Low-Mass Dwarf Template Spectra from the Sloan Digital Sky Survey

We present template spectra of low-mass (M0-L0) dwarfs derived from over 4,000 Sloan Digital Sky Survey (SDSS) spectra. These composite spectra are suitable for use as medium-resolution (R ~ 1,800) radial velocity standards. We report mean spectral propert

AcceptedforpublicationinAJ

APreprinttypesetusingLTEXstyleemulateapjv.6/22/04

LOW-MASSDWARFTEMPLATESPECTRAFROMTHESLOANDIGITALSKYSURVEY

JohnJ.Bochanski1,AndrewA.West1,2,SuzanneL.Hawley1,KevinR.Covey1

AcceptedforpublicationinAJ

arXiv:astro-ph/0610639v1 20 Oct 2006

ABSTRACT

Wepresenttemplatespectraoflow-mass(M0-L0)dwarfsderivedfromover4,000SloanDigitalSkySurvey(SDSS)spectra.Thesecompositespectraaresuitableforuseasmedium-resolution(R~1,800)radialvelocitystandards.Wereportmeanspectralproperties(molecularbandheadstrengths,equivalentwidths)andusethetemplatestoinvestigatethee ectsofmagneticactivityandmetallicityonthespectroscopicandphotometricpropertiesoflow-massstars.

Subjectheadings:stars:lowmass—stars:fundamentalparameters—stars:Mdwarfs—stars:

activity

1.INTRODUCTION

Low-massdwarfsarethedominantstellarcompo-nentoftheGalaxy.Theseubiquitousstars,withmainsequencelifetimesgreaterthantheHubbletimeetal.havebeenemployedinavari-etyofGalacticstudies:tracingGalacticDiskkinemat-icsGizisetal.L´epineetal.2003;2005),describingage-velocitydispersionrelations(Westetal.2006),andingGalacticstructurecomponentsetal.Kerberetal.2001;Pirzkaletal.2005).Modellingoftheirinternalstructure,atmosphericpropertiesandmag-neticactivityet1993;Bara eetal.Allardetal.presentsinterestingtheoreticalproblems.Observationally,thespectraofthesestarsaremarkedbythepresenceofstrongmolecularabsorp-tionfeatures,particularlytitaniumoxide(TiO),whichdominatestheopticalopacityoftheircoolatmospheres.TheTiOfeatures,alongwithmolecularbandheadsin-troducedbyvanadiumoxide(VO)andcalciumhydride(CaH)areusedtode nethewidelyacceptedMspectralsubtypeclassi cationschemeetInordertoincreasetheutilityoflow-massstarsinlargestudiesofgalacticstructureanddynamics,wehavebeenengagedinanalyzingspectroscopicdatafromtheSloanDigitalSkySurvey(SDSS;Yorketal.2000),resultinginaseriesofpapersthatdescribeourmethodsforpho-theseobjects2002;Walkowiczetal.2004;Westetal.anddiscussingtheirmagneticactivityproperties(Westetal.2004,2006).However,wehavebeenunabletoexploitthevelocityinforma-tioncontainedinthespectraduetotheinabilityoftheSDSSpipelinereductionstoprovideaccuratevelocitesforMdwarfsOurmotivationforthepresentworkisthedesiretoproduceasetofra-dialvelocitytemplatesbycombiningnative,high-quality,SDSSspectraateachspectralsubtypeintheMdwarf

AstronomyDepartment,UniversityofWashington,Box351580,Seattle,WA98195

email:bochansk@astro.washington.edu

2AstronomyDepartment,UniversityofCalifornia,601Camp-bellHall,Berkeley,CA94720-3411

1

sequence.Additionally,wesplitthespectraateachsub-typeintoactiveandinactivestars,andexaminethespec-troscopicandphotometricpropertiesofthesetemplatesseparately,todeterminewhethertheactivityisimprint-ingasignaturethatmaya ectourvelocityanalysis,andtofollowuponprevioussuggestionsthatcolorsandde-tailedabsorptionfeaturesmaychangedependingonac-tivitylevel1996;1997;Theradialvelocity(RV)ofanobjectistheprojec-tionofitsintrinsicmotionontothelineofsightofanobserver.InordertoaccuratelydeterminetheRVofagivenstar,onemustcarefullyaddressthesystematicsimposedbythetimeandlocationoftheobservation.Thisisusuallyaccomplishedbyshiftingtheframeoftheobservertoaheliocentric(sun-centered)orbarycen-tric(center-of-masscentered)restframe.Thestan-dardmethodofdeterminingstellarandgalacticRVshasbeencross-correlation,asintroducedbyTonry&Davis(1979).Thismethodcomparesthespectrumofasciencetargetagainstaknowntemplate,usingcross-correlationtodeterminethewavelengthshift(andthereforeveloc-ity)necessarytoalignthetargetwiththetemplate.Thus,correlatingwithatemplatespectrumthatissim-ilartothesciencetargetinallwaysexceptvelocityen-suresthemostaccuratedeterminationoftheRV.

Inthefollowingsections,wereportonoure ortstoestablishasetoflow-massstartemplatespectra3suit-ableforRVanalysisusingSDSSspectraatmedium(R~1,800)resolution.In§wedescribetheobserva-tionalmaterialfromtheSDSSandintroducetheprob-lemswiththeRVsreportedforlow-massstarsbythestandardSDSSspectroscopicpipeline.Theobservationswerespectral-typed,inspectedforsignsofchromosphericactivity,andcoaddedtoformtemplatesateachspectraltype,asdiscussedin§Theresultingspectraltem-plates,theiraccuracyasRVstandards,andtheirspec-tralandphotometricpropertiesaredetailedin§4.Ourconclusionsfollowin§2.DATA

2.1.SDSSPhotometry

TheSloanDigitalSkySurvey(Yorketal.2000;1998;Fukugitaetal.1996;Hogget3

Availableathttp://www.astro.washington.edu/slh/templates/

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