A parsec-scale outflow from the luminous YSO IRAS 17527-2439

0.46 MB·English

by  Watson P. Varricatt

Astronomy&Astrophysicsmanuscriptno.17527˙wpv (cid:13)c ESO2011
January10,2011
A parsec-scale outflow from the luminous YSO IRAS 17527-2439
WatsonP.Varricatt
JointAstronomyCentre,660N.AohokuPl.,Hilo,HI-96720,USA
e-mail:[email protected]
ReceivedOct19,2010;acceptedDec17,2010
ABSTRACT
1 Aims.Weseektounderstandthewaymassivestarsform.ThecaseofaluminousYSOIRAS17527-2439isstudiedintheinfrared.
1 Methods.ImagingobservationsofIRAS17527-2439areobtainedinthenear-IRJHKphotometricbandsandinanarrow-bandfilter
0 centredatthewavelengthoftheH21-0S(1)line.Thecontinuum-subtractedH2imageisusedtoidentifyoutflows.Thedataobtained
2 inthisstudyareusedinconjunctionwithSpitzer,AKARI,andIRASdata.TheYSOdrivingtheoutflowisidentifiedintheSpitzer
images.Thespectralenergydistribution(SED)oftheYSOisstudiedusingavailableradiativetransfermodels.
n Results.Aparsec-scalebipolaroutflowisdiscoveredinourH lineimage,whichissupportedbythedetectioninthearchivalSpitzer
2
a images.TheH imageexhibitssignsofprecessionofthemainjetandshowstentativeevidenceforasecondoutflow.Thesesuggestthe
J 2
possibilityofacompaniontotheoutflowsource.Thereisastrongcomponentofcontinuumemissioninthedirectionoftheoutflow,

7 whichsupportstheideathattheoutflowcavityprovidesapathforradiationtoescape,therebyreducingtheradiationpressureonthe
accretedmatter.ThebulkoftheemissionobservedclosetotheoutflowintheWFCAMandSpitzerbandsisrotatedcounterclockwise

] withrespecttotheoutflowtracedinH ,whichmaybeduetoprecession.AmodelfittotheSEDofthecentralsourcetellsusthatthe
A 2
YSOhasamassof12.23M andthatitisinanearlystageofevolution.
⊙
G
Keywords.Stars:formation–Stars:pre-mainsequence–Stars:protostars–ISM:jetsandoutflows–circumstellarmatter
.
h
p
- 1. Introduction H O maseremissionfromIRAS17527.Fromthe radialveloc-
o 2
ityofthemaser(V =-1.81kms−1)theyestimatedakinematic
r Low-andintermediate-massstarsareknowntoformbygravita- peak
t distance of 17.9kpc, which is quite different from the distance
s tionalcollapseandsubsequentaccretionoftheirparentmolecu-
a estimatedfromradialvelocityofthedensegastracersNH3 and
lar clouds,and drivingcollimatedoutflows.However,themain
[ CS.InmassiveYSOs,H Omaserisoftenconsideredtobeex-
2
mechanismleadingtotheformationofmassivestarsisdebated
citedinjets(e.g.Felli,Palagi&Tofani1992;Goddietal.2005).
1 astowhetheritiseitherdiskaccretionsimilartothatforlower
The blueshift of the wavelength of the maser emission in this
v massstars(e.g.Yorke&Sonnhalter2002)oramergeroflower-
regionwithrespecttothevelocityofthedensegastracersindi-
0
massstars(e.g.Bonnell,Bate &Zinnecker1998).Manyofthe
catesthatH OmasernearIRAS17527alsomaybeexcitedbya
1 2
recentCOlinesurveysshowoutflowsfrommassiveYSOs(e.g.
5 jet.Henceweadoptthedistanceestimateof3.23kpc(Molinari
Zhang et al. 2005; Beuther et al. 2002). Several massive YSO
1 et al. 1996) for the calculations in this paper. Surveys by van
outflows have been observed in the near-IR, where the spatial
. der Walt, Gaylard & MacLeod (1995), Walsh et al. (1997) and
1 resolutionisbetterthanthatinsingle-dishCOlineobservations.
Slyshetal.(1999)didnotdetectany6.7GHzClass-IImethanol
0 Arecentnear-IRimagingsurveybyVarricattetal.(2010)shows
maser from this region.Edris, Fuller & Cohen (2007)detected
1
1 that massive stars up to at least late-O spectral types form pri- faint(0.4Jy)OHmaseremissionatVpeak=11.53kms−1,located
: marily by disk accretion. The case of a luminous YSO taking ∼6′ NW of IRAS 17527. Nevertheless, this offset is less than
v birthbyaccretionispresentedinthispaper.
their beam size. Therefore it remains to be investigated at bet-
Xi IRAS 17527-2439 (hereafter IRAS 17527) is a luminous terspatialresolution.ThefaintnessofthedetectedOHmaseris
YSO located in a dark cloud situated close to the Galactic consistentwiththeirobservationthattheOHmasersassociated
ar plane (l = 4.8273◦, b = 0.2297◦) in the Ophiuchus region. It with youngersourcesare weakerthan theonesassociated with
is associated with emission from dense gas and dust typical HiiorUCHiiregions.
of massive YSOs. Molinari et al. (1996) detected NH3 emis- TheVLAsurveyofHughes&MacLeod(1994)detected6-
sion lines from this region. From the radial velocity of the cmemissionfromIRAS17527withapeakfluxof5.3mJy.The
NH3 lines(VLSR=13.3kms−1),theyestimatedakinematicdis- sourcewas howeverrejected as a UCHii candidatebecausethe
tance of 3.23kpc, with the distance ambiguity resolved. Based radioemissionwasdiffuse.
on the IRAS colours they classified IRAS 17527 as a “high”
source,whichispossiblyinaUCHiiphase.(Notethatat12µm,
the IRAS catalogue gives only an upper limit flux for this 2. Observationsanddatareduction
source). In their 97.981-GHz CS(2-1) survey of UCHii candi-
2.1.UKIRTdata
dates, Bronfman,Nyman & May (1996) detected IRAS 17527
atVLSR=13.5kms−1,similar tothevelocityatwhichMolinari Observations were carried out on 2010 Apr. 15 UT using the
etal.(1996)detectedNH3emission. United Kingdom Infrared Telescope (UKIRT) and the Wide
Massive star formation is often associated with H O, Field Camera (WFCAM; Casali et al. 2007). WFCAM has
2
CH OH and OH maser emission. Palla et al. (1991) detected a pixel scale of 0.4′′ pix−1 and employs four 2048×2048
3
1
WatsonP.Varricatt:Aparsec-scaleoutflowfromtheluminousYSOIRAS17527-2439
achievedforallobjectsinthefieldwhenweuseaK-bandimage
A to subtractthe continuumfromtheH image.Fig. 2 showsthe
2
continuum-subtractedH image.
2
+
*
2.2.Archivaldata
This source was detected well by IRAS at 25 and 60µm. At
12µm, the IRAS flux density is only an upper limit. The flux
density at 100µm is of poorqualityand is affected by infrared
cirrus.HencetheIRAS12and100-µmfluxesarenotusedinour
analysis.IRAS17527wasobservedintheskysurveyconducted
byAKARIsatellite(Murakamietal.,2007).Inthemid-IR,the
Infrared Camera (IRC) on board AKARI detected a source at
9and18µm. TheAKARIFar-InfraredSurveyor(FIS)alsode-
tectedasourceinall4bands-at65,90,140and160µm.
TheSpitzerspacetelescopeobservedIRAS17527asapart
of the GLIMPSE II survey using the Infrared Array Camera
(IRAC;Fazioetal.2004) in bands1–4,centredat3.6,4.5,5.8
and8.0µmrespectively.Spitzeralsoobservedthisregionusing
theMultibandImagingPhotometerforSpitzer(MIPS;Riekeet
al.2004)at24µm.ThereducedSpitzerimagesandpointsource
photometry in a 5′×5′ field around IRAS 17527 were down-
loaded from the NASA/IPAC Infrared Science Archive. Fig. 3
Fig.1. WFCAM JHK colour-composite image (J-blue, H- shows a colour composite image of a 5′×5′ region constructed
green, K-red) in a 2.5′×2.5′ field centred on IRAS 17527. An fromtheSpitzerimagesat3.6,4.5and8.0µm.
expandedviewofthecentral0.5′×0.5′ fieldisshowninthein-
set. ‘+’ shows the location of the Spitzer source identified and
‘*’showstheIRASposition. 3. Resultsanddiscussion
3.1.Theoutflow
HgCdTe HawaiiIIRG arrays. Eacharrayhas a field of view of Our near-IR images (Figs. 1, 2) reveal a spectacular outflow
13.65′×13.65′. Observations were performed by dithering the oriented NE-SW associated with IRAS 17527. A source with
object to 9 points separated by a few arcseconds and using a large near-IR colours is labelled ‘A’ (see § 3.2) in Fig. 1. The
2×2 microstepping.Hence the final pixel scale is 0.2′′ pixel−1. continuum-subtracted H image (Fig. 2) shows the outflow in
2
Observations were obtained in J,H and K MKO filters and H lineemission;adashedline(labelled‘1’)isdrawnonFig.2
2
in a narrow-band MKO filter centred at the wavelength of the toguidetheeyes.Theoutflow‘1’hasalengthof48′′intheSW
H2 (1-0) S1 line at 2.1218µm. The data were reduced by the and34′′intheNEiftheoutflowsourceislocatedatornear‘A’.
Cambridge Astronomical Survey Unit (CASU); the archival This length corresponds to 0.75pc in the SW, at a distance of
and distribution of the data are carried out by the Wide Field 3.23kpc.TheoutflowisseeninH to bebentinan‘S’-shaped
2
AstronomyUnit(WFAU). fashion,suggestinga precessionofthejet.Thedirectionofthe
The sky conditions were not photometric during the ob- outflowmeasuredfromthe H imagesis∼68◦ NorthofEastat
2
servations. However, since the K magnitude estimated here is the base. The detection of a well defined outflow suggests that
fromanaveragezeropointcalculatedforasetofisolatedpoint the YSO associated with IRAS 17527 is taking birth through
sources presentin all dithered frames aroundIRAS 17527and diskaccretion.Thereisalsotentativedetectionoftwoadditional
usingtheir2MASSmagnitudes,thephotometricqualityisgood. H emissionfeaturesclosetoIRAS17527,whichareenclosedin
2
Fig. 1 shows a JHK colour composite image created from the ellipsesonFig.2andlabelled‘2a’and‘2b’;thisneedstobeveri-
WFCAMdataina2.5′×2.5′fieldcentredonIRAS17527. fiedbydeeperH imaging.Ifasecondbipolaroutflowisproduc-
2
The H image was continuum-subtractedusing the K-band ing‘2a’and‘2b’,itmaybeatanangleof209◦. Thus,thepos-
2
image. The average of the ratio of counts, for a few isolated sibilityofacompanionneedstobeexploredthroughdeeperH2
pointsources,betweenthe K andH imageswasobtained.The imagingandthroughimaginginthenear-andmid-IRathigher
2
background-subtracted K-band image was scaled by this ratio angularresolution.ThemodelfittotheSED(see§3.2.1)gives
andwasthensubtractedfromthebackground-subtractedH im- anangleofinclinationofthediskaxiswithrespecttothelineof
2
age. In regions where the near-IR colours do not vary widely sighttobe18◦,whichimpliesasimilarline-of-sightinclination
overthesources,thisproceduresubtractsouttheextendedemis- forthe outflow.Thecomparablebrightnessforthe two outflow
sion well, and the point sources get subtracted out well when lobesof‘1’seeninH2suggestsahigherinclination(eventhough
the seeing is similar for K and H images. However, the K/H itcouldbearguedthatthisismainlyduetonon-uniformdistri-
2 2
ratiohasadependenceontheapparentnear-IRcolours.Forob- bution of exciting material rather than higher inclination). The
jects like IRAS 17527,which are located in dark cloudsin the outflows ‘1’ and ‘2a+2b’ are assigned names MHO 2147 and
galactic plane, the sources in the field are subjected to a wide MHO 2148 respectively in the catalog of Molecular Hydrogen
rangeofinterstellarextinctionandseveralsourcesmayhavein- emission-lineObjects1(Davisetal.2010).Someadditionalline
fraredexcessduetocircumstellaremission,resultingina wide emission features detected in the continuum-subtractedH2 im-
range of near-IR colours. Hence, for these regions, even when
the seeing is stable, a perfect continuum-subtractioncannot be 1 http://www.jach.hawaii.edu/UKIRT/MHCat/
2
WatsonP.Varricatt:Aparsec-scaleoutflowfromtheluminousYSOIRAS17527-2439
7
2a
A
6
5 +
2b
4
1
3
Fig.2.TheContinuum-subtracted2.122-µmimageofIRAS17527overa5′×5′field,smoothedwitha2-pixelFWHMGaussianto
enhancetheappearanceofthefaintemissionfeatures.‘+’showsthelocationoftheoutflowsourcederivedfromtheSpitzer5.8-µm
image.ThecontoursgeneratedfromtheSpitzer4.5-µmimageareoverlaid.Anenlargedviewofthecentralregionisshowninthe
inset. The dashed line ‘1’ shows the directionof the main outflow detected here. The ellipses ‘2a’ and ‘2b’ enclose H emission
2
featureswhichareprobablyduetoasecondoutflow.AdditionalH emissionfeaturesdetectedarecircledandlabelled‘3–7’.The
2
imagescaleis0.2′′pix−1
.
agearecircledandlabelled‘3–7’inFig.2.Itisnotclearifthese colours arising from extinction or excess or both, as discussed
areproducedbyoutflow‘1’orbydifferentoutflows. in§2.1.ThecontoursgeneratedfromtheSpitzer-IRAC4.5-µm
Thereisasignificantamountofemissionalongtheoutflow imageareover-plottedinFig.2.Awayfromtheoutflowcentre,
inourJHKandunsubtractedH imagesandintheSpitzer-IRAC thecontoursofthefaintregionsofthe4.5-µmemissiontracethe
2
images.Amajorportionoftheemissionseenalongtheoutflow outflowdetectedinH2 intheNE,butarerotatedcounterclock-
in the H2 image is subtracted out upon continuum-subtraction wise with respectto the H2 knots in the SW. Close to the base
andFig.2showsonlyachainoflineemissionknots.Thissug- ofthe outflow,thecontoursofthe brightregionsofthe 4.5-µm
gests the presenceof a largeamountof continuumemission in emissionarenearlyEW.The4.5-µmcontourstracethebrightre-
thedirectiontheoutflow.Continuumemissionclosetotheout- gionsoftheK-bandemissionreasonablywell;closetothebase
flow is likely to be due to radiation from the YSO escaping ofthe outflow,thecontoursofthe brightregionsofthe 4.5-µm
throughthe outflow cavity. It has been proposed before that in emissionhaveaslightcounterclockwiserotationwithrespectto
massive star formation, the optically thin cavity carved out by the bright regions of the emission in K in the east. In general,
the bipolar outflow may provide a path for radiation from the the bright regions of emission seen in the near-IR and Spitzer
central source to escape, which reduces the radiation pressure images,closetotheoutflow,arerotatedcounter-clockwisewith
on the accreted matter and aids the growth of a massive star. respecttothedirectionoftheoutflowimpliedbythepresumably
(Krumholz,McKee&Tan2005). shock-excitedH2 emission knotsin ‘1’.Thisrotation,again,is
Fig.2exhibitsnegativeresidualsalongthebrightregionsof likelytobeduetotheprecessionofthejet,butneedstobethor-
emission in the near-IRimages, seen as darklanesclose to the oughlyinvestigated.Thebrightestregionofthisemissioninthe
outflowtracedbytheH knotslabelled‘1’.Thenegativeresid- nearIR towardsthe SW lobeof theoutflowis seen throughout
2
ualsclosetotheoutflowarelikelytobecausedbylargenear-IR the1–8µmwavelengthrange.Itshouldbenotedthattransitions
3
WatsonP.Varricatt:Aparsec-scaleoutflowfromtheluminousYSOIRAS17527-2439
IRAS 17527
Fig.4. The IRACcolour-colourdiagram.The open(black)cir-
Fig.3.A colour-compositeimageproducedfromSpitzer-IRAC cles show the coloursof objectsdetected in all fourbandsin a
data adopting blue, green and red, respectively for the 3.6, 4.5 5′×5′fieldcentredonIRAS17527.Thefilled(red)circleshows
and 8.0-µm images. The image coversa 5′×5′ field centredon the outflow source. The blue rectangle shows the location of
IRAS17527. ClassIIsources.Thedashedhorizontallineshowstheboundary
between Class I/II objects(below)and Class I objects (above).
ThedottedredarrowsshowreddeningvectorsforA =45.
V
ofH arepresentthroughoutthe1–8µm wavelengthrangedis-
2
cussedhere(Smith1995;Neufeldetal.2009).Spectroscopyin
the near- and mid-IR will enable us to understand if the emis- theoutflowswillbecontributingtotheobservedfluxes.Forthe
sion seen in in these bandsclose to the outflow‘1’ are line- or SEDfitting,weadoptedanerrorof0.18mag.
continuum-dominated. If continuum-dominated, the emission,
We identify the source detected in the Spitzer data as the
especially in short wavelengths like J, will imply radiation es-
YSO driving the outflow ‘1’. A deeply embedded object seen
capingfromthehotcentralsource.
only in K and H , located near the centre of the outflow, is la-
2
belled ‘A’ (α=17:55:48.95, δ=-24:40:18.31) in Fig. 1. ‘A’ ap-
pearsslightlyextendedinKandissurroundedbynebulosity.Its
3.2.Thesourcedrivingtheoutflow
coordinatesareoffset1.65′′ NE fromthatofthe Spitzersource
Thebrightobjectsandasignificantfractionofthereddenedob- measuredat8µm.Photometrywithinanapertureof2′′diameter
jects in the WFCAM images are detected in the IRAC images, gives a K magnitue of 12.82±0.04for ‘A’. It remains to be in-
ascanbeseenfromtheIRAC4.5-µmcontoursaroundthepoint vestigatedthroughhighangularresolutionimagingatnear-and
sourcesinthecontinuum-subtractedH image(Fig.2).Themost mid-IRwavelengthstounderstandif‘A’isthenear-IRcounter-
2
prominentamongtheseisabrightinfraredsourcedetectednear part of the outflow source. The K magnitude of ‘A’ is close to
the centre of the outflow lobesin the IRAC and MIPS images. whatisimpliedbythefittotheSED(Fig.5).However,“A”has
This source is saturated in the 24-µm MIPS image. Its coordi- a positionaloffset from the Spitzer source, which, even though
natesderivedfromtheIRAC8.0-µmimageareα=17:55:48.91, small, issignificant,andthe SED fittinggivesaninclinationof
δ=-24:40:19.92; it is only at a separation of 2′′ from the IRAS 18◦ with respectto the line of sightforthe disk axis. Fromthe
position.TheIRACcatalogdoesnotlistthemagnitudesforthis appearanceoftheoutflow‘1’,theangleappearstobehigher(§
source in the 3.6 and 4.5-µm bands. At these wavelengths, the 3.1).Ahigherinclinationofthediskwillposeahighercircum-
source appears elongated in the Spitzer images and the emis- stellar extinction for the outflow source, making it too faint to
sionfromitisblendedwith theemissionfromtheoutflow.For detectinthenear-IR.Inaddition,thethemagnitudeof‘A’esti-
the purpose of fitting the SED, we derived the 3.6 and 4.5- matedhereislikelytobecontaminatedbynebulosity.Withthese
µm magnitudesof the outflow source from the Spitzer images. considerations,wearetreatingtheKmagnitudeof‘A’asonlyan
Relativephotometrywasperformedbyadoptinganapertureof upperlimitformodellingtheSEDoftheYSO(§3.2.1).
8-pixel (4.8′′) diameter. For each band, an average zero point IRAS 17527 is detected well in all mid- and far-IR bands
wasderivedfromafewwelldetectedandisolatedpointsources of AKARI satellite. The coordinates given in the AKARI -
(whichhaveIRACmagnitudesavailable)spreadovertheimage. IRC point source catalog is only 1.2′′ NW of the Spitzer po-
We derived a magnitude of 9.33±0.03 in the 3.6-µm band and sition. At far-IR wavelengths, AKARI - FIS detected a bright
7.45±0.05in the 4.5-µm band. The errorsgiven are the formal object (AKARI-FIS-V1 1755489-244001; α=17:55:48.89 δ=-
errorsinthezeropoints.Evenatthisaperture,theemissionfrom 24:40:0.82)inall4bands.ThecoordinatesoftheFISdetection
isoffset18.75′′towardsthenorthofthesourcedetectedbyIRC.
2 allcoordinatesgiveninthispaperareinJ2000 This offset is more than the positional accuracy quoted by the
4
WatsonP.Varricatt:Aparsec-scaleoutflowfromtheluminousYSOIRAS17527-2439
Table1.ResultsfromSEDfitting
Parameter Bestfitvaluesa
Stellarmass(M ) 12.23(+1.4,-0.97)
⊙
Stellarage(yr) 2.08(±1)×104
Stellarradius(R ) 39.94(+54,-12.9)
⊙
Stellartemperature(K) 8093(+2000,-2600)
Diskmass(M ) 9.79(+29,-7.3)×10−2
⊙
Diskaccretionrate(M yr−1) 4.16(+139,-3.2)×10−6
⊙
Disk/envelopeinnerradius(AU) 5.91(+7.9,-0.83)
Diskouterradius(AU) 28.6(+69,-12)
Envelopemass(M ) 1.56(+1,-0.67)×103
⊙
Envelopeaccretionrate(M yr−1) 2.42(+1.9,-0.84)×10−3
⊙
Envelopeouterradius(AU) 1.00(+0,-0.079)×105
TotalLuminosity(L ) 6.17(+2,-1.5)×103
⊙
Angleofinclinationofthediskaxis(◦) 18
a The values given in parenthesis are the rmsof the differences, in
parametervaluesofmodelswith(χ2−χ2 )perdatapoint<3, Fig.5.ThefilledcirclesshowthedatafromSpiter-IRACat3.6,
bestfit
aboveandbelowthoseofthebestfitmodel,estimatedwithrespect 4.5,5.8and8µm,IRASat25and60µm,andAKARIat9,18,
totheparametervaluesofthebestfitmodel.Adistanceof3.23kpc 65,90,140and160µm.Thedownwarddirectedtriangleshows
isadoptedforIRAS17527.
the K-band data, which is treated as an upper limit only. The
continuouslineshowsthebestfitmodelandthegraylinesshow
subsequent good fits for (χ2 −χ2 ) per data point < 3. The
bestfit
AKARI point source catalogue. However, since it is the only dashedlinecorrespondstothestellarphotosphereforthecentral
far-IR source in the region,and the coordinatesof the infrared sourceofthebestfittingmodel,asitwouldlookintheabsence
source detected in this region by Spitzer and IRAS agree well, ofcircumstellardust(butincludinginterstellarextinction).
weascribetheFISdetectiontoIRAS17527.
The IRAC ([5.8]-[8.0],[3.6]-[4.5]) colour-colour diagram
can be used to roughly identify YSOs of different evolution- Fig. 5 shows the SED of IRAS 17527 and the model fit.
ary stages. Fig. 4 shows the IRAC colours of objects, within Table 1 shows the parameters of the best fit model. The fore-
a 5′×5′ field around IRAS 17527. The large concentration of groundvisualextinctionAV is estimated to be 45.43mag.The
sources around ([5.8]-[8.0],[3.6]-[4.5])=0 are foreground and fittinggivesastellarmassof12.23M⊙ andatotalluminosityof
backgroundstarsanddisklesspre-main-sequence(ClassIII)ob- 6.17×103L⊙. The mass of the YSO and the systemic luminos-
jects. The dashed horizontal line shows the boundary between ityarereasonablywelldetermined,soaretheenvelopeparame-
Class I/II (below) and Class I objects (above). The rectangle ters.However,theradiusoftheYSO,thediskaccretionrateand
(0<([3.6]-[4.5])<0.8and 0.4<([5.8]-[8.0]<1.1)shows the loca- thediskmassandradiihavelargeerrors.Thenear-andmid-IR
tion of Class II objects. Thesourceswith ([3.6]-[4.5])>0.8and fluxeshaveasignificantinfluenceonthereliabledetermination
([5.8]-[8.0])>1.1arelikelytobeClassIobjects,whicharepro- oftheseparameters.Contaminationofthesourcemagnitudesat
tostars with infalling envelopes (Allen et al. 2004; Megeath et thesewavelengthsduetothecontributionfromtheoutflowand
al. 2004; Qiu et al. 2008). The dotted red arrows in Fig. 4 are froma possible companionmay be the cause forthe pooresti-
reddeningvectorsforA =45calculatedfromtheextinctionlaw mateoftheseparameters.Hence,photometryathighsensitivity
V
given in Mathis (1990). The location of IRAS 17527 in Fig.4 andspatialresolutioninthe2–20-µmwavelengthrangeiswar-
suggeststhatitisahighlyreddenedClassIobject.Asseenfrom rantedforamoreaccuratedeterminationofthestellaranddisk
the SED modelling in Fig. 5, the emission from the envelope parameters.Photometryatsub-mmwavelengthsalsoisrequired
contributessignificantlytotheluminosity,whichisexpectedfor forthissourcetobetterconstrainthemodelfit.
ClassIobjects.
4. Conclusions
3.2.1. Thespectralenergydistribution
1. IRAS 17527 appears to be a luminous YSO taking birth
The K magnitude measured from the WFCAM data, magni- throughdisk accretion. A well-collimatedparsec-scale out-
tudes in the Spitzer bands 1–4, IRAS 25 and 60-µm data and flowisdiscoveredinIRAS17527inH lineemission.
2
the AKARI data from 9 to 160µm were used to construct the 2. Theoutflowisseentobebentinan‘S’-shapedfashion,sug-
SEDofthesourcedrivingtheoutflow.Colourcorrectionswere gestingaprecessionofthejet.Thereisatentativedetection
appliedto the IRAS and AKARI data using the correctionfac- ofasecondoutflowintheH image.Thepossibilityofmore
2
torsgivenintheirrespectivepointsourcecatalogs(Beichmanet thanoneYSOinIRAS17527needstobeexplored.
al. 1988; Kataza et al. 2010; Yamamuraet al. 2010). The SED 3. TheH imageexhibitsastrongcontinuumcomponentinthe
2
was modelled using the on-line SED fitting tool of Robitaille emission along the outflow, which may be caused by radi-
etal.(2007),whichusesagridof2Dradiativetransfermodels ation escapingthroughthe outflow cavity. This, in turn,re-
presented in Robitaille et al. (2006), developed by Whitney et ducestheradiationpressureontheaccretedmatterandaids
al.(2003,2003b;etc.).Thegridconsistsof20,000YSOmodels growthofthecentralsourcethroughaccretion.
withSEDscoveringawiderangeofstellarmasses(0.1–50M ) 4. The bulk of the emission in the direction of the outflow,
⊙
andevolutionarystages(fromtheearlyenvelopeinfallstage to observed in K and the Spitzer bands, is rotated counter-
thelatedisk-onlystage),eachat10differentviewingangles. clockwisewithrespecttothedirectionoftheoutflowtraced
5
WatsonP.Varricatt:Aparsec-scaleoutflowfromtheluminousYSOIRAS17527-2439
by the H2 line emission knots.It is probablya resultof the Zhang,Q.,Hunter,T.R.,Brand,J.,Sridharan,T.K.,Cesaroni,R.,Molinari,S.,
precessionofthejet.Spectroscopyinthethenear-IRthrough Wang,J.,Kramer,M.,2005,ApJ,625,864
Spitzer-IRACbandsisrequiredforaproperunderstandingof
this.
5. The model fit to the SED shows that the central source is
probablyaClass-Iprotostar;thisissupportedbyitslocation
intheSpitzer-IRACcolour-colourdiagram.TheYSO hasa
massof∼12.23M andatotalluminosityof∼6.17×103L .
⊙ ⊙
6. The disk parametersand the disk accretionratio are poorly
determined by the SED fitting. This may be caused by the
contribution to the source magnitudes from emission from
theoutflowandfromapossiblecompanion.Observationsat
high angular resolution are required in the 2-20µm wave-
lengthrangeforamoreaccuratedeterminationofthesource
magnitudesatthesewavelengths.
Acknowledgements. TheUKIRTisoperatedbytheJointAstronomyCentreon
behalfoftheScienceandTechnologyFacilitiesCouncil(STFC)oftheUK.The
UKIRTdatapresentedinthispaperareobtainedduringtheUKIDSSbackup
time.IthanktheCambridgeAstronomicalSurveyUnit(CASU)forprocessing
theWFCAMdata,andtheWFCAMScienceArchive(WSA)formakingthedata
available.ThisworkmakesuseofdataobtainedwithAKARI,aJAXAproject
withtheparticipation ofESA,andIRASdatadownloadedfromtheSIMBAD
database operated by CDS, Strasbourg, France. The Spitzer archival data are
downloadedfromNASA/IPACInfraredScienceArchive,whichisoperatedby
theJetPropulsionLaboratory,Caltec,undercontractwithNASA.Ialsothank
theanonymousrefereeandtheeditorMalcolmWalmsleyfortheircommentsand
suggestionswhichhaveimprovedthepaper.
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