IRAC Observations of Taurus Pre-Main Sequence Stars

We present infrared photometry obtained with the IRAC camera on the Spitzer Space Telescope of a sample of 82 pre-main sequence stars and brown dwarfs in the Taurus star-forming region. We find a clear separation in some IRAC color-color diagrams between o

5

2

y

a

M

6

1

1

v

32

3

5

5

/

h

p

-

o

rt

sa

:v

i

X

r

aIRACObservationsofTaurusPre-MainSequenceStarsLeeHartmann1,S.T.Megeath1,LoriAllen1,KevinLuhman1,NuriaCalvet1,PaolaD’Alessio2,RamiroFranco-Hernandez2,GiovanniFazio1hartmann@cfa.harvard.eduABSTRACTWepresentinfraredphotometryobtainedwiththeIRACcameraontheSpitzerSpaceTelescopeofasampleof82pre-mainsequencestarsandbrowndwarfsintheTaurusstar-formingregion.We ndaclearseparationinsomeIRACcolor-colordia-gramsbetweenobjectswithandwithoutdisks.Afew“transition”objectsarenoted,whichcorrespondtosystemsinwhichtheinnerdiskhasbeenevacuatedofsmalldust.Separatingpuredisksystemsfromobjectswithremnantprotostellarenvelopesismoredi cultatIRACwavelengths,especiallyforobjectswithinfallatlowratesandlargeangularmomenta.Ourresultsgenerallycon rmtheIRACcolorclassi cationschemeusedinpreviouspapersbyAllenetal.andMegeathetal.todistinguishbetweenpro-tostars,TTauristarswithdisks,andyoungstarswithout(inner)disks.TheobservedIRACcolorsareingoodagreementwithrecentimproveddiskmodels,andingeneralaccordwithmodelsforprotostellarenvelopesderivedfromanalyzingalargerwave-lengthregion.WealsocommentonafewTaurusobjectsofspecialinterest.OurresultsshouldbeusefulforinterpretingIRACresultsinother,lesswell-studiedstar-formingregions.Subjectheadings:accretiondisks-infrared:stars-stars:formation-stars:pre-mainsequence

1.Introduction

TheTaurus-Aurigamolecularcloudhaslongservedasatouchstoneforunderstandingpre-mainsequenceevolution.TheproximityofTaurus,plustherelativelylowextinctioninthearea,hasenabledresearcherstodevelopareasonablycompletecensusofthepre-mainsequencepopulation.ThesepropertiesalsomeanthatthecharacterizationofprotostellarenvelopesandcircumstellardisksismoreextensiveanddetailedforTaurusobjectsthanforanyotherstar-formingregion(see,e.g.,Kenyon&Hartmann1995=KH95).

We present infrared photometry obtained with the IRAC camera on the Spitzer Space Telescope of a sample of 82 pre-main sequence stars and brown dwarfs in the Taurus star-forming region. We find a clear separation in some IRAC color-color diagrams between o

WeareconductingasurveyofknownTauruspre-mainsequencestarsusingtheIRACcamera

onboardtheSpitzerSpaceTelescope.Althoughagreatdealisalreadyknownabouttheinfrared

spectralenergydistributions(SEDs)ofTaurusmembers,theunprecedentedphotometricsensitivity

ofIRACinthemid-infraredpermitsthestudyofmanymoreobjectsinthe～3 9µmwavelength

rangethanpreviouslypossiblefromground-basedstudies.TheIRACdataalsoprovideanimpor-

tantlinkbetweenmeasurementsofstellarphotosphericemission(whichgenerallypeaksataround

1µm)andforthcomingdetailedspectraofTaurusmembersobtainedwiththeIRSspectrographon

Spitzer(whichcoversthe～5 35µmrange).Morebroadly,ourIRACobservationsofpreviously

well-characterizedsystemsinTauruscanserveasaguidetotheinterpretationofIRACdataof

other,muchmoredistantregionswhichcannowbestudiedwiththeunparalleledsensitivityof

Spitzer.

InthispaperwereportpreliminaryresultsfromourIRACsurvey,withresultsfor82Tau-

russystems.Afulleraccountingofthe～200pre-mainsequenceTaurussystemsintheIRAC

GuaranteedTimeprogramwillbepublishedlater,asdatabecomeavailable.

2.Observations

TheobservationsreportedherewereobtainedwiththeIRACinstrumentonboardtheSpitzer

SpaceTelescope(Fazioetal.2004).IRACobservationsaremadewithfour lters;herewereferto

thembytheirapproximatewavelengthcentersof3.6,4.5,5.8,and8µm.Asequenceofobservations

inallfour lterbandsrequiresaminimumoftwopointingsforagiventarget,sinceeachofthetwo

IRAC eldsofviewservesservestwoimagingchannels.Foralloftheobservationsreportedhere,

wemadethreespatialdithersineachbandtoimprovesignal-to-noiseandcosmicrayrejection.We

usedthe“HighDynamicRange”(HDR)12secondintegrationmode,whichinvolvestakingtwo

frameswithe ectiveexposuretimesof10.4and0.4seconds.

Thepre-mainsequencestarsinTaurusarewidelydispersedonthesky.Thismeansthat

mappingmethodsareine cientexceptinsomeregionssuchasL1551andL1495(whichwillbe

reportedseparately).Theobservationsreportedhereweremostlytakenin“clustermode”,which

involvesidentifyinginpidualtargetsclusteredwithinaonedegreeradiusofacommoncenter.In

allbutafewcases,onlyoneTaurusmember(system)wasobservedinasingleIRAC eld.

TheTaurusdataweretakenduringtwoIRAC“campaigns”onFebruary9-14,2004,andMarch

6-9,2004.ForcomparisonweincludeIRACdatafortheinteresting10Myr-oldstarTWHya,taken

onDec.20,2003.

ThedataframeswereprocessedbythepipelineversionS9.5attheSpitzerScienceCenter.

Photometrywasextractedfromthebasiccalibrateddataframesusingtheaperturephotometry

routineaper.prointheIDLPHOTpackage(Landsman1993).TheIDLPHOTroutineswereinte-

gratedintoacustomIDLprogramwhichusetheWCSinformationintheimageheaderstoidentify

theimagescontainingagivenstarand ndthestarwithintheimages.Theprogramthenobtains

We present infrared photometry obtained with the IRAC camera on the Spitzer Space Telescope of a sample of 82 pre-main sequence stars and brown dwarfs in the Taurus star-forming region. We find a clear separation in some IRAC color-color diagrams between o

thecentroidofthestarandextractsthephotometry.A5pixelaperturewasusedforeachstar,

withaskyannulusextendingfrom5pixelsto10pixels.Sincethezeropointsarereferencedtoa

starmeasuredwitha10pixelapertureandaskyannulusspanningradiifrom10to20pixels,we

scaledthephotometrywithanaper …… 此处隐藏：39916字，全部文档内容请下载后查看。喜欢就下载吧 ……