Astronomy&Astrophysicsmanuscriptno.benedettini (cid:13)cESO2017 January17,2017 The shocked gas of the BHR71 outflow observed by Herschel(cid:63): indirect evidence for an atomic jet M.Benedettini1,A.Gusdorf2,3,B.Nisini4,B.Lefloch5,S.Anderl5,6,G.Busquet7,C.Ceccarelli5,C.Codella8,S. Leurini9,L.Podio8 1 INAF,IstitutodiAstrofisicaePlanetologiaSpaziali,viaFossodelCavaliere100,00133Roma,Italy e-mail:[email protected] 2 LERMA,ObservatoiredeParis,PSLResearchUniversity,CNRS,UMR8112,75014,Paris,France 3 SorbonneUniversités,UPMCUniv.Paris6,UMR8112,LERMA,75005,Paris,France 4 INAF,OsservatorioAstronomicodiRoma,viadiFrascati33,00040,MontePorzioCatone,Italy 7 5 Univ.GrenobleAlpes,IPAG,F-38000Grenoble,France 1 6 CNRS,IPAG,F-38000Grenoble,France 0 7 InstitutdeCiènciesdel’Espai(IEEC-CSIC),CampusUAB,CarrerdecanMagrans,s/n,E-08193,Barcellona,Catalunya,Spain 2 8 INAF,OsservatorioAstonomicodiArcetri,LargoE.Fermi5,50125,Firenze,Italy n 9 Max-Planck-InstitutfürRadioastronomie,AufdemHügel69,53121,Bonn,Germany a J Received;accepted 6 1 ABSTRACT ] Context.IntheBHR71region,twolow-massprotostarsIRS1andIRS2drivetwodistinguishableoutflows.Theyconstituteanideal A laboratorytoinvestigateboththeeffectsofshockchemistryandthemechanismsthatledtotheirformation. G Aims. We aim to define the global morphology of the warm gas component of the BHR 71 outflow and at modelling its shocked component. . h Methods.WepresentthefirstfarinfraredHerschelimagesoftheBHR71outflowssystemintheCO(14–13),H O(2 –1 ),H O 2 21 10 2 p (2 –1 ) and[Oi] 145µmtransitions,revealingthepresenceofseveralknotsofwarm,shockedgasassociatedwiththefastoutflow- 12 01 - inggas.Intwooftheseknotsweperformedadetailedstudyofthephysicalconditionsbycomparingalargesetoftransitionsfrom o severalmoleculestoagridofshockmodels. r t Results.TheHerschellinesratiosintheoutflowknotsarequitesimilar,showingthattheexcitationconditionsofthefastmovinggas s donotchangesignificantlywithinthefirst∼0.068pcoftheoutflow,apartattheextremityofthesouthernblue-shiftedlobethatis a expandingoutsidetheparentalmolecularcloud.Rotationaldiagram,spectrallineprofileandLVGanalysisoftheCOlinesinknot [ 1 Acomshpoawctth(1e8p(cid:48)(cid:48)r)e,swenacrmeo(fTtw=o1g7a0s0c–om2p2o0n0eKnt)s:wointheselxigtehntldyedlo,wcoelrdd(eTns∼ity80(nK(H)a2n)d=d2e×ns1e04(n–(H62×)1=043c×m1−035).–I4n×t1h0e6twcmo−b3r)igahntdesatnkonthoetsr v (whereweperformedshockmodelling)wefoundthatH2andCOarewellfittedwithnon-stationary(young)shocks.Thesemodels, 3 however,significantlyunderestimatetheobservedfluxesof[Oi] andOHlines,butarenottoofaroffthoseofH2O,callingforan 4 additional,possiblydissociative,J-typeshockcomponent. 2 Conclusions. Ourmodellingindirectlysuggeststhatanadditionalshockcomponentexists,possiblyaremnantoftheprimaryjet. 4 Direct,observationalevidenceforsuchajetmustbesearchedfor. 0 Keywords. Stars:formation–ISM:jetsandoutflows–ISM:individualobjects:BHR71–Infrared:ISM . 1 0 7 1. Introduction H CO, and H O (e.g. Bachiller et al. 2001; Garay et al. 1998, 1 2 2 2002; Benedettini et al. 2007; Arce et al. 2007; Codella et al. :Intheearlyprotostellarstages,fastjetspoweredbythenascent v 2010). Such enrichment reveals the activation of endothermic istar,possiblysurroundedbyawideranglewind,stronglyinter- reactionsbyshockheatingandthemechanicalerosionandpro- Xactwiththeparentalmediumthroughmolecularshocks,produc- cessingofgrains.Therefore,outflowshocksalsoofferaunique ringaslowermovingmolecularoutflowcavity.Severalepisodes laboratoryfortestingastrochemicalmodels.However,uptonow a ofbowshocksareusuallypresentwithintheoutflowlobes(e.g. enough observations to allow detailed chemical studies that in- Bachiller&PérezGutiérrez1997;Bourkeetal.1997;Leeetal. cludemultiplemolecularspecieshavebeenmadeinonlyahand- 2006). In several outflows, fast and well collimated molecular fulofoutflows. bullets,tracinginternalshockswithinthejetarealsoseen(e.g. One interesting target for studying shocks associated with Gueth&Guilloteau1999;Nisinietal.2007;Tafallaetal.2010). Outflow shocks significantly affect the gas chemical composi- outflows is the BHR71 system. Located at a distance of about 175pc(Bourkeetal.1995),theBokglobuleBHR71isawell- tion,withabundanceenhancementsuptoseveralordersofmag- knownexampleofanisolatedstarformationwithaclearbipo- nitudeforvariousmolecularspeciessuchasSiO,CH OH,CS, 3 lar outflow close to the plane of the sky observable from the (cid:63) HerschelisanESAspaceobservatorywithscienceinstrumentspro- southernhemisphere(seeFig.1).Theregioncomprisestwodis- videdbyEuropean-ledPrincipalInvestigatorconsortiaandwithimpor- tinctoutflows(Bourkeetal.1997,2001;Pariseetal.2006)pow- tantparticipationfromNASA. eredbytwoprotostellarsources,IRS1andIRS2whichhavelu- Articlenumber,page1of16 A&Aproofs:manuscriptno.benedettini Fig.1.DoubleoutflowofBHR71breakingoutfromitsparentalBokglobule.ThegreyscaleimageisfromtheDSS2-redacquiredwiththeUK SchmidtTelescope((cid:13)c1993-1995bytheAnglo-AustralianTelescopeBoard).BlueandredcontoursarerespectivelyCO(3–2)andH 0–0S(5) 2 emission(G15).Blackstarsindicatethepositionofthetwoprotostars-IRS1andIRS2-thatdrivetheoutflows.Thewhiteandgreentriangles indicatethepositionofthepeaksoftheHerschellineemissionandarelabelledfromAtoEinorderofdecreasingdeclination.Yellowrectangle showstheapproximateextentofthelarge-scaleHerschel-PACSmaps.Thetwocyancrossesindicatethepositionsobservedwithadditionalpointed Herschelobservations. minosities of 13.5 and 0.5 L , respectively (Chen et al. 2008) thewarmgascomponentandtoderivegeneralindicationonits (cid:12) and are separated by ∼3400 AU (assuming a distance of 200 physicalcondition.Moreover,inthetwobrightestinfraredknots pc, Bourke et al. 2001). A first view of the global energetics weperformedadetailedstudyoftheshockconditionsbyfitting and physical conditions of the outflows have been derived by a large set of molecular transitions from different species with low J COandH observations(Neufeldetal.2009;Giannini shockmodels.Thepaperisorganisedasfollows.InSect.2we up 2 et al. 2011). Bright HH objects, HH320 and HH321 (Corporon present the new data acquired with Herschel and the reduction &Reipurth1997),andseveralotherknotsofshockedgashave method.TheresultsandtheanalysisperformedontheHerschel beenfoundintheoutflows.Theseknotsarousedagreatdealof data are described in Sects. 3 and 4. In Sect. 5 we present the interest,andtheirshockconditionshavebeenstudiedinseveral deeper analysis of the large set of CO transitions available for papers(Gianninietal.2004;Gusdorfetal.2011,2015,hereafter the brightest knot of the northern lobe. Shock models for this G15).ThetwoHHobjectshavebeenimagedalsointheSiitran- knotananotherknotofthesouthernlobearepresentedinSect. sitionat6711Å,indicatingthatatleastpartoftheoutflowsare 6.ThefinalconclusionsarereportedinSect.7. dissociative(Corporon&Reipurth1997).Infact,suggestionsof thepresenceofanatomicjethavebeenrecentlyfoundby[Oi] observations(Nisinietal.2015). 2. Observationsanddatareduction In this paper we present the first far infrared images of the BHR71 outflows system observed with Herschel-PACS, map- We present observations carried out towards the BHR71 out- ping the region of 200(cid:48)(cid:48) centred on the powering sources, plus flows system with the PACS (Poglitsch et al. 2010) and HIFI somepointedspectraofCOtransitionsobservedwithHerschel- (deGraauwetal.2010)instrumentson-boardHerschel(Pilbratt HIFI.Theimagestracethenot-yet-studiedwarmgas,atinterme- et al. 2010). For the scientific analysis we also make use of al- diateexcitationconditionswithrespectthecoldergastracedby readypublishedHerschelandAPEXobservations.Inparticular, lowJ COlines(Pariseetal.2006;G15)andthehotgastraced themapinthe[Oi]3P –3P line(Nisinietal.2015)andinthe up 1 2 byH rotationallines(Neufeldetal.2009;Gianninietal.2011). CO(6–5) line(G15).AsummaryofthenewHerschelobserva- 2 Themainaimofthisworkistodefinetheglobalmorphologyof tionsispresentedinTable1. Articlenumber,page2of16 Benedettinietal.:TheBHR71outflowobservedbyHerschel Table1.ObservationstowardstheBHR71outflow. 220(cid:48)(cid:48)×100(cid:48)(cid:48),spatiallyNyquist-sampledmaps Species transition E /k Frequency Wavelength Instrument FWHM Spectralresolution up B (K) (GHz) (µm) ((cid:48)(cid:48)) (kms−1) H O (2 –1 ) 159.8 2773.977 108.07 PACS 9.4 318 2 21 10 [Oi] 3P –3P 326.6 2060.069 145.53 PACS 10.2 260 0 1 H O (2 –1 ) 80.1 1669.905 179.53 PACS 13.2 210 2 12 01 CO (14–13) 580.5 1611.794 186.00 PACS 13.2 195 47(cid:48)(cid:48)×47(cid:48)(cid:48) at9(cid:48).(cid:48)4spatialsamplingmaps CO (22–21) 1397.3 2528.172 118.58 PACS 9.4 300 OH 2Π −2Π J = 5−− 3+ 120.7 2514.298 119.23 PACS 9.4 300 3 3 2 2 OH 2Π2 −2Π2J = 5+− 3− 120.7 2509.934 119.44 PACS 9.4 300 3 3 2 2 2 2 CO (20–19) 1109.2 2299.570 130.37 PACS 9.4 275 CO (18–17) 944.9 2070.616 144.78 PACS 10.2 260 [Oi] 3P –3P 326.6 2060.069 145.53 PACS 10.2 260 0 1 CO (14–13) 580.5 1611.794 186.00 PACS 13.2 195 Singlespectra CO (14–13) 580.5 1611.794 186.00 HIFI 13.2 0.093 CO (9–8) 248.9 1036.912 289.12 HIFI 21.7 0.14 CO (5–4) 83.0 576.268 520.23 HIFI 39.0 0.26 13CO (5–4) 79.3 550.926 540.73 HIFI 40.8 0.27 2.1. Herschellinemaps Table2.Knotscoordinates. The BHR71 outflows system was mapped with PACS in CO Knotslabel RA(J2000) Dec(J2000) (14–13),H2O(221–110),H2O(212–101)and[Oi]3P0–3P1byus- A 12h01m36s.0 -65◦07(cid:48)30(cid:48).(cid:48)0 ing the line spectroscopy observing mode. The final extended B 12h01m32s.0 -65◦08(cid:48)09(cid:48).(cid:48)0 mapwasbuiltcombiningthree47(cid:48)(cid:48)×47(cid:48)(cid:48) partiallyoverlapping, C 12h01m36s.5 -65◦08(cid:48)09(cid:48).(cid:48)0 Nyquist-sampledsub-maps(seeFig.1).Datawerereducedwith IRS1 12h01m36s.6 -65◦08(cid:48)48(cid:48).(cid:48)5 the HIPE1 v9.0 package, where they were flat-fielded and flux- IRS2 12h01m34s.0 -65◦08(cid:48)44(cid:48).(cid:48)5 calibratedbycomparisonwithobservationsofNeptune.Theflux D 12h01m36s.0 -65◦09(cid:48)29(cid:48).(cid:48)0 calibration uncertainty amounts to ∼ 20%, while the Herschel E 12h01m37s.2 -65◦10(cid:48)27(cid:48).(cid:48)0 pointingaccuracyis∼2(cid:48)(cid:48).Post-pipelinereductionstepswereper- formedtolocallyfitandremovethecontinuumemissionandto constructintegratedlinemaps(seeFig2). are averaged in order to increase the signal-to-noise ratio. The observed lines are well resolved already at the WBS resolution 2.2. Herschelsinglepointing thereforeinourscientificanalysiswewillusethosespectra.Cal- ibrationoftherawdataontotheT∗ scalewasperformedbythe Two positions (shown in Fig. 1) were observed in additional in-orbitsystem,whilethespectrawAereconvertedtoaT scale mb spectral lines: CO (5–4), 13CO (5–4), CO (9–8), CO (14–13) byadoptingaforwardefficiencyof0.96andthemainbeameffi- with HIFI and CO (14–13), (18–17), (20–19), (22–21), OH at cienciesgiveninRoelfsemaetal.(2012). 119 µm and [Oi] at 145 µm with PACS. The two positions In the northern pointing, the CO (14–13) line has been de- correspond to local H2 peaks, namely the SiO knot (Gusdorf tectedbybothPACSandHIFI.Thereisadifferencebetweenthe et al. 2011) in the northern lobe (R.A.(J2000) 12h01m36.00s, twomeasurementsof∼25%thatcanbeconsideredastheesti- Dec.(J2000) -65◦07(cid:48)34(cid:48)(cid:48)) and knot 8 (Giannini et al. 2004) in mate of the intercalibration error between the two instruments. the southern lobe (R.A.(J2000) 12h01m38.90s, Dec.(J2000) - Therefore, in the following analysis we assume a conservative 65◦10(cid:48)07(cid:48)(cid:48)). These observations were performed with a single erroroftheabsolutefluxesof30%thattakesintoaccountboth pointingthereforeforeachlinetheHIFIdataconsistofasingle theinstrumentalcalibrationerrorandtheerrorofcrosscalibra- spectrumwhilethePACSdataiscomposedby25spectracom- tionbetweenthedifferentinstruments. bined in a 47(cid:48)(cid:48)×47(cid:48)(cid:48) map, not Nyquist-sampled with respect to thepointspreadfunction(PSF).PACSdatawerereducedinthe same way as the extended maps exposed in the previous sub- 3. Results section by using the chopping-nodding pipeline v10.1.0 within PACSlinemapsaredisplayedinFig.2.Itisworthnotingthatthe HIPE.HIFIdata,boththeWideBand(resolution1.1MHz)and PACSlinesarespectroscopicallyun-resolved,thereforeitisnot HighResolution(resolution0.25MHz)Spectrographbackends possibletoseparatethecontributionoftheredandblueoutflow (WBS and HRS, respectively), were reduced with the standard lobes.Tothisaim,inthesamefigurewealsoshowtheemission product generation (SPG) v11.1.0 within HIPE. After consis- oftheCO(6–5) lineobservedwithAPEX(G15),integratedover tencycheck-ups,thehorizontalandverticalpolarisationspectra theredandbluewingsthatshowstherelativepositionofthetwo 1 HIPEisajointdevelopmentbytheHerschelScienceGroundSeg- outflows.Northofthetwoexcitingsourcestherearetheredlobe ment Consortium, consisting of ESA, The NASA Herschel Science oftheIRS1outflowandthebluelobeoftheIRS2outflow,and Center,andtheHIFI,PACSandSPIREconsortia. the two lobes are spatially well separated. The situation of the Articlenumber,page3of16 A&Aproofs:manuscriptno.benedettini Fig.2.IntegratedlinemapsfromHerschel-PACSoftheinnerregionoftheBHR71outflowsystem.ThebottomrightpanelshowstheH 0-0S(5) 2 (Neufeldetal.2009)andthered(from0to20kms−1)andblue(from−20to−9kms−1)wingsoftheCO(6–5) emission(G15).Firstlevelisat 3σ,namely:2.1×10−5ergs−1cm−2sr−1 for[Oi] 63µm,3×10−6ergs−1cm−2sr−1 for[Oi] 145µm,5×10−6ergs−1cm−2sr−1 forCO(14–13), 7.5×10−6ergs−1cm−2sr−1 forH O179µm,4.5×10−6ergs−1cm−2sr−1 forH O108µm and6Kkms−1 forCO(6–5).Stepscorrespondsto8% 2 2 ofthemaximumofeachlineuptothe70%ofthemaximum.CyancirclesindicatethepositionofthepeaksoftheHerschellineemission,labelled fromAtoEinorderofdecreasingdeclinationplustheprotostellarsourcesIRS1andIRS2.Thetwoyellowcrossesindicatethetwopositions observedwiththeadditionalpointedHerschelobservations.TheblackcirclesinthebottomrightpartofeachpanelshowtheFWHMofthemap. southern lobes is more complicated, with the fainter red lob of indecreasingvalueofdeclination.Afirstseriesofknots,namely the IRS2 outflow overlapping the more extended and brighter A,C,DandEarewellalignedalonganorth-southstraightline bluelobeoftheIRS1outflow. crossing IRS1 and have a separation of ∼ 40(cid:48)(cid:48) in the northern lobe and ∼ 60(cid:48)(cid:48) in the southern lobe. They likely might indi- The emission of the PACS lines appears to be clumpy with cate the direction of the driving jet emitted by IRS1. Knot B is several individual peaks surrounded by a low level extended the only knot clearly associated with the blue lobe of the IRS2 emission.Thestrongestpeakisobservedtowardstheprotostel- outflow. No clear, strong peak along the straight line connect- larsourceIRS1(Lbol=13.5L(cid:12)),theexcitingsourceofthemore ingBtoIRS2ispresentinthesouthernlobesuggestingthatin extendedoutflow.ThesecondprotostellarsourceIRS2(Lbol=0.5 this lobe the emission in the PACS lines should be dominated L(cid:12))isweakerbutstillvisibleasalocalmaximuminthemaps. by the blue lobe of the IRS1 outflow, as also suggested by the WenamedthefiveknotslocatedintheoutflowlobesfromAtoE Articlenumber,page4of16 Benedettinietal.:TheBHR71outflowobservedbyHerschel CO (6–5) map. The emission peaks are spatially coincident in all the observed PACS lines and are roughly located at the po- sitionsofshockedspotspreviouslyidentifiedthroughH obser- 2 vations (Neufeld et al. 2009). We measured the position of the knots from the peak of CO (14–13) emission, apart from knot E whose coordinates are measured from the [Oi] 63 µm map. InTable2thecoordinatesofthefiveoutflowknotsandthetwo protostarsarelisted. The additional single pointing observations with Herschel PACS and HIFI were acquired towards knot A in the northern lobe and about 15(cid:48)(cid:48) north-east of knot E in the southern lobe, indicatedbytwocrossesinFigs.1and2.Thespectraofthefour linesobservedwithHIFIareshowninFig.3.TowardsknotA,all thefourlinesaredetectedwithgoodsignal-to-noiseratio,with wingsextendingupto∼60kms−1,avelocityhigherthanprevi- ouslyreported(∼45kms−1,G15).TheCO(5–4) linepresentsa self-absorptionfeatureatthevelocityoftheenvironmentalcloud (−4.5 km s−1, Bourke et al. 1995), observed in all CO lines up to the (6–5) (G15). From the 12CO (5–4)/13CO (5–4) ratio we measuredtheopticaldepthofthe12CO(5–4)linethatresultsto be optically thin only in the red wing at (cid:51) (cid:62) 2 km s−1. The in- Fig.3.PlotofthelinesobservedwithHIFItowardsknotAinthenorth- tensity peak of the CO lines moves towards higher velocity for ernlobe(upperpanel)andabout15(cid:48)(cid:48) north-eastofknotEinthesouth- lineswithhigher Jup,indicatingthatthelowandhigh Jup lines ernlobe(lowerpanel).Spectrawererebinnedatacommonspectralres- are emitted from different layers of the shocked region. In the olutionof0.5kms−1.Intheinsetsazoominthelineswingsisshown. southernlobepointingthelinesprofilesaredifferent,despitethe bluewingsextendinguptoavelocity((cid:51) ∼ −60kms−1)similar tothatobservedintheredlobe.Inparticular,noself-absorption 4. Analysisoftheextendedoutflow and no peak shifting is observed in the southern tip of the blue 4.1. Thedistributionofthewarmgas lobe. Moreover, the CO (14–13) was not detected and the line ratioCO(9–8)/CO(5–4) islower,indicatingthattheexcitation The far-infrared PACS lines with excitation temperatures be- condition at this position is lower than in knot A. This is also tween 80 and 580 K allow for the first time to have a com- confirmedbythefactthatthenorthernpointingcorrespondstoa pleteviewofthedistributionofthewarmgascomponentinthe peakofthehighexcitationtransitionsobservedwithPACSwhile BHR71outflowsystem,tracingtheintermediateexcitationcon- thesouthernpointingisnotcentredonapeak.The12CO(5–4)/ ditionbetweenthecoldgastracedbylowJ COlines(Pariseet up 13CO (5–4) ratio shows that also in the southern blue lobe the al.2006;G15)andthehotgastracedbyH (Neufeldetal.2009; 2 12CO (5–4) line is optically thin only in the wing, at v < −10 Gianninietal.2011).TheemissioninthePACSlinesshowsthe kms−1.TheCO(9–8) lineinthispointofthesouthernlobeisat presenceofsevenbrightknotssurroundedbyalowlevelemis- velocitybluerthansystemic((cid:51) < −4.5kms−1)whileintheCO sion. Two knots correspond to the two protostars that generate (5–4) lineasmallredwingispresent.Thereareseveralpossible theoutflowssystemandtheotherfiveknotsareclosetoclumps explanations for this. The first possibility is the larger beam of ofhightemperaturegas(T (cid:62)1000K)alreadyobservedinH ro- 2 the CO (5–4) line with respect to the CO (9–8), secondly, the tationaltransitions(seeFig.2).Theyarealsoassociatedwiththe excitation condition of the gas in the red lobe of the IRS2 out- gasmovingatthehighestvelocityasshownbythecomparison flowcouldbeinsufficiencytopopulatetheCO J =9level,and ofthe[Oi] 63µm mapwiththemapofthereddest(from10.5 up athirdpossibliltyisthattheemissionatredvelocityoftheCO km s−1 to 40 km s−1) and bluest (from −30 km s−1 to −19.5 (9–8) lineisunderthesensitivitylevelofHIFIspectrograph.In km s−1) velocities of the CO (6–5) line wings (Fig. 5). They allcaseswecanconcludethattheredlobeoftheIRS2outflow most likely represent shock spots where the fast jet that drives does not contribute to the measured flux of the transitions with outflowsimpactagainstthelowerexpandinggas. highexcitationlevels. SincethePACSlineshavecoarsespectralresolution,wecan- not spectroscopically separate the contribution of the two out- flowstothetotalemission.Thisisnotaproblemforthenorth- Towardsthetwooutflowpositions(indicatedinFigs.1and ernlobessincethetwooutflowsarespatiallywellseparatedbut 2) we also acquired PACS maps of high J CO transitions, itcouldbeaproblemforthesouthernlobesthatpartiallyover- up namelyCO(14–13),CO(18–17),CO(20–19),CO(22–21),and lap.However,thespectralprofileoftheCOlinesobservedwith of the OH 119 µm and [Oi] 145 µm lines. Towards knot A, HIFI at the tip of the southern lobe close to knot E, shows that theCOlinesarebright,whiletheOHand[Oi] arelessintense the percentage of the emission at velocity redder than the sys- (Fig.4).Allthelineshaveasimilar,partiallyresolved,roundish temic velocity (−4.5 km s−1) with respect to the total emission form with the peak at the centre of the map and a deconvolved decreases for increasing J , being only the 3% for the CO (9– up circular size of 18(cid:48)(cid:48), indicating that they are emitted from the 8) transition.Thereforewecanexpectanevenlowerpercentage same extended gas component. Towards the southern pointing fortheCO(14–13) lineandfortheotherPACSlinesfrom[Oi] only a ∼ 3σ level CO (14–13) emission is detected while the and water, that trace the same warm gas component, as shown otherlinesarenotdetected,confirmingonceagainthelowerex- from Fig. 2 for BHR71 and as also observed in other outflows citationconditionofthisposition. (Santangelo et al. 2013; Busquet et al. 2014).In conclusion, at Articlenumber,page5of16 A&Aproofs:manuscriptno.benedettini Fig.4.MapsofthefourCOlines,OH119µm and[Oi] 145µm observedwithPACStowardsknotAintheredlobeoftheIRS1-drivenoutflow. Firstlevelandlevelstepsare9×10−18 Wm−2,correspondingto3σ.Thecrossesmarkthecentralpositionofthe25spatialpixelsofthePACS FOV.ThearrowinthetopleftpanelindicatesthedirectionoftheIRS1protostar. the tip of the southern lobe the contribution of the red lobe of and the higher J CO (6–5) and (14–13) showing a roundish up the IRS2 outflow to the PACS lines is negligible. The situation structurewithspatiallycoincidentpeaks. in the southern positions closer to the two protostars could be different since in the uppest J available CO line, the CO (6– AdisplacementintheemissionpeakoftheCOlineswithin- up creasing J wasalsoobservedtowardstheflowcontainingthe 5) observed with APEX, the emission in the red wing is still up Herbig-HaroobjectHH54(Bjerkelietal.2014).InHH54,how- significant.However,towardsthebrightknotDthesimilarmor- ever, the gradient goes in the direction of the exciting source, phology of the blue wing of the CO (6–5) and the PACS lines that is, in the opposite direction with respect what we observe (Fig.2)showsthateveninthisknotthecontributionofthered in knot A of BHR71. Bjerkeli et al. (2014) interpreted the ob- lobeoftheIRS2outflowtothePACSlinesshouldbenegligible. serveddisplacementoftheCOlinespeakastheconsequenceof thepresenceofanunder-dense,hotclumpupstreamoftheHH54 InSect.3wealreadynoticedthattowardsknotsAthepeak shockwave,tracedbyawelldefineddistinctgascomponentin velocityoftheCOlinesmovestohighervelocityforlineswith thespectraofthelow J COlines.Althoughnodistinctveloc- up higher J .InFig.6wecomparethespatialmorphologyofCO itycomponentsarepresentintheCOspectraoftheBHR71out- up (3–2), CO (6–5) and CO (14–13) emission in knot A and we flow,theobserveddisplacementofthelocationoftheemission find that the peak of the CO emission moves towards north for maximumofCOwithincreasing J inoursourcecouldbeat- up CO lines with higher J , with a separation of about 20(cid:48)(cid:48) be- tributedtodifferentlayersofshockedgasimpactinganambient up tween theCO (3–2) and theCO (14–13) peaks. Moreover, the medium with a significant stratification of particle density. The peakofthehighestexcitationCOlineistheclosertothepeakof differenceinthemorphologyoftheCOlinesemissionbetween H 0-0S(5)(E =4586K)emissiontracinghotgas.Thepeak knots A and D is probably due to the different environmental 2 up shifting is along the straight-line connecting knots A, C and D conditionsinwhichthetwoshockshavebeenoriginatedand/or andcrossingIRS1,suggestingthattheshiftislinkedtothebow togeometricaleffectsthatcouldchangetheangleofviewunder shockgeneratedbytheimpactofthehigh-velocityjetagainstthe whichthetwoshocksareobserved.Infact,asclearlyvisiblein slowermovingambientshell.ThesituationinthebrightknotD Fig. 1 that compares the outflow traced by CO (3–2) with an ofthesouthernlobeisdifferent(seeFig.6),withthelowJ CO optical image of the region at 0.54 µm, the outflow is breaking up (3–2) line having the classical morphology of the cavity walls outfromitsparentalBokglobulewithmorethanhalfoftheblue Articlenumber,page6of16 Benedettinietal.:TheBHR71outflowobservedbyHerschel Fig. 5. Map of the high velocity wings of CO (6–5) overlaid to [Oi] 63µm. The red wing (red line) is integrated from 10.5 km s−1 to 40 kms−1 andthebluewing(blueline)from-30kms−1 to-19.5kms−1. COlevelsareat50%,70%and90%ofthemaximum.Thepositionof thetwoprotostarsareindicatedwithatriangle. southernlobeprojectedoutsidetheobscuredregionwhileinthe red northern lobe only the very final part is projected outside Fig.6.MapoftheH 0-0S(5)line(grey-scalemap)comparedwithCO the globule. Although it is more difficult to understand what is (3–2)(redline),CO2(6–5)(blackline)CO(14–13) (greenline).Upper really happening on the rear side of the globule, the measured panel is centred on knot A, lower panel on knot D. Contours start at muchlargermassandkineticenergyoftheredlobewithrespect 90%ofthepeakvalueinordertohighlightthepositionofthepeakof thebluelobe(Bourkeetal.1997)confirmswhatFig.1suggests. the emission. The circles show the HPBW of the different lines. The OurHerschel-PACSmapcoversthepartofthenorthernlobestill arrowsindicatethedirectionofIRS1. fully embedded in the obscured and denser medium inside the moleculardarkcloudwhilethefinalpartofthemappedportion 4.2. Lineratios ofthesouthernlobeispropagatingoutsidethecloud.Inthisre- spectknotsAandDareinadifferentenvironment:thenorthern Withonlytwolinesperspeciesitisimpossibletoconstrainthe knotAislocatedcompletelyinsidethecloudwhilethesouthern physicalparametersoftheemittinggas.However,wecanderive knot D is located at the border of cloud, likely in a less dense some general indications on if and how the physical and exci- medium. Moreover, while knot A is associated to only the red tationconditionofthegaschangealongtheoutflow,comparing lobeoftheIRS1outflowinthepositionofknotDtwodifferent theratiosoflinesofthesamespeciesintheseveninfraredknots. lobescoexist. In order to avoid different beam filling effects we smoothed all Remarkably, towards knot A the peak of the high J CO the PACS maps at the common spatial resolution of 13(cid:48).(cid:48)2 and up correspondstothepeakofatomiclinessuchas[Oi] 63µm and extracted the brightness in the position of the seven Herschel [Feii] 26 µm and of the H rotational lines (Fig. 7) as also ob- knots. In Fig. 8 we show the H O 179µm/108µm, the CO (6– 2 2 served in other bright, outflow shocks such as L1157-B1 and 5)/(14–13)andthe[Oi] 63µm/145µm ratiosinthesevenknots HH54 (Benedettini et al. 2012; Bjerkeli et al. 2014). This im- alongtheoutflow.Theratiobetweenthetwowaterlinesisquite plies that the presence of a dissociative and ionising shock but constant in all the knots but IRS1 where it is higher of about a alsothatthejetmaterialisalreadypartlymolecular,ormolecules factoroftwo.AhigherH O179µm/108µm isanindicationofa 2 reformation is efficient after the passage of the shock front. A lowerparticledensityor/andlowerwatercolumndensity.IRS1 modeloftheshocktowardsknotAandDispresentedinSect.6. isalsotheknotwiththelowerCO(6–5)/(14–13)ratiowhichin- Articlenumber,page7of16 A&Aproofs:manuscriptno.benedettini Fig.8.PACSlinesratiosofH O179µm/108µm (leftpanel),CO(6–5)/(14–13)(middlepanel)and[Oi] 63µm/145µm (rightpanel)intheseven 2 infraredknots.Arrowsrepresentlowerlimits. E)wemeasuredaslightlylowerratio(15),indicatingthatinthe latterpositionsthedensitycouldbelower.Itisworthnotingthat the lowest ratio of 6.5 observed towards IRS2 is not compati- blewithmodelpredictions.Unpredictedlow[Oi] 63µm/145µm ratios have been already observed in several sources (Liseau et al.2006)andinterpretedasduetoself-absorptionofthe63µm line. This interpretation was corroborated by the recent obser- vationofaspectroscopicallyresolved[Oi] 63µm linetowards a high-mass source which shows a very prominent absorption (Leurinietal.2015).Theself-absorptionofthe[Oi] 63µm line couldbethereasonoftheextremelylow63µm/145µm ratioob- servedtowardsIRS2.IndeedIRS2hasbeenclassifiedasaClass 0 protostar and it is likely at an earlier evolutionary stage with respecttoIRS1(Chenetal.2008)thereforeitshouldbedeeply embedded in its dusty envelope whose extinction capability is stillefficientat63µm butitdoesnotaffectlinesathigherwave- lengths.Wecannotexcludethepossibilitythatthe[Oi] 63 µm linetowardsIRS1isalsopartiallyabsorbedthereforethedensity inferredformthe[Oi] linesratioshouldbeconsideredalower Fig. 7. Map of the H2 0-0 S(5) line compared with CO (14–13) (red limit. line),[Oi] 63µm (greenline),[Feii]26µm (blueline)towardsknot A.Contourlevelsis70%,80%and90%ofthelocalmaximaofeach line.ThecirclesshowtheHPBWofthedifferentlines. 5. ModellingoftheCOlinesinknotA ForthebrightestpointoftheredlobeoftheIRS1outflow(knot dicatesamuchhighertemperature(T >1200K)forthissource. A) we have measurements of CO lines from J = 3 to J = 22 up up Thisisnotunexpectedsincetowardsveryyoungprotostarsahot thatallowsustomakeadeepanalysisofthephysicalconditions CO component was usually observed, traced by CO lines with presentinthispureshockposition.Theregionhasalreadybeen excitation temperature higher than 1500 K (e.g. Dionatos et al. modelledinseveralpapers(Gusdorfetal.2011;G15),herewe 2013;vanKempenetal.2010;Karskaetal.2013).Inparticular, addthe newcontributionof thehigh J COlines observedby up towardsIRS1Karskaetal.(2013)detectedtheCO(24–23)line, PACS that trace a gas component not traced by the transitions indicatinghightemperatureforthegassurroundingtheprotostar. modelledbypreviousworks. The CO (6–5)/(14–13) ratio shows a decreasing trend from the northernlobeknotstothesouthernlobeknotsandthisisindica- 5.1. Rotationaldiagram tiveofalowertemperatureatthesoutherntipoftheoutflowthat confirmsourresultsonthelowerexcitationconditionpresented Wecalculatedtherotationaltemperaturefromtherotationaldi- intheprevioussections. agram of the CO lines, which gives a lower limit to the kinetic Theratioofthetwo[Oi] linesgivesanestimateofthehy- temperatureifthegasisnotinlocalthermodynamicequilibrium drogen particle density. We compared our observed ratios with (LTE). In order to enlarge our data set as much as possible we theoreticallineintensityratioscalculatedfromthenon-LTEcode alsousedthelow J COlineobservedwithAPEXandSOFIA up alsousedinNisinietal.(2015)thatconsidersthefirstfivelevels (G15).WesmoothedalltheCOmapsatthecommonresolution of oxygen. The three main peaks of the IRS1 outflow have ra- of24(cid:48)(cid:48).FourCOlines,namelyCO(5–4),CO(9–8),CO(11–10) tiohigherthan22,indicativeofdensitybetween104–105cm−3 andCO(16–15),however,havebeenobservedonlywithasingle while on sources and at the southern peak of the outflow (knot pointingandwithadifferentbeam(excepttheCO(11–10) that Articlenumber,page8of16 Benedettinietal.:TheBHR71outflowobservedbyHerschel Fig.9.RotationaldiagramofCOlines.ForthelowJ linesthederived up rotational temperature and column density are values averaged in the 24(cid:48)(cid:48) beam,assumingafillingfactor1.Forthehigh J linesasizeof up 18(cid:48)(cid:48) isassumed. wasobservedwithabeamof24(cid:48)(cid:48))andarenotusedinthefitting. Inbuildingtherotationaldiagramwetookintoconsiderationthe measuredsizeoftheCOemission,assumingthatlineswith J up from 3 to 11 are extended over the beam of 24(cid:48)(cid:48)while the lines with J from14to22haveasizeof18(cid:48)(cid:48) (seeSect.3).Forthe up spectrally resolved lines observed with APEX and SOFIA the linefluxwascalculatedintegratingtheemissioninthevelocity rangebetween-4.5kms−1 and50kms−1 asinG15,whilefor Fig.11.BestfitoftheLVGmodelforCOlinesinknotAconsidering two components. The parameters of the first component (dotted line) the unresolved Herschel-PACS lines we used a Gaussian fit to are:N(CO)=6×1016cm−2,size=24(cid:48)(cid:48),T=70K,n(H )=4×106cm−3:they the line profile. We attribute to each line flux an uncertainty of 2 arethephysicalparametersofthelowexcitationgascomponentaver- 30%inordertotakeintoconsiderationtheintercalibrationerror agedinsidethe24(cid:48)(cid:48) beamcentredtowardstheknotAposition;thiscom- betweendifferentinstruments.Therotationaldiagramisshown ponentis,however,moreextendedthanthebeam.Theparametersofthe inFig.9. secondcomponent(dashedline)are: N(CO)=3×1015 cm−2,size=18(cid:48)(cid:48), Two components are clearly present: a low excitation com- T=2200K,n(H )=4×104cm−3.Thesolidlinerepresentsthesumofthe 2 ponent fitting the low J lines and a higher excitation compo- twocomponents. up nentfittingthehigh J lines.Toderivethecolumndensityand up therotationaltemperatureofthetwocomponentswefittedtwo sets of lines separately, grouping the lines measured with the has been found for the profile of the high Jup CO lines in the same instrument, i.e. the APEX (J =3, 4, 6, 7) and the PACS B1 shock of the L1157 outflow (Lefloch et al. 2012) and also lines(Jup=14,18,20,22),respectiveulpy.Indeedthepointatwhich theseauthorsattributetheemissionoftheCOlinewith Jup(cid:62)13 the slope of the fitting stray-line changes is between the two to shock excited gas. Another indication that the high Jup CO sets of transitions. The best fit parameters are: T =68 K and lines are dominated by the high excitation gas related to the rot N(CO)=6×1016cm−2 forthelow J APEXlinesandT =267 shockisthatalsothelineprofileofSiO(Gusdorfetal.2011),a up rot K and N(CO)=6×1015cm−2 for the high J PACS lines. Note speciesintroducedinthegasphasebytheshockthroughsputter- up ingfromthedustgrainsorvaporisationingrain-graincollisions thattheHIFIandtheSOFIAmeasurements,notusedinthefit- (e.g.Guilletetal.2009)iswelldescribedbythesameexponen- ting itself, are in agreement with the fitting results. It is worth tiallaw(Fig.10). noting that the low J lines, at least the ones with J ≤5, are up up notopticallythinatallvelocitiessothatcolumndensityderived fromtherotationaldiagramrepresentsalowerlimitandthero- 5.2. LVGanalysis tationaltemperatureanupperlimit.Thetworotationaltempera- tures are similar to those found in other shock positions along We compared the CO lines emission with a grid of Large Ve- protostellar outflows as L1157 and Cep E (Benedettini et al. locity Gradient (LVG) models calculated with the Ceccarelli 2012;Leflochetal.2012,2015). et al. (2003) code. The molecular data were taken from the These two different gas components show a different line BASECOL2 database (Dubernet et al. 2013) and the line width profile. In fact, the spectral profile of the CO (14–13) and CO (FWHMofthelineprofile)wassettoafixedvalueof9kms−1, (16–15) lines is well described by a single exponential law asmeasuredintheHIFIspectra.Weconsiderthefirst41levels I ((cid:51)) = I (0) exp(-(cid:51)/(cid:51) ) with the same slope (cid:51) = 10 km s−1 correspondingtoenergylevelsupto2000K.Theexploredrange CO CO 0 0 forthetwolines(Fig.10),whilethelowerJ lineshaveamore inCOcolumndensityisfrom4×1015to1×1018cm−2,therange up complex profile indicating that different gas components con- tribute to the total emission. A similar slope ((cid:51) = 12 km s−1) 2 http://basecol.obspm.fr 0 Articlenumber,page9of16 A&Aproofs:manuscriptno.benedettini Fig.10.ExponentialfitofthelineprofileforCOandSiOlinestowardsknotA.Thelinerepresentthefittothelineprofilewiththeexponential lowI((cid:51))=I(0)exp(-(cid:51)/10kms−1). Table3.ParametersoftheLVGfittingoftheCOlinestowardsknotAataresolutionof24(cid:48)(cid:48). Component N(CO) size T n(H ) 2 cm−2 (cid:48)(cid:48) K cm−3 cold 2×1016–6×1016 >24 ∼80 3×105–4×106 warm 3×1015–9×1015 18 1700–2200 2×104–6×104 in particle density is from 5×103 to 3×108 cm−3, the range in a slightly lower density (n(H ) = 2×104 – 6×104 cm−3). The 2 temperatureisfrom25to2000K. comparison between the observed CO line fluxes and the best fitmodelisshowninFig.11.Thetemperatureofthewarmgas ItisimpossibletofitalltheobservedCOlinesfrom J =3 up derived from CO is in agreement with the temperature derived to J =22withasinglegascomponent,whileatwo-component up fromtheH lines(Gianninietal.2011)confirmingthathighJ modelgivesagoodfittothedata.Inordertoreducethefreepa- 2 up CO lines and rotational H lines trace the same gas component rameterswefixedalltheparametersthatarewellconstrainedby 2 asalsosuggestedfromthespatialcoincidenceoftheiremission the observations. In particular, the size of the two components (Fig.7).Thecolumndensityandtemperatureofthefirstcolder can be measured from the maps: the low J component is ex- up componentisinagreementwiththeestimatesderivedinthepre- tended, that is, we assume a filling factor of 1, and the size of vioussectionwiththerotationaldiagram,indicatingthatitisnot thehigh J transitionsismeasuredfromthePACSmapstobe up farfromLTE.Thetemperatureisalsocompatiblewiththelower 18(cid:48)(cid:48). The CO column density of the low J lines is well con- up limitsofthekinetictemperatureofthelowerexcitationgasde- strainedfromthefittingoftheAPEXlinesat N(CO)∼6×1016 rivedfromlowJ COlinesinotherpositionsalongtheoutflow cm−2,avalueconsistentwiththatderivedfromtherotationaldi- (Pariseetal.200u6p). agram.IfwefixthesethreeparametersthefittingwiththeLVG grid of models constrains the other model parameters, as given inTable3.ThefirstgascomponentfittingthelowJ linesisex- up 6. Comparisonwithshockmodels tended(size>24(cid:48)(cid:48)),cold(T ∼80K)anddense(n(H )=3×105 2 –4×106cm−3);thesecondcomponentfittingthehighJ lines Inthissection,wepresentcomparisonsofourobservationswith up is compact (size=18(cid:48)(cid:48)), warm (T = 1700 – 2200 K) and with outputs of the Paris-Durham shock code (Flower & Pineau des Articlenumber,page10of16