LP 400-22, A very low-mass and high-velocity white dwarf(4)

We report the identification of LP 400-22 (WD 2234+222) as a very low-mass and high-velocity white dwarf. The ultraviolet GALEX and optical photometric colors and a spectral line analysis of LP 400-22 show this star to have an effective temperature of 1108

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TABLE2

LP400-22Parameters

Parameter

E ectiveTemperatureSurfaceGravityMassMV

Distance

ProperMotionKinematics

Measurement

11080±140K6.32±0.080.17±0.01M⊙9.1±0.2mag430±45pcµ=0′′.203yr 1,0′′.205yr 1

θ=73.9,75.0

U= 388±43kms 1V= 81±22kms 1W= 83±22kms 1

Kawkaetal.

measurementsagreewithinerrorbars.However,aseriesofradialvelocitymeasurementsshouldbeobtainedtoestablishwhetherornotLP400-22isinaclosebinarysystem.

YetanotherpossibilityfortheoriginofLP400-22isthatitmayhaveoncebeeninaclosedouble-degeneratebinary,wherethecompanionhasgonethroughasuper-novaeventthatdisruptedthebinarylosingtheremnantofthedonorstarwithahigh-velocityandalowmass(Hansen2003).

5.SUMMARY

Reference

111112,32,3111

References.—(1)Thiswork;(2)Luyten(1979);Salim&Gould(2003);(3)Lepine&Shara(2005)

HαintheAPOhigh-dispersionspectratoobtainahe-liocentricvalueof 50±20kms 1,whichisdi erentthanthevelocitymeasuredforthereddwarf(7.3kms 1)bySilvestrietal.(2002).WecalculatedU,V,WforLP400-22usingJohnson&Soderblom(1987)toobtainU= 388±43,V= 81±22,W= 83±22kms 1.Thesevelocitycomponentsdonotagreewitheitherdiskorhalopopulations(Chiba&Beers2000)andsuggestadi erentoriginforitspeculiarmotion.TheGalacticorbitforLP400-22shouldbecalculated.

MostwhitedwarfswithM<0.2M⊙arecompanionstopulsars.WesearchedforradiosourcesinthevicinityofLP400-22usingVizieR4,andthenearestwasthatofthegalaxyKUG2234+223～7.5′away.Therefore,ifLP400-22isacompaniontoaneutronstar,thenitisprobablyadeadpulsar.AnotherpossibilityisthatLP400-22hasaverycoolcompanion,whichshouldbedetectableasinfraredexcess.However,LP400-22wasnotdetectedby2MASS.Thetwohigh-dispersionvelocity

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WehavedemonstratedthatLP400-22isahigh-velocitywhitedwarfwithaverylowmass(M=0.17M⊙)andatemperatureof11080K.Table2sum-marizesthepropertiesofLP400-22.Sincewhitedwarfswithmassesbelow0.4M⊙musthavebeenformedinclosebinarysystems,radialvelocitymeasurementsandinfraredphotometryarerequiredtodeterminewhetherLP400-22hasaclosecompanion.Ontheotherhand,alackofradialvelocityvariationswouldindicatethatLP400-22lostitsclosemassivecompanionfollowingatypeIasupernovaevent.

ThisresearchissupportedinpartbyaNASA/GALEX

ˇgrant(NNG05GE33G).A.K.issupportedbyGACR

205/05/P186.T.D.O.acknowledgessupportfromtheNSF(AST0206115).J.A.S.wassupportedonaNASAGSRPTrainingGrant,NGT-51086.N.M.S.acknowl-edgessupportfromaNASAGSRPgrant(NST200415)andNSFAST02-05875.WethankPaulHintzenforac-quiringtheoriginalKPNOspectrumofLP400-22.ThisresearchhasmadeuseoftheVizieRcatalogueaccesstool,CDS,Strasbourg,France.BasedonobservationsobtainedwiththeAPO3.5mtelescope,whichisownedandoperatedbytheAstrophysicalResearchConsortium.

http://vizier.u-strasbg.fr/viz-bin/VizieR

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