Abstract
Red opticaland near-infrared spectroscopy are presented for SDSS J125637.13 022452.4,one of only fourL subdwarfsreported to date.Thesedata conrm thelow-tem perature,m etal-poornature ofthissource,asindicated by prom inentm etal-hydride bands,alkalilines,and collision-induced H2 absorption. The opticaland near-infrared spectra ofSDSS J1256 0224 are sim ilar to those ofthe sdL4 2M ASS J16262034+3925190,and we derive a classication ofsdL3.5 based on the prelim inary schem eofBurgasser,Cruz,& Kirkpatrick.The kinem aticsofSDSS J1256 0224 areconsistentwith m em bership in the Galactic inner halo,with estim ated U V W space velocities indicating a slightly prograde,eccentricand inclined Galacticorbit(3.5 . R. 11 kpc; jZm axj = 7.5 kpc).Com parison to synthetic spectra com puted with the Phoenix code,including the recentim plem entation ofkinetic condensate form ation (D rift-Phoenix),indicate Teff � 2100{2500 K and (M /H) � 1.5 to 1.0 forlogg � 5.0{5.5 (cgs),although therearecleardiscrepanciesbetween m odeland observed spectra particularly in thered opticalregion.Thestrongerm etal-oxidebandspresentin the D rift-Phoenix m odelspectra,a resultofphase-non-equilibrium abundancesofgrain species,appearsto contradict priorsuggestionsthatgrain form ation isinhibited in m etal-pooratm ospheres;conclusivestatem ents on the m etallicity dependence ofgrain form ation eciency are as yet prem ature. In addition,an apparentshiftin thetem peraturescaleofL subdwarfsrelativeto L dwarfsm ay obviatetheneed for m odied grain chem istry to explain som eoftheform er'suniquespectralcharacteristics. Subjectheadings: stars: chem ically peculiar | stars: individual( SDSS J125637.13 022452.4)| stars:low m ass,brown dwarfs| subdwarfs
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