Warm Molecular Hydrogen and Ionized Neon in the HH2 Outflow

We report on spectro-imaging observations of the Herbig-Haro 2 outflow with the ISOCAM camera onboard the Infrared Space Observatory (ISO). The [Ne II}] 12.81 microns and [Ne III]15.55 microns lines are detected only towards the jet working surface (HH 2H)

WarmMolecularHydrogenandIonizedNeonintheHH2

Out ow1

B.Le och1

Laboratoired’Astrophysique,ObservatoiredeGrenoble,BP53,F-38041GrenobleC´edex9,

France

Bertrand.Lefloch@obs.ujf-grenoble.fr

J.Cernicharo2

arXiv:astro-ph/0305108v1 7 May 2003ConsejoSuperiordeInvestigacionesCient´ cas,InstitutodeEstructuradelaMateria,Serrano123,E-28006MadridS.Cabrit3LERMA,ObservatoiredeParis,UMR8112duCNRS,France3A.Noriega-Crespo4SIRTFScienceCenter,CaltechJPL,Pasadena,CA91125,USAA.Moro-Mart´ n5StewardObservatory,UniversityofArizona,Tucson,AZ,85721,USAD.Cesarsky6Max-PlanckInstitutf¨urExtraterrestrischePhysik,85741Garching,Germany

ABSTRACT

Wereportonspectro-imagingobservationsoftheHerbig-Haro2out ow

withtheISOCAMcameraonboardtheInfraredSpaceObservatory(ISO).The

[NeII]12.81µmand[NeIII]15.55µmlinesaredetectedonlytowardsthejetworkingsurface(HH2H),consistentwiththehighexcitationofthisknotintheopticalrange,whileH2purerotationalemissionisfoundallovertheshockedregionHH2.ThelowenergytransitionS(2)traceswarmgas(T～400K)peakedtowardsknotsE-Fandextendedejecta(T～250 380K)withmassesofafew10 3M⊙inthehigh-velocityCOout owextendingbetweenthepoweringsourceandHH2.Suchemissioncouldarisefromlow-velocityC-typeshocks

We report on spectro-imaging observations of the Herbig-Haro 2 outflow with the ISOCAM camera onboard the Infrared Space Observatory (ISO). The [Ne II}] 12.81 microns and [Ne III]15.55 microns lines are detected only towards the jet working surface (HH 2H)

(v 10 15kms 1).ThehighertransitionsS(3)-S(7)tracetheemissionofhotshockedgas(T=1000 1400K)fromindividualopticalknotsintheHH2region.Theorthotopara(OTP)ratioexhibitslargespatialvariationsbetween

1.2(E)and2.5(H),wellbelowitsvalueatLTE.TheemissionoftheS(3)-S(7)linesiswellaccountedforbyplanarC-shockmodelswithatypicalvelocityVs=20 30kms 1propagatingintoamediumofdensityni=104 105cm 3withaninitialOTPratiocloseto1inthepre-shockgas.Intheleadingedgeofthejet,wherethegeometryoftheemissionallowsasimplemodelling,agoodagreementisfoundwithvelocitiesderivedfromtheopticalpropermotionsmea-suredintheionizedgas.

Subjectheadings:ISM:Herbig-Haroobjects—ISM:individual(HH1/2)—ISM:jetsandout ows—ISM:molecules-stars:formation

1.Introduction

Bipolaroutlowsfromembeddedyoungstellarobjects(YSOs)areperhapsoneofthemostspectacularmanifestationsofthestarformationprocess.Oneofthebeststudiedandbrightestout owsisthatoftheHerbig-Haro(hereafterHH)1/2system(Reipurth1993).TheHH1/2systemliesintheOrionmolecularcloudat440pcandsubtendsa～2′angle.TheVLA1embeddedsource(Pravdoetal.1985)drivesahighlycollimatedjetthatreachesatomicgasvelocitiesof～480kms 1(Eisl¨o eletal.1994)andproducesshocksof～100kms 1atitsmainworkingsurfaceorbowshock(Noriega-Crespoetal.1989).Atopticalwavelengthsthereareatleast3distinctjet owsarisingwithin5′′oftheVLA1sourceandtheHH1/2bowshocksdisplayacomplexmorphologyinhighspatialresolutionHSTimages(Ballyetal.2002).Theopticaljetisassociatedwithamolecularout owwhosehigh-velocity(the”molecularjet”)coversdeprojectedvelocitiesof15 80kms 1withrespecttotheambientcloud(Moro-Mart´ netal.1999).BecauseofthesecharacteristicstheHH1/2systemisaperfecttargettostudythegaspropertiesinashockheatedenvironmentaswellasthespatialdistributionandthenatureoftheseshocks.OneofthepromisesofISOwaspreciselytobeabletodiscernbetweenthedi erentshocks,eitherC-typeorJ-type,occurringinamolecularenvironment.

We report on spectro-imaging observations of the Herbig-Haro 2 outflow with the ISOCAM camera onboard the Infrared Space Observatory (ISO). The [Ne II}] 12.81 microns and [Ne III]15.55 microns lines are detected only towards the jet working surface (HH 2H)

Wepresentherespectro-imagingobservationsoftheVLA1counter-jetandtheHH2regionobtainedbetween5and17µmwiththeISOCAMcameraonboardISO.We ndthattheH2purerotationallinesS(2)toS(7)arisefromtwophysicallydistinctregions:afaintextendedwarmgascomponentassociatedwiththehigh-velocityCOjet,seenmainlyinS(2),andseveralmorecompactpeakstracinghottershockedgasintheindividualknotsA-LofHH2detectedinalllines.Wereportalsoonthepresenceofthe[NeIII]15.55µmand

[NeII]12.8µmlines.HH2istheonlyout owoflow-luminositywheretheseinfraredlineshavebeendetectedsofar(seeCabritetal.1998).

2.Observations

AllobservationswereobtainedwiththeISOsatellite(Kessleretal.,1996)andtheISOCAMinstrument(Cesarskyetal.1996).Thelowresolutionspectra(λ/ λ=40)between5and17µmwereobtainedinrevolution691withtheCircularVariableFilter(CVF)withapixelscaleof6′′andatotal eldofviewof3′centeredontheHH2object.Thelastpipelineversionofthedata(OLP10)hasbeenprocessedfollowingthepackagedevelopedattheInstitutd’AstrophysiqueSpatiale,whichremovesreasonablywelltheproblemoftransients.Thesize(HPFW)ofthePointSpreadFunction(PSF)is≈6′′forapixelscaleof6′′.

Inordertoestablishaccurateastrometry,weusedasecondCVFmapcontainingtheopticallyvisibleCohen-Schwartz(CS)star,takeninrevolution873witha3′′pixelscale.Thisseconddatasetwasprocessedinthesamewayasmentionedabove.Unfortunately,internalre ectionsbetweentheCVFandthe eldlensproducedspuriousghostsoftheCSstar,whichisastrongIRemitter,overthefull eld,preventinganyquantitativeanalysisoftheH2lineemissionintheseconddataset.However,thepresenceoftheVLA1protostarinbothdatacubesallowstoderiveanaccurateastrometryforthe rstCVFimagetakenwitha6′′pixelscale.ThedataarepresentedinFigure1.Coordinatesareo sets(arcsec)relativetothepositionofVLA1:α2000=05h36m22.6s,δ2000= 06 46′25′′.TheinterstellarextinctiontowardsHH2wasestimatedbyHartmann&Raymond(1984),whomeasuredtypicalreddeningsE(B V)=0.11 0.44.Basedontheextinc …… 此处隐藏：18397字，全部文档内容请下载后查看。喜欢就下载吧 ……