksuniversiteit te leiden vigotti , m. , grueff , g. , perley , r. , clark , b. , & bridle , a. 1989 , , 98 , 419 lclcc mg 0018 + 0940 & i & 1995 sep 01 & keck & 600 & s & 1995 sep 01 & keck & 1500 mg 0046 + 1102 & i & 1995 sep 01 & keck & 1050 & s & 1995 sep 01 & keck & 3000 mg 0122 + 1923 & i & 1995 sep 01 & keck & 600 & s & 1997 sep 12 & keck & 2400 mg 0148 + 1028 & i & 1996 oct 15 & lick & 1260 & s & 1997 dec 23 & keck & 1800 mg 0308 + 0720 & i & 1996 oct 15 & lick & 600 & s & 1997 dec 23 & keck & 1800 mg 0311 + 1532 & i & 1994 jan 11 & mdm & 600 & s & 1995 aug 31 & keck & 3600 mg 0422 + 0816 & i & 1992 nov 25 & lick & 200 & s & 1995 oct 25 & keck & 1800 mg 0511 + 0143 & i & 1992 nov 25 & lick & 1500 & s & 1995 oct 25 & keck & 1800 mg 1142 + 1338 & i & 1994 apr 07 & mdm & 1800 & s & 1995 feb 03 & keck & 2400 mg 1251 + 1104 & i & 1995 mar 14 & keck & 1200 & s & 1995 mar 15 & keck & 4500 mg 1401 + 0921 & i & 1997 jul 01 & keck & 900 & s & 1997 jul 02 & keck & 2400 mg 2037@xmath230011 & i & 1994 sep 30 & mdm & 1500 & s & 1995 jul 23 & keck & 3600 & s & 1995 jul 24 & keck & 3600 & s & 1995 aug 31 & keck & 3600 mg 2041 + 1854 & s & 1996 jun 16 & keck & 300 mg 2058 + 0542 & i & 1992 aug 01 & lick & 1400 & i & 1993 aug 17 & lick & 1500 & s & 1994 jul 10 & keck & 3000 mg 2109 + 0326 & i & 1993 sep 14 & lick & 1100 & s & 1994 jul 09 & keck & 6550 mg 2121 + 1839 & i & 1992 aug 01 & lick & 1200 & s & 1994 jun 10 & keck & 4500 mg 2308 + 0336 & i & 1995 jul 25 & keck & 600 & s & 1995 jul 23 & keck & 2400 [ obsns ] lcll mg 0018 + 0940 & r & 00 18 55.23 & + 09 40 06.9 & o & 00 18 55.24 & + 09 40 06.8 & a & 00 18 53.93 & + 09 40 24.6 mg 0046 + 1102 & r & 00 46 41.40 & + 11 02 52.6 & o & 00 46 41.38 & + 11 02 52.5 & a & 00 46 43.88 & + 11 02 33.3 mg 0122 + 1923 & r & 01 22 29.95 & + 19 23 39.1 & o & 01 22 29.90 & + 19 23 38.6 & a & 01 22 31.27 & + 19 24 10.2 mg 0148 + 1028 & r & 01 48 28.85 & + 10 28 21.3 & o & 01 48 28.83 & + 10 28 22.0 & a & 01 48 26.23 & + 10 27 52.3 mg 0308 + 0720 & r & 03 08 41.90 & + 07 20 44.3 & o & 03 08 41.98 & + 07 20 44.9 & a & 03 08 40.35 & + 07 21 18.3 mg 0311 + 1532 & r & 03 11 56.89 & + 15 32 54.8 & o & 03 11 56.83 & + 15 32 55.4 & a & 03 11 54.52 & + 15 32 49.7 mg 0422 + 0816 & r & 04 22 24.00 & + 08 16 19.2 & o & 04 22 23.97 & + 08 16 18.7 & a & 04 22 23.95 & + 08 16 31.2 mg 0511 + 0143 & r & 05 11 04.77 & + 01 41 57.8 & o & 05 11 04.76 & + 01 42 00.3 & a & 05 11 02.89 & + 01 41 54.7 mg 1142 + 1338 & r & 11 42 23.6 & + 13 38 01.3 & o & 11 42 23.69 & + 13 38 01.4 & a & 11 42 22.80 & + 13 37 51.9 mg 1251 + 1104 & r & 12 51 00.02 & + 11 04 19.9 & o & 12 51 00.02 & + 11 04 21.6 & a & 12 50 58.67 & + 11 04 45.7 mg 1401 + 0921 & r & 14 01 18.3 & + 09 21 23.7 & o & 14 01 18.50 & + 09 21 21.2 & a & 14 01 16.66 & + 09 20 51.5 mg 2037@xmath230011 & r & 20 37 13.41 & @xmath2300 10 58.5 & o & 20 37 13.41 & @xmath2300 10 58.5 & a & 20 37 12.90 & @xmath2300 10 56.9 mg 2041 + 1854 & r & 20 41 24.2 & + 18 55 02.0 & o & 20 41 24.09 & + 18 55 00.9 & a & 20 41 25.20 & + 18 55 11.1 mg 2058 + 0542 & r & 20 58 28.95 & + 05 42 51.0 & o & 20 58 28.82 & + 05 42 50.7 & a & 20 58 30.13 & + 05 42 43.7 mg 2109 + 0326 & r & 21 09 21.71 & + 03 26 52.7 & o & 21 09 21.80 & + 03 26 51.6 & a & 21 09 20.93 & + 03 26 30.8 mg 2121 + 1839 & r & 21 21 25.48 & + 18 39 08.7 & o & 21 21 25.48 & + 18 39 09.0 & a & 21 21 25.35 & + 18 38 53.6 mg 2308 + 0336 & r & 23 08 25.0 & + 03 37 03.0 & o & 23 08 25.15 & + 03 37 03.6 & a & 23 08 26.07 & + 03 36 22.3 [ astrom ] lcccccccc mg 0018 + 0940 & 1.586 & 23.0 & 0.237 & 132 & 1.08 & 0.0 & & 34.70 mg 0046 + 1102 & 1.813 & 23.1 & 0.209 & 74 & 1.07 & 0.0 & & 34.61 mg 0122 + 1923 & 1.595 & 23.3 & 0.105 & 134 & 1.06 & 0.0 & & 34.70 mg 0148 + 1028 & 2.845 & 21.4 & 0.157 & 176 & 0.71 & 0.0 & & 35.39 mg 0308 + 0720 & 2.975 & 21.1 & 0.801 & 164 & 0.95 & 0.0 & & 35.56 mg 0311 + 1532 & 1.986 & 23.6 & 0.405 & 62 & 1.21 & 5.1 & 161 & 34.72 mg 0422 + 0816 & 0.294 & 20 : & 0.721 & 68 & 1.06 & 0.0 & & 32.53 mg 0511 + 0143 & 0.596 & 22 : & 0.393 & 98 & 1.06 & 3.9 & 171 & 33.4 2 mg 1019 + 0534 & 2.765 & 23.7 & 0.037 & 100 & 1.22 & 1.3 & 103 & 35.40 mg 1142 + 1338 & 1.279 & 23.9 & 0.093 & 149 & 1.03 & 0.0 & & 34.46 mg 1251 + 1104 & 2.322 & 24 : & 0.000 & 62 & 1.21 & 0.0 & & 34.94 mg 1401 + 0921 & 2.093 & 23.3 & 0.013 & 92 & 0.89 & 3.5 & 138 & 34.81 mg 2037@xmath230011 & 1.512 & 24.8 & 0.397 & 119 & 1.03 & 0.0 & & 34.57 mg 2041 + 1854 & 3.056 & 20 : & 0.441 & 217 & 0.76 & 0.0 & & 35 . 10 mg 2058 + 0542 & 1.381 & 23.7 & 0.425 & 283 & 1.19 : & 0.0 & & 34.90 mg 2109 + 0326 & 1.634 & 22.0 & 0.281 & 119 & 0.75 & 0.0 & & 34.55 mg 2121 + 1839 & 1.860 & 22.7 & 0.341 & 69 & 1.09 & 6.3 & 145 & 34.63 mg 2144 + 1928 & 3.592 & 23.5 : & 0.449 & 58 & 1.54 & 8.5 & 177 & 35.76 mg 2308 + 0336 & 2.457 & 23 : & 0.173 & 148 & 0.85 & 3.0 & 175 & 35.20 [ prop ] lcccc mg 0018 + 0940 & 132 & 156 & 159 @xmath97 22 & 190 @xmath97 14 mg 0046 + 1102 & 74 & 98 & 100 @xmath97 15 & mg 0122 + 1923 & 134 & 115 & 117 @xmath97 16 & mg 0148 + 1028 & 176 & 192 & 193 @xmath97 27 & mg 0308 + 0720 & 164 & 161 & 165 @xmath97 23 & 213 @xmath97 15 mg 0311 + 1532 & 62 & 53 & 54 @xmath97 9 & mg 0422 + 0816 & 68 & 113 & 116 @xmath97 17 & 102 @xmath97 12 mg 0511 + 0143 & 98 & 104 & 107 @xmath97 16 & 102 @xmath97 12 mg 1019 + 0534 & 115 & 115 & 132 @xmath97 19 & 100 @xmath97 12 mg 1142 + 1338 & 149 & 125 & 127 @xmath97 18 & mg 1251 + 1104 & 62 & & & mg 1401 + 0921 & 92 & 89 & 92 @xmath97 14 & 66 @xmath97 11 mg 2037@xmath230011&119 & 114 & & 179 @xmath97 14 mg 2041 + 1854 & 217 & 173 & 178 @xmath97 24 & mg 2058 + 0542 & 283 & 424 & 427 @xmath97 59 & 356 @xmath97 21 mg 2109 + 0326 & 119 & 81 & 86 @xmath97 14 & 75 @xmath97 11 mg 2121 + 1839 & 69 & 61 & 65 @xmath97 10 & mg 2144 + 1928 & 58 & 71 & 76 @xmath97 11 & mg 2308 + 0336 & 148 & 158 & 163 @xmath97 23 & 160 @xmath97 13 [ radflux ] lccccc mg 0018 + 0940 & 1549 & 4004.4 & 8.1 & 145 & 1.584 & 1640 & 4243.7 & 4.2 & 92 & 1.588 & ] 1909 & 4934.6 & 8.7 & 161 & 1.585 & ] 2326 & 6016.7 & 6.5 & 137 & 1.587 & [ ] 3426 & 6263.8 & 3.1 & 90 & 1.584 & 2798 & 7236.7 & 8.8 & 227 & 1.585 & 3203 & 8291.3 & 3.1 & 64 & 1.589 mg 0046 + 1102 & 1549 & 4357.2 & 6.5 & 99 & 1.812 & 1640 & 4615.8 & 5.5 & 83 & 1.814 & ] 1909 & 5366.5 & 7.9 & 124 & 1.811 & ] 2326 & 6542.6 & 7.4 & 120 & 1.813 & [ ] 3426 & 6813.2 & 1.9 & 29 & 1.811 & 2470 & 6947.5 & 2.0 & 30 & 1.813 & 2798 & 7875.6 & 11.8 & 176 & 1.814 mg 0122 + 1928 & 4 & 4033.9 & 3.2 & 54 & 1.604 & 2 & 4262.9 & 3.8 & 81 & 1.599 & 3 & 4958.0 & 3.2 & 60 & 1.597 & 2 & 6047.3 & 2.3 & 64 & 1.600 & 2 & 7273.3 & 3.1 & 77 & 1.598 mg 0148 + 1028 & ly@xmath19 & 4676.1 & 101.8 & 116 & 2.845 & 4 & 5965.3 & 116.3 & 128 & 2.851 & 2 & 6304.9 & 26.0 & 29 & 2.844 & 3 & 6400.8 & 8.4 & 9 & 2.849 & 3 & 7333.8 & 57.8 & 67 & 2.842 mg 0308 + 0720 & ly@xmath19 & 4858.3 & 181.8 & 71 & 2.995 & 5 & 4905.8 & 529.3 & 221 & 2.956 & & 5587.0 & 56.3 & 26 & 2.991 & 4 & 6162.9 & 155.9 & 75 & 2.979 & 3 & 7565.2 & 69.8 & 39 & 2.963 mg 0311 + 1532 & 4 & 4634.1 & 3.4 & 160 & 1.991 & 2 & 4903.5 & 2.0 & 103 & 1.990 & 3 & 5703.8 & 2.1 & 97 & 1.988 & 2 & & & & & 4 & 7239.3 & 1.1 & 50 & 1.988 mg 1019 + 0534 & & 4584.3 & 8.4 & 268 & 2.770 & 5 & 4664.8 & 2.3 & 66 & 2.762 & 4 & 5838.9 & 10.4 & 257 & 2.769 & 2 & 6174.9 & 8.5 & 170 & 2.765 & 3 & 7179.6 & 4.9 & 93 & 2.760 mg 1142 + 1338 & 3 & & @xmath983.0 & & & ] 2326 & & @xmath981.6 & & & [ ] 3426 & 7783.6 & 5.4 & 112 & 1.272 & [ ] 3727 & 8495.1 & 13.6 & 232 & 1.279 mg 1251 + 1104 & ly@xmath19 & 4040.5 & 23.1 & 148 & 2.324 & 1549 & 5148.4 & 3.0 & & 2.324 & 1640 & 5453.2 & 3.0 & & 2.325 & ] 1909 & 6326.7 & 5.2 & 298 & 2.314 & ] 2326 & & @xmath984.5 & & mg 1401 + 0921 & 1549 & 4793.9 & 4.1 & 165 & 2.095 & 1640 & 5072.8 & 5.0 & 171 & 2.093 & ] 1909 & 5901.1 & 3.4 & 83 & 2.091 & ] 2326 & 7187.2 & 1.7 & 89 & 2.090 & [ ] 2423 & 7521.8 & 2.9 & 121 & 2.104 mg 2037@xmath230011 & ] 1909 & 4782.2 & 4.4 & 123 & 1.505 & ] 2326 & 5843.5 & 1.0 & 39 & 1.512 & [ ] 2424 & 6093.9 & 1.0 & 43 & 1.514 mg 2041 + 1854 & ly@xmath19 & 4986 & 788.5 & 141 & 3.100 & ] 1400 & 5695:&130.8 & 28 & 3.05 : & 1549 & 6283 & 417.8 & 54 & 3.056 & ] 1909 & 7785 : & 68.3 & 25 & 3.08 : mg 2058 + 0542 & ] 1909 & 4541.3 & 7.1 & 152 & 1.379 & ] 2326 & 5537.6 & 4.1 & 120 & 1.381 & 2798 & 6667.0 & 6.6 & 206 & 1.381 & [ ] 2423 & 5769.6 & 1.3 & 45 & 1.380 & [ ] 3426 & & @xmath982.0 & & & [ ] 3727 & 8877.4 & 12.0 & 240 & 1.382 mg 2109 + 0326 & 1549 & & @xmath981.0 & & & 1640 & 4323.7 & 3.2 & 148 & 1.636 & ] 1909 & 5029.4 & 2.1 & 105 & 1.635 & ] 2326 & 6136.6 & 2.3 & 110 & 1.638 & [ ] 2423 & 6386.8 & 1.3 & 40 & 1.635 & 2798 & 7364.9 & 0.9 & 22 : & 1.631 mg 2121 + 1839 & 1549 & 4431.7 & 5.3 & 134 & 1.861 & 1640 & 4709.3 & 1.4 & 28 & 1.872 & ] 1909 & 5462.6 & 2.4 & 47 & 1.861 & ] 2326 & 6675 : & 1.5 : & 45 : & 1.869 & [ ] 3426 & & @xmath981.0 & & & 2798 & & @xmath980.5 & & mg 2144 + 1928 & ly@xmath19 & 5586.8 & 61.5 & 686 & 3.596 & 1549 & 7112.2 & 5.8 & 234 & 3.589 & 1640 & 7534.4 & 3.5 & 362 & 3.594 mg 2308 + 0336 & ly@xmath19 & 4209.2 & 29.3 & 284 & 2.462 & 1240 & 4288.2 & 5.7 & 118 & 2.458 & 1549 & 5357.9 & 6.3 & 91 & 2.458 & 1640 & 5669.1 & 3.9 & 78 & 2.457 & ] 1909 & 6589.1 & 4.5 & 110 & 2.452 & ] 2326 & 8036.9 & 8.3 & 412 & 2.455 [ lines ] lccccc ly@xmath19 & 1216 & 515 & 116 & 1130 & ly@xmath19 & 1216 & 606 & 106 & 1140 & & 1240 & 53 & 13 & 1420 & & 1549 & 131 & 31 & 1540 & doublet & 1640 & 94 & 23 & 1150 & ] & 1909 & 100 & 28 & 1260 & ] & 2326 & 83 & 30 & 1720 & & 2424 & 49 & 16 & 1780 & & 2470 & 17 & 5 & 930 & & 2800 & 116 & 42 & 2100 & doublet & 3727 & 188 & 142 & 1060 & [ composite ] lccccccc ly@xmath19 & 1216 & 515 & 1766 & 1000 & 239 & 485 & 253 & 1240 & 53 & 88 & & & 128 & & 1549 & 131 & 207 & 218 & 81 & 224 & 217 & 1640 & 94 & 181 & 37 & 4 & 26 & 62 ] & 1909 & 100 & 100 & 100 & 100 & 100 & 100 ] & 2326 & 83 & 52 & & 32 & 19 & 20 & 2424 & 49 & 51 & & @xmath988 & & 8 & 2470 & 17 & 23 & & 7 & & & 2800 & 116 & 43 & 33 & 113 & 113 & 117 & 3727 & 188 & 207 & 103 & & & 0.3 [ compare ]

we present optical identifications and redshifts for seventeen new high redshift radio sources . fifteen of these sources are radio galaxies ; the remaining two are high redshift , steep spectrum , radio loud quasars . two published mg radio galaxy spectra , we synthesize a composite mg radio galaxy spectrum and discuss the properties of these galaxies in comparison to other , more powerful , radio galaxies at similar redshifts . 5 5 4 2 3 ] 3 ] 2 ] 4 [ ] 2 2 [ ] 2b 3 [ ] , 5007 # 1 # 1 # 1to 0pt#1 3 2 3mpch^-3mpc^3 0 0 # 1 # 110^#1 # 1to 0pt#1 a&a # 1;#2;#3;#4 # 1 , # 2 , # 3 , # 4 # 1#2#3#4 , # 3 , # 4 # 1#2#3 # 1

we present optical identifications and redshifts for seventeen new high redshift radio sources . fifteen of these sources are radio galaxies ; the remaining two are high redshift , steep spectrum , radio loud quasars . these objects were discovered as part of an ongoing study of compact ( ) , moderately steep spectrum ( ) sources from the mit green bank ( mg ) radio catalog ( mjy ) . spectra for the optical counterparts were obtained at the w.m . keck telescopes and are among the optically faintest radio galaxies thus far identified . redshifts range between 0.3 and 3.6 , with thirteen of the seventeen at redshifts greater than 1.5 . combining these new radio galaxies with two published mg radio galaxy spectra , we synthesize a composite mg radio galaxy spectrum and discuss the properties of these galaxies in comparison to other , more powerful , radio galaxies at similar redshifts . we suggest a radio power ionization state relation . 5 5 4 2 3 ] 3 ] 2 ] 4 [ ] 2 2 [ ] 2b 3 [ ] , 5007 # 1 # 1 # 1to 0pt#1 3 2 3mpch^-3mpc^3 0 0 # 1 # 110^#1 # 1to 0pt#1 a&a # 1;#2;#3;#4 # 1 , # 2 , # 3 , # 4 # 1#2#3#4 , # 3 , # 4 # 1#2#3 # 1

astro-ph0403490

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one of the main advantages of the spitzer space telescope ( formerly known as the space infrared infrared telescope facility ; sirtf , gallagher et al . 2003 ) is the possibility to make extragalactic surveys of large regions of the sky in a relatively short time covering wavelengths from the near - ir to the far - ir with the instruments irac ( fazio et al . 1998 ) and mips ( rieke et al . 1996 ) . compared to _ s predecessors ( e.g. iras , soifer et al . 1983 , and iso , kessler et al . 1996 ) , there are improvements in the detectors ( number of pixels and better responsivity ) , the collecting area of the primary mirror ( 85 cm diameter ) , and sun - earth - moon avoidance constraints due _ spitzer _ s heliocentric orbit . _ spitzer _ can also make observations simultaneously in multiple bands ( with irac3.6 and 4.5 or 5.8 and 8 @xmath10 m ; with mips24 , 70 and 160 @xmath10 m ) . many extragalactic surveys are already scheduled with _ spitzer _ as legacy programs ( swire , lonsdale et al . 2003 ; goods , dickinson & giavalisco 2001 ) or as observations by the instrument teams ( wide , deep and ultra - deep _ spitzer _ surveys which will cover regions like the botes field of the noao deep wide - field survey , the groth strip , lockman hole , xmm - deep and so on , see e.g. dole et al . the first look survey utilizes 112 hours of director s discretionary time on _ spitzer _ and includes extragalactic , galactic , and ecliptic components . these data will be available to all observers when the spitzer science archive opens in may , 2004 . the purpose of the fls is to characterize the mid - infrared sky at previously unexplored depths and make these data rapidly available to the astronomical community . the extragalactic component is comprised of a 4 square degree survey with irac and mips near the north ecliptic pole centered at j1718 + 5930 . these observations were executed on 2003 december 1 - 11 . to fully exploit the _ spitzer _ fls data we have obtained ancillary surveys at optical ( this paper ) and radio wavelengths ( condon et al . 2003 ) . given the modest spatial resolution of the _ spitzer _ imagers ( the point spread function is large , especially in the mid and far - ir , e.g. 5.7 arcseconds full width at half maximum , fwhm , for the 24 @xmath10 m channel ) , the first problem to solve for the infrared sources detected by _ spitzer _ will be to associate these sources with an optical counterpart , when possible . this will then allow the higher spatial resolution of the available optical images to assist with the source classification ( e.g. as stars , galaxies or qso ) and enable targeting of subsets of the sources for spectroscopy with optical or near - ir spectrographs . since many of the infrared sources that will be detected by _ spitzer _ will be dust - obscured galaxies with faint optical counterparts , the complementary optical imaging must be relatively deep . although a deep multi - wavelength optical survey would be more useful , allowing one to compute photometric redshifts ( e.g. the noao deep wide - field survey , jannuzi and dey 1999 , brown et al . 2003 ) , the task of deeply covering a large region of sky in a homogeneous manner is quite time - consuming . therefore , for the initial optical ancillary survey we chose to observe the entire field in the r - band . noao provided 4 nights of director s discretionary time on the kpno 4 m in may , 2000 , for this survey . we have limited multi - wavelength optical observations to the central portion of the fls field . the sloan digital sky survey included the fls field in their early release observations ( stoughton et al . 2002 ) and mosaics and catalogs for the region are also now available ( hogg et al . 2004 ) . in this paper , we present the r - band optical observations made with the mosaic-1 camera on the mayall 4 m telescope of kitt peak national observatory . centered on the main fls field , a region 9.4 square degrees in area was imaged . in addition , 2.3 square degrees covering the elais - n1 field was also observed . although originally the elais - n1 field was planned to be part of the fls program , the fls observations of the elais - n1 field have now been revised to a very deep 10@xmath910 pointing to evaluate the confusion limits of the mips instrument . the remainder of the elais - n1 field will now be imaged as part of a larger survey in this region , a portion of the swire _ spitzer _ legacy survey ( lonsdale et al . , 2003 ) . in section 2 we review the overall observing strategy and describe the mosaic-1 observations . in section 3 we discuss the techniques used in the data reduction including the astrometric and photometric calibration of the images . we describe in section 4 the data products made publicly available . we detail in section 5 the criteria used to detect , classify , and photometrically measure objects in the images . section 5 also includes a description of the information available in our catalogs . in section 6 we examine the quality of the imaging data by comparing them with other available data sets . finally , a brief summary is given in section 7 .

the fls was designed to characterize the mid - infrared sky at depths 2 orders of magnitude deeper than previous surveys . the extragalactic component is the first cosmological survey done with _ spitzer_. source catalogs extracted from the r - band images are also presented . the r - band images were obtained using the mosaic-1 camera on the mayall 4 m telescope of the kitt peak national observatory . while both of these fields were in early plans for the fls , only a single deep pointing test observation was made at the elais - n1 location . the larger legacy program swire ( lonsdale et al . , 2003 ) will include this region among its surveyed areas . typical delivered image quality in the images is 1.1 arc - seconds full width at half maximum . these limits in depth are sufficient to identify a substantial fraction of the infrared sources which will be detected by _ spitzer_.

we present r - band images covering more than 11 square degrees of sky that were obtained in preparation for the spitzer space telescope first look survey ( fls ) . the fls was designed to characterize the mid - infrared sky at depths 2 orders of magnitude deeper than previous surveys . the extragalactic component is the first cosmological survey done with _ spitzer_. source catalogs extracted from the r - band images are also presented . the r - band images were obtained using the mosaic-1 camera on the mayall 4 m telescope of the kitt peak national observatory . two relatively large regions of the sky were observed to modest depth : the main fls extra galactic field ( j2000 ; l , b ) and elais - n1 field ( j2000 ; l , b ) . while both of these fields were in early plans for the fls , only a single deep pointing test observation was made at the elais - n1 location . the larger legacy program swire ( lonsdale et al . , 2003 ) will include this region among its surveyed areas . the data products of our kpno imaging ( images and object catalogs ) are made available to the community through the world wide web ( via the spitzer science center and noao science archives ) . the overall quality of the images is high . the measured positions of sources detected in the images have rms uncertainties in their absolute positions of order 0.35 arc - seconds with possible systematic offsets of order 0.1 arc - seconds , depending on the reference frame of comparison . the relative astrometric accuracy is much better than 0.1 of an arc - second . typical delivered image quality in the images is 1.1 arc - seconds full width at half maximum . images are relatively deep since they reach a median 5 depth limiting magnitude of r=25.5 ( vega ) , as measured within a 1.35 fwhm aperture for which the s / n ratio is maximal . catalogs have been extracted using sextractor using thresholds in area and flux for which the number of false detections is below 1% at r=25 . only sources with s / n greater than 3 have been retained in the final catalogs . comparing the galaxy number counts from our images with those of deeper r - band surveys , we estimate that our observations are 50% complete at r=24.5 . these limits in depth are sufficient to identify a substantial fraction of the infrared sources which will be detected by _ spitzer_.

astro-ph0403490

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a deep noao / kpno survey in the r band has been carried out to observe a field of more than 9 square degrees centered at 17:18:00 + 59:30:00 ( j2000 ) aimed to find optical counterparts for the _ first look survey _ which surveys 7 different infrared wavelengths with the instruments irac and mips using the spitzer space telescope . another 2.3 square degrees have been surveyed in the elais - n1 region which will be observed in the _ spitzer _ swire legacy survey . this paper describes the observation strategy , the data reduction and the products which are publicly available to the astronomical community on the world wide web at the spitzer science center and the noao science archives . the overall quality of the data is good and homogeneous : the average seeing is 1.1 and typically varies between 0.9 and 1.2 . the limiting magnitude of the images , measured inside an aperture of 1.35 @xmath9 fwhm for which the s / n ratio is maximal , is around r=25.5 at 5@xmath8 , deep enough to detect optical counterparts for a substantial fraction of the new _ spitzer _ selected objects . an average number of 35000 extragalactic sources are detected in each subfield ( 40 @xmath9 40 , approximatively ) with a 50% completeness limit of r=24.5 as deduced by comparing the counts with other deeper surveys . images and catalogs are available to the astronomical community along with the first release of the fls infrared data to exploit in the best way the wealth of extragalactic data expected from the new infrared observatory _ we are grateful to those that built , maintain , and operate the mosaic-1 camera and mayall 4 m telescope at kitt peak national observatory , a part of the national optical astronomy observatory , which is operated by the association of universities for research in astronomy , inc . ( aura ) , under a cooperative agreement with the national science foundation . we thank the former director of noao , dr . sidney wolff , for allocating the directors discretionary time used to gather the optical data we present in this paper , m. j. i. brown for assistance with software used to prepare the images for the data release , and t. lauer for useful discussions about photometric depth measurements . we wish to thank also the anonymous referee for his comments about the sloan photometric calibration . we acknowledge the support of the extragalactic first look survey team members at the spitzer science center ( b.t . soifer , p. appleton , l. armus , s. chapman , p. choi , f. fang , d. frayer , i. heinrichsen , g. helou , m. i m . , m. lacy , s. laine , f. marleau , d. shupe , g. squires j. surace , h. teplitz , g. wilson , l. yan , j. colbert , and i. drozdovsky ) jannuzi , b. t. , & dey , a. 1999 , in asp conf . ser . 191 , photometric redshifts and high redshift galaxies , ed . r. j. weymann , l. j. storrie - lombardi , m. sawicki , & r. j. brunner ( san francisco : asp ) , p. 111 soifer , b.t . , neugebauer , g. , beichman , c.a . , houck , j.r . , rowan - robinson , m. 1983 , in infrared technology ix ; proceedings of the ninth annual meeting , san diego , ca , august 23 - 25 , 1983 . bellingham , wa , spie - the international society for optical engineering , 297 cccc fls 2 & 17:17:48.12 & + 61:06:00.0 & 3 + fls 4 & 17:08:32.33 & + 60:32:00.0 & 3 + fls 5 & 17:13:13.17 & + 60:32:00.0 & 3 + fls 6 & 17:17:45.01 & + 60:32:00.0 & 3 + fls 7 & 17:22:25.85 & + 60:32:00.0 & 3 + fls 8 & 17:27:06.69 & + 60:32:00.0 & 3 + fls 9 & 17:05:44.94 & + 59:57:00.0 & 3 + fls 10 & 17:10:12.89 & + 59:57:00.0 & 5 + fls 11 & 17:14:48.65 & + 59:57:00.0 & 5 + fls 12 & 17:19:24.61 & + 59:57:00.0 & 4 + fls 13 & 17:23:59.47 & + 59:57:00.0 & 5 + fls 14 & 17:28:29.33 & + 59:57:00.0 & 3 + fls 15 & 17:05:56.30 & + 59:22:00.0 & 3 + fls 16 & 17:10:25.14 & + 59:22:00.0 & 3 + fls 17 & 17:14:54.99 & + 59:22:00.0 & 4 + fls 18 & 17:19:20.82 & + 59:22:00.0 & 4 + fls 19 & 17:23:53.67 & + 59:22:00.0 & 3 + fls 20 & 17:28:22.51 & + 59:22:00.0 & 3 + fls 22 & 17:10:18.66 & + 58:47:00.0 & 3 + fls 23 & 17:14:46.17 & + 58:47:00.0 & 3 + fls 24 & 17:19:12.00 & + 58:47:00.0 & 3 + fls 25 & 17:23:37.32 & + 58:47:00.0 & 3 + fls 26 & 17:28:02.83 & + 58:47:00.0 & 3 + fls 28 & 17:12:58.88 & + 58:12:30.0 & 3 + fls 29 & 17:17:19.44 & + 58:12:00.0 & 3 + fls 30 & 17:21:40.00 & + 58:12:30.0 & 3 + elais 2 & 16:10:01.00 & + 55:23:06.0 & 3 + elais 5 & 16:08:00.00 & + 54:48:06.0 & 5 + elais 6 & 16:12:06.76 & + 54:48:06.0 & 7 + elais 9 & 16:08:02.04 & + 54:13:06.2 & 9 + elais 10 & 16:12:06.76 & + 54:13:06.2 & 4 + ccccc 2000 may 4 & fls04 & 3 @xmath9 600 . & 1.4 - 1.5 & light cirri on sunset + & fls05 & 3 @xmath9 600 . & 1.4 - 1.45 & photometric + & fls06 & 3 @xmath9 600 . & 1.5 - 1.6 & + & fls07 & 3 @xmath9 600 . & 1.2 - 1.5 & + & fls08 & 3 @xmath9 600 . & 1.2 - 1.3 & + & fls10 & 5 @xmath9 600 . & 0.98 - 1.15 & + & fls11 & 3 @xmath9 600 . & 0.97 - 1.15 & + & fls12 & 4 @xmath9 600 . & 0.79 - 1.3 & + & fls17 & 4 @xmath9 600 . & 0.8 - 0.95 & + 2000 may 5 & elais05 & 3 @xmath9 600 . & 1.07 - 1.25 & photometric + & fls15 & 3 @xmath9 600 . & 1.05 - 1.12 & + & fls16 & 3 @xmath9 600 . & 0.98 - 1.04 & + & fls20 & 3 @xmath9 600 . & 0.88 - 0.9 & + & fls19 & 3 @xmath9 600 . & 0.85 - 0.87 & + & fls18 & 4 @xmath9 600 . & 0.77 - 0.88 & + & fls24 & 3 @xmath9 600 . & 0.87 - 0.95 & + & fls23 & 3 @xmath9 600 . & 0.9 - 0.94 & + & fls22 & 3 @xmath9 600 . & 0.81 - 0.86 & + & fls25 & 3 @xmath9 600 . & 0.85 - 0.9 & + & fls13 & 1 @xmath9 600 . & 0.9 & + 2000 may 6 & fls13 & 4 @xmath9 600 . & 1.05 - 1.25 & light cirri + & fls11 * & 2 @xmath9 600 . & 0.95 - 1.1 & non - photometric + & elais06 * & 4 @xmath9 600 . & 0.88 - 0.95 & + & elais09 * & 4 @xmath9 600 . & 0.86 - 0.95 & + & elais10 * & 4 @xmath9 600 . & 0.87 - 1.0 & + & fls14 * & 4 @xmath9 600 . & 0.84 - 0.85 & + 2000 may 7 & elais02 & 3 @xmath9 600 . & 1.09 - 1.2 & cirri + & fls26 & 3 @xmath9 600 . & 1.0 - 1.2 & non - photometric + & fls28 & 3 @xmath9 600 . & 0.96 - 1.0 & + & fls29 & 3 @xmath9 600 . & 0.95 - 1.2 & + & fls30 & 3 @xmath9 600 . & 1.02 - 1.07 & + & fls09 & 3 @xmath9 600 . & 1.05 - 1.1 & + & fls02 & 3 @xmath9 600 . & 0.94 - 0.98 & + & fls05 & 3 @xmath9 600 . & 0.9 - 1.06 & + & fls06 & 3 @xmath9 600 . & 0.9 - 0.91 & + & elais05 & 2 @xmath9 600 . & 0.9 - 1.1 & + & elais06 & 3 @xmath9 600 . & 0.9 - 1.1 & + & fls14 & 3 @xmath9 600 . & 0.86 - 0.92 & + 2000 may 9 & elais09 & 5 @xmath9 600 . & 1.0 - 1.2 & non - photometric + cccccccrcc fls_r_j171814.3 + 604643 & 17:18:14.303 & + 60:46:43.93 & 21.44 & 0.02 & 21.44 & 0.03 & 38.8 & 0.997 & 0.071 + fls_r_j171804.5 + 604644 & 17:18:04.511 & + 60:46:44.00 & 23.60 & 0.12 & 23.66 & 0.12 & 8.8 & 0.753 & 0.071 + fls_r_j171847.4 + 604644 & 17:18:47.496 & + 60:46:44.22 & 24.12 & 0.20 & 24.19 & 0.21 & 5.2 & 0.735 & 0.073 + fls_r_j171822.5 + 604644 & 17:18:22.536 & + 60:46:44.07 & 22.99 & 0.07 & 22.95 & 0.09 & 12.2 & 0.975 & 0.071 + fls_r_j171840.3 + 604644 & 17:18:40.368 & + 60:46:44.40 & 23.61 & 0.12 & 23.60 & 0.12 & 9.1 & 0.936 & 0.072 + fls_r_j171729.6 + 604645 & 17:17:29.639 & + 60:46:45.47 & 24.08 & 0.19 & 23.53 & 0.18 & 6.0 & 0.784 & 0.069 + fls_r_j171739.6 + 604645 & 17:17:39.672 & + 60:46:45.69 & 24.65 & 0.32 & 24.36 & 0.17 & 6.4 & 0.802 & 0.070 + fls_r_j171808.7 + 604643 & 17:18:08.784 & + 60:46:43.96 & 20.72 & 0.01 & 20.69 & 0.01 & 104.4 & 0.983 & 0.071 + fls_r_j171824.5 + 604644 & 17:18:24.575 & + 60:46:44.11 & 20.84 & 0.01 & 20.73 & 0.02 & 67.4 & 0.983 & 0.071 + fls_r_j171817.5 + 604644 & 17:18:17.567 & + 60:46:44.65 & 22.51 & 0.04 & 22.49 & 0.06 & 18.8 & 0.960 & 0.071 + fls_r_j171851.9 + 604644 & 17:18:51.984 & + 60:46:44.61 & 20.75 & 0.01 & 20.71 & 0.01 & 94.4 & 0.984 & 0.073 + fls_r_j171914.2 + 604645 & 17:19:14.232 & + 60:46:45.44 & 22.62 & 0.05 & 22.58 & 0.06 & 18.3 & 0.973 & 0.074 + fls_r_j171734.8 + 604646 & 17:17:34.872 & + 60:46:46.05 & 23.22 & 0.09 & 23.12 & 0.09 & 12.0 & 0.851 & 0.070 + fls_r_j171912.1 + 604647 & 17:19:12.191 & + 60:46:47.13 & 24.28 & 0.23 & 24.29 & 0.23 & 4.7 & 0.652 & 0.074 + fls_r_j171841.0 + 604646 & 17:18:41.087 & + 60:46:46.91 & 23.66 & 0.13 & 23.64 & 0.13 & 8.6 & 0.944 & 0.072 + fls_r_j171747.7 + 604648 & 17:17:47.712 & + 60:46:48.53 & 24.61 & 0.31 & 24.45 & 0.18 & 6.1 & 0.758 & 0.070 + fls_r_j171726.8 + 604646 & 17:17:26.807 & + 60:46:46.12 & 23.29 & 0.09 & 22.58 & 0.11 & 10.3 & 0.851 & 0.069 + fls_r_j171827.8 + 604646 & 17:18:27.887 & + 60:46:46.99 & 23.30 & 0.09 & 22.86 & 0.11 & 9.6 & 0.873 & 0.072 + fls_r_j171834.5 + 604648 & 17:18:34.560 & + 60:46:48.28 & 23.94 & 0.17 & 23.89 & 0.14 & 7.6 & 0.945 & 0.072 + fls_r_j171838.2 + 604644 & 17:18:38.279 & + 60:46:44.40 & 20.22 & 0.01 & 20.19 & 0.01 & 155.1 & 0.985 & 0.072 + fls_r_j171631.4 + 604647 & 17:16:31.487 & + 60:46:47.20 & 23.47 & 0.11 & 21.60 & 0.06 & 18.8 & 0.947 & 0.064 + fls_r_j171731.9 + 604646 & 17:17:31.967 & + 60:46:46.99 & 23.09 & 0.08 & 22.29 & 0.09 & 11.6 & 0.749 & 0.069 + fls_r_j171821.9 + 604645 & 17:18:21.911 & + 60:46:45.91 & 23.17 & 0.08 & 22.98 & 0.11 & 9.6 & 0.434 & 0.071 + fls_r_j171719.7 + 604649 & 17:17:19.704 & + 60:46:49.00 & 23.81 & 0.15 & 23.74 & 0.21 & 5.1 & 0.928 & 0.068 + fls_r_j171618.3 + 604647 & 17:16:18.312 & + 60:46:47.63 & 24.48 & 0.27 & 24.22 & 0.18 & 6.0 & 0.671 & 0.063 + fls_r_j171843.1 + 604648 & 17:18:43.128 & + 60:46:48.39 & 23.74 & 0.14 & 23.84 & 0.14 & 7.6 & 0.955 & 0.073 + fls_r_j171733.5 + 604649 & 17:17:33.503 & + 60:46:49.40 & 23.62 & 0.12 & 23.33 & 0.16 & 6.7 & 0.974 & 0.069 + fls_r_j171730.6 + 604649 & 17:17:30.671 & + 60:46:49.58 & 24.10 & 0.19 & 23.08 & 0.14 & 7.8 & 0.879 & 0.069 + fls_r_j171851.1 + 604645 & 17:18:51.143 & + 60:46:45.26 & 19.53 & 0.00 & 19.49 & 0.00 & 258.5 & 0.985 & 0.073 + fls_r_j171646.7 + 604647 & 17:16:46.751 & + 60:46:47.28 & 22.53 & 0.05 & 22.05 & 0.07 & 16.4 & 0.043 & 0.065 + cccccccc fls 2 & 17:17:45.70 & 61:05:44.12 & 1.08 & 25.59 & 26.15 & 34766 & 6787 + fls 4 & 17:08:27.23 & 60:32:10.74 & 1.57 & 24.72 & 25.28 & 18016 & 2962 + fls 5 & 17:13:10.74 & 60:31:44.01 & 1.06 & 25.64 & 26.20 & 36372 & 5012 + fls 6 & 17:17:42.13 & 60:31:42.33 & 1.02 & 25.78 & 26.34 & 36988 & 5050 + fls 7 & 17:22:21.27 & 60:32:06.70 & 1.54 & 24.86 & 25.42 & 19959 & 1316 + fls 8 & 17:27:02.18 & 60:32:07.10 & 1.36 & 25.09 & 25.64 & 22392 & 3049 + fls 9 & 17:05:42.63 & 59:56:46.44 & 1.14 & 25.58 & 26.13 & 34985 & 5254 + fls 10 & 17:10:07.30 & 59:57:07.22 & 1.24 & 25.63 & 26.19 & 32253 & 3309 + fls 11 - 17 & 17:14:47.10 & 59:39:33.96 & 1.04 & 25.86 & 26.41 & 72709 & 6865 + fls 12 & 17:19:19.96 & 59:57:03.33 & 1.00 & 25.86 & 26.42 & 35905 & 4352 + fls 13 & 17:23:54.12 & 59:57:09.50 & 1.16 & 25.41 & 25.96 & 30797 & 5496 + fls 14 & 17:28:26.67 & 59:56:39.57 & 0.98 & 25.51 & 26.06 & 34672 & 5114 + fls 15 & 17:05:50.01 & 59:22:06.83 & 1.22 & 25.14 & 25.69 & 25218 & 4450 + fls 16 & 17:10:19.12 & 59:22:07.62 & 1.17 & 25.25 & 25.80 & 26996 & 4313 + fls 18 & 17:19:14.84 & 59:22:07.54 & 0.92 & 25.91 & 26.46 & 37922 & 4228 + fls 19 & 17:23:48.01 & 59:22:07.27 & 0.97 & 25.64 & 26.19 & 34771 & 4409 + fls 20 & 17:28:17.04 & 59:22:08.13 & 1.00 & 25.59 & 26.15 & 35297 & 4278 + fls 22 & 17:10:12.41 & 58:47:07.63 & 0.94 & 25.77 & 26.33 & 35201 & 4259 + fls 23 & 17:14:40.18 & 58:47:07.50 & 1.06 & 25.67 & 26.22 & 34624 & 4313 + fls 24 & 17:19:06.04 & 58:47:04.74 & 1.03 & 25.71 & 26.26 & 31151 & 4277 + fls 25 & 17:23:30.85 & 58:47:10.81 & 0.99 & 25.76 & 26.31 & 33847 & 4682 + fls 26 & 17:28:00.70 & 58:46:43.81 & 1.22 & 25.21 & 25.77 & 22636 & 5538 + fls 28 & 17:12:56.31 & 58:12:15.54 & 1.12 & 25.37 & 25.93 & 30609 & 5830 + fls 29 & 17:17:16.96 & 58:11:44.23 & 1.12 & 25.52 & 26.07 & 34524 & 6264 + fls 30 & 17:21:37.91 & 58:12:14.09 & 1.20 & 25.49 & 26.05 & 38493&10099 + elais 2 & 16:09:58.00 & 55:22:51.47 & 1.20 & 25.18 & 25.74 & 26960 & 3802 + elais 5 & 16:07:55.71 & 54:47:58.39 & 1.22 & 25.59 & 26.14 & 33876 & 3240 + elais 6 & 16:11:59.38 & 54:47:43.34 & 1.11 & 25.49 & 26.05 & 34736 & 3406 + elais 6s & 16:11:58.89 & 54:23:29.02 & 0.98 & 25.82 & 26.38 & 41506 & 3160 + elais 9 & 16:07:59.66 & 54:12:59.29 & 1.11 & 25.77 & 26.32 & 38231 & 2926 + elais 9s & 16:07:58.67 & 53:48:27.43 & 1.01 & 25.78 & 26.33 & 38167 & 3538 + elais 10s & 16:11:56.45 & 53:48:23.99 & 1.02 & 25.72 & 26.28 & 36497 & 3496 + fls 2 & 2004&[email protected] & [email protected] & [email protected] & 23 & [email protected] & [email protected] + fls 4 & 1523 & [email protected] & [email protected]&[email protected] & & & + fls 5 & 1523&[email protected] & [email protected] & [email protected] & 84 & [email protected] & [email protected] + fls 6 & 1967&[email protected] & [email protected] & [email protected]&117 & [email protected] & [email protected] + fls 7 & 1501 & [email protected] & [email protected] & [email protected] & 76 & [email protected] & [email protected] + fls 8 & 1571 & [email protected] & [email protected] & [email protected] & & & + fls 9 & 1319&[email protected] & [email protected] & [email protected] & & & + fls 10 & 1509 & [email protected] & [email protected] & [email protected]&125 & [email protected] & [email protected] + fls 11 - 17&2810&[email protected] & [email protected] & [email protected]&269 & [email protected] & [email protected] + fls 12 & 2132&[email protected] & [email protected] & [email protected]&121 & [email protected] & [email protected] + fls 13 & 1412 & [email protected] & [email protected] & [email protected]&128 & [email protected] & [email protected] + fls 14 & 1590&[email protected] & [email protected] & [email protected] & 29 & [email protected] & [email protected] + fls 15 & 1335 & [email protected] & [email protected] & [email protected] & & & + fls 16 & 1379 & [email protected] & [email protected] & [email protected]&106 & [email protected] & [email protected] + fls 18 & 2294&[email protected] & [email protected] & [email protected]&144 & [email protected] & [email protected] + fls 19 & 1614&[email protected] & [email protected] & [email protected]&142 & [email protected] & [email protected] + fls 20 & 1608&[email protected] & [email protected] & [email protected] & 58 & [email protected] & [email protected] + fls 22 & 1461&[email protected] & [email protected]&[email protected] & 61 & [email protected]&[email protected] + fls 23 & 1510 & [email protected] & [email protected] & [email protected]&121 & [email protected] & [email protected] + fls 24 & 2044&[email protected] & [email protected] & [email protected]&143 & [email protected] & [email protected] + fls 25 & 2022&[email protected] & [email protected] & [email protected]&117 & [email protected] & [email protected] + fls 26 & 1539&[email protected] & [email protected] & [email protected] & 34 & [email protected] & [email protected] + fls 28 & 1273&[email protected]&[email protected] & [email protected] & & & + fls 29 & 1769&[email protected]&[email protected] & [email protected] & 57 & [email protected] & [email protected] + fls 30 & 3198&[email protected] & [email protected] & [email protected] & 23 & [email protected] & [email protected] + average & & [email protected] & [email protected] & [email protected] & & [email protected] & [email protected] +

we present r - band images covering more than 11 square degrees of sky that were obtained in preparation for the spitzer space telescope first look survey ( fls ) . the data products of our kpno imaging ( images and object catalogs ) are made available to the community through the world wide web ( via the spitzer science center and noao science archives ) . the overall quality of the images is high . images are relatively deep since they reach a median 5 depth limiting magnitude of r=25.5 ( vega ) , as measured within a 1.35 fwhm aperture for which the s / n ratio is maximal . , we estimate that our observations are 50% complete at r=24.5 .

we present r - band images covering more than 11 square degrees of sky that were obtained in preparation for the spitzer space telescope first look survey ( fls ) . the fls was designed to characterize the mid - infrared sky at depths 2 orders of magnitude deeper than previous surveys . the extragalactic component is the first cosmological survey done with _ spitzer_. source catalogs extracted from the r - band images are also presented . the r - band images were obtained using the mosaic-1 camera on the mayall 4 m telescope of the kitt peak national observatory . two relatively large regions of the sky were observed to modest depth : the main fls extra galactic field ( j2000 ; l , b ) and elais - n1 field ( j2000 ; l , b ) . while both of these fields were in early plans for the fls , only a single deep pointing test observation was made at the elais - n1 location . the larger legacy program swire ( lonsdale et al . , 2003 ) will include this region among its surveyed areas . the data products of our kpno imaging ( images and object catalogs ) are made available to the community through the world wide web ( via the spitzer science center and noao science archives ) . the overall quality of the images is high . the measured positions of sources detected in the images have rms uncertainties in their absolute positions of order 0.35 arc - seconds with possible systematic offsets of order 0.1 arc - seconds , depending on the reference frame of comparison . the relative astrometric accuracy is much better than 0.1 of an arc - second . typical delivered image quality in the images is 1.1 arc - seconds full width at half maximum . images are relatively deep since they reach a median 5 depth limiting magnitude of r=25.5 ( vega ) , as measured within a 1.35 fwhm aperture for which the s / n ratio is maximal . catalogs have been extracted using sextractor using thresholds in area and flux for which the number of false detections is below 1% at r=25 . only sources with s / n greater than 3 have been retained in the final catalogs . comparing the galaxy number counts from our images with those of deeper r - band surveys , we estimate that our observations are 50% complete at r=24.5 . these limits in depth are sufficient to identify a substantial fraction of the infrared sources which will be detected by _ spitzer_.

astro-ph0701075

i

weak absorbers ( those with @xmath20 rest frame equivalent width @xmath21 ) represent a population or populations distinct from the stronger absorbers which are directly associated with luminous galaxies ( l @xmath22l@xmath23 ) . this conclusion is based partly upon a rapid rise in the equivalent width distribution of @xmath24 at values below @xmath25 @xcite . it is also partly based upon the excess of single - cloud weak absorbers , over that expected from the poisson distribution of number of clouds per system found for strong absorbers @xcite . the single - cloud weak absorbers comprise @xmath26 of the weak absorber population at @xmath16 , with the remainder having multiple clouds in absorption . the single - cloud weak absorbers tend to have metallicities @xmath27 times the solar value , and in some cases greater than the solar value @xcite . though data are limited , it is clear that most single - cloud weak absorbers are not produced by lines of sight very close to luminous galaxies , though most are found at impact parameters of @xmath28-@xmath29 kpc @xcite . thus their high metallicities are surprising . furthermore , the large ratio of to column density in some weak absorbers indicates that `` in situ '' star formation is responsible for their enrichment @xcite . photoionization modeling of the single - cloud weak absorbers has established the existence of two phases , a high density region that is @xmath30 pc thick and produces narrow ( @xmath31few ) low ionization lines , and a kiloparsec scale , lower density region that produces somewhat broader , high ionization lines . there are often additional , similar low density regions within tens of of the one that is aligned with the absorption . @xcite argue that filamentary and sheetlike geometries are required for the single - cloud , weak absorbers , based on a census of the absorber populations at @xmath32 , and discussed possible origins in satellite dwarf galaxies , in failed dwarf galaxies , or in the analogs to milky way high velocity clouds . the earlier work of @xcite considered population iii star clusters , star clusters in dwarf galaxies , and fragments in type ia supernovae shells as possible sites for production of weak absorbers . most recently , @xcite have argued that the close alignment in velocity of the and absorption is also suggestive of a layered structure such as expected for supernova remnants or for high velocity clouds sweeping through a hot corona . single - cloud weak absorbers have possible implications for star formation in dwarf galaxies and in the intergalactic medium , and for tracking the populations of dwarf galaxies and/or high velocity clouds to high redshifts . for example , @xcite noted that the peak at @xmath33 of the star formation rate in dwarf galaxies may be related to the evolution of the weak absorbers . to understand the relative importance of the processes that produce weak absorption , it is crucial to have accurate measures of the evolution of their number densities . multiple - cloud weak absorbers may also be important as a tool to trace evolution of dwarf galaxies and other metal - rich gas too faint to see at high redshifts . because of their abundance , the dwarf galaxy population should present a significant cross section for absorption , yet so far their absorption signatures have been hard to recognize . although some of the multiple - cloud weak absorbers are surely an extension of the strong absorber population , others are kinematically compact , and are possibly related to dwarf galaxies @xcite . it is of interest to have a survey of weak absorbers large enough to separately consider the evolution of multiple - cloud weak absorbers . there have been three comprehensive surveys for weak absorbers , each focused on a different redshift regime . * hereafter crcv99 ) report on a survey for weak systems in the interval @xmath16 , @xcite covered the range @xmath34 , and more recently ( * ? ? ? * hereafter lct06 ) discovered weak systems in the redshift interval @xmath19 . these studies followed the earlier , smaller surveys by @xcite and @xcite , who first established that the equivalent width distribution of absorbers continues to rise below @xmath35 . the number density ( @xmath6 ) constraints from the surveys collectively demonstrate an evolution in the absorber population over the redshift interval @xmath36 , comprising the last @xmath37 gyr history of the universe . for their survey of weak systems , crcv99 searched a redshift pathlength of @xmath38 in the hires / keck spectra of 26 qsos . thirty weak systems were identified in the interval @xmath39 in that survey , which was @xmath40% complete down to an rest frame equivalent width sensitivity limit of @xmath41 . from the weak systems identified , they estimated a redshift path density @xmath42 for @xmath43 , and for @xmath44 . later , using stis / hst uv echelle spectra of 20 quasars , @xcite found that analogs to weak absorbers at @xmath45 also exist in the present universe . from the six systems detected in a redshift pathlength of @xmath46 within the redshift window @xmath47 , a @xmath6 of @xmath48 was estimated for @xmath49 . lct06 presents the most recent survey for weak absorbers . from a data set of 18 qsos , observed using the uves / vlt , a total of 9 weak systems were found over a redshift path of @xmath50 in the interval @xmath19 , yielding a @xmath51 for @xmath52 . that survey was @xmath53 complete down to a rest frame equivalent width of @xmath3 . in order to interpret the apparent evolution in the @xmath6 of weak absorbers it is necessary to consider the effect of the changing extragalactic background radiation ( ebr ) . the ebr is known to diminish in intensity by @xmath54 dex from @xmath55 to @xmath56 , and by @xmath57 dex from @xmath45 to @xmath58 @xcite . this changing ebr will have an effect on , what might otherwise be a static population of absorbers , due to a change in the balance between high and low ionization gas . however , what we would predict from the ebr evolution would be an increase in @xmath6 from @xmath59 to @xmath58 . this makes the smaller observed @xmath6 at @xmath60 quite significant , in that it implies a real decrease in the population from @xmath12 to @xmath60 @xcite . similarly , lct06 found that the increase in @xmath6 from @xmath8 to @xmath12 was significantly larger than that predicted from the effect of the changing ebr ( and the expected cosmological evolution ) . thus , in light of the results from the three surveys , it can be argued that there has been a slow build up of weak systems from high redshift , with their number density reaching a peak at @xmath45 , and subsequently evolving away until the present time . the goal of the present study is to determine more precisely how @xmath6 evolves at @xmath61 . the lct06 survey identified an overall trend in number density evolution , but was limited by small sample size . our sample covers @xmath62 times more lines of sight than lct06 . this will allow us to constrain @xmath6 for smaller redshift bins in order to measure a peak redshift for the incidence of weak absorption . a larger sample will also allow us to look separately at the evolution of the single - cloud and multiple - cloud weak absorption , which is important because they are likely to originate in different types of structures . finally , we will examine the equivalent width distribution for weak absorbers , and consider its evolution . in [ sec:2 ] we describe the vlt / uves dataset and outline our procedures for reducing the spectra and for searching for weak doublets . [ sec:3 ] presents the formal results of our survey , including the redshift path density for @xmath63 absorbers at @xmath1 , separates this into single - cloud and multiple - cloud weak absorbers , and presents the equivalent width distributions at @xmath12 and @xmath8 . a summary and discussion is given in the final section of the paper .

, we identified 112 weak systems within the redshift interval with % completeness down to a rest - frame equivalent width of , covering a cumulative redshift path length ofz . from this sample thus we find evidence for an evolution in the population of weak absorbers , with their number density peaking at . , there is evidence for a turnover from a powerlaw of the form at . based on these results , we discuss the possibility that some fraction of weak absorbers , particularly single cloud systems , are related to satellite clouds surrounding strong systems . these structures could also be analogs to milky way high velocity clouds . in this context , the paucity of high redshift weak absorbers is caused by a lack of _ isolated _ accreting clouds on to galaxies during that epoch .

we present results from a survey of weak absorbers in the vlt / uves spectra of qsos obtained from the eso archive . in this survey , we identified 112 weak systems within the redshift interval with % completeness down to a rest - frame equivalent width of , covering a cumulative redshift path length ofz . from this sample , we estimate that the number of weak absorbers per unit redshift ( ) increases from at to at and thereafter decreases to at and at . thus we find evidence for an evolution in the population of weak absorbers , with their number density peaking at . we also determine the equivalent width distribution of weak systems at and . at , there is evidence for a turnover from a powerlaw of the form at . this turnover is more extreme at , where the equivalent width distribution is close to an extrapolation of the exponential distribution function found for strong absorbers . based on these results , we discuss the possibility that some fraction of weak absorbers , particularly single cloud systems , are related to satellite clouds surrounding strong systems . these structures could also be analogs to milky way high velocity clouds . in this context , the paucity of high redshift weak absorbers is caused by a lack of _ isolated _ accreting clouds on to galaxies during that epoch .

astro-ph0603249

i

this work studies the interaction of a rapidly rotating magnetized star with an accretion disk under conditions where the corotation radius of the star , @xmath0 , is less than the inner radius of the disk , @xmath1 . the radius @xmath2 is determined by the star s magnetic field and angular velocity as well as the mass accretion rate of the disk @xmath3 and the disk viscosity and magnetic diffusivity . disk accretion is disrupted for radii @xmath4 . at distances @xmath5 the disk plasma acquires additional angular velocity due to friction " with the magnetosphere of the star which rotates faster than the keplerian motion of the disk . the behavior of the matter at @xmath2 depends on the ratio between angular velocity of the star and keplerian angular velocity at @xmath2 . the matter tends to be expelled from the disk if the centrifugal force is sufficiently larger than the gravitational force . this regime of interaction between a magnetized star and an accretion disk is called propeller " regime ( illarionov & sunyaev 1975 ) . this regime was investigated analytically ( e.g. , davies , fabian , & pringle 1979 ; lovelace , romanova , & bisnovatyi - kogan 1999 , hereafter - lrbk99 ; ikhsanov 2002 ; rappaport , fregeau , & spruit 2004 ; eksi , hernquist , & narayan 2005 ) , and numerically ( romanova et al . 2004b - hereafter rukl04 ; romanova et al . 2005 - hereafter rukl05 ) . in the disk - magnetosphere interaction the magnetic field plays the main role in two processes . firstly , it disrupts the inner regions of the disk and thus determines the inner radius of the disk . secondly , the magnetic field determines the direction of plasma flow . matter of the disk at a distance @xmath6 is accelerated in the azimuthal direction if it is threaded by field lines connecting it with a star rotating more rapidly than the disk ; that is @xmath7 . in the opposite case where @xmath8 , the azimuthal motion of the disk matter is slowed down . in the first case the disk plasma gains angular momentum from the star and moves outward . in second case the disk plasma loses angular momentum and moves inward . thus , in the inner regions of the disk the action of magnetic field leads to enhanced accretion rate , while in the outer regions to reduced accretion or even to outflow of matter . the disk - magnetosphere interaction depends essentially on the ratio of the inner radius of the disk @xmath2 to the corotation radius @xmath9 . in the model studied here the location of the radius @xmath2 depends mainly on the magnetic field of the star and the disk accretion rate . in the absence of external plasma the magnetic field of the star is considered to be a dipole field with the magnetic moment @xmath10 parallel to the rotational axis . consequently the magnetic stresses are proportional to @xmath11 . for @xmath12 , disruption of the disk is accompanied by the formation of `` funnel flows '' ( e.g. , ghosh & lamb 1978 ; knigl 1991 ; shu et al . funnel flows were recently investigated numerically using 2d and 3d mhd simulations ( romanova et al . 2002 , 2003 , 2004a ) . in this paper we consider the opposite limit where @xmath13 . in this limit one expects that the closed field region of the star will contain relatively low - density plasma rotating with the star s angular velocity . outside of this region there is a relatively dense disk plasma threaded by open magnetic field lines . interaction between the two regions occurs by two processes : ( 1 ) by matter flow from open field lines to the closed field lines as a result of magnetic diffusivity ; and ( 2 ) angular momentum exchange between fast rotating matter of magnetosphere and slowly rotating disk . the first process can lead to penetration of significant amounts of matter with low angular momentum to the closed field lines . this can in turn lead to significant deformation of the field lines and possibly to their opening . the second process may lead to azimuthal acceleration of the disk matter sufficient to stop the accretion and to eject matter from the disk . an outflow from the system may occur . this paper treats disk accretion to a rotating magnetized star using magnetohydrodynamics . for the initial set up of the system we divide the space into the `` disk '' and the `` corona '' with a smooth transition between them . the disk is relatively cold and dense while the opposite is true for the corona . the disk and corona are separated by a specified level of density . in the disk we take into account viscosity and magnetic diffusivity of the plasma . we consider that both the viscosity and the magnetic diffusivity of the disk plasma are due to turbulent fluctuations of the velocity and magnetic field . we adopt the standard hypotheses where the molecular transport coefficients are substituted with the turbulent coefficients . to estimate the value of these coefficients , we use the @xmath14-model of shakura and sunyaev ( 1973 ) where the coefficient of the turbulent kinematic viscosity @xmath15 , where @xmath16 is the isothermal sound speed and @xmath17 is the keplerian angular velocity at the given location . similarly , the coefficient of the turbulent magnetic diffusivity @xmath18 . here , @xmath19 and @xmath20 are dimensionless coefficients which are treated as parameters of the model . our numerical simulations have shown that the mhd flows which appear as a result of interaction between a rapidly rotating magnetized star and accretion disk can be divided to two types : `` weak '' and `` strong '' propeller . in the first case , no outflows are observed ( rukl04 ) , while in the second case a large fraction of the mass accretion of the disk goes to the outflows ( rukl05 ) . in this paper we investigate regime of strong " propellers in detail . the inner disk radius @xmath2 is determined by the disk interaction with the magnetized star . the value @xmath2 varies with time significantly . we can consider however an average value of @xmath2 . this value depends on the parameters of the model which characterize both the star , its mass @xmath21 , magnetic moment @xmath22 , and angular velocity @xmath23 ; and the disk , the coefficients of viscosity and magnetic diffusivity , density , temperature and connected with them the accretion rate in the disk . the corona may also have a significant role . in order to decrease the influence of corona we have taken its density to be as low as possible . from the parameters of the model we can construct in addition to the corotation radius another important length termed the nominal alfvn radius , @xmath24^{1/7}$ ] ( e.g. , davidson & ostriker 1973 ) . here , @xmath3 is the disk accretion rate at large distances , which can be obtained from the simulations . another characteristic length can be obtained from the following . close to the star the magnetic field dominates , that is , the magnetic pressure is larger than the @xmath25 component of the momentum tensor of the matter @xmath26 . inside the region where the magnetic field dominates , the plasma flow is controlled by the magnetic field and the flow is along the magnetic field lines . the boundary of this region follows from @xmath27 . this surface intersects the equatorial region along the circle with the radius @xmath28 , which we will call the magnetospheric radius . the strength of the propeller is determined by the value of the dimensionless ratio , @xmath29 or @xmath30 , and also by other dimensionless parameters of the model such as the @xmath14-coefficients of the viscosity and magnetic diffusivity . the characteristic feature of the disk - magnetosphere interaction in the strong propeller regime is the formation of an outflow of the disk matter along the opened magnetic field lines . this outflow is termed the `` wind . '' the matter outflows are strongest in the vicinity of the neutral line of the poloidal field , which starts approximately at the inner radius of the disk . this is the region of the most intense angular momentum transport from the fast rotating magnetosphere to the disk due to viscous " stresses . at the same time there is a magnetically dominated ( poynting ) `` jet '' which flows out along the opened magnetic field lines extending outward from the star . the wind has a large inclination angle relative to the rotational axis and for a very strong propeller it flows almost along the disk surface . in contrast , the jet becomes more collimated as the strength of the propeller increases . as the strength increases there is a sharp decrease of the accretion rate to the star . section 2 discusses theoretical approach to the problem . section 3 discusses our numerical model . section 4 discusses results and section 5 summarizes the work .

the main parameters of the system are the star s angular velocity and magnetic moment , and the disk s viscosity and diffusivity . two types of magnetohydrodynamic flows have been found as a result of simulations : weak " and strong " propellers . = cmmib10 at 10pt

we present results of axisymmetric magnetohydrodynamic simulations of the interaction of a rapidly rotating , magnetized star with an accretion disk . the disk is considered to have a finite viscosity and magnetic diffusivity . the main parameters of the system are the star s angular velocity and magnetic moment , and the disk s viscosity and diffusivity . we focus on the propeller " regime where the inner radius of the disk is larger than the corotation radius . two types of magnetohydrodynamic flows have been found as a result of simulations : weak " and strong " propellers . the strong propellers are characterized by a powerful disk wind and a collimated magnetically dominated outflow or jet from the star . the weak propellers have only weak outflows . we investigated the time - averaged characteristics of the interaction between the main elements of the system , the star , the disk , the wind from the disk , and the jet . rates of exchange of mass and angular momentum between the elements of the system are derived as a function of the main parameters . the propeller mechanism may be responsible for the fast spinning - down of the classical t tauri stars in the initial stages of their evolution , and for the spinning - down of accreting millisecond pulsars . = cmmib10 at 10pt

astro-ph0603249

r

we performed simulations of accretion to a star in the propeller " regime for a wide range of parameters , @xmath22 , @xmath23 , @xmath19 and @xmath20 . in the following we discuss results for the reference case @xmath229 , @xmath230 , @xmath281 , and @xmath282 . the reference case was calculated out to a time corresponding to @xmath283 rotation periods of the star . we observed that the process of interaction between the magnetosphere and the disk is accompanied with ( 1 ) oscillations of the disk , ( 2 ) quasi - periodic opening and closing of the magnetic field , ( 3 ) quasi - periodic outbursts to winds and jets . this evolution arises from the diffusive mixing of the disk matter with the magnetic field of the star , the opening of the magnetic field lines linking the star and disk , unloading of the disk matter to the star and to the outflows , and the outflow of angular momentum from the star and from the disk . the left - hand panel of figure 7 shows the variation of the inner radius of the disk which was calculated at the density level , @xmath284 . note that near the disk - corona boundary , @xmath285 , the density gradient is very large so that the choice of @xmath286 is not important . during an initial time @xmath287 , part of the magnetic flux outgoing the star opens and subsequently varies about an average value . to determine this magnetic flux we calculated the dependence of the maximum value of the magnetic flux function @xmath288 , @xmath289 on time at the sphere of radius @xmath290 . the magnetic field lines along which @xmath291 , are evidently closing inside the sphere of radius @xmath292 . the value @xmath293 determines the location of the last closed field line at this distance , in particular the radius at which this field line crosses equatorial plane @xmath294 . that is , @xmath295 shows the radius of the closed magnetosphere . the right - hand panel of figure 7 shows that this radius @xmath296 varies with time in a fashion similar to @xmath297 ; however , the amplitude is much smaller . an important aspect of the interaction between a rapidly rotating magnetized star and an accretion disk is the transport of angular momentum . the equation for the conservation of angular momentum can be obtained from ( [ eq16 ] ) by multiplying it by @xmath298 , @xmath299\right\ } + \ ] ] @xmath300\right\ } = 0~,\ ] ] where @xmath301 and @xmath302 are the components of non - viscous " part of the stress tensor . the angular momentum conservation equation evidently has the form of a continuity equation , @xmath303 where @xmath304 is the specific angular momentum and the angular momentum flux density is @xmath305 the first term on the right - hand - side @xmath306 gives the transport of angular momentum by the matter ; the second term is magnetic field contribution ; and the third term is the transport due to viscous stress . figure 8 ( a , b , e - g ) shows the angular momentum fluxes at @xmath307 . the streamlines show the direction of the fluxes , while the background shows the magnitude of the flux . figures 8 ( a , e ) show the distribution of the angular momentum fluxes carried by the magnetic field at large and small scales . figures 8(b , f ) show the corresponding fluxes carried by the matter . from figure 8e it is clear that the angular momentum outflow from the star is due mainly to the twisting of the magnetic field . note that a larger part of angular momentum is carried along the open field lines . other part of angular momentum which is along the closed field lines is transported from the star to the disk . angular momentum carried by matter is largest in the disk and in the conical outflow in the vicinity of the neutral layer ( fig . 8b ) . here magnetic pressure is not very high , while pressure and density of matter play larger role . bottom panels show energy fluxes carried by the magnetic field ( fig . 8c ) and by matter ( fig one can see from figure 8c that significant energy is carried from the star by a poynting flux . figure 8 g shows the angular momentum flux carried by the viscous stress . this stress is large at the boundary between the disk and magnetosphere in the vicinity of the equatorial plane . this is the place of significant gradients of the angular velocity of matter , as one can see from the figure 9 ( shown at the same time @xmath307 ) . this figure also shows the distribution of density , entropy ( logarithm scale at the right ) , and radial velocity @xmath308 in the equatorial plane . it is evident that the disk has a sharp boundary both in density and in entropy . next , we evaluate the directions where most of the matter and angular momentum outflows . for this we calculated the distribution of the fluxes of matter and angular momentum as a function of @xmath266 ( the colatitude ) as a function of time at a given distance @xmath309 . figure 10 shows a plot of these distributions as a function of time . one can see that the matter flux to the wind is mainly in the range @xmath310 . thus , most of the matter flows into a wide - angle hollow - cone with a large inclination angle to the @xmath216axis ( figure 10a ) . there is also a flux of matter towards the star which is associated with the equatorial region of the disk . the angular momentum flux carried by matter has distribution similar to the distribution of the matter flux ( see figure 10b ) . the angular momentum flux carried by the magnetic field ( figure 10c ) is concentrated in two stripes : @xmath311 ( near the axis ) , and @xmath312 ( closer to the disk ) . the larger flux is associated with the angular momentum outflow in collimated jet , along the field lines which start at the surface of the star . the other stripe , at larger angles @xmath266 is connected with the disk wind . the wide - angle , hollow - cone disk wind is similar to the stationary magnetocentrifugally driven winds predicted by blandford and payne ( 1982 ) and lovelace , berk , and contopoulos ( 1991 ) and first obtained and analyzed in mhd simulations by ustyugova et al . ( 1999 ) . for such winds the angle of the poloidal field to the @xmath216axis at the surface of the disk @xmath313 is predicted to be @xmath314 . on the other hand a magnetically dominated ( or poynting ) outflow from a disk or star can have the angle @xmath315 less than @xmath316 ( ustyugova et al . 2000 ; lovelace et al . 2002 ) . the narrow - angle , hollow - cone jet along the open field lines of the star has much smaller values of @xmath315 and it is magnetically dominated . figure 11 shows the distribution of different physical quantities in the computational region ( top panels ) and on a smaller scale ( bottom panels ) . figures 11 ( a , d ) show distribution of the matter flux @xmath317 , and streamlines of matter flow at time @xmath307 . one can see that matter flows with the disk , then turns near the magnetosphere of the star and flows outward in a disk wind . some matter goes around the magnetosphere and flows to the jet along the field lines starting at the stellar surface . the white line shows the escape velocity @xmath318 . above this line @xmath319 . the color background of figures 11 ( b , e ) shows the plasma @xmath320 parameter . the dashed white line corresponds to @xmath321 . figures 11 ( c , f ) show isocontours of the @xmath322 which is the poloidal current flow through a horizontal disk @xmath323 centered on the @xmath216axis . figure 12 shows plots of different variables as a function of distance along a magnetic field line which starts from the disk in the vicinity of the neutral field line where the matter flux to the wind is the largest . the solid line shows the projection of the poloidal velocity onto this field line , the dashed line shows the projection of the velocity component normal to the magnetic field line . one can see that the poloidal velocity is nearly parallel with the poloidal field , which is in accord with the theory of stationary axisymmetric flows of ideally conducting plasma ( see , e.g. , ustyugova et al . the sound speed @xmath16 and escape velocity @xmath324 are also shown . one can see that the flow becomes supersonic and that the flow velocity exceeds the escape velocity @xmath324 . earlier , ustyugova et al . ( 1999 ) obtained dependences similar to those of figure 12 for the case of an ordered magnetic field threading a disk around a non - magnetized star . interaction of the magnetized star with the accretion disk can lead to the outflow and escape of a significant fraction of the matter incoming in the disk . we find in general that there is a _ jet _ and a _ disk wind _ giving outflows of energy , angular momentum , and matter from the system . the _ jet _ is identified as the flow in the region within the neutral line of the poloidal magnetic field . the magnetic flux in the jet is the flux emanating from the star . the _ disk wind _ is the flow outside of the neutral line of the poloidal magnetic field . for both outflows we take into account only the matter which has a velocity higher than the escape velocity @xmath324 . thus , the simulation region includes three flow regions , the disk , the jet , and the wind . these regions do not constitute the entire simulation volume because part of it is filled with relatively rarefied matter of magnetosphere and corona . accreting matter which is not accelerated to escape speed goes into the magnetosphere or the corona . these regions do not have a significant role in the matter and angular momentum flow . the star has an important role in absorbing mass and losing angular momentum . the star influences the plasma dynamics through the inner boundary of the simulation region . however the influence of the plasma on the star is noticeable on only an extremely long time scale . figure 13 shows the interactions between the different elements of the system . evidently , matter which comes through an accretion disk flows in part to the disk wind , in part to the jet , and in part accretes to the star . there is also angular momentum transport between different elements . the star represents a large reservoir of angular momentum which is transported to the disk through the closed field lines and to the jet through the open field lines . the positive direction of the fluxes is shown by arrows . in all cases the fluxes of matter and angular momentum oscillate strongly in time , but always vary around an average value . see for example figure 10 . for this reason we calculated the time - averaged fluxes and investigated their dependences on the parameters of the model . we took as a base the mentioned reference case with dimensionless parameters @xmath325 , @xmath230 , @xmath281 , and @xmath282 . a series of simulations was then done to obtain the dependences of the time - averaged fluxes on different parameters . only one parameter was varied in each series . figures 14 - 16 show the derived dependences . figure 14 ( a - d ) show the dependences of the matter fluxes on our main parameters . here , @xmath326 is the mass accretion rate in the disk at the radius @xmath327 @xmath328 is the accretion rate to the star , @xmath329 is the matter flux to the wind , @xmath330 is the matter flux to the jet . as we mentioned , we distinguish between strong " ( with outflows ) and weak " ( no outflows ) propellers . results of modeling of the strong " propellers are marked with the filled symbols , while the weak " propeller results are indicated by open symbols . different symbols show different dependences : @xmath331 ( squares ) , @xmath332 ( circles ) , @xmath333 ( triangles ) , and @xmath334 ( gradient signs ) . the solid lines show approximations of these dependences . most of dependences could be approximated by a simple power law and have a clear sense . for example , the larger the magnetic moment @xmath22 and the larger the angular velocity of the star @xmath23 , the larger matter fluxes to the wind and jet and the smaller the accretion rate to the star . at smaller @xmath22 and @xmath23 , ejection of matter to the wind and jet becomes less efficient and we enter the weak " propeller regime with very weak or no outflows ( see fig . 14 a , note , that all weak " propellers are on the left - hand side of the plots . it is interesting to look at dependences on viscosity , @xmath19 ( see fig . we see that matter fluxes to the wind / jet strongly increase with increase of viscosity , while the accretion rate to the star decreases . we conclude that the viscous stress contributes to launching the outflows . at sufficiently small viscosity , @xmath335 , outflows are absent . the role of the viscosity is twofold . from one side , at larger viscosity , the friction " between the inner regions of the disk and magnetosphere is larger . from other side , the radial velocity in the disk is proportional to @xmath19 , so that viscosity increases the matter flux per unit area and the inner region of the disk come closer to the inner regions of the fast rotating magnetosphere . both factors lead to enhanced outflows , but it is difficult to separate the two factors . in rukl05 test simulations were done for a case with @xmath336 , and with the density in the disk doubled . this of course increased the accretion rate but it also enhanced the outflows . figure 14d shows the dependence on the magnetic diffusivity . the dependence of the matter fluxes to the wind / jet on @xmath337 is more complicated than other dependences . namely , for @xmath338 , the fluxes @xmath329 and @xmath330 decrease with @xmath20 , because the mixing of the disk matter with the magnetic field of the magnetosphere become less and less efficient , and correspondingly the angular momentum transport from the star to the disk matter decreases . on the other hand , for @xmath339 , the diffusivity become too high , and the inner regions of the disk and magnetosphere are not coupled sufficiently to transport angular momentum . this explains the parabolic approximations of these dependences . we took into account all dependences shown in figures 14 ( a - d ) , and approximated them with analytic functions . we approximated the dependences on @xmath20 with power laws to the left and to the right of the dividing value @xmath340 . in figures 14 ( c - d ) , we show the dependences around @xmath341 and @xmath342 . we have made additional runs not shown in the plot at much smaller @xmath19 and @xmath20 , down to @xmath343 . also we have made runs for much larger values , up to @xmath344 . we show below dependences which incorporated all these runs , separately , for @xmath345 and @xmath346 . the matter fluxes to the wind @xmath329 , to the jet @xmath330 , through the disk @xmath326 , and to the star @xmath347 were approximated as : @xmath348 \displaystyle{\left(\frac{\alpha_{\rm d}}{0.2}\right)^{2 } } & \alpha_{\rm d } < 0.2 \end{array } \right.,\ ] ] @xmath349 \displaystyle{\left(\frac{\alpha_{\rm d}}{0.2}\right)^{1.7 } } & \alpha_{\rm d } < 0.2 \end{array } \right.,\ ] ] @xmath350 @xmath351 the matter flux to the disk wind increases with @xmath22 almost linearly and strongly increases with @xmath23 , while the accretion rate to the star @xmath352 strongly decreases . we note that dependences on @xmath22 and @xmath23 have a threshold character . namely , the matter fluxes to the wind and to the jet strongly decrease for @xmath353 and @xmath354 , where the system enters the weak " propeller regime ( see open symbols in figures 14 a , b ) . one can see from the figure 14b that the dependence of @xmath332 and @xmath331 on the angular velocity of the star @xmath23 also has a threshold behavior for @xmath355 . these threshold dependences reflect the qualitative difference between strong " propellers ( with outflows ) and weak " propellers ( with no outflows ) . as a measure of the efficiency of the propeller interaction with the disk , we take the ratio of the outflow rate to the disk wind and jet to the accretion rate through the disk , @xmath356 . for the larger values of @xmath357 , less matter reaches the surface of the star . correspondingly , a larger part of the disk matter acquires additional angular momentum and flows to the jet and/or wind . figures 15 a - d show the dependences of the value @xmath357 on the parameters of the model . the efficiency of the propeller depends weakly on the magnetic moment of the star . the larger the angular velocity of the star and the larger the @xmath14-coefficient of viscosity , the higher is the efficiency of the propeller . the dependence of the efficiency on the @xmath14-coefficient of magnetic diffusivity has a maximum near @xmath358 . we found the following dependences , @xmath359 \displaystyle { \left(\frac{\alpha_{\rm d}}{0.2}\right)^{1.7 } } & \alpha_{\rm d } < 0.2~. \end{array } \right.\ ] ] another measure of the efficiency of the propeller is the ratio of the total matter flux going to the wind / jet to the matter flux to the star , @xmath360 \displaystyle{\left(\frac{\alpha_{\rm d}}{0.2}\right)^{2.1 } } & \alpha_{\rm d } < 0.2~. \end{array } \right.\ ] ] the ratio of outflow to accretion increases strongly with @xmath22 and @xmath23 . next , we discuss angular momentum transport from the star and its dependence on main parameters of the model . the outflow of angular momentum from the star causes it to spin down . part of the angular momentum is carried by the matter , another part by the tension of the magnetic field lines , and a further part by the viscous stress . the flux of angular momentum from the star was calculated as @xmath361~ , - \nu_t \rho r \sin \theta \nabla \omega \right]~ , % % % % % % % % % % % % % % % % % % % % % \ ] ] where the integration was over the surface of the inner boundary of the simulation region which is close to the surface of the star and where @xmath362 is the surface element directed outward to the region . simulations show that close to the star angular momentum flux is determined mainly by the magnetic stress . part of the flux is associated with the closed field lines . these are field lines connecting a star and the disk . other part is associated with the open field lines , which connect a star with the low - density corona . we calculated a total flux @xmath363 and also a flux associated with the closed field lines , @xmath364 , that is angular momentum flux transported from the star to the disk . figure 16 shows fluxes @xmath365 ( gradient signs ) and @xmath366 ( circles ) . we found the following dependences on different parameters : @xmath367 \displaystyle{\left(\frac{\alpha_{\rm d}}{0.2}\right)^{0.14 } } & \alpha_{\rm d } < 0.2~ , \end{array } \right.\ ] ] @xmath368 \displaystyle{\left(\frac{\alpha_{\rm d}}{0.2}\right)^{0.5 } } & \alpha_{\rm d } < 0.2~. \end{array } \right.\ ] ] figure 16 ( a , b ) shows that both fluxes increase with @xmath22 and @xmath23 . they increase with a similar rate so that the lines in figures 16 ( a , b ) are almost parallel . figures 16 ( c , d ) show that the fluxes depend only weakly on the @xmath14 coefficients of viscosity and diffusivity . they have maximum at @xmath358 . note that the angular momentum flux carried by the open field lines of the jet @xmath369 is similar to that carried by the closed field lines . that is , a star in the propeller regime in our range of parameters spins - down due to both : open and closed field lines . now , we can estimate the time - scale of spin - down for cttss and accreting neutron stars for parameters given in 3.4 . for cttss , the loss of the angular momentum of the star in our main case is @xmath370 . the star s angular velocity is @xmath371 , its angular momentum is @xmath372 , where @xmath373 . taking @xmath374 , the spin - down time - scale is @xmath375 years . note , that this time - scale was calculated for a magnetic field @xmath376 and a relatively low accretion rate , @xmath377 . the time - scale decreases with magnetic field of the star as @xmath378 and will be @xmath379 years for @xmath380 . time - scale also decreases with matter flux . thus , if cttss have a strong magnetic field in the past , then they were at the propeller regime and were spun - down in @xmath381 years . this time - scale is shorter than typical life - time of the cttss , which is @xmath382 years . we conclude that propeller mechanism may be responsible for fast spinning - down of cttss to presently observed slow rotation in the early stages of their evolution . for an accreting neutron star , @xmath383 , @xmath384 . the star s angular momentum is @xmath385 . the time - scale of spin - down is @xmath386 years . this time - scale is shorter than expected life - time of millisecond pulsars in the accreting stage . however , millisecond pulsars have a different history of evolution compared to cttss , and they expected to be spined up during accreting stage ( bisnovatyi - kogan & komberg 1974 ) . however , the pulsar mechanism may be responsible for fast spinning - down of the pulsar during periods of decreased accretion rate .

the weak propellers have only weak outflows . we investigated the time - averaged characteristics of the interaction between the main elements of the system , the star , the disk , the wind from the disk , and the jet . rates of exchange of mass and angular momentum between the elements of the system are derived as a function of the main parameters

we present results of axisymmetric magnetohydrodynamic simulations of the interaction of a rapidly rotating , magnetized star with an accretion disk . the disk is considered to have a finite viscosity and magnetic diffusivity . the main parameters of the system are the star s angular velocity and magnetic moment , and the disk s viscosity and diffusivity . we focus on the propeller " regime where the inner radius of the disk is larger than the corotation radius . two types of magnetohydrodynamic flows have been found as a result of simulations : weak " and strong " propellers . the strong propellers are characterized by a powerful disk wind and a collimated magnetically dominated outflow or jet from the star . the weak propellers have only weak outflows . we investigated the time - averaged characteristics of the interaction between the main elements of the system , the star , the disk , the wind from the disk , and the jet . rates of exchange of mass and angular momentum between the elements of the system are derived as a function of the main parameters . the propeller mechanism may be responsible for the fast spinning - down of the classical t tauri stars in the initial stages of their evolution , and for the spinning - down of accreting millisecond pulsars . = cmmib10 at 10pt