A Mid-Infrared Spitzer Study of the Herbig Be Star R Mon and the Associated HH 39 Herbig-Haro Object

0.34 MB·English

by  M. Audard

NonamemanuscriptNo.
(willbeinsertedbytheeditor)
A Mid-Infrared Spitzer Study of the Herbig Be Star R Mon and the
Associated HH 39 Herbig-Haro Object
M.Audard · S.Skinner · M.Gu¨del · T.Lanz · F.Paerels · H.Arce
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Abstract WereportoninitialresultsofourSpitzerCycle2 ofR Mon.A PAH emission featureat 11.3 m m is detected

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program to observe the young massive star R Mon and its ontopofthestrongcontinuum;althoughnostrongemission
v
associated HH 39 Herbig-Haro object in the mid-infrared. orabsorptionlinesareobserved,wewillseektodetectfaint
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0 Our program used all instruments on-board Spitzer to ob- lines. The combined IRAC, IRS, and MIPS data of the R
9 tain deepimageswith IRACof theHH 39 complexandof Mon/HH39systemwillhelpustounderstandcircumstellar
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R Monand its surroundings,a deep imageof HH 39at 24 diskprocessing,andtheconnectionbetweenjets,outflows,
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and 70 m m with MIPS, and mid-infrared spectra with the andHHobjects.
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0 SH,LH,andLLmodulesofIRS.Theaimofthisprogramis Keywords HerbigBestar·Herbig-HaroObject·Accre-
/ tostudythephysicallinksinayoungmassivestarbetween
h tion·Infrared·Spitzer
p accretion disk, outflows and jets, and shocksin the associ-
- atedHHobject.Ourpreliminaryanalysisrevealsthatseveral
o PACS 95.85.Gn · 95.85.Hp · 97.10.Bt · 97.10.Gz ·
knots of HH 39 are clearly detected in most IRAC bands.
r
t In IRAC4 (8 m m), diffuse emission, probably from PAHs, 97.21.+a·97.82.Jw
s
a appears as foregroundemission covering the HH 39 emis-
:
v sion. The HH 39 knots are detected at 24 microns, despite
1 Introduction
i the factthatdustcontinuumemission coversthe knotsand
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showsthesamestructureasobservedwithIRAC4.TheIRS HerbigAe/Bestars(hereafterHAEBEs;Herbig,1960)form
r
a spectra of HH 39 show weak evidenceof [Ne II] 12.8 m m aclassofmassive,youngstarswithhighluminosities(10−
and0–0S(1)H217.0m mlines.Amoredetailedanalysisis, 1000L⊙)andwithastronginfrared(IR)excessduetocir-
however, required due to the faintness of the Herbig-Haro cumstellardust (Waters andWaelkens, 1998).The spectral
knots. Finally, we obtainedthe SH and MIPS SED spectra energydistribution(SED)ofHAEBEscanbeexplainedby
circumstellarenvelopeswithpolycyclicaromatichydrocar-
M.Audard bons(PAHs;3.3,6.2,7.7,and11.3m m;Brookeetal.,1993;
ISDC&GenevaObservatory,UniversityofGeneva,Ch.d’Ecogia16,
Meeusetal.,2001),andbydustemissionfromamorphous
1290Versoix,Switzerland
Tel.:[phone],Fax:[phone] or crystalline silicate bands (8−12 m m) or molecular and
E-mail:[email protected] atomictransitions.Accretiondisksandoutflowsin theless
S.Skinner massive classical T Tau stars (CTTS) are intimately con-
UniversityofColorado nected,thusthepresenceofoutflowsinsomeHAEBEssug-
M.Gu¨del geststhatdiskscouldbepresentaswell(e.g.,Corcoranand
PaulScherrerInstitut Ray,1998a).CorcoranandRay(1998b)alsofoundthatthe
T.Lanz wind mass-loss rate correlates with the IR excess over 5
UniversityofMaryland orders of magnitude in luminosity and from 0.5 to 10 M⊙
F.Paerels whenusingbothCTTSandHAEBEs.OutflowsinHAEBEs
ColumbiaUniversity are ∼ 2−3 times faster (v ∼ 600−900 km s−1) than in
H.Arce CTTS,butgenerallyshowsimilarcollimation(3◦−10◦),al-
AmericanMuseumofNaturalHistory thoughthefractionofpoorlycollimatedoutflowsinHAEBEs
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(50◦−120◦)islarger(e.g.,MundtandRay,1994).Complex
shocksoccurattheinterfacebetweenthejetandthemolecu-
larmaterial(Draine,1980),heatingupthegaswhichinturn
coolsdownradiatively.ThisgasisdetectedasHerbig-Haro
objects (HH) in excited lines in the optical, in the near-IR
(e.g.,H ro-vibrationallinesaround2m m),andinthemid-
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IR ([O I] 63 m m; Nisini et al., 1997; Liseau et al., 1997;
Molinarietal.,2000).
2 TheRMonandHH39System Fig. 1 (Left) The HH 39 Herbig-Haro knots in the R band (from
WalshandMalin,1985).(Right)3-colorIRACimageofHH39(red=
TheHerbigBe starRMon(d=800pc)isassociatedwith 3.6m m,green=4.5m m,blue=5.8m m).
NGC2261,areflectionnebulathatgraduallyfaintswithin-
creasingwavelength(Closeetal.,1997).Abipolaroutflow
and a high-velocity jet (v∼100 km s−1) pointing toward 1985).Severalknotsarelabeled,andinparticularknotAhas
thenearbyHH39knots(r=7.5′,PA=350◦)weredetected beenidentifiedastheworkingsurfaceofthejetontothesur-
roundingmolecularmaterial.Therightpaneloffig.1shows
(Canto´ et al., 1981; Brugel et al., 1984; Movsessian et al.,
a 3-color IRAC image of HH 39 (red = 3.6 m m, green =
2002).Evidenceforacircumstellardiskissubstantiatedas
4.5m m,blue=5.8m m).Severalknotsareclearlydetectedin
well(e.g.,Beckwithetal.,1986;Fuenteetal.,2003;Fuente
themid-infrared.Fig.2showsfalse-colorimagesoftheHH
et al., 2006). A faint CTTS companion at a separation of
0.7′′ and with K′ flux of 34 mJy is mentioned by Close et 39knotsineachofthefourIRACbands.KnotsD,G,C,and
EareclearlydetectedinallIRACbands,andknotHistenta-
al. (1997) and Weigelt et al. (2002).The HH 39 cluster of
knotscoversanareaabout25′′×45′′(Fig.1;JonesandHer- tivelydetected.Adiffuseemissionisobservednearthepo-
sitionofknotAinIRAC1only.Thefeaturecouldbedueto
big, 1982; Walsh and Malin, 1985), and the northernmost
H linesor3.3m mPAH.Sincethisfeatureisnotdetectedin
knot,knotA,isbelievedtobetheworkingsurfaceofthejet 2
IRAC2,thisisa“PAH”-freeband,itisverylikelythatPAHs
(SchwartzandSchultz,1992).
Near-IRspectraofRMonexistmostlyinthe0.9−2.5m m contributetothediffuseemissionnearknotA.H2 lines,on
range with low (∼400) spectral power (Kelly et al., 1994; the other hand, most likely contribute to the emission in
ReipurthandAspin,1997;Porter etal.,1998).ISOneither knots D, G, C, and E. Supporting evidence comes from a
observedRMonnorHH39.TheIRASLRSspectrum(9− faint0–0S(1)rotationalH2 linedetectedintheIRSspectra
21 m m) of R Mon is classified as an “unusual spectrum at17.03m mofthebrightknots(0.7−1.0×10−20Wcm−2).
showing a flat continuum with unusual features” (Chen et Incontrast,IRSspectraofknotsA+A′donotshowevidence
al., 2000). Aspin et al. (1988) and Yamashita et al. (1989) ofH2lineemissioninexcessofthenearbycontinuum.Note
claimedtodetectanextendedemissioneastwardofRMon, that faint [Ne II] emission at 12.81 m m is measured in the
bright knots and at the position of knots A+A′ (of the or-
butitremainedundetectedbyCloseetal.(1997)withIRTF
at 3.16 m m down to 1s ∼0.05 mJy arcsec−2 (CVF filter derof0.5×10−20Wcm−2).At8 m m,thebrightknotsare
withanexposureof60s). barely visible on top of a diffuse emission that sweeps in
through the knots. This extended emission is likely of due
to PAHs (7.7 m m) and is also seen in the dust continuum
3 Spitzerobservations 24m mMIPSimage(Fig.3and4).Itsoriginisunclearbutit
couldbetheupperwalloftheNGC2261reflectionnebula
We have obtained 4.2 hrs of Spitzer time to study the R
cavity.
Mon/HH39system.Ourprogram(PID20034)usesallin-
Fig. 3 shows the MIPS images of the HH 39 region at
struments:IRACandMIPSimagesofHH39;IRACimages
24 and 70 m m together with an optical Deep Sky Survey
of R Mon and its jets; IRS spectra of R Mon, its jets, and
image.DustcontinuumemissionisdetectedacrosstheHH
severaloftheHH39knots;andMIPSSEDofRMon.The
39knots,in particularat24 m m.NeverthelessfaintHH 39
observationsweretakenatdifferentepochs,spanningfrom
knotsarealsodetectedat24m m(Fig.4),butthereisnoclear
October2005toApril2006.
evidenceoftheknotsinthe70m mimage.Ontheotherhand,
itshouldberemindedthattheFWHMPRFat70m mis18′′,
3.1 TheHerbig-HaroobjectHH39 i.e., about the distance from knot A to the group of knots
(G, D, E, C, H). Therefore, since the MIPS 70 m m image
Fig. 1 (left) shows the contour profiles of the Herbig-Haro does not, apparently,observe the same diffuse emission as
object HH 39 see in the R band (from Walsh and Malin, at24m mor8m m,itispossiblethatthefaintemissionatthe
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Fig.3 MIPS24and70m mimages(leftandmiddle)oftheHH39re-
giontogetherwithaDSSimage(right)ofRMon,thereflectionnebula
NGC2261andHH39,onthesamescale.
Fig.2 (a)IRACfalse-colorimagesofHH39.Backgroundsurfaceflux
densitiesareoftheorder0.30,0.35,2.1,10.5MJysr−1 inIRAC1,2,
3,and4,respectively(zodiestimates:0.12,0.37,1.72,10.4MJysr−1;
ISM light estimates: 0.15,0.20,0.56,4.79 MJy sr−1). In con-
trast, the bright knots have peak surface flux densities of about
0.95,1.1,3.2,11.8MJysr−1.
positionoftheclusterofknotsisinfactpartiallydueto[O
I]63m mlineemissionfromtheknots.
Emission from the upperpartof NGC 2261is also de-
tectedinMIPSat24m m.ThebrightemissionSWofHH39
is the IR source IRAS 06362+0853. There is no evidence
fordiffuseemissionin2MASSaroundIRAS06362+0853,
suggestingthatitisofinterstellarcirrusnature.Surfaceflux
densities at 24 m m are around 42 MJy sr−1 for the “blue” Fig.4 IRAC3.6m mand8m m,andMIPS24m mand70m mfalse-
color regions and go up to 43.1 MJy sr−1 across HH 39. colorimagestogether withthepositionsofHH39knotsdetected in
IRAC1.TheIRAC8m mandMIPS24m mdetectPAHanddustemis-
PeaksurfacefluxdensitiesforIRAS06362+0853areabout
sionacrossHH39,likelyduetotheupperwalloftheNGC2261reflec-
44.4 MJy sr−1 and 46.7 MJy sr−1 for the dust emission tionnebulacavity.Incontrast,at70m m,theupperwallisnotdetected,
of NGC 2261. At 70 m m, “blue” regions are about 31− andtheHH39knotsarenotclearlydetected(seetext).
33 MJy sr−1, whereas the emission across HH 39 is 48−
50MJysr−1,and80−85MJysr−1nearIRAS06362+0853.
The SPOT backgroundestimates are 37.6 MJy sr−1 (zodi) aimedtodeterminewhetherafainteastwardextendedemis-
and2.96MJysr−1(ISM)at24m mand10.8MJysr−1(zodi), sionfeaturedetectedby Aspinet al. (1988)and Yamashita
21.9MJysr−1 (ISM),and0.2MJysr−1 (cosmic)at70m m. etal.(1989),butundetectedbyCloseetal.(1997),couldin-
deedbedetectedwiththehighlysensitiveIRACdetectors.
Thesurfacefluxdensitiesinthe“blue”regionsareofsimilar
Thetotal(zodiandcirrus)backgroundfluxdensitiesare
valuesastheestimatedtotal.
0.35, 2.86, 15.5 MJy sr−1 (based on SPOT). However,the
brightnessofRMonissuchthatthePRFilluminatesthefull
3.2 RMon sub-arraydetector.Aperturephotometry(witharadiusof10
pixels=12′′,requiringnoaperturecorrection),thetotalflux
Fig.5showstheIRACimagesoftheHerbigBestarRMon densities for R Mon are 17.59±0.29 Jy, 30.41±0.40 Jy,
anditsimmediatesurroundings.NotethatIRAC2couldnot and31.37±0.36Jy in IRAC 1,3, and4, respectively.The
be used, even in sub-array mode, due to R Mon’s bright- estimated background fluxes over a circle of 10 pixel ra-
ness at 4.5 m m. The main goal of these observations was dius are negligible (0.004, 0.03, 0.17 Jy) compared to R
to detectanyfaintemissionfromthejets (NSdirection)or Mon’sbrightnessand theRMS uncertainties.Notethatthe
fromthecircumstellardisk(EWdirection).Inparticular,we abovefluxesincludeanycontributionfromRMonB,sepa-
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Fig. 5 IRAC 3.6 m m, 5.8 m m, and 8 m m images (log scale) of the
HerbigBestarRMon.IRAC2couldnotbeobtained,duetoRMon’s
brightnessat4.5m m,evenwithasub-arraymode.
ratedfromRMonby0.7′′ (Closeetal.,1997).However,in
comparisonwithRMon,thecompanionisexpectedtocon-
tribute negligibly (0.0013,0.0085,0.035Jy in JHK′; Close
etal.,1997).ThenextstepwillbetosubtractthePRFofR
Montopossiblydetectemissionfromthediskandthejets.
WewillneedtocreateIRACsub-arrayPRFsfromsub-array
dataofstarsobserved,e.g.,intheFEPSprogram.
Finally, Fig. 6 shows the IRS SH spectrum of R Mon
(top)andits rawSED from1 to 100 m m(bottom).Forthe
latter,we usedIRACfluxes,the IRSSH spectrum,andthe
MIPS SED and complemented them with values from the
literature(Closeetal.,1997;andMSX).TheIRSSHspec-
trumshowsaclearPAH featureat11.3 m mandotherfaint
featuresmightbepresentaswell.Adetailedanalysisison-
goingtoremoveinstrumentaleffects(e.g.,defringing).
Acknowledgements This work is based on observations made with Fig. 6 (Top): IRS SH spectrum of R Mon. (Bottom): R Mon’s raw
theSpitzerSpaceTelescope,whichisoperatedbytheJetPropulsion (notdereddened) SEDfrom1to100 m m.IRACfluxesareshownas
Laboratory, California Institute of Technology under a contract with triangles(theerrorbarsaresmallerthanthesymbol),theIRSSHspec-
NASA.SupportforthisworkwasprovidedbyNASAthroughanaward trumasablackline,andtheMIPSSEDasaredline.Valuesfromthe
(JPLCIT1275416)issuedbyJPL/Caltech.MAalsoacknowledgessup- literature(Closeetal.,1997andMSX)areshownasbluediamonds.
portfromaSwissNationalScienceFoundationProfessorship(PP002–
110504).
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