1996AJ 112.1141H THE ASTRONOMICALJOURNALVOLUME112,NUMBER3SEPTEMBER1996 1141 Astron.J.112 (3),September1996 0004-6256/96/112(3)/1141/28/$10.00 ©1996Am.Astron. Soc.1141 © American Astronomical Society • Provided by theNASA Astrophysics Data System knot inthejet.Thesewispshave anarcuatemorphology,withtrailingwingswhichsweep backatan body ofthejetweidentifymanyshocksinwhichBaimeremission arisespredominantlyfromcollisional Astronomy, DepartmentofAstrophysical,PlanetaryandAtmosphericSciences,UniversityColorado,CampusBox389,Boulder, detected asanHafilamentwhere theshockfrontliesalmosttangenttolineofsight.The factthatwe oblique angletothedirectionof theflow.Theythusresembleone-sidedbowshocksthatextend intoand Balmer-line filamentsareonly0"2-0'.'3widebutcanbeupto2" long.Eachisassociatedwitha[Sll]-bright marking whereshockwavesaredrivenintothe(apparently) neutralgassurroundingthejet.These The jethasacomplicatedstructureconsistingofsinuouschain ofemissionknotsandstrands.The[Sll] excitation inthethinheatingzoneatshockfront.Thebody of thejetisseenprimarilyin[Sll]emission. unprecedented detail.Inparticular,weareabletoresolvethesizesofemissionknotsandfilaments, high signal-to-noiseoftheseimages,allowsustostudythiscollimatedoutflow,drivenbyayoungstar,in resolution oftheWFPC2images(correspondingto45AUatdistanceHH46/47),coupledwith We presenthigh-resolutionemission-lineimagesoftheremarkableHerbig-HarojetHH46/47obtained 1 Center forAstrophysicsandSpaceAstronomy.DepartmentofAstrophysical,PlanetaryAtomosphericSciences,University Space TelescopeScienceInstitute,3700SanMartinDrive,Baltimore,Maryland21218andCenterforAstrophysics accelerate theambientgas.All knotsinthejetmayexcitesimilarshockwaves,however,these areonly visible inthebestground-basedimages.Weidentifythesewisps asBalmer-lineemittingshockfronts Hawe seewithabsoluteclaritythedelicatewispsandfilaments borderingthejetthatwereonlybarely of timevariabilityinthevelocityanddirectionejection may explainthejetssinuousstructure.In emission inthejetappearstoarisewhereshocksareexcited thejetmaterialbyitsinteractionwith observed structuresintermsofradiativeshockmodels.Both themajorworkingsurfacesandalong determine thestructureandscaleofcoolingzonebehind shockwavesintheflow.Wediscuss transmits Ha.Theexposuresthrougheachfilterhadatotalintegrationtimeof11,900s.O'.'lspatial narrowband filterswereused,F673Nwhichisolatesthe[Sil]XX6716,6731doublet,andF656N surrounding gasandbycollisionsbetweenfasterslowermoving segmentsoftheflow.Acombination with theWideFieldandPlanetaryCamera2(WFPC2)aboardHubbleSpaceTelescope.Two Department ofPhysicsandAstronomy,UniversityMissouriatSt.Louis,8001NaturalBridgeRoad,63121 HUBBLE SPACETELESCOPEOBSERVATIONSOFTHEHH47JET:NARROWBANDIMAGES Cetro TololoInter-AmericanObservatory,NationalOpticalAstronomyObservatories,Casilla603,LaSerena,Chile Department ofSpacePhysicsandAstronomy,RiceUniversity,Houston,Texas77251-1892 Department ofAstronomy,UniversityMaryland,CollegePark,Maryland20742-2421 European SouthernObservatory,Casilla19001,Santiago19,Chile Colorado, CampusBox389,Boulder,Colorado80309 Received 1996March15;revisedMay28 Electronic mail:[email protected] Electronic mail:[email protected] Electronic mail:[email protected] Electronic mail:[email protected] Electronic mail:[email protected] Electronic mail:[email protected] Electronic mail:[email protected] Richard D.Schwartz Patrick Hartigan Steve Heathcote James M.Stone Jon A.Morse Bo Reipurth Colorado 80309 John Bally ABSTRACT 1142 HEATHCOTE ET AL. : THE HH47 JET 1142

see strong Baimer emission from the shock fronts, and that high excitation lines such as [Olll] are not detected in ground-based spectra, implies that the shocks driven into the ambient medium are weak 1 {Vsh< 100 km s" ). However, proper motion measurements show that these shock systems propagate along the jet at —300 km s-1. Hence material alongside the jet flows away from the source at an appreciable fraction of the jet’s velocity. We believe that the dominant process that accelerates the gas surrounding the jet is prompt entrainment, where the major bow shocks HH 47D and HH 47A, aided by the lesser but more frequent Baimer-arc-shocks, push material ahead and away from the axis of the jet. The very extended wings of HH 47D and HH 47A suggest that their influence may be felt far from the jet’s axis. Prompt entrainment by these bow shocks might drive the weak, approaching lobe of the molecular flow associated with the HH 47 complex. The long term meandering of the jet, evident from the misalignment between the bow shocks and the jet, may further widen the flow channel. As the jet changes direction, the newly ejected gas will entrain material from the cloud, and this could produce the observed filaments in the reflection nebula that extend roughly parallel to the northern boundary of the jet. Our high-resolution images show no clear evidence for a turbulent mixing layer at the interface between the jet and its surroundings. In the HH 47A working surface at the terminus of the jet we resolve the double shock structure expected from theory. Both the forward (or bow) shock and reverse shock (or Mach disk) have collisionally excited Ha components that delineate the positions of the respective shock fronts. Sandwiched between these two shock waves is a region, luminous in [S li], where the shock-heated gas cools. The turbulent structure seen in [S ll] suggests that instabilities fragment the cooling, compressed material into clumps, as seen in some hydrodynamical simulations of jets. Our realization that the Ha luminosity of the Mach disk arises from collisional excitation at the shock front, and our discovery of a similar Ha-bright leading shock, leads us to reassess the relative strengths of the two shocks. We conclude that they are of comparable strength, and hence that the jet is of similar density to its surroundings. This is contrary to the earlier findings that the HH 47 jet was a rare example of a “light” stellar jet. © 1996 American Astronomical Society.

1. INTRODUCTION The HH 47 jet emanates from an isolated Bok globule (Bok 1978), which harbors an embedded infrared source Herbig-Haro jets have, in recent years, emerged not only (e.g., Emerson et al. 1984; Cohen et al. 1984). A view of the as interesting astrophysical laboratories for the study of entire HH 47 complex is given in Fig. 1, a composite of shock physics and chemistry, but also as key phenomena for Ha and [S ll] images obtained at the ESO New Technology understanding the mechanisms at work in assembling a star. Telescope. The flow is bipolar, with the northeastern lobe Among the known Herbig-Haro jets, the HH 46/47 jet (here- approaching us and the southwestern lobe receding. Both after the HH 47 jet) occupies a prominent position. Discov- lobes terminate in extended bow shocks, HH 47D in the blue ered by Schwartz (1977), it was the first HH object to be lobe and HH 47C in the red lobe, located symmetrically recognized as a jet driven by a young star (Dopita et al. about the embedded source. At an assumed distance of 450 1982). HH 47 is so bright that an impressive battery of (pre- pc the total projected extent of the system from HH 47D to dominantly ground-based) observational techniques have HH 47C is 0.57 pc (Dopita et al. 1982; Graham & Elias been employed in its study. 1983). The HH 47 jet itself, located in the approaching lobe, Ground-based images obtained in excellent seeing have terminates in the bright bow shock HH 47A. A faint coun- been used to investigate its structure (Reipurth & Heathcote terjet has been found in the red lobe (Reipurth & Heathcote 1991; Eislöffel & Mundt 1994); radial velocities and excita- 1991). The counter-flow is partly obscured as it burrows be- tion conditions have been probed using high-resolution slit- low the surface of the globule, but even infrared observations spectra (e.g., Meabum & Dyson 1987) and Fabry-Perot in- have failed to detect a counterpart to the HH 47 A bow shock terferometry ( Hartigan et al. 1993; Morse et al 1994); and (Eislöffel et al. 1994). Combining the radial velocities mea- transverse velocities have been estimated from proper- sured by Morse et al. (1994) with the proper motions deter- motion measurements (Schwartz et al. 1984; Eislöffel & mined by Eislöffel & Mundt (1994; corrected from the 350 Mundt 1994). This wealth of observational data has in turn pc distance they assumed to the 450 pc adopted here), one stimulated theoretical efforts to understand various aspects of calculates that the axis of the jet makes an angle of —28° to HH 47 and similar objects (e.g., Raga et al. 1990; Stone & the plane of the sky. The jet moves away from the source at Norman 1993; Gouveia Dal Pino & Benz 1994; Biro et al. -1 1995). Together, these observational and theoretical efforts a space velocity of —300 kms , while space velocities of have led to a comprehensive and, more or less, self- similar magnitude are seen in the counter flow. consistent picture of the HH 47 outflow. The presence of multiple bow shocks in the blue lobe suggests that the HH 47 outflow has been episodic with the

1 source undergoing major outbursts at intervals of 500-1000 Based on observations made with the NASA/ESA Hubble Space Telescope, years (Dopita 1978a, 1978b; Reipurth 1989; Reipurth & obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA Heathcote 1991). Added support for this comes from the contract NAS5-26555. kinematics of HH 47A and HH 47D ( Hartigan et al. 1990;

© American Astronomical Society • Provided by the NASA Astrophysics Data System 1996AJ 112.1141H be relatedtothe FUOrionisphenomenon (Dopita 1978a,b; phology andkinematicsofHH 47andsimilarsystems(e.g., pulsed jetsarequitesuccessful inreproducingthegrossmor- Reipurth 1989). Spectraofthebrightreflection nebulaatthe Raga etal.1990;Stone&Norman 1993;GouveiaDalPino Reipurth etal.1992;andHH 34:Reipurth&Heathcote loss hasbeenfoundinseveralotherHHjets(e.g.,111: tial velocity.Thisisexpectedifittravelsinthewakeof an that isalreadystreamingawayfromthesourceatasubstan- Morse etal.1994).HH47Aappearstobeoverrunninggas & Benz1994). Therecurrenteruptionsof the sourcemight outburst ofthesource.Similarevidenceforepisodicmass disturbance, indicatingthatitisnottheresultoffirst vance intogassetinmotionbythepassageofayetearlier older bowshock,HH47D.Intum,47Dappearstoad- of HH47withintheWFPC2fieldview. obtained attheESO3.5mNewTechnologyTelescope.Thefieldis7:4Xandnorthupeasttoleft.grayrectanglesindicate placement of theglobuleiscausedbyluminoushotstarsatcenterGumNebulatowardsnorthwest.ThisimagesumHaand [S n]images Fig. 1.TheHH47jetcomplexanditsassociatedBokglobulearehereseenagainstthebackgroundemissionofGumNebula.windswept appearance 1992; Bally&Devine1994) andtheoreticalmodelsof 1143 HEATHCOTEETAL.:THEHH47JET © American Astronomical Society •Provided bythe NASAAstrophysics Data System Raga &Cabrit 1993). TheFabry-Perotdata of Hartiganetal this way,beresponsiblefor drivingassociatedmolecular lent” entrainment).Ithasbeen suggestedthatjetsmay,in the bowshock(aprocessknown as“prompt”entrainment) to thesurroundinggasdraggingitoutward(DeYoung1986; base ofthejetshowthat,currently,sourceisinanactive outflows (e.g., Masson &Chemin1993;Raga etal.1993b; Chemin etal.1994).Momentum transfermayoccurbothat lobe. Asitadvances,aHerbig-Harojettransfersmomentum metric withawell-developedredlobe,butonlyweakblue nin &Masson1991;Olbergetal.1992).Thisflowisasym- Heathcote 1991). T Tauriphase(e.g.,Graham&Heyer1989;Reipurth & and inaboundarylayeralong theedgeofjet(“turbu- (1993) showthat gasontheaxisofHH47 jetflowsfaster The HH47jetisassociatedwithamolecularflow(Cher- 1143 1996AJ 112.1141H -1 -1 -1 here. 47 jet(Raymondetal1994),however,were-evaluatethese data inthecontextofhigh-resolutionimagingpresented resolution ofthesenewimagesenablesustostudythisstel- scope throughHaand[Sll]filters.Theoutstandingspatial dence forturbulententrainmentalongtheedgesofHH of theHH47complexobtainedwithHubbleSpaceTele- than thatalongtheedges.Thishasbeeninterpretedasevi- even thebestground-baseddata.Inparticularweareableto lar jetinmuchgreaterdetailthanhasbeenpossiblewith the complexstructureofHH47Aworkingsurface.They the jetwhereitinteractswithsurroundinggas.Ingeneral, spatially resolvethecoolingzonebehindanumberof shock wavesitcontains.Ourobservationsallowustoprobe they leadustoquestionwhetherturbulententrainmentis our resultsconfirmandelaboratethepictureofHH47 also providethefirstclearviewofzonealongedge outflow builtuponthebasisofground-baseddata.However, ideas onhowsuchjetsarecollimated. operating alongthejet,andchallengesomecontemporary 1144 HEATHCOTEETAL:THEHH47JET Trauger etal.1994).Briefly,theWFPC2isareimaging and PlanetaryCamera2(WFPC2)aboardtheHubbleSpace camera thatsplitsthefocalplaneoftelescopeintofour CCDs. Correctiveopticsincludedintheinstrumentcompen- Telescope (HST).Thisinstrumentisdescribedindetailthe in thetelescopeprimarymirror,anddelivernearly diffraction-limited images.Threeofthecameras,referredto sections, thenimageseachofthesesectionsontoonefour WFPC2 InstrumentHandbook(Burrows1995;seealso WF3 CCDwithitsaxisrunningalongthediagonalof pixel (—21AU). the PlanetaryCameraor“PCI,”providesascale—0.046 cal planeatascaleof—O'.'lpixel(correspondingto sate forthesphericalaberrationcausedbyafabricationerror within theWFPC2fieldofview,jetwasplacedon as theWideFieldCamerasor“WF2-WF4,”imagefo- HH 47D,wasprimarilyimagedonthePCIchip,althoughits chip (seeFig.1).Consequently,thefaintouterbowshock, Two narrowbandfilterswereused,F673Nwhichisolatesthe wings spilledoverontotheadjacentWF2andWF4CCDs. Ha (withaminorcontributionfromthelinesof[Nil]XX — 45AUpixelatthedistanceofHH47).Theother,called the remainder3100s.Thesamenominaltelescopepointing was maintainedthroughoutthe sequence.However,there obtained throughthe[Sll]filterinsuccessiveHSTorbitson 6548,6583 inthewingsofpassband).Fourimageswere [S il]XX6716,6731doublet,andF656Nwhichtransmits tained duringasecond“visit” on 1994March29.Thepo- Ha exposures(again1X2600 s plus3X3100s)wereob- were small(sub-pixel)shifts from orbit-to-orbit,which somewhat complicatedthe datareduction.Four sitioning ofthe objectonthedetectorswasreproduced to 1994 March26.Thefirstexposurehadadurationof2600s, In thispaperwepresentimagesoftheapproachinglobe We obtainedimagesoftheHH47jetwithWideField To fittheentireapproachinglobeofHH47outflow © American Astronomical Society • Provided by theNASA Astrophysics Data System 2. OBSERVATIONSANDDATAREDUCTION 2 be quitenegligiblegiventheshortintervalbetweenvis- within afractionofpixel.Shiftsduetopropermotionswill its. environment. ThestandardWFPC2pipelineproceduresand masking badpixels,correctionofanalog-to-digitalconverter calibration fileswereusedforthefirstthreereductionsteps: the lastsixcolumnsofoverscanstrip.Theremaining errors, andsubtractionoftheaveragebiaslevelderivedfrom used calibrationfilesprovidedbytheWFPC2instrument team, preparedaccordingtotheprescriptiongivenbyHoltz- high signal-to-noise,on-orbit,“superbias”frame,obtained man etal(1995a).Thelow-levelbiasstructureremaining scribed indetailbyHoltzmanetal.(1995a).Indoingsowe steps wereperformedusingtheoptimumproceduresde- taken theWFPC2CCDswerebeingoperatedat—76°C.At close tothedateofobservation.Attimeourdatawere after theoverscancorrectionwasremovedbysubtractinga many hotpixels,thenumberandbrightnessofwhich this temperaturethemeandarkcurrentishigh,andthereare long exposures.Darkcurrentsubtractionwasaccomplished changes rapidlywithtime.Thusthecorrectsubtractionof dark currentwasofparticularconcern,especiallygivenour in atwo-stageprocess.First,highsignal-to-noise“super- pixels thatvariedsignificantlywereadjustedbysubtractinga correct pixelsthathaveconstantdarkrate.Thenthosehot dark” framewasscaledandsubtractedfromeachimageto but themosthighlydeviantpixels.Tocorrectforpixel- tions andthe“superdark,”whichwasmaskedtoremoveall frame takennearintime(1994March29)toourobserva- to-pixel responseandvariationsintheillumination,weap- region ofWF3(whereweplacedtheHH47jet),andwere plied thelateston-orbitflatfieldsforeachfilterandCCD so-called “delta-dark.”Thisisthedifferencebetweenadark plied bytheratioofexposuretimes(3100/2600)afterflat per unitareaineachchip(seeHoltzmanetal.1995a).The chip. Theflatfieldswerenormalizedtounityinthecentral be detectedandeliminatedbyintercomparisonoftheframes cross-normalized togivethesamenumberofcounts(ADU) by theslight(sub-pixel)displacementsbetweensuccessive in eachsequence.Thisprocesswasmademorecomplicated contained manycosmicrays(CRs).Thesewouldnormally fielding, tomatchthesignallevelthatinotherframes. shorter exposureineachemission-linesequencewasmulti- them, tomaintainthehighestpossiblespatialresolution. images. Wewantedtoregistertheimagesbeforecombining ringing oftheinterpolator.Wethereforewroteamodified the CRs(manyofwhichweresinglepixelevents)dueto However, shiftingtheimagesintroducedsevereartifactsnear version oftheSTSDAStaskcrrejwhichdetectsCRsby The ImageReductionandAnalysisFacility (IRAF)isdistributedbythe vidual frames.Likethestandardtaskthiscompares,pixel- comparing multipleimages,butexcisesthemfromtheindi- ciation ofUniversitiesforResearchin Astronomy, Inc.,undercooperative National OpticalAstronomyObservatories, whichisoperatedbytheAsso- ence DataAnalysisSystem(STSDAS) is distributedbytheSpaceTelescope agreement withtheNationalScienceFoundation. TheSpaceTelescopeSci- Science Institute. 2 The datawerereducedintheIRAF/STSDASsoftware Again duetothelongexposures,ourindividualimages 1144 1996AJ 112.1141H -21 the inputimagethenreplacesallpixelsjudgedtobecon- to theinputdatavalueminussigmaclippedmean.Else- taminated withthemeanvalue.Obviously,simplyaveraging where ithasthevaluezero.SubtractingCRimagefrom ever apixelintheinputimageisrejectedCRset mal outputofcrrej.However,itisnowpossibletoshiftthe these cleanedimagesproducesaresultidenticaltothenor- outputs a“cosmicrayimage”foreachinputimage.Wher- boring pixels.OncetheCRshadbeenremoved,itwasap- ployed a5crrejectionthreshold,with3(7forneigh- quite highenergiesandarethuseasilyrecognized.Weem- Holtzman etal.(1995a),theCRsinWFPC2imagesallhave cleaned imagesslightlypriortoaveraging.Asdescribedby to discardpixelsadjacentaCRhit.Themodifiedprogram may beiterated,andamorestringentthresholdused forms themeanofremainingpixels.Therejectioncycle parent thatseveralhotpixelshadnotbeencorrectedbythe were identifiedandrepaired. were patchedusingimedit.Similarly,severalcoldpixels the CRcleanedimagesusingIRAFtaskcosmicraysand in maskingthe“delta-dark.”Thesepixelswereidentified dark subtraction,becausetheyfellbelowthethresholdused pixel. Thusneithertheinter-chiprotations,norfielddis- The shiftsbetweenimageswereatmostasmallfractionof using 61starsspreadoverthefourCCDchipsastiepoints. images, totheexpectednoise,andrejectsoutliers.Itthen by-pixel, thescatterofdatavaluesinstackinput placements was—0.01WFpixels.Duringeachsequenceof need betakenintoaccountwhenmeasuringorcorrecting tortions introducedbytheWFPC2optics(seeBurrows1995) them. Thermsscatterinthemeasuredframe-to-framedis- mosaicked usingwmosaic(WFPC2version). ing illustrationsonly,theimagesfromfourcameraswere the WFPC2opticswerecorrectedusingcoefficients combined frames.Thegeometricaldistortionsintroducedby interpolation. Afterregistration,thefourexposuresforeach posures ineachsequencewas—0.27WFpixels.Theimages positioning leadingtoashiftbetweenthefirstandlastimage exposures (F673N,F656N)therewasasteadydriftinthe given byHoltzmanetal.(1995a).Forthepurposeofprepar- were alignedwiththeIRAFtaskimshiftusingcubicspline of —0.15WFpixels.Thedisplacementbetweenthefirstex- the fluxby: filter wereaveragedtoformthefinalcleaned,shiftedand electrons detectedinagivenpixelontheCCDisrelatedto dure developedbytheWFPC2instrumentteam(Sparks applicable toemission-lineobjects.Insteadweusedaproce- culated bydividingeachaveraged imageby3100sandthen where Fisthefluxinergscmspixelatwavelength quantum efficiency),andA^isthe countrateinelectronsper cludes thetelescopeandfilter transmissionandtheCCD scope andafactorofhe.The count rateperpixelwascal- second. Theconstantfoldsinthe collectingareaofthetele- X (inA),7\isthetotalsystem throughputatX(whichin- 1145 HEATHCOTEETAL.:THEHH47JET 1995; seealsoHoltzmanetal.1995b).Thenumberofphoto- x el All oftheimageswereregisteredtofirst[Sn]image The standardWFPC2fluxcalibrationprocedureisnot f\ =4.39X © American Astronomical Society • Provided by theNASA Astrophysics Data System - - These curveswerederivedbyreconcilingprelauncheffi- Holtzman etal.1995b)fortheF673NandF656Nfilters. throughput wasestimatedfromtheefficiencycurvesin multiplying bythegainofWF3CCD,6.9e/ADU.The the filterbandpass,soweadoptedthroughputatrest tometric standards.TheradialvelocitiesintheHH46/47jet ciency measurementstoon-orbitobservationsofspectropho- wavelength ofeachline.ThethroughputtheF673Nfilter members ofthe[Sll]doublet,someantwovalues are notlargeenoughtoshifttheemissionsignificantlywithin was used. differs byonly—0.5%betweenthewavelengthsoftwo effective sensitivityacrossthechip(Holtzmanetal. cies intheWFPC2CCDscauseasystematicgradient WFPC2 InstrumentHandbook(Burrows1995;seealso the backgroundlevelincreases.Togetherdarkcurrentand this effectcanexceed10%,butdecreasesinimportanceas problem mightbereducedto—5%(Holtzmanetal.1995b). F656N, butwithconsiderablespatialvariation.Atsuchlev- emission fromtheunderlyingnebulositycontributeaback- els thegradientinsensitivitycausedbychargetransfer ground levelof-60^”intheF673Nimagesand—80e servations. Intheworstcaseofzerobackground,size here arenotdependentonaccurateabsolutefluxmeasure- estimate thatourabsolutefluxesareaccurateto—10%.This in ourdata.Inviewofthechargetransferproblem,and ground inourimageswemadenoattempttocorrectforthis especially giventhecomplexstructureofemissionback- due tothechargetransfereffect,cancelinsuchrelativemea- Ha and[Sii].Boththeuncertaintiesinfluxcalibration, of thesamefeature,orcloselyneighboringfeatures,in ments. Ourchiefconclusionsrestontherelativebrightness using thesamefluxcalibrationtechnique(e.g.,Tsvetanov accuracy achievedforotherWFPC2emission-lineimages data andground-basedfluxmeasurements,aswellthe is consistentwiththeresultsofacomparisonbetweenthese various uncertaintiesinthefluxcalibrationprocedure,we Since thisproblemhasyettobefullycharacterized,and residual opticalandopto-mechanicaleffectsinthetelescope the resultingimagesarenotquitediffractionlimiteddueto et al.1996).Westresshoweverthattheresultspresented White andJingerMo(STScI).A spatiallyvaryingPSF(SV- by himself,DavidRedding(JPL), RobertHanisch,Richard tion (PSF).TheportionofourHH47Ha(F656N)and[Sll] improve thespatialresolutionanddynamicrangeofob- noise data,deconvolution(imagerestoration)techniquescan assembly largelycorrectthetelescope’ssphericalaberration, surements. 1995a,1995b). Thiseffectwasespeciallypronouncedatthe tion, modifiedby anassessmentofthetime-varying opto- PSF) wasmodeledbasedonthe nominalopticalconfigura- and instrument,chargemigrationintheWFPC2CCDs — 76°Coperatingtemperature,usedatthetimeofourob- volved byAndrewBoden(JPL) usingalgorithmsdeveloped servations, givenareliablemodelofthepointspreadfunc- (Holtzman etal.1995a).Consequently,forhighsignal-to- (F673N) imagesrecordedon the WF3chipweredecon- It hasbeenfoundthatparallelchargetransferinefficien- Although thecorrectiveopticsincludedinWFPC2 1145 1996AJ 112.1141H 1 182 jects (e.g.,Reipurth&Heathcote1991).However,aswe features visibleintheHSTimages, workingoutwardfrom plete identificationsoftheknots inHH47aregivenby kms“; Hartiganetal1987;1994).Differ- tios correspondingtohighershockvelocities(for Reipurth &Heathcote(1991; see alsoEislöffel&Mundt where wehavelabeledvarious features fordiscussion.Com- ferent fromtheintegratedvalueforshockasawhole. interpreting theseexcitationdifferencesintermsofshock best seeinggroundbasedimages).Careisthenrequiredin identifying regionsofdifferentexcitationinHerbig-Haroob- ence imageslikeFig.4havebecomeapowerfultoolfor strength, becausethelocalHa/[Sll]ratiomaybeverydif- may beresolvedatthespatialresolutionofHST(andin discuss inSec.4,thethicknessofpostshockcooling-zone often usedasadiagnosticofshockstrength,withlargerra- gions appearredandpureHagreen.TheHa/[Sll]ratiois is acolorcompositeimageinwhichpure[Sll]emittingre- result ofsubtractingtheHaand[Sll]imagesdisplayedin present twodifferentcompositeimages.Figure4showsthe readout noiseperrebinnedpixel.TheFWHMofstellarim- WF chips;sincethenoiseisdominatedbyreadnoiseand ages inthecombinedframesis—1.5pixels. on thePCICCDisafactor—1.41greaterduetolarger the upperlefthandcomerofmosaicwhichwasimaged the brightnessofbackgroundnebula.Thermsnoisein dark currentitissimilarinbothfiltersandonlyvaries background is—1.0X10“ergcm”s”pixel“onthe shown inblack,whileHa-brightregionsarewhite.Figure5 such awaythatregionsemitpredominantlyin[Sll]are emphasize thefaintest,diffusefeatures.Eachimagerepre- of theoutflow,inwhich“stretch”hasbeenchosento mosaic ofalltheCCDscoveringentireapproachinglobe WF3 CCD;gray-levelshavebeenchosentodisplayfeatures tween thesourceandHH47A,whichfellentirelyon panel ineachfigureshowsthebrightsectionofHH47,be- volved) areshowninFigs.2and3,respectively.Themain slightly overtheframe,despitesignificantvariationin sents atotalexposuretimeof3.3hours.Thermsnoiseinthe in therelativelybrightbodyofjet.Theinsetshowsa 1994). torations tohighsignal-to-noisestructuresonly. images toreducenoiseamplificationandrestricttheres- the HH47imagesweredeconvolvedfor200iterations.A code, calledMPLucy(Bodenetal1995;White1994),and smooth backgroundmodelwasinitiallysubtractedfromthe was fedtoadampedLucy-Richardsonimagerestoration cycles, aswellchargediffusionintheCCD.TheSV-PSF tion retrievaltargets.TheSV-PSFmodelingaccountedfor secondary mirrorde-focusduetosolar-inducedthermal mechanical stateoftheffiT/WFPC2system(Reddingetal 1993,1994) usingstarsintheWF3fieldofviewasprescrip- 1146 HEATHCOTEETAL.:THEHH47JET In theremainderofthissection wediscusstheprinciple Finally, Fig.6showsthesumofHaand[Sll]images, To aidinrelatingthefeaturesseen[Sll]andHawe Our finalcombined[Sll]andHaimages(notdecon- © American Astronomical Society • Provided by theNASA Astrophysics Data System 3. OVERALLMORPHOLOGY Am this curiousfeature furtherinSec.6.5. from thetipofHH46segment ofthejet.Wewilldiscuss only —073wideandappearsto trailbackatanobliqueangle image (Fig.4).Thefilamenthas alengthof—377butis rms noiselevelofthelocal“background”is—3%inboth filament istheonlyfeaturethat remainsinthedifference equally brightinbothfilters.Consequently, theHa-bright flection nebulahasacomplexstructureinthisregionis formly mustardcoloredreflectionnebula.Althoughthere- where itappearsasavividgreenstreakcrossingtheuni- that ofitssurroundings,whilein[Sll]itisundetected(the In Hathisobjecthasabrightnesssome30%greaterthan north ofHH46,yetthereisnotracethisfeaturein[Sll]. posed onthebrightestpartofreflectionnebulato Ha anarrow,almoststraight,emissionfilamentissuper- the highvelocityoutflow. löffel &Mundt1994)clearlyindicatethattheyformpartof filters). Thisfilamentisreadilyapparentininset4ofFig.5 that are[Sii]-bright.However,theirhighradialvelocity respect theydifferfromtheknotsinmainbodyofjet therefore arenotprominentinthedifferenceimage.Inthis They havesimilarsurfacebrightnessinHaand[Sll] the infraredsource.Equivalentlyourorderofpresentationis, known fromgroundbasedstudies.Theseknotsareresolved the Ha-[Sll]imageFig.4(thedifferencebetweenHa tion inHaisoffsetbythebroaderbandpassof[Sll] Heathcote 1991).Butbygoodfortunethebrighterillumina- reflection nebulaisonlyanunwelcomecomplicationwhen perhaps bearwitnesstoaninteractionbetweentheoutflow be seenstretchingoutparalleltotheaxisofjet.These interferometric measurementsofCuriel(1996)ismarked globule andisonlydetectableatIRlongerwavelengths which drivestheHH47outflowisdeeplyembeddedin quent sections. from themostrecentlyejected,tooldestpartsofflow. in theframeworkofanepisodicoutflowmodelHH47, and appeardiffuse,lackinganyobviousinternalstructure. in inset4ofFig.5.Thesectionthejetclosestto the subtraction). filter, sothatthereflectionnebulaisvirtuallyeliminatedin nebula. Inparticularseveralthinfilamentsorstreamerscan its northwestedge.Ourhigh-resolutionimagesrevealcon- nebula thatenvelopesthebaseofjetandextendsalong with acrossinFig.6.Thesourceilluminatesreflection Specific regionswillbeanalyzedinmoredetailsubse- (e.g., Morseetal1994)andsubstantialpropermotions(Eis- spatially inourHSTimages(theyare—077-O'.8width) and [Sll]bandwidthexplainswhystarsarenoteliminatedby and thedensematerialalongitsedges. source, HH46,istracedbyalineofthreeknotsalready [S ll],becausethestarhasstrongHaemission(Reipurth& studying thelowerpartofjet.ItisbrighterinHathan siderable structureinthedustymaterialofreflection (e.g., Emersonetal1984;Cohen1984).Itsposition, a=082543?79, <5=-5r00'35'.'8(J2000)fromtheradio Our HSTimagesdorevealaremarkablenewfeature.In From thepointofviewpresentinvestigation, A detailedviewoftheregionatbasejetisgiven The baseoftheJetandReflectionNebula:source 1146 1996AJ 112.1141H bright reflectionnebulawhichenvelopes thebaseofjetandextendsalongitsnorthwesternedge.Thebody ofthejet,verybrightin[Sn],consistsa images inthispaper,northisrotated about11°clockwisefromthevertical. CCDs showingtheentireapproaching lobeoftheflow.ThefaintouterbowshockHH47Dliesinupper comerofthemosaic.Inthis,andremaining IR sourcelocatednearthelowerrighthandcomerofframe.The illuminatesthewallsofcavitythroughwhichjetemerges,producinga Fig. 2.AnHSTimageoftheHH47outflowtakenthrougha[Sn]filter. ThemainpanelshowsadetailedviewoftheHH47jet.jetispoweredbyan winding chain of brightknots,theHaframe showsadelicateofthejet, whiletheHaemissioncomes predominantlyfrom anee ofthejet inHaand[SII].While [SII]weseeaHere seethatthe[Sll]-brightknots delineatethe“core” sinuous chainofknots.Theworking surface,ofthejet,HH47A,isseenatupperlefthandcomer.Theinset isamosaicoftheimagesfromallWFPC2 1147 HEATHCOTEETAL:THEHH47JET sion givenby our HSTimagesisthevery different appear-twostructures becomesclearinthe Ha-[S il]image(Fig.4). The bodyofthejet:Atfirstglance, thestrongestimpres-traceryofnarrowfilaments. Therelationshipbetweenthese © American Astronomical Society •Provided bythe NASAAstrophysics Data System 1147 1996AJ 112.1141H back alongitsnorthwesternwing. becoming lostinthephotoionizedbright rimoftheglobule.TheHH47Dbowshockismoreprominentin Ho- andfaintpatchesofemissioncanbeseenfar leaving behindonlyafinetraceryof faintwispsandfilaments.AlongstreamerofHaemissiontrailsbehind HH47Aonitsnorthwesternsideeventually Fig. 3.AnHSTimageoftheHH47 outflowthroughanHafilter.Inmarkedcontrasttothe[Sn]imageof Fig. 2,thebodyofjethasallbutdisappeared 1148 HEATHCOTEETAL.:THEHH47JET © American Astronomical Society •Provided bythe NASAAstrophysics Data System # Ha 1148 1996AJ 112.1141H 1149 HEATHCOTEETAL.:THEHH47JET knots inthecoreofjetlikewingsminiaturebow do notsubtractout,becausethe[Sn]filterismuchwiderthanHafilter. Thereflectionnebulahasalmostdisappearedbecausebychancethepresenceof white. ThewispsandfilamentsseenintheHaimagearelocatedat edgesofthe[Sii]-brightjetwhereitshowsabruptchangesindirection.Fieldstars Fig. 4.AnHa—[Sn]differenceimageoftheHH47jetbasedonHST imagesinFigs.2and3.[Sii]-strongregionsareblack,Ha-strong the zonealongedgesofjet.Themostprominent Ha emissionfromtheembeddedTTauristarcompensatesforwider bandwidthofthe[Sn]filter. HST. The[Sll] structuresinthecoreof jet appearlargely Ha-bright filaments(see,e.g.,inset3ofFig.5)trailbehind thin skinofHaemission(seeinset3Fig.5).Thissegre- the Hafilaments,severalof which areunresolvedevenwith However, ournewimagesreveal theremarkablethinnessof cote (1991)whichalsoshow someofthetrailingfilaments. gation of[Sii]-brightandHa-bright materialwasalready relatively smooth strandsofemission. resolved, and consist ofcompactknotsoften connectedby apparent intheground-based imagesofReipurth&Heath- shocks. Manyoftheotherknotsappeartobecloakedin a © American Astronomical Society Provided bytheNASA Astrophysics l)ata System -1 -1 have sketchedtheapproximatedividinglinesbetween moves muchfasterthanthatalongtheedges.InFig.7 we that the[Sii]-brightcoreof jetisfastmoving,whilethe the exactdivisionchosenis somewhat arbitrary,itisclear to —80kms;seeFig.3 of Hartiganetal1993).While Ha-bright envelopeisslowmoving. with severalabrupt changesinitsapparent direction.We s) and“slow”movingjet gas(radialvelocityfrom—140 (1993) showthatmaterialnearthecenterofHH47 jet stress thatour images onlyshowthegaswhere itisradiating “fast” moving(radialvelocitybetween—230and—170km The ground-basedFabry-PerotdataofHartiganetal. Especially in[S n],thejetshowsconsiderable wiggling 1149 1996AJ 112.1141H 1150 HEATHCOTEETAL:THEHH47JET © American Astronomical Society •Provided bythe NASAAstrophysics Data System

Fig. 5. A color composite picture derived from the HST images in Figs. 2 and 3 in which [S n] bright material appears red and Ha-bright material is green. The insets provide a close up view of a number of specific 1150 regions discussed in the text: (1) the HH 47 A working surface; (2) the region near knot A16 located at a substantial bend in the jet; (3) the Ha filaments associated with knots A22 and A26 ; (4) the base of the jet including HH 46 and its associated Ha filament. 1996AJ 112.1141H 1151 HEATHCOTEETAL:THEHH47JET jet’s trajectory isprobablygivenbythe edges ofthefast behind shocks.Itisveryunlikely thattheflowtrulyfollows ballistically awayfromthesource. Abetterindicationofthe the tortuouspathmappedout bythe[Sli]emission.Each have clearlybeen substantialchangesinthe outflowdirec- moving, [Sll]-bright coreoutlinedinFig. 7. Evensothere fluid elementinsuchahighly supersonicflowwillmove Fig. 6.ThesumoftheHaand[Sn]HSTimagesHH47jetfrom Figs.2and3.Variousfeaturesarelabeledforsubsequentdiscussion. © American Astronomical Society •Provided bythe NASAAstrophysics Data System best Hafilamentsoccuratbends inthejet,andinvariablylie for aperfectlystraightjet.Itis noteworthythatseveralofthe interaction withtheambient medium thanwouldbethecase tion ofthejet.Thismeandering ofthejetallowsmuchmore nantly seeemission fromthejetmaterialitself, theHaimage on the“outside” ofthesebends. We willargue inSec.6thatwhile[Sll] wepredomi- Ha +[Sill 1151 1996AJ 112.1141H remarkable faint veilthatsweepsbackwards fromHH47A possible toseethecomplex “turbulent”structureinthe how thintheMachdiskis.At thishighresolutionitisalso Mach disk,wherethejetmaterial isdecelerated,asexpected cooling zonesandwiched betweentheleading andtrailing from theory.Themajorsurprise ofthepresentHSTimagesis where theambientmaterialis accelerated,andajetshockor bright HH47Aworkingsurface(inset1ofFig.5).The Fig. 7.Thelineswhichdividefastmovinggasatthecoreofjetfrom theslowmovinggasatedges(Hartiganetal.1993)aresuperposedon ground-based observationsofReipurth&Heathcote(1991) Ha filamentsmarkthelocationofshocksdriveninto the Ha+[S n]imageofFig.6.Theboxesmarktheareasshowninmoredetail insubsequentfigures. showed thatthisworkingsurfaceconsistsofabowshock, shock fronts.Another featureseeninourHST imagesisthe surrounding gas. shows theinteractionzoneatedgeofjetandthat the 1152 HEATHCOTEETAL.:THEHH47JET The HH47AWorkingSurface.jetterminatesinthe © American Astronomical Society •Provided bythe NASAAstrophysics Data System Figs 9,10 14 based images. However, thehigherresolution oftheHST brightness, ourHSTimages (Figs. 2and3)reveal,atfirst of thebowshock (especiallyinHa),and ofthediscrete images highlights thesharpnessofeastern (leading)rim inspection, fewfeaturesthat are notrecognizableinground- in thebluelobeofjetcomplex isHH47D(Dopitaetal. We willdiscusstheHH47Aworkingsurfaceincludingthis terpart in[Sn].ItisbestseentheHa+[Sll]image(Fig. the “Hair”isbrightestinHaalthoughthereafaintcoun- outlying “Hair”inSec.5. lost inthephotoionizedbrightrimatedgeofglobule. 6) whereitcanbetracedformorethan13"beforebecomes along itsnorthwesternside.Thisfeaturewhichwereferto as 1982; Graham&Elias1983). Owingtoitslowsurface The HH47DWorkingSurface: Theoutermostbowshock Fig 15 [Sil] +Ha Fig 16 1152 1996AJ 112.1141H 2 front itself(Chevalier&Raymond1978).Hydrogenatoms has beeninterpretedasevidencethatHH47Dadvancesinto reflection nebula;thenorthwestwingcanjustbediscernedin by theOstars£PupandyVellocatedtonorthwestof our Ha+[Sil]HSTimage.Thebrightnessofthe[Oll]lines rial interiortoHH47Dmustbeamixtureofambientgas HH 47(Hartiganetal.1990;Morse1994).Themate- gas, beyondtheedgeofglobule,thatiskeptfullyionized ern edgewhereemissionisdetectedallthewaybackto 47D hasveryextendedwingsespeciallyalongitsnorthwest- This bubbleofshock-processedmaterialisthepreshockme- overrun bytheHH47Dbowshock,and“spent”jetgas. lar, the[Oll]imageofHartiganetal(1990)showsthatHH 4. BALMERFILAMENTSANDRESOLVEDCOOLINGDISTANCES dium forHH47Aandtheshocksininteractionzone unusually brightinthe[OII]W3726,3729lines.Inparticu- our observationsalsoprobethephysicalstateofthisgas. at theboundaryofjet.AsdiscussedinSecs.5.3and6.1 HH 47aretheremarkablysharpfilamentsofHaemission in Sec.7. 47D workingsurface,andtheexcitationconditionswithinit, but canbe10-20pixelslong.Anycorrespondingfeaturein that appearatseveralplacesalongthejet.Thesefilaments features behindit.WefurtherdiscusstheshapeofHH the [Sll]imageiseitherabsent,ormuchfainterandmore are typicallyonlytwotothreepixelswide(—90-135AU), present hereourargumentsthatthese“Balmerfilaments” diffuse. Inordertofacilitateourdiscussioninsubsequent forbidden linesofmetalsvariousionizationstates(e.g., from theshockarisesincoolingzonewheregasemits much moreextended“coolingzone.”Mostoftheradiation front wherethegasisheatedandionized,followedbya distances behindtheshocks. nent inourHaimagesbecauseHSTresolvesthecooling mark thepositionofshockfrontsinjet.Theyarepromi- sections oftheseandotherfeaturesthroughoutthejet,we there mayalsobesignificantBalmeremission/romtheshock entering theshockpenetratesomedistanceintopost- [O III],ll],l]),andrecombinationlinesofhydrogen. mechanism yieldsnarrowlinewidthsthatreflectthelow 1153 HEATHCOTEETAL.:THEHH47JET be treatedtogetherforthepurposes ofthepresentdataset. This leadstoBalmeremissioneitherwhenchargeexchange trals maybesubjecttochargeexchangewithhotprotons. temperature ofthepreshockmedium.Alternatively,neu- dergo collisionalexcitationfollowedbyradiativedecayre- shock regionbeforebeingionized.Theseneutralsmayun- of thepost-shockplasma.Both thebroadandnarrowemis- emission linesarethenbroad,reflecting thehightemperature excitation ofthenewlycreated hotneutral.Theresulting occurs directlyintoanexcitedstateorthroughsubsequent sulting inBalmeremissionlines.This sion componentsariseveryclose totheshockfrontandcan Various ground-basedstudieshaveshownthatHH47Dis Perhaps themoststrikingfeaturesinHSTimagesof A radiativeshockconsistsofaverythinlayeratthe However, ifthepreshockmaterialispartiallyneutral, Collisional excitation ofmetalsfollowedbyradiation of © American Astronomical Society • Provided by theNASA Astrophysics Data System 4 -1 -3-1 6 -3 1 -1 1 -1 1 4 -1 Balmer emissiondominatesattheshockfrontbyseveral forbidden linesalsooccursattheshockfront.However,met- radiative shockswheremostoftheopticalforbiddenlines hydrogen isunimportantinthecooler(T—10K)regionsof to populatetheupperlevelsofhydrogen. form, becausethetemperaturethereistoolowforcollisions orders ofmagnitude.Conversely,collisionalexcitation als havesuchlowabundanceswithrespecttohydrogenthat where nistheparticledensityandacollisionalcross is ontheorderofameanfreecollisionalpath,—(ncr), rc—100 cm,ß—30/¿G,and100kmswefinda magnetic fieldandVistheshockvelocity).Ifwetake typical collisionallengthof—10AUandagyroradius about equaltothesizeofgyroradiusmcVJeB{Bis behind theshockfront,aspredictedbyradiative in ourimages. HH 47sothethicknessofshockfrontcannotberesolved section. Theshockcanbemuchthinnerforchargedparticles, emission producedinthecoolingzone.Toillustratethiswe and thusseparateBalmeremissionattheshockfrontfrom code developedbyJ.Raymond(seeHartiganetal.1994for discuss howtheHaand[Sll]brightnessvarieswithdistance smaller thanthewidthofonepixel(45AU)atdistanceto were madeforthreerepresentativeshockvelocities:35,70 full detailsofthemodelasemployedhere).Computations Lyman continuumphotonsemittedbytheshock,whichcan — 3X10”AU.Thesespatialscalesarebothconsiderably mond 1985).Themodelscalculatethepreshockionization ionize thegasbeforeitentersshockfront(Cox&Ray- ization stateofthepreshockmediummaybemodifiedby density of100cmandmagneticfield30/xG.Theion- and 120kms.Ineachcasethepreshockmediumhada ted asafunctionofdistancebehindtheshockforeach ionized. the shock.Thishasimportantconsequencethatwhile that wouldappearinanemissionlineimageofthesystem(if under eachhistograminFig.8isproportionaltotheintensity tance isafluxperunitareaofshockfront.Thusthe models. Theproductofthevolumeemissivityanddis- fraction, hydrogenenteringthe120kms“shockisfully gas infrontoftheslowershockshasanappreciableneutral self-consistently takingintoaccounttheionizingfluxfrom Both the35and70kmsmodelsshowalargespikeof the shockfrontwereorientedtangentialtolineofsight). front asdescribedabove.Inthe35kms~modelpost- collisional excitationofneutralhydrogenneartheshock Ha emissionattheshockfront.Mostofthisresultsfrom never becomesmorethan—3%ionized.Thepaucityoffree s extended coolingdistanceproduces thebroadplateauof cooling distancewithrespectto the70kmsmodel.This collisional excitationinthepostshock gasandlengthensthe electrons behindthe35kms~shockreducesrateof shock gasreachesatemperatureof—3X10K,butthe s model(bottompanelofFig. 8),theHaemissionpeaks [S ll]emissionseeninFig.8. Conversely, inthe120km some distancebehind theshockfrontandis considerably The thicknessoftheshockfrontforincomingneutralgas However, wecanresolvethepostshockcoolingdistance, Figure 8depictstheHaand[Sn]volumeemissivityplot- 1153 1996AJ 112.1141H _1 -1 -1 _3 1 -3 -1 -3 -3 1 km s(middle),and120s“(bottom).Theareaundereachhistogramisproportionaltothenumberofcountsthatwouldappearinanemissionline the shockfront.Inthiscase,hydrogeninpreshockme- broader. Thereisessentiallynoemissionatthepositionof hydrogen attheshockfront.Thereisanextendedcoolingzonefor[Sn]emissionin35kmsmodel.Thephysicaldistancescaleonabscissa Fig. 8.Volumeemissivitiesof[Sn]X.X.6717,31andHaplottedasafunctiondistancebehindtheshockfrontforvelocities35kms(top),70 n thescaleonabscissashouldbemultipliedby(100cm/).EachpixelinourHSTimagesprojectstoabout45AUatdistanceofHH47.Further image oftheseobjects.Aprominent“spike”Ho'emissioninthe35and70kms~modelsiscausedprimarilybycollisionalexcitationneutral be spreadoutovertensofpixels, andmightbeinvisibleeven produced asthegascoolsandrecombines.In120km dium iscompletelyionizedbyLymancontinuumphotons details ofthemodelsaredescribedintext. appropriate forapreshockdensityof100cm.Thecoolinglengthisinverselyproportionaltothedensity;henceotherdensities, pixel). Conversely,attheadopted preshockdensityof100 but peaksatsomewhatcoolertemperatures(largerdistances emission alsooccursprimarilyintherecombinationregion, combination generatesthebroadpeakofHaemission~50 generated intheshock,andallpostshockHaemissionis though the[Sll]/Haratiointegrated overtheentirepost- cm andmagneticfieldof30¡ulG, the[Sn]emissionwould with thesamespatialresolution asourHSTdata(45AU fall withinasinglepixelinanemission-lineimagetaken from theshockfront)thandoesHaemission. AU behindtheshockfront(forn=10cm).The[Sll] 1154 HEATHCOTEETAL:THEHH47JET s" modelthegasbecomeshalfneutralat8300K,andre- shock regionis —1.13.Wewouldthensee a narrowHa 0 0 1 The Hafluxfromthe35kms~shockinFig.8would © American Astronomical Society • Provided by theNASA Astrophysics Data System 0 200400600 Distance fromShockFront(AU) m 2 3- -3 -1 -1 Thus asthepreshockdensityisincreasedentirecooling portional tothepreshockdensity(e.g.,Hartiganetal.1987) emission. Thepostshockcoolingdistanceisinverselypro- filament superposedonweakorundetectablediffuse[Sll] M=V/a^20 (whereB/(4ttp)istheAlfvénve- threshold beyondwhichthemagnetic fieldwouldbecome portional to5forlargeB. For theparametersadopted locity inthepreshockgas), cooling lengthisindependent more complex.Forshockswith“AlfvénMachnumber” density of—10cmessentiallyallthe[Sll]andHaemis- zone willfitintoasmallernumberofpixelsuntil,for other preshockdensitiesbymultiplying(100cmM). important. Thus forastrongermagneticfieldthe [Sll]emis- of B.Forweakershocksthecooling lengthisroughlypro- dence ofthecoolinglengthonpreshockmagneticfieldis noticeable spatialseparationbetweentheselines.Thedepen- so thatdistancesalongtheabscissainFig.8maybescaledto sion wouldfallwithinasinglepixel,andtherebeno V~ 1.75kmssothatthe35 kmsmodelliesnearthe as 0 a 1154 1996AJ 112.1141H bow shock(Bührkeetal1988;Morse1992)andthe been resolvedfromtheground,forexampleinHH34 partially neutral. HH 111bowshock(Reipurthetal1992;Morse1993), Balmer andforbiddenlinesbecomeseasiertoobserveinthe the forbiddenlines.Thespatialseparationbetween where theBalmerlinespeakclosertoshockfrontthando ments alsorequiresthatthepreshockmediumbeatleast likely tobelow;and(3)theexistenceofsuchBalmerfila- counterpart, thentheshockvelocityanddensityareboth ity shocks;(2)iftheBalmeremissionlacksaforbiddenline wings ofthebowshockbecauseeffectivevelocity than thatshowninFig.8. is lowerthere,consistentwiththepredictionsofshock should delineatethepositionofshockfrontinlowveloc- bow shocksmustbemostlyneutraltoexplaintheobserva- models inFig.8.Thepreshockmaterialthewingsofthese sion wouldbespreadoveranevenmoreextendedregion tions ofsomesupernovaremnants(e.g.,Chevalier&Ray- tions. mond 1978;Hesteretal1994;Smith1994).These features arealsobelievedtocorrespondBalmeremission 1155 HEATHCOTEETAL.:THEHH47JET very fast,butpropagatesintoanextremelytenuousneutral coming fromtheshockfront.However,inSNRsis medium. Thehighshockvelocitiesandlowpreshockdensi- ties resultinverylongcoolingtimes.Furthermore,thepost- propagate intothepreshockmedium,butphotoionization lengths. Thehardphotonsinthisionizingspectrum cross-section atthesehighenergiesisverylowsothathy- shock gasissohotthatitemitsprimarilyatx-raywave- drogen enteringaSNRshockcanremainmostlyneutral. Most ofthisobjectisbrightin[Sll];however,Haemission predominates inasmallregionatthetrailing(southwestern) zones ofdistinctexcitation(Reipurth&Heathcote1991). surface attheterminusofjet,canbedividedintotwo edge. Reipurth&HeathcotesuggestedthatthisHa-bright for thiscomesfromtheFabry-PerotobservationsofMorse zone marksthepositionofMachdisk.Furthersupport jet axis.TheHSTimagesshow, forthefirsttime,thatHa the jet,andsubstantiallyblue-shiftedrelativetorestof HH 47A. distinct, havingaradialvelocitysimilartothatofthetip et al(1994)whichshowthatthisregioniskinematically deduced fromthebestground-basedimages,butshowa ages showingHH47A.Theseconfirmthegrossmorphology barely resolvedevenwithHST, runningperpendiculartothe trailing edgeofHH47Aisseen tobeanarrowfilament,only wealth offine-scalestructure.TheHa-brightzoneatthe 47A. Therewefindathinribbon ofHaemission,most emission isalsoenhancedalong theleadingedgeofHH clearly seenin the Ha—[Sil]differenceimage (Fig.9c). Cooling distancesinthebowshocksofstellarjetshave We concludefromthisexercisethat:(1)Haemission Similar Baimer-dominatedfilamentsareseeninobserva- Ground-based imagesshowthatHH47A,theworking We presentinFig.9anenlargementofourWFPC2im- © American Astronomical Society • Provided by theNASA Astrophysics Data System 5. THEHH47AWORKINGSURFACE 14-2 14-2_ Near theapexthisHafilamentcloselyfollowssharply 4 -3 to somefainteremission.Tothenorthwest,averyfaintout- defined rimofHH47A.However,inthewingsitliesinterior lying Hafilamentapparentlyprojectsinfrontof,andwraps which werefertoasthe“Hair,”inSec.5.3. around, theheadofjet.Wewilldiscussthisfeature, layers isacentral[Sli]-brightcorewithanextentofabout Fainter emissionfansoutbehindthiscoreextendingovera bright knotsandfilamentsthataretypicallyabout0'.'2to region ~10"indiameter.The[Sll]emissionconsistsof 3" alongthejetaxisand6"intransversedirection. 074 indiameterspacedatintervalsrangingfrom072to image, althoughthesearefainterandoftenmorediffuse. trace thepositionofshockfrontsinflow.Weidentify disk thatslowstheimpingingjetmaterial.Asdiscussedin lower velocityupstreamgas,andthereverseshockorMach shocks, theforwardshockorbowthataccelerates Ha-bright leadingedgeofHH47A(includingtheoutlying Sec. 4,weexpectHafilamentslikethoseseeninHH47Ato ment withthereverseshock.Wesketchpossiblelocation 170. MostofthesefeatureshavecounterpartsintheHa Fig. 9(d).Ininterpretingourimagesitisimportanttore- of theseshockfronts,andtheflowgasthroughthem,in member thattheHH47jet,andshockwavesitexcites, When projectedontheplaneofskyshockfrontswill are emergingatalargeangletothelineofsight(—62°). Mach diskshowprotrusions,bendsandbifurcationssuggest- line ofsight(e.g.,Hester1987).Boththebowshockand ing thattheHaemissiontracesasurfaceofcomplextopol- appear brightestwherevertheyliealmosttangentialtothe “Hair”) withtheforwardshock,andtrailingHafila- ogy, ratherthantheidealizedformsdepictedinFig.9(d). bient gasandshockedjetmaterialcoolthroughforbidden corresponds totheroughlyisobariclayerwhereshockedam- line emission.Thestructureinthispostshockcoolingzone ing featuresdirectlybehindtheapexofbowshock[Fig. otic. Thebrightest[Sll]emissioncomesfromapairofcurl- löffel &Mundt1994).Thepeaksurfacebrightnessinthese 9(a); seealsoFig.10(c)],formerlylabeledknotAbyEis- features is~7.5X10~ergcmsarcsecin[Sll]and (well tracedbythe[Sll]emission)appearsturbulentorcha- if notmost,oftheknotslabeledinpreviousground-based imaging studiesarebrokenintosmallerstructures.The clumpy structureofthisregionsuggeststhatdynamicalin- trast betweendense,rapidlycoolinggasandmoretenuous et al1990;Stone&Norman1993,1994).Radiativecooling ~3.0X 10“ergcmsarcsecinHa.Evidentlymany, stabilities arefragmentingthepost-shockgas(e.g.,Blondin thermal pressureoncethegas cools tobelow—10K.A n~ 1000cm,andmagnetic field —140¡iGforHH47A emissivity, thevariationsin[S ll] brightnesswillbegreater slower coolinggas.Becauseofthedensitydependence strongly amplifiessuchinstabilitiesbyenhancingthecon- still. Inaddition,giventhe observed preshockdensity, 0 sufficiently chaotic magneticfieldcouldalso causelarge (Morse etal1994),magnetic pressure maydominateover 0 Sandwiched betweentheleadingandtrailingHa-bright A workingsurfacelikeHH47Ashouldconsistoftwo The [Sll]-brightregiontrappedbetweenthesetwoshocks 1155 1996AJ 112.1141H 1156 HEATHCOTEETAL.:THEHH47JET reverse shocksandthevelocityofgasasseeninrestframeworkingsurface. Fig. 9.AdetailedviewoftheHH47Aworkingsurface:(a)Ha;(b)[Sn];(c)Ha-and(d)asketchshowingpostulatedpositions forwardand HH 47A. topology andcorrugatedappearanceoftheleadingedge of ing clumpystructuremayberesponsibleforthecomplex Raymond &Curiel1995).Theseinstabilitiesandtheresult- variations inthedensityandhence[Sll]brightness(e.g., the sizesofknotsinpostshock coolingzoneofaHerbig- Haro object.Becauseof the highsignal-to-noiseratio resolved theknots. InFig.10wecompare thedeconvolved knotty features, andhelpstogaugewhether wehavetruly techniques. Thisisespecially usefulforsharpeningthethin, enhance thespatialresolution byapplyingdeconvolution achieved inourimagesofHH 47A,wewereabletofurther and rawimages ofHH47A.While(reassuringly) thedecon-. The HSTresolutionallowsustostudy,forthefirsttime, 5.1 DeconvolvedImagesandKnotSizes American Astronomical Society •Provided bythe NASA Astrophysics Data System (c) Ha-[SII] (a) H« ï ÏÏ ; volved imagesrevealnonewfeatures,theknot-to-interknot To quantifythecharacteristicknotsizewe,therefore,auto- ciation ofthecomplexfilamentarystructure. contrast hassignificantlyincreasedallowingabetterappre- correlated sub-imagesoftheHH47Aregion.Theresulting it hardtomeaningfullymeasurethesizesofindividualknots. due tosmallknots,surroundedbyasymmetricplateau,pro- emission structure.TheFWHM ofthecentralpeak extended plateauindicatesthe relative“knottiness”ofthe fuse emission.Thecontrastbetween thecentralpeakand duced byresolvedfilamentary structuresandunderlyingdif- autocorrelation functions(seeFig.11)haveacentralpeak, case ofagaussian knot. autocorrelations is~1.5times theFWHMinidealized 2.8 pixelsFWHM intherawimages.This decreasesto The chaotic,turbulentstructurerevealedinFig.10makes In thiswaywe findthatthecharacteristic knotsizeis mx 1156 1996AJ 112.1141H 1157 HEATHCOTEETAL.:THEHH47JET jet axisof2'.'8. AspurofHa-brightmaterial extendstothe parison, usingthesamemethod,FWHMofstellarimages frame; (d)thedeconvolved[Sn]image. Fig. 10.AcomparisonbetweenrawanddeconvolvedHSTimagesofHH47A:(a)theoriginalHaframe;(b)image;(c) original [Sn] measure —1.5pixelsintheoriginalframes,and—1pixel in cooling zonesarepartiallyresolved,andmeasure,from the the deconvolvedframes.Thusknotsinpostshock 47A astheMachdisk[Fig. 9(d)]. Thisstructurehasavery tions. Thisresultisconsistentwiththevisualimpression central peaksandtheextendedplateausinautocorrela- emission, judgingfromthemuchhighercontrastbetween the deconvolved images,—110AUFWHM.Inaddition, the given byFig.10. [S ll]emissionissignificantlymoreknottythantheHa west), buttheintensityfallsoff moregraduallyintheoppo- sharp (iSO'.'l)edgeontheside facingthesource(thesouth- south oftheline drawninFig.9(d)andisalso likelypartof site direction.The filamenthasanextension transversetothe — 2.4pixelsFWHMinthedeconvolvedimages.Forcom- # We identifytheHafilament atthetrailingedgeofHH American Astronomical Society •Provided bythe NASA Astrophysics Data System 5.2 TheMachDisk 14 21 14-2_ Ha fluxfromthebrightlinearsectionis—1.0X10“erg the Machdisk.ThepeakHasurfacebrightnessin back edges.Rather,thenarrownessandsharpedge of to thejetaxis,thenitsminor-to-majoraxisratioshould be the faintsouthwardextension.Ifthisfilamentactuallyrepre- cm“ s“withperhapshalfasmuchfluxagaincomingfrom disk is—1.8X10“ergcmsarcsec.Theintegrated then benodifferenceintheintensityprofileatfrontand the jetaxismakestoplaneofsky.Thereshouldalso the isobaricregionorslightdirectional variationsoftheim- ing oftheMachdiskmaybe a transienteffect(e.g.,Blondin lies nearlytangentiallytoour lineofsight.Thistiltorwarp- the Hafilamentcoupledwithitslargesurfacebrightness, pinging jetmaterial. Sucheffectsmayalso explainthelack et al1990)producedbythe developmentofinstabilitiesin sented aroughlycircularplaneshockorientedperpendicular of symmetry theMachdiskwithrespectto thebowshock. suggest thatweareviewing a portionoftheMachdiskthat — 0.5,ratherthanthe—0.1observed,given-28°angle If, asweexpect, theHafilamenttraces position ofthe 1157 1996AJ 112.1141H 1158 HEATHCOTEETAL.:THEHH47JET Fig. 11.NormalizedautocorrelationfunctionsoftheHSTimagesHH47A.Theautocorrelationswerecalculatedforsectionsdeconvolved the Haimage.Thedashedlineshowsautocorrelationfunctionofafieldstarforcomparison. images showninFig.10,andhavebeenazimuthallyaveraged.Thesolidlineshowstheautocorrelationfunctionfor[Sn]imagedotted The straightsegmentoftheHafeature[labeledMachdiskin Fig. 9(d)]hasalengthof2"8,whichcorrespondsto shock front,thenwecanmeasurethesizeofMachdisk, part oftheMachdisk,thenwidthjetcouldbeas and thereforethewidthofjet,directlyfromitsextent. with thelowionizationfractionestimatedforthisjet(Harti- make theMachdiskbrightinHa(seeSec.4),consistent much astwicethisvalue.Thejetmustbemostlyneutralto emission extendingtothesouthoflinearsegmentisalso ratio betweentheimpingingjetanddownstreammaterial; gan etal.1994). this ratioislessthanonefor“lightjets”andgreater — 1300AUatthedistanceofHH47.IfspurHa which regimeappliestoHH47Abycomparingthestrength one for“heavyjets.”Inprincipleitispossibletodecide of theforwardandreverseshocks.Forinstance,ifden- factor of3;theMachdiskisstrongershockwhenjet is strongerforaheavyjet(Hartigan 1989).Thisshouldbe is lessdensethantheambientmedium,whilebowshock behind thetwoshocks.Previously (e.g.,Reipurth&Heath- readily detectablebycomparing theexcitationofgas sure balancetherelativeshockvelocitieswoulddifferbya sity contrastwerelarge,sayoforderten,thenbyrampres- Ha emissionfromtheMachdisk indicatedthattheshock cote 1991;Morseetal.1994), wearguedthatthebright excitation washigher behindtheMachdisk,and therefore, A keyparameterthatentersintojetmodelsisthedensity © American Astronomical Society • Provided by theNASA Astrophysics Data System jets aredenserthantheirsurroundings(whichiswhyproper that thiswasthestrongershock;placesusinregime lines occurbehindthebowshock,ratherthanMach motions instellarjetsarelarge,andthehighestexcitation of alightjet.Thisresultwassurprisingbecausemoststellar tance behindtheMachdiskwasnotresolvedspatially.Itis The leadingbowshockalsohasarelativelyfainterHaedge. now clearthattheMachdiskderivesmostofitsHaflux disk). However,thisanalysisassumedthatthecoolingdis- If thiscomponentisneglectedinbothshocks,thentherela- from thecollisionallyexcitedcomponentatshockfront. tive excitationintheemittingregionsandwichedbetween the twoshocksappearssimilar.Thereiscertainlynoclear- brightness oftheMachdiskcomparedtoleadingedge Ha brightnessoftheshockfrontdependsondensity cooling zoneanduncertaintiesduetoprojectioneffects.The this analysisiscomplicatedbythechaoticstructureof cut divisionintozonesofhighandlowexcitation,although the bowshocksuggeststhatimpingingjetmaterialis the preshockmedium.Thusitmightbethoughtthat much denserthanthegasaheadofbowshock.However, the surfacebrightnessalsodepends onfactorssuchasthe bered thatweare onlyseeingasnapshotof the HH47A presently beclosetoone.Itshould inanycaseberemem- trailing shocks,thenthejet-to-downstream densityratiomay into accounttherelativesurface areasoftheleadingand extent oftheshockfrontalong thelineofsight.Ifwetake 1158 1996AJ 112.1141H point. Itistemptingtosuppose thattheHfilamentrepre- occupies thegap betweenthebrightcoreof HH47Aandthe Another brighter, butbroaderandlessextensive Hafilament coincidence caused byprojectioneffectscannot beruledout. H filamentcanbetracedfor afurther—12"beyondthis ratio thanispresentintheionizationrim.Eislöffelet al. where theHairbecomeslost in theglobulesbrightrim.The H filamentappeartooverlapspatiallyforanextent of ernmost partoftheHairandnorthernmostsectionthis ionization frontsinceithasasignificantlyhigher[Sn]/Ha edge oftheglobule.However,Hairisunlikelytobe an Hair disappearsintotheionizationrimalongnorthern its northwest,foradistanceofatleast—13".Eventually the sents thesouthwardextension oftheHair,however,aspatial It sweepsbackwardrunningparalleltothejet,some~5" to core ofHH47Atothenorth.Thisfeature,whichwerefer Here weseethatafaintHafilamentwrapsaroundthebright with thecontrastsettoemphasizefainteststructures. to revisitthisissueinafuturepaper. stretches paralleltothejetonitsnorthwestside.Thesouth- as the“Hair,”appearstoconnectHH47Anearitsapex. Fig. 12.AnHa+[Sn]imageshowingamoreextensiveregionaroundtheHH47Aworkingsurfacedisplayedsoastoemphasizefaintest features. The gas itoverrunsislikelytobeveryinhomogeneous.Wehope addition sinceHH47Afollowsinthewakeof47D dynamical instabilitiesasisseeninnumericalsimulations forward andreverseshockswillvarywithtimeasaresultof working surface.Itislikelythattherelativestrengthsof discovered byEislöffeletal(1994). — 3".ThebrightestHemission comesfromapointcloseto (1994) detectedafaintfilamentofHemissionwhichalso (e.g., Blondinetal1990;Stone&Norman1993,1994).In “Hair” andtheotherfeatureswhichtraceextendedwingsofHH47Aareindicated.Thedashedlinemarksapproximateposition Hfilament 1159 HEATHCOTEETAL.:THEHH47JET 2 2 2 2 2 2 Figure 12showsalargerregionsurroundingHH47A, American Astronomical Society •Provided bythe NASA Astrophysics Data System 5.3 TheHairofHH47A 1 most tangentially tothelineofsight. HH 47Abow shock wherethefront locallyrunsal- HH 47A.Overall,thekinematics andexcitationoftheHair its apex,couldappearinprojection toconnectthetipof far sideofthebowshock,located closertothesourcethan material islocatedinsideHH47A.Giventhe-28°angle the roughly bisectsthis“umbrella”ofemission,althoughit is It thusmightbeidentifiedastheapexofHH47Abow most northeasterlysectionliesalmostnormaltothejetaxis. their Fig.3),stronglyreminiscentofHH47D.Thejetaxis the velocityresolvedimagesofHartiganetal.(1993, see kinematically associatedwiththelowvelocitymaterialalong suggest thatitrepresentsafold intheirregularwingof axis ofthejetmakestoplane ofthesky,afeatureon emission formsabubble-likeshell,especiallywellseen in the wingsofHH47Abowshock.Atsamevelocity, shock, wereitnotforthefactthatfastestandbrightest on thesoutheastsideofjetand—10"fromitsaxisare closely parallelsthecurvingnorthernsectionofHair.As Hair. ThisconnectstoapointonthewingofHH47Aand situated tothenorthofapparentsymmetryaxis. & Heathcote(1991).Togetherallthisfaint,low-velocity some faintemissionfilamentslabeledAandbyReipurth ated [Sll]emission,andwebelievetheymarkthelocationof with theotherBalmerfilamentsalongjet,Haemis- s“ withrespecttotheambientcloud.Itthusappearsbe show thattheHairisblueshiftedwithavelocity—-50km shock fronts. sion inboththesefeaturesismuchsharperthantheassoci- 67 The Hairisenveloped bytheextendedbow shockwings The HairappearstoconnectthetipofHH47Aandits The ground-basedFabry-Perotdata(Hartiganetal.1993) 1159 1996AJ 112.1141H _1 -1 region, whichhasapparentlyalreadybeenshockedbyHH Even intheabsenceofionizingphotonsitishardtounder- penetrate intotheinteriorofHH47Dbubble.Another photons withenergiesgreaterthan13.6eVareunableto of HH47D,which,asdiscussedinSec.3,isbelievedto reform behindtheshock,ornewmolecularcloudmaterial 47D. Possiblytheneutralsandmoleculeshavehadtimeto diation oftheOstarsispresenceHemissionin indication thatthisregionisshieldedfromtheionizingra- least partiallyneutralgastoaccountforthestrongHaemis- filaments elsewherealongthejetmustbeoverrunningat et al1994).Ontheotherhand,HairandsimilarBaimer advance intophotoionizedgas(Hartiganetal.1990;Morse tom fromtheedgesofcavityaroundflow(possiblydue area ofHH47A(Eislöffeletal.1994;Curiel1995). may becollidingwithslowermovingneutral(andmolecu- with thegasoverrunbyHH47D.Alternatively,47A to variationsinthejetdirection;seeSec.6.3)hasbeenmixed stand howtheHinHH47AandHairsurvivethis sion fromtheseshockfronts(seeSec.4).Thusitappearsthat 1160 HEATHCOTEETAL.\THEHH47JET lar) jetmaterial. very differentinour[Sll]andHaimages.Whilethe emission isclumpyandoutlinesaseriesofbends bright knotandaresweptbackatanobliqueangle.The the sharpwispsofemissionoffsetfromaxisjet wiggles, themostprominentfeaturesofHaimageare clearest examplesofthisphenomenonarethefilamentsas- We interpretthese“Balmerarcs”asshockwavesdriven hydrogen attheshockfront,ratherthantotheirbeingstrong Reipurth SiHeathcote1991).However,wehereattributethe into thesurroundingmediumbydisturbancesinjet( 2 (see Fig.5).Mostofthesefilamentsarerootedina[Sn]- behind theHa-brightportionofAfilament.Weinter- fact thattheyarebrightinHatothecollisionalexcitationof sociated withknotsAandshownindetailFig.13. counterpart. However,faintforbidden-lineemissionextends 2 pret thisasemissionfromthespatiallyresolvedcoolingzone shocks. Fig.13showsthattheAfilamentlacksa[Sn] neutral medium(e.g.,the35kmsmodelinFig.8).Inte- of alowvelocityshockmovingthroughrelativelytenuous, leading Hafilamentandthetrailing[Sll]emission) grated overthefullthicknessofshock(including hard todetectagainstthemottledbackgroundofglob- viewed almostedge-on,suchfaintshockswouldbevery [S II]/Haratiois—1.7consistentwithashockvelocityof ule’s brightrim. appear asfilamentsduetoprojectioneffects.Exceptwhere be mostlyneutraltoproducethe brightBalmeremissionat Firstly, thepreshockmaterialahead ofthesefilamentsmust plications concerningthemedium surroundingthejet. shocks wraparoundtheir“parent”[Sll]knots,andonly the shockfront. Thus,thismaterialmustbeshielded from — 20-40kms(Hartiganetal.1994).Presumablythese 22 2622 26 The jet,especiallyinitsfainternorthernsegment,appears The factthatweseetheseBalmer arcshasimportantim- © American Astronomical Society • Provided by theNASA Astrophysics Data System 6.1 BaimerArcsintheJet 6. THEHH47JET -3 3- - -1 -1 _1 northern edgeoftheglobule,or,asalreadymentionedin the ionizingradiationofOstarstonorth,eitherby tance behindtheseshocksmustbe^500AU.Thelong ments iseitherabsentorfaintanddiffuse,thecoolingdis- cause the[Sn]emissionassociatedwithBalmerfila- Sec. 5.3,bythebubbleoutlinedHH47D.Secondly,be- Balmer arcsareprobablyconsiderablylower(^100cm) cooling distancesuggeststhatthedensitiesaheadof than thosealongtheaxisofjet(—1.4X10cm;Har- tigan etal.1994).Finally,theshockvelocitymustbelow toionize thepreshockmedium.Anevenmorestringentlimit enough (110kms^thattheshockdoesnotitselfpho- likely evenlowerstill.However,iftheBalmerarcsareco- where weseeanextendedcoolingzone,theshockvelocityis moving withtheassociated[Sn]knotsthentheyhavespace along thejet(Morseetal.1994).InthosecaseslikeA (V^90 kms)issetbytheabsenceof[Oill]emission nearly normaltothedirectionofmotion.Thesefactscan Although thetrailingwingsofBalmerarcsarehighly velocities of—200to300kms(Eislöffel&Mundt1994). the HH47Dbubble)movesoutwardatasubstantialfraction oblique, theleadingsectioncloseto[Sn]knotsaremore only bereconciledifthematerialadjacenttojet(within of thevelocityjet.Takingthesepointstogether,it at asubstantialfractionofthejetvelocity. tenuous, neutralmaterialthatmovesoutwardsupersonically seems thatthejetissurroundedbyabubbleofrelatively for sometime(Solf1987)thatjetshavehigherradial turbulent entrainmentalongtheHH47jet.Ithasbeenknown ity gradientcouldariseifthejetentrainsmaterialfrom velocities alongtheiraxesthanatedges.Suchaveloc- much fasterthanthatalongtheedges.Inadditionthesedata Cantó &Raga(1991).InthecaseofHH47jet cess hasbeendiscussedfromatheoreticalperspectiveby 22 5 ground-based Fabry-PerotobservationsofHartiganetal. surrounding mediuminaturbulentmixinglayer.Thispro- Ha/[S ll]ratiostranslateintohighershockvelocities(for axis ofthejet.Raymondetal.(1994)interpretedtheseob- show thattheHa/[Sll]ratiogrowswithdistancefrom bulent entrainmentmodelinwhichthestrongestshocks (1993) clearlyshowthatmaterialinthecoreofjetmoves rial isacceleratedbythejet. servations asevidenceforturbulententrainment.Larger the chaoticturbulentstructurethatmightbeexpectedofa least inthenorthernsectionofjet,weseenoevidencefor enhanced HaemissionattheboundaryofHH47jet.At distance, ratherthanhighshockvelocities,accountforthe should occurintheboundarylayerwhereambientmate- mixing layer.Insteadtheedges ofthejetemitHaalong y^80 kms;Hartiganetal.1987),consistentwithatur- driven intothesurroundinggas. Thepassageofasuccession gas attheedgeofjet(“prompt” entrainment;DeYoung of suchradiativeshockswillalso sweepupandaccelerate several well-definedfilaments that weinterpretasshocks 1986). Thiscan alsoaccountfortheobserved velocity gra- 5 Our observationscastdoubtonground-basedevidencefor However, ourHSTimagessuggestthataresolvedcooling 6.2 Entrainment 1160 1996AJ 112.1141H 1161 HEATHCOTEETAL.:THEHH47JET Fig. 13.Adetailedviewoftheregionincluding[Sn]-brightknots 2 andAtheHa-brightfilamentsassociatedwiththem:(a)Ha;(b)[Sn];(c) Ha-[S n];(d)acartoonshowingthepossiblelocationsofshockfronts andtheirmotion. the gaslessrapidlythansectionnearaxis.Prompt dient sincetheobliquetrailingwingsoftheseshockspush veia DalPino&Benz1994)orvariabledirection(Biroet al. of jetswithvariablevelocity(Stone&Norman1993;Gou- entrainment isseentobeparticularlyeffectiveinsimulations 47D andHH47A. effects ofpromptentrainment ofcloudmaterialbyminor gas surroundingthejet(Sec. 6,1) resultsfromthecumulative Ha emissionfeatures probablymarktheposition ofshock and B,isless clear.Aselsewhereinthejet, thefilamentary shocks alongthejetaswell asthemajorbowshocksHH 1995) ,orinKelvin-Helmholtz unstablejets(Stoneetal. 226 1996) . Webelievethatthestreamingmotionof tenuous n The situationin thejetclosertosource, betweenB 3 © American Astronomical Society •Provided bythe NASAAstrophysics Data System _____ (c) Ha-[SH]\(d)il] (a) H«m(b)[SII] waves intheflow.However,Haand[Sn]emissionbe- mixing layer,buttheshocksmightalsobecausedbyvari- tween Bandoverlaptoformacomplexstructure of how eachshockpropagates, whichwouldhelpclarifythe possible tofollowthemotion oftheHafilamentsandlearn filaments andknots.Onemightidentifythisregionwith a boundary ofthe bubbleofgasoutlinedbyHH 47D.Herethe dynamics ofthisportionthe flow. analyzing futureHSTimages ofthisregion,itshouldbe ability ofthejetasdiscussedinfollowingsection. By sion. Evidence forsuchweakshocksisfound intheHarcs shocks maybe weakandthusmaynotproduce opticalemis- 3n 2 A turbulentmixinglayermight alsoexistattheouter \ % \ 1161 1996AJ 112.1141H jet. ThebestcandidateisAwhichlocatedwherethefast Hat wisps(allofwhichareorientedasiftheyrepresentthe Raga 1995).Someoftheshocksalongjet,including variations mayhaveoccurredonshortertimescales.Several variations inthemassoutflowratefromsourceontime 47D) intheHH47flowshowsthattherehavebeenmajor wakes ofejectionsfromthesource),mightcorrespondto Hartigan &Raymond1993;StoneNormanFalle workers havediscussedhowsuchvelocityvariationsdrive et al1990;Reipurth&Heathcote1991).Smalleramplitude has graduallydecreasedoverthelastthousandyears of ejectiontheHH47outflow.Thelocationbow scales ofseveralhundredyears(Dopitaetal1982;Hartigan 47D, whichrepresentsanoldejection,liestothesouthof such “internalworkingsurfaces.” slower movinggasejectedearlier(e.g.,Ragaetal1990; shocks alongthejetasfastermovingmaterial“overtakes” which showsfilamentsofdustymaterialapparentlystretched hence wouldproduceneitherHemissionnoraprominent There arealsoclearlychangesindirectionalongthewhole The youngestmaterialinthejet,HH46,points—13°north line thatconnectsthesourcetoHH47A.Theapexandbright consequence ofsuchaninteraction. out paralleltotheaxisflow,mightbeoneobservable CO flow(Chemin&Masson1991;Olbergetal1992).The lobe oftheHH47flow(Eislöffeletal1994).Theapproach- region isshownindetailFig.14wherewesketchthe collide withslowermovinggasalongitsedge,driving length ofthejetasshowninFig.7. of thelineconnectingsourcetoapexHH47A. apparent axisofthejetwhereitentersworkingsurface. core ofHH47Aare,inturn,displacedtothesouth shocks andthejetshowthatpositionangleofflow ing lobeoftheflowmaybeentrainingmostlyatomicgasand possible locationoftheshockfronts,andvelocities core ofthejetchangesdirectionbyseveraldegrees.This shocks intoboththejetanditssurroundings(e.g..Ragaetal stmcture ofthereflectionnebulatonorthwestjet, and shellsalongtheperipheryofreceding(southwest) gas withrespecttothesurroundingmedium.The[Sll]emis- are foundatseveralplacesalongthenorthernsectionof (Reipurth &Heathcote1991).Forinstance,theapexofHH rapidly thanmore tenuousregions. probably resultsfromthegrowth ofcoolinginstabilitiesin not meanthattheflowchangesdirectionbysuchalarge the postshockregion,asdenser parcelsofgascoolmore low excitationlinesareseenalong theHH47jet(Morse large angleswithoutproducingashockwavethatemits angle. Itisnotpossibletoturnasupersonicflowthrough sion nearAappearstobendbyalmost60°,butthisdoes 1162 HEATHCOTEETAL:THEHH47JET 16 et al1994).Theclumpystructure seeninthe[Sn]images strongly inhighionizationlines suchas[Oill]X5007;only 1993a; Biroetal1995).Possibleexamplesofthisprocess 2 16 The existenceofmultiplebowshocks(HH47AandHH There isalsoclearevidenceforvariabilityinthedirection Directional variabilitymaycausesegmentsofthejetto © American Astronomical Society • Provided by theNASA Astrophysics Data System 6.3 TimeVariabilityandWiggles 1- -1 _1 jet, andissurroundedbyslowergas.Theexistingproper- Mach diskinHH47A,~2'.'8,isprobablyabetterindication necessarily traceallofthemassinflow.Thesize not toover-interpretthe“wiggles”seenin[Sll]image. the radiatinggasatpositionA.Nevertheless,apparent Our imagesonlyshowthegaswhereitradiates,anddonot if clumpsoccurredatrandomlocationsintheflow.Some wiggles inthe[Sll]imagearemorethanwouldbeexpected of thetruewidthjetthansubarcsecondextent tion mightexplaintheobservations.Recentsimulations combination ofvariabilityinvelocityanddirectionejec- thus thismechanismmayalsoplayaroleinproducingthe ity canproducelargeanglebendsandkinksinthejetbeam; Mach numberofthejet.Thekinematicsarenotconsistent either casethegaswillmoveballisticallygivenhigh which thedirectionofejectionoscillatesfromsidetoside.In natures arecompatiblewitheitheraprecessingjetoronein radially awayfromtheexcitingsource.Thesekinematicsig- motion datasuggestthatthefastestmaterialalwaysmoves observed structures. magnetic field(e.g.,Todoetal1993). with ajetinwhichthegasisconstrainedtofollowspiral show thatthefastestmaterialisconfinedtoaxisof (Stone etal1996)showthattheKelvin-Helmholtzinstabil- high resolutionslitspectra.TheHadispersionisalmostas knot inthejet.Furthermore,theyfoundavelocitydispersion the sourcethanthatresponsibleforHH47A.However,they therefore suggestedthatHH47Bmarkedyetanotherwork- high asthatmeasuredforHH47Aandhigherthanseen is, apartfromtheHH47Aworkingsurface,brightest is associatedwithaparticularlyspectacularHa-bright ing surfaceintheflowdrivenbyamorerecenteruptionof downstream ofthispoint.Reipurth&Heathcote(1991) ence inthebrightnessandcharacterofjetupstream anywhere elseinthejet.Thereisalsoaverymarkeddiffer- of —90kms“inHaand—60s[Sn]fromtheir also notedthatHH47Bliesatanobviousbendinthejetand is theresultofachangeindirectionjet. the velocityslicedimagesofHartigan etal.(1993).While long separatesthesetwocores,whileapairofparticularly west ofthe[Sll]knot.Anarrow,almoststraightridge dered tothesouthbydiffuseemission.InHathereisa streamer. Thus,analternativeexplanationwasthatHH47B 9 this rangeofvelocities,butcomes fromthepositionof the Haknotisprominentat velocities between—50and Ha knotsalsohavedistinctkinematicsasdeterminedfrom fine BalmerarcstrailbehindtheHacore.The[Sn]and [S ll]emissionorientedalmostparalleltothejetand—3" similar brightcore,butthisisdisplaced—1"tothenorth- [S ll]-brightcore (faintHaemissionisalsoseen overthe 15. In[Sil],HH47Bconsistsofabrightcompactcorebor- — 140and—200kms.Faint Haemissionisalsoseenin —110 kms,the[Sll]knotis seenatvelocitiesbetween The precedingdiscussionshowsthatwemustbecautious The radialvelocitiesmeasuredfromthegroundclearly As discussedbyReipurth&Heathcote(1991),HH47B The regioncontainingHH47BisshownindetailFig. 6.4 HH47B 1162 1996AJ 112.1141H 1163 HEATHCOTEETAL.:THEHH47JET possible locationsoftheshockfrontandflowgasinfast core ofthejet. Fig. 14.Adetailedviewoftheregionaroundknotlocatedatapronounced bendinthejet:(a)Ha;(b)[Sn];(c)Ha+[S(d)acartoonshowing both knots,leadingtoahighHavelocitydispersion. Reipurth &Heathcote(1991)includedcontributionsfrom extent ofthe[Sll]knotinFig.15).Theslitspectra of points inthejet.Thusitappears thatHH47Bmayjustbean previously thought,indeednot muchhigherthanthatatother In additionthevelocitydispersion inthisknotislessthan of aglancingcollisionbetween thejetandsurroundinggas. like HH47A.Rather,itsuggeststhatwehereseetheresult does notresemblethatofamajor(internal)workingsurface in thejet.On otherhand,boththedirection andvelocity extreme exampleoftheshock systemsfoundatotherbends of thejetmight changeasaresultofan eruptionofthe source. Themarked changeinthebrightness ofthejetat 16 Thus themorphologyofHH47BseeninourHSTimages © American Astronomical Society •Provided bythe NASAAstrophysics Data System position ofHH47Bsuggeststhatthiscouldhavebeen the recent directionofthejet.As describedinSec.6.3,theaxis case. Futurepropermotionandspectroscopicobservations the reflectionnebula,threeemission knotsdefinethemost proper motions (Morseetal.1994;Eislöffel &Mundt1994). of thissegmentthejetdiffers bymorethan10°fromthat should helptofurtherclarifythenatureofthisinteraction. of thenextsegment.These knotsareresolvedspatially (~0'.'7-0"8 in width),andhavehighradial velocitiesand In HH46,locatedneartheinfrared sourceatthebaseof Nowhere inthis systemdoweobserveanything likethe 6.5 TheBaseoftheJet 1163 1164 HEATHCOTE ET AL : THE HH47 JET 1164

HH 30: Burrows et al 1996; HH 34: Hester et al 1996; HH h—i 111: Reipurth et al. 1996) also do not show any evidence for focusing shocks or nozzles. In the case of HH 30 there is 1” relatively little intervening extinction and it is possible to see to within —100 AU of the source. Our new images do reveal a remarkably linear Ha fila- ment superposed on the reflection nebula about one arcsec- ond north of the main axis of the jet (Fig. 16). This feature has no counterpart in [S ll]. Our narrow band images clearly demonstrate that the spectrum of this feature is radically dif- ferent from that of the underlying reflection nebula. We be- lieve that it is most likely a Balmer filament similar to those seen elsewhere along the jet. If this is the case, then its ori- entation suggests that it outlines a shock driven into the sur- rounding material by the recent change in the direction of the jet. Future proper motion and spectroscopic observations of this object should help to clarify how such features form and evolve. Another curious feature seen in Fig. 16 is the com- pact Ha-bright knot, Bn. This feature lies at the base of the “B section” of the jet and thus is the last visible trace of the material ejected prior to the reorientation of the jet. How- ever, it also lies exactly on the extension of the axis defined by the knots in HH 46, although separated from them by -7".

7. THE HH 47D WORKING SURFACE 7.7 Morphology Owing to the low surface brightness of HH 47D, at first inspection, our HST images (Figs. 2 and 3) reveal few fea- tures that are not recognizable in ground-based images. However, the higher resolution of the HST images highlights the sharpness of the eastern (leading) rim of the bow shock (especially in Ha), and of the discrete features behind it. The features discussed in this section are identified in Fig. 17 using the nomenclature of Eislöffel & Mundt 1994). The bow shock appears to divide into two filaments near the apex, the outer one being relatively [S ii]-bright. On each flank of the bow shock, roughly equidistant from the apex are two “ears.” These are especially evident in the Ha im- age as somewhat diffuse structures about 7" in diameter. Fur- ther clumps of diffuse emission (D5 and D2i) are seen be- yond the west “ear” along the northwestern wing of the bow shock. These lie just interior to the smooth rim of the bow shock seen in the [O n] image of Hartigan et al. (1990). However, on the southeast side, the wing of the bow shock appears to end at the east “ear” both in our HST images and in [O ll]. A [S ii]-bright region a few arcseconds behind the apex of HH 47D has been identified as the Mach disk of HH 47D (c) Ha - [SU] (Hartigan et al. 1990; Reipurth & Heathcote 1991; Morse et al. 1994). The low-excitation knot D13 is the brightest Fig. 15. A close up view of HH 47B: (a) Hcr, (b) [S il]; (c) Ha-[S n]. structure in this region. It appears as a narrow arc of emis- sion, convex toward the exciting star in both Ha and [S ll]. focusing shock or de Laval nozzle that some models pre- Although the S/N is very low, it appears that in Ha this arc dicted might collimate the jet (Ouyed & Pudritz 1993; Raga lies slightly ( —O'.'l, equivalent to —45 AU) closer to the & Cantó 1989). If such a structure exists in HH 47, then it source than in [S ll]. This would suggest that the Ha emis- must be in the region close to the source hidden from view sion corresponds to collisional excitation at the shock front by overlying extinction. HST images of other regions (e.g. while the [S ll] arises in the downstream cooling zone. Such © American Astronomical Society • Provided by the NASA Astrophysics Data System 1996AJ 112.1141H -1 location ofaproposedshockfront. Fig. 16.AcloseupoftheregionnearbasejetincludingHH46 ing star.ThisfilamentisbroaderthanD,andasbestwe excitation, buthasaconcaveshapewithrespecttotheexcit- estimated fortheMachdisk(Morseetal.1994).KnotD, projected geometryofthebowshockbymeasuringanumber the axisofsymmetry.Wehaveattemptedtodetermine case. can telltheHaand[Sn]emissionareco-extensiveinthis file, itsfragmentarystructuremakesitdifficulttoestablish about 20"behindtheapexofbowshock,isalsolow- a resolvedcoolingzonewouldbeexpectedgiventhelow shock velocity—20-30kmsandlowpreshockdensity 1165 HEATHCOTEETAL:THEHH47JET 13 6 Although HH47Dhasanunmistakablebowshockpro- © American Astronomical Society •Provided bythe NASAAstrophysics Data System Fig. 17.AnHa+[S n]imageoftheHH47Dbowshock inwhichwehavelabeledthevarious featuresdiscussedinthetext. and 2 of positionsalongitswingsinboththeHaand[Sll]images. images indicatethatavarieswithZsuchatlargerthe the orthogonaldirection.Foraparabolaa(Z)isindependent measured (inarcseconds)fromtheaxistobowwavein marked inFig.17.Thepointsalongthebowshockwerethen Bisecting theresultantcurveyieldsanapexpositionwhichis its associatedBalmerfilament:(a)Ha;(b)[Sn];(c)asketchshowingthe wings ofthebowshocklieclosertosymmetryaxisthan ground-based [On]image.OurmeasurementsontheHST of Z.Hartiganetal.(1990)measureda=0.034fromtheir arcseconds) fromtheapexalongaxisofsymmetry,andR fit toafunctionoftheformZ=a(Z)Rwithmeasured(in 1165 1996AJ 112.1141H 162 2 3 The [Sn]imagesuggestsaslightlywiderbowwavestruc- medium aheadofHH47DfrommeasurementstheHa through amediumwithdecreasingdensity.Suchdecrease two HSTimages.Theincreaseofa(Z)withincreasingZis of Z.Reanalysisthe[Oll]image(Fig.3inHartiganetal. ture withavaryingfrom0.037to0.040overthesamerange expected foraparabolicfit.FortheHaimage,valueof emission wasdetected.Thedetectionof[Oill]constrainsthe were restrictedtotheregionnearapexwhere[Oill] flux intheirFabry-Perotimages.TheHameasurements the shock. diminishing pressuresupportwithincreasingdistancebehind might occurbecauseradiativecoolingofthehotgasleadsto tended wings,leadingtoanaccelerationoftheshockat 0.043 atZ=30",intermediatebetweenthevaluesfromour from theapextoavalueof0.050about30"apex. peated theanalysisofMorseetal,measuringHaflux effective shockvelocityandhencetheHaemissivityof flow isexperiencingalowerpreshockdensitythantheex- dense environsofthedarkcloud.Ineffect,apex in densitycouldplausiblyoccurastheflowrecedesfrom how the[SIl]/HaratiovarieswithinHH47D.Nearapex Ha and[Sll]fluxesfromtheHSTimagesdetermine by theseworkersthenleadstoapreshockdensityof by Morseetal(1994).Carryingthroughtheanalysisusing apex relativetotheextendedwings.Alternatively,thiseffect suggestive ofwhatisexpectedfromabowshockadvancing the samereddeningcorrectionandshockparametersadopted lengthwise alongtheaxisofsymmetryandcovering from ourHSTimageusingasmaller2.8"X5",oriented aperture usedforthefluxmeasurementsalsoincludedasub- shock. Theresultwasrendereduncertainbecausethelarge bow shock.Converselythevaluesinwest“ear”are the apex[SIl]/Haratioincreasesreaching—1.8in of thebowshock,andalongsharplydefinedrimtoits an Hasurfacebrightnessof1.8X10“ergcm“sec“ stantial portionoftheMachdisk.Wehave,therefore,re- a variesnearlymonotonicallyfrom0.036atposition4" 1166 HEATHCOTEETAL.:THEHH47JET east wingtothe bowshockinthe[Oll]image (Hartigan photoionization source.Theabsence ofanextendedsouth- of HH47D,ontheotherhand,may beself-shieldedfromthe heating byphotoionizationdue to theultravioletlightof northwest flankofthebowshock issubjecttoadditional would beexpectedforshockexcitedgasinthewingsofa east “ear”the[Sll]/Haratioishigh,averaging—2.0as lie infrontoftheHarimduetoprojectioneffects.In arcsec“ almostafactorof2smallerthanthevalueobtained OB starstothenorthwestof globule.Thesoutheastflank situated onthefarsideofbowshock,onlyappearingto [S Il]-brightleadingfilament.Thisfeaturemayactuallybe southeast, the[Sll]/Haratiois—1.1.Tonorthwestof 1990) indicatesavalueofrangingfrom0.037atZ=4"to surprisingly low,—0.2.Itispossiblethatthematerialon ~9±5 cm“. ~ 5"regionof[OIII]emission.Themeasurementyields Morse etal(1994)estimatedthedensityofpreshock We havealsoused“aperturephotometry”tomeasurethe © American Astronomical Society • Provided by theNASA Astrophysics Data System 7.2 ShockConditions be shieldedfromionizingphotons. et al1990)mightalsobeduetothiscause.Asdiscussedin have obtainedthefollowingresults: Sec. 5.3and6.7,thegasinteriortoHH47Dappears signal-to-noise, Haand[Sll]imagesoftheHH47jet.We (1) ThroughouttheHH47complex,weseenarrowfilaments (2) TheHa/[Sll]ratioisfrequentlyusedasanindicatorof (3) WeconfirmthepresenceofanHabrightregionat Using HSTwehaveobtainedhighspatialresolution, HH 47)butcanbetensofpixelslong.Any[Sll]emis- pixels wide(onepixelequals45AUatthedistanceof of Haemission.Thesearetypicallyonlytwotothree tected isofmuchlowersurfacebrightnessandspread hence itsluminosityisspreadovermanypixels.Forthe the post-shockcoolingzoneisspatiallyresolved,and tribute theirfaintnessin[Sll]tothefactthat,withHST, the preciselocationofshockfrontsinflow.Weat- collisional excitationofneutralhydrogenimmediately we arguethatthestrongHaemissionisresultof over abroaderregion.Basedonradiativeshockmodels, cooling zonetobesoextendedboththeshockvelocity behind theshock.Thusthese“Balmerfilaments”trace sion fromthesefilamentsiseitherabsentorwhende- and thepreshockdensitymustbelow. no longeratrustworthyindicatorofshockstrengthbe- ger shocks.However,atthespatialresolutionofHST misconceptions regardingHH47andsimilarjetsaswe cause itslocalvaluemaygreatlyexceedthatintegrated cooling zonemayberesolved.TheHa/[Sll]ratioisthen shock strengthwithlargervaluescorrespondingtostron- bow shock.Betweenthesetwoshockfrontsisa[Sn]- leading edgeofHH47Aisalsoboundedbyan of hydrogen.Ourimagesshow,forthefirsttime,that with theshockfrontofMachdiskorreverse trailing edgeofHH47Ainferredfromground-basedim- detail below. over theshockasawhole.Thishasledtonumberof bright layerwherewesee(superposedinprojection) Ha-bright filamentwhichweascribetotheforwardor and attributeitsbrightnessinHatocollisionalexcitation ages. AtthesuperiorresolutionofHSTthisisseentobe (and thebestseeingground-basedimages)postshock emission fromthecoolingzonesbehindbothforward a remarkablynarrowfilament.Weidentifythisfeature Mach diskshockwasHa-bright.Wenowseethatthe emission inthe[Sll]-brightregionandthatentire was supposedthatthebowshockcontributedall dynamical instabilitiesinthecoolinggas.Previouslyit that thedensityofjetandambient materialareprob- cooling zonebehindtheMach disk isspatiallyresolved, and reverseshocks.Thisregionhasachaoticorturbulent ably similar. and reverseshocksare,infact,of comparablestrengthso collisionally excitedzoneatthe shockfront.Theforward and thattheHa-brightfilament onlymarksthenarrow structure consistingofmanyknotswithtypicalsizes — 110AU.Thisclumpystructuremaybetheresultof 8. CONCLUSIONS 1166 1996AJ 112.1141H (4) AstrikingHa-brightfilament,whichwedubthe‘‘Hair’’ 1167 HEATHCOTEETAL.:THEHH47JET (5) TheHH47jetappearsverydifferentinour[Sll]and (6) Theregionalongtheedgeofjetshowsnosign Bührke, T,Mundt,R.,&Ray,T.P.1988, A&A,200,99 Burrows, CJ.(Ed.)1995,“WideField andPlanetaryCamera2Instrument Bok, BJ.1978,PASP,90,489 Boden, A.,etal.1995,BAAS,27,2 Blondin, J.M.,Königl,A.,&Fryxal,B.A. 1990,ApJ,360,370 Bally, J.,&Devine,D.1994,ApJ,428, L65 (7) TheflowdirectionoftheHH47jetevidentlychanges Biro, S.,Raga,A.C.,&Cantó,J.1995, MNRAS,275,557 -1 -1 matically thisfilamentappearstobeassociatedwiththe trails behindHH47Aalongitsnorthwesternedge.Kine- We suggestthatthisHafilamenttracesanextended low velocitymaterialinthewingsofHH47Abow HH 47D.AfaintHfilamentseeninIRimages(Eislöffel wing ofHH47A,similartothatseenin[Oll]images the “Hair.” shock, andtosomefaintemissionknotsthesouthwest. row wispsandfilamentsfoundalongtheedgesofjet. Ha images.Whilein[Sll]weseeasinuouswiggling et al1994)mightbeafurthersouthwardextensionof hind [Sll]-brightknotsontheaxisofjet.Inmany These filamentsareseentotrailatanobliqueanglebe- chain ofknots,thedominantfeaturesinHaarenar- We believetheseBalmerfilamentsmarkthelocationsof cases theylieontheoutsideofapparentbendsinjet. in thejet,andpresumablyassociatedBalmerfila- low density,partlyneutralmedium.Yetthe[Sll]knots must beweak(V<10kms),andtravelintoa at theshockfront,andno[Om]emission,theseshocks turbances inthejet.SinceweseebrightBalmeremission jet andtheoreticalmodelsofwigglingjets.Thesource is neutral,andmovesoutwardatasubstantialfractionof ments, havespacevelocities—200-300kms.These shock frontsdrivenintothesurroundingmediumbydis- the jet’svelocity. facts canonlybereconciledifthegasadjacenttojet chaotic structurewhichmightbeexpectedofaturbulent mixing layer.Insteadweseeaseriesofwelldefined believe thatthegasatedgesofjetissweptupand cause theyarestrongshocks,butratherbecause 2 cause thejetmaterialtocollidewithsurroundinggas diative shocks,aprocessknownaspromptentrainment. dragged outwardprimarilybyasuccessionofweakra- is morethanapassingresemblancebetweentheHH47 ments doappeartoariseatbendsinthejet.Indeedthere driving shocksintobothfluids.SeveraloftheHafila- trainment isoperatingalongtheHH47jet.Rather,we our images.Thusweseenoevidencethatturbulenten- shock fronts.TheseshocksappearHa-bright,notbe- gone severalmajoreruptions.Someoftheshocksseen that drivestheHH47outflowhasalsoevidentlyunder- substantially alongitslength.Thismeanderingmay so weakthattheirextendedcoolingzonesareresolvedin along thejetmaycorrespondtointernalworkingsurfaces S © American Astronomical Society • Provided by theNASA Astrophysics Data System (8) Thejetisalreadyhighlycollimatedwherewefirstseeit. (9) ThebrightnessofHH47Din[Oll]hasbeenattributedto kindly providedanaccurateradiocontinuumpositionforHH paper (Reipurthetal.1996). 47IRS inadvanceofpublication.Wearegratefultoan ing outthedeconvolutionofourimages.SalvadorCuriel and otherjetsobservedwithHSTisdeferredtoafuture discussion ofthesimilaritiesanddifferencesbetweenHH47 improved thepresentationofthispaper.Supportfor the SpaceTelescopeScienceInstitute. 5504.04-93A, GO-5504.05-93A,andGO-5504.06-93Afrom 5504.01-93A, GO-5504.02-93A,GO-5504.03-93A,GO- work wasprovidedbyNASAthroughgrantnumbersGO- anonymous refereewhosecommentsandsuggestionshave Chemin, L.M.,&Masson,C.R.1991, ApJL, 382,L93 Cantó, J„&Raga,A.C.1991,ApJ,372, 646 Burrows, C.J.,etal.1996,ApJ(inpress) Chevalier, R.A.,&Raymond,J.C.1978, ApJ,225,L27 Chemin, L.,&Masson,C,GouveiaDal Pino,E.M.,&Benz,W.1994,ApJ, 426, 204 Handbook,” Version3.0(SpaceTelescope ScienceInstitute,Baltimore) We thankAndrewBodenandhiscollaboratorsforcarry- In thispaperwehaveconsideredHH47inisolation.A Future proper-motionstudiesmadeusingHSTshould We seenosign,intheregionclosetosource,ofany nisms) atwork. help toclarifythenatureofmechanism(ormecha- exciting shocksinthejetandsurroundingmedium. Kelvin-Helmholtz instabilitiescouldalsoplayarolein driven bymoreminorchangesintheoutflowvelocity. which couldberesponsibleforcollimatingthejet.What- by thebandofheavyextinctionwhichoverlies ever thecollimatingagencyis,itmustbehiddenfromus structure (e.g.,adeLavalnozzleorfocusingshock) tion thanoldersectionsoftheoutflow. the tipofHH46whichistravelinginadifferentdirec- may beanobliqueshockdrivenintotheenvironmentat adjacent toHH46,theyoungestsectionofjet.This northwest ofHH47.However,thepresenceBalmer photoionization ofthepreshockgasbyOstarsto source. 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