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arXiv:0807.2241v1[astro-ph]14Jul2008DraftversionJuly14,2008PreprinttypesetusingLATEXstyleemulateapjv.03/07/07SPITZERANDHHTOBSERVATIONSOFBOKGLOBULEB335:ISOLATEDSTARFORMATIONEFFICIENCYANDCLOUDSTRUCTURE1AmeliaM.Stutz2,MarkRubin3,MichaelW.Werner3,GeorgeH.Rieke2,JohnH.Bieging2,JocelynKeene4,MijuKang2,5,6,YancyL.Shirley2,K.Y.L.Su2,ThangasamyVelusamy3,DavidJ.Wilner7DraftversionJuly14,2008ABSTRACTWepresentinfraredandmillimeterobservationsofBarnard335,theprototypicalisolatedBokglobulewithanembeddedprotostar.UsingSpitzerdatawemeasurethesourceluminosityaccurately;wealsoconstrainthedensityprofileoftheinnermostglobulematerialneartheprotostarusingtheobservationofan8.0μmshadow.HHTobservationsof12CO2–1confirmthedetectionofaflattenedmolecularcorewithdiameter∼10000AUandthesameorientationasthecircumstellardisk(∼100to200AUindiameter).Thisstructureisprobablythesameasthatgeneratingthe8.0μmshadowandisexpectedfromtheoreticalsimulationsofcollapsingembeddedprotostars.Weestimatethemassoftheprotostartobeonly∼5%ofthemassoftheparentglobule.Subjectheadings:ISM:globules–ISM:individual(Barnard335)–infrared:ISM–stars:formation1.INTRODUCTIONBok&Reilly(1947)andBok(1948)werethefirsttosuggestthat“Bokglobules”couldbethesitesofiso-latedstarformation.Withthisinmind,B335(CB199inthecatalogofClemens&Barvainis(1988))wasexten-sivelystudiedinmolecularlines(Martin&Barrett1978;Dickman1978)andinthefar-infraredbyKeeneetal.(1980)andKeene(1981).Frerking&Langer(1982)discovereda“pedestal”source,i.e.,amolecularout-flow,indicatingthepossiblepresenceofaprotostarwithinthecloud.Thepresenceofaprotostarwasquicklyconfirmedwithadditionalfar-infraredobser-vationsbyKeeneetal.(1983).Assumingadistanceof250pc,assuggestedbyTomitaetal.(1979)andasadoptedbymostsubsequentobservers,Keeneetal.(1983)determinedtheluminosityofthesourcewithinB335tobeabout3L⊙.B335hassubsequentlybeenobservedatfar-infraredandsubmillimeterwave-lengthsby,e.g.,Geeetal.(1985),Mozurkewichetal.(1986),Chandleretal.(1990),Huardetal.(1999),andShirleyetal.(2000);itisthefirstexampleofaClass0youngstellarobjecttobesothoroughlystudied.Itisthereforethetemplatesourceformanyofourconceptsabouttheearlystagesoftheformationoflow-massstars.Modelinghasestablishedthattheglobulematerialisstillundergoingstrongnoncircularmotionsthataremostlikelyinfall(e.g.,Zhouetal.1990;Choietal.1995;Velusamyetal.1995).Althoughthisscenarioofinfall,1ThisworkisbasedinpartonobservationsmadewiththeSpitzerSpaceTelescope,whichisoperatedbytheJetPropulsionLaboratory,CaliforniaInstituteofTechnology,underNASAcon-tract1407.2DepartmentofAstronomyandStewardObservatory,Univer-sityofArizona,933NorthCherryAvenue,Tucson,Arizona85721;astutz@as.arizona.edu.3JetPropulsionLab,CaliforniaInstituteofTechnology,4800OakGroveDrive,Pasadena,CA91109.4Caltech,Pasadena,911255KoreaAstronomyandSpaceScienceInstitute,Hwaam61–1,Yuseong,Daejeon305–348,SouthKorea6DepartmentofAstronomyandSpaceScience,ChungnamNa-tionalUniversity,Daejeon305–348,SouthKorea7Harvard-SmithsonianCenterforAstrophysics,60GardenStreet,Cambridge,MA02138andmorespecificallyofinside-outcollapse,isplausi-ble,importantdiscrepanciesremain(e.g.,Wilneretal.2000;Harveyetal.2001;Evansetal.2005;Choi2007).Modelsandobservationsimplythatthecoreisastarofmass∼0.5M⊙(Zhouetal.1990)withacircumstel-lardisk∼100to200AUindiameter(Harveyetal.2003a).Thissourcehasastrongbipolaroutflow(e.g.,Cabrit&Bertout1992;Hiranoetal.1988),orientednearlyintheplaneofthesky,thatmaintainsacavityintheinterstellarmedium(ISM)andisassociatedwiththeobservedshockedmaterial(Gˆalfalk&Olofsson2007).WedescribeobservationswithallthreeinstrumentsonSpitzerandwiththeHeinrichHertzSubmillimeterTelescopethatallowusto1)measurethedensitydis-tributioninthecenteroftheglobule;2)constrainthegeometryoftheoutflowandthustheprotostellardisk;and3)measurethesourceluminosityaccurately.Thesemeasurements(withareviseddistanceof150pc)revealaflattenedmolecularcloudcore,consistentwithnumericalsimulationsofcloudcollapse;providetightconstraintsontheopeningangleoftheoutflow;anddemonstratein-ternalconsistencybetweentheglobuleluminosity(andothercharacteristics)andthoseexpectedfora0.3to0.4M⊙youngstar.2.OBSERVATIONSANDPROCESSING2.1.SpitzerdataB335wasobservedbytheSpitzerSpaceTelescopeon2004April20and21withtheInfraredArrayCam-era(IRAC;Fazioetal.2004)AORKEYs4926208and4926464;2004October15withtheMultibandImag-ingPhotometer(MIPS;Riekeetal.2004)AORKEY12022106;and2004October14withtheInfraredSpec-trograph(IRS;Houcketal.2004)AORKEY3567360.Observationsweremadeattwocloselyseparatedepochstopermittheeliminationofasteroidsfromthefinalmo-saic.ThefieldofviewwithcoverageinallfourIRACbandsis5.5′×13.6′,withalargerfieldcoveredinatleasttwobands.ForeachIRACband,3overlappingpositionsarrangedalongacolumnwereimaged.Ateachposi-tionfivesmallGaussiandithersof10.4sdurationweretaken.Intheregionwherewehadcoverageinallfour2Fig.1.—GalleryofimagesofB335(CB199)attheindicatedwavelengths.Imagesareshownwithalogarithmicintensityscaleandare1.′6onaside.Northisupandeastistotheleft.bands,thisresultedinanaverageexposuretimeofabout120sec.Foreachdither,the10.4
本文标题:Spitzer Observations of Bok Globule B335 Isolated
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