High resolution observations of the outer disk around T Cha: the view from ALMA

0.47 MB·English

by  N. Huelamo

Astronomy&Astrophysicsmanuscriptno.tcha˙accepted (cid:13)c ESO2015
January27,2015
High resolution observations of the outer disk around T Cha: the
view from ALMA
N.Hue´lamo1,I.deGregorio-Monsalvo2,3,E.Macias4,C.Pinte5,6,M.Ireland7,P.Tuthill8,andS.Lacour9
1 CentrodeAstrobiolog´ıa(INTA-CSIC);ESACCampus,P.O.Box78,E-28691VillanuevadelaCan˜ada,Spain
e-mail:[e-mail]
2 JointALMAObservatory(JAO),AlonsodeCo´rdova3107,Vitacura,SantiagodeChile
3 EuropeanSouthernObservatory,GarchingbeiMu¨nchen,D-85748Germany
4 InstitutodeAstrof´ısicadeAndaluc´ıa,CSIC,GlorietadelaAstronom´ıas/n,E-18008Granada,Spain
5
5 UMI-FCA,CNRS/INSUFrance(UMI3386),andDpto.deAstronom´ıa,UniversidaddeChile,Casilla36-DSantiago,Chile
1
6 Univ.GrenobleAlpes,IPAG,38000Grenoble,France;CNRS,IPAG,38000Grenoble,France
0
7 ResearchSchoolofAstronomyandAstrophysics,AustralianNationalUniversity,CanberraACT2611,Australia
2
8 SydneyInstituteforAstronomy,SchoolofPhysics,UniversityofSydney,NSW2006,Australia

n 9 LESIA,CNRSUMR-8109,ObservatoiredeParis,UPMC,Universite´ParisDiderot,5placeJulesJanssen,92195Meudon,France
a
J Received—,—;accepted—-,—-

6
2 ABSTRACT

] Context.Transitionaldisksarecircumstellardiskswithdustgapsthought toberelatedinsomecaseswithplanetformation.They
R canshedlightontheplanetformationprocessbytheanalysisoftheirgasanddustproperties.TChaisayoungstarsurroundedbya
S transitionaldiskwithsignaturesofplanetformation
Aims.TheaimofthisworkistostudytheouterdiskaroundTChaandtoderiveitsmainproperties.
.
h Methods.Wehaveobtainedhigh-resolutionandhigh-sensitivityALMAobservationsintheCO(3–2),13CO(3–2),andCS(7–6)emis-
p sionlinestorevealthespatialdistributionofthegaseousdiskaroundthestar.Inordertostudythedustwithinthediskwehavealso
- obtainedcontinuumimagesat850µmfromtheline-freechannels.
o
Results.WehavespatiallyresolvedtheouterdiskaroundTCha.UsingtheCO(3-2)emissionwederivearadiusof∼230AU.We
r
t alsoreportthedetectionofthe13CO(3-2)andtheCS(7-8)molecularemissions,whichshowsmallerradiithantheCO(3-2)detection.
s Thecontinuumobservationsat850µmallowthespatialresolutionofthedustydisk,whichshowstwoemissionbumpsseparatedby
a
∼40AU,consistentwiththepresenceofadustgapintheinnerregionsofthedisk,andanouterradiusof∼80AU.Therefore,TCha
[
issurroundedbyacompactdustydiskandalargerandmorediffusegaseousdisk,aspreviouslyobservedinotheryoungstars.The

1 continuumintensityprofilesaredifferentatbothsidesofthedisksuggestingpossibledustasymmetries.Wederiveaninclinationof
v i(◦)=67±5,andapositionangleofPA(◦)=113±6,forboththegasanddustdisks.ThecomparisonoftheALMAdatawithradiative
3 transfer models shows that the gas and dust components can only be simultaneously reproduced when we include a tapered edge
8 prescriptionforthesurfacedensityprofile.ThebestmodelsuggeststhatmostofthediskmassisplacedwithinaradiusofR<50AU.
4 Finally,wederiveadynamical massfor thecentral object of M∗=1.5±0.2M⊙,comparable totheone estimatedwithevolutionary
6 modelsforanageof∼10Myr.
0
Key words. stars: pre-main sequence — stars: kinematics and dynamics — stars: individual: T Cha — protoplanetary disks —
.
1 techniques:interferometry
0
5
1
1. Introduction more ’tenuous’ disk, with a very steep surface density profile.
:
v Both family of models suggest a very peculiar outer disk with
i T Chamaeleontis (T Cha) is a young (∼7±5Myr) nearby littleornodustbeyond∼40AU.Ontheotherhand,thecoldgas
X
(108pc) T Tauri star in the ǫ-Cha association, surrounded intheTChaouterdiskhasbeenstudiedbySaccoetal.(2014).
r by a transition disk (Alcalaetal. 1993; Brownetal. 2007; Theirspatiallyunresolvedobservationssuggestthepresenceof
a
Torresetal. 2008; Murphyetal. 2013). There is evidence of a agaseousdiskwithanouterradiusofR ∼80AUinKeplerian
CO
dustgapwithinthedisk,andayetunconfirmedsubstellarcom- rotation.
panion inside the gap (see Hue´lamoetal. 2011; Olofssonetal. Overall, the disk aroundT Cha shows propertiessimilar to
2013). If confirmed,the disk aroundT Cha can give us impor- theso-called’faint’disks,characterizedbyweakmillimetercon-
tantcluesaboutthephysicalconditionsforsubstellarformation tinuumemissionthatcanberesultofdifferentpropertiesorpro-
atearlyevolutionaryphases. cesses(e.g.Pie´tuetal.2014).InthecaseofTChathereisevi-
TChaissurroundedbyaverynarrowinnerdiskthatextends denceofdustclearing,graingrowth,andahighdiskinclination
from 0.13 to 0.17AU (Olofssonetal. 2013), and an outer disk (Brownetal.2007;Pascucci&Sterzik2009).
whose main properties have been inferred from the modeling Inthiswork we presenthighqualityobservationsof T Cha
ofitsspectralenergydistribution(SED,e.g.Brownetal.2007). obtained with the Atacama Large Millimeter Array (ALMA),
Ciezaetal.(2011)showedthatthemodelsarehighlydegenerate whichhaveallowedustospatiallyresolvetheouterdiskaround
and can fit the SED of T Cha equally well either with a very T Cha for the first time. ALMA has allowed us to derive basic
compactouterdustdisk(afewAUswide)oramuchlargerbut parametersoftheouterdisk,tobreakthedegeneracyofradiative
1
Hue´lamoetal.:ALMAobservationsofTCha
transfermodelsbased on SED fitting, andto understandif it is sion is spatially resolved, with a radius R ∼ 170AU after
13CO
peculiarincomparisonwithothercircumstellardisks. deconvolutionwiththesynthesizedbeam.
The radial intensity profiles of the CO(3-2) and 13CO(3-2)
transitionsaredisplayedinFigure3.Theyhavebeencomputed
2. Observations usingslicesalongthesemi-majoraxisofthedisk(dashedwhite
lineinFig.1,leftpanel)inthegasemissionmaps.Wedonotsee
The observations were performed on 2012 July 01, 26 and
a significant difference of the profiles at both sides of the disk
November03atBand7,aspartoftheALMACycle0program
(NEandSW)suggestingasymmetricdistributionofthegas.
2011.0.00921.S.The field of view was ∼ 18′′. A total of three
Gas emission from CS(7–6) is also spatially resolved and
data sets were collected, using between 18 and 23 antennas of
shows a deconvolved radius of R ∼ 100AU. The integrated
CS
12m diameter and accounting for 6 hours of total integration intensity emission above 3σ is 0.54 ± 0.08 Jykms−1. To our
time including overheads and calibration. Weather conditions
knowledge,thisisthefirsttimethatsuchahightransitionofthe
weregoodandstable,withanaverageprecipitablewatervapor
CSmoleculeisspatiallyresolvedinadiskaroundalate-typestar
of0.7mm.Thesystemtemperaturevariedfrom150to250K.
(thefirstdetectioninaHerbigstarhasbeenrecentlyreportedby
The correlator was set to four spectral windows in
vanderPlasetal.2014).Sulfur-bearingmolecules(likeCSand
dual polarization mode, centered at 345.796 GHz (CO(3–2)),
SO )studiesarescarce(e.g.Dutreyetal.2011;Guilloteauetal.
2
342.883 GHz (CS(7–6)), 332.505 GHz (SO (4(3,1)–3(2,2))),
2 2012),butinterestingsincethesetypeofmoleculesare present
and 330.588 GHz (13CO(3–2)). The effective bandwidth used
in comets (e.g. Hale-Bopp; Ikedaetal. 2002, and Shoemaker-
was 468.75MHz, providing a velocity resolution of ∼ 0.11 Levy/9; Matthewsetal. 2002) and their presence in the inner
kms−1afterHanningsmoothing. part of the disks offers the possibility of studying the chem-
The ALMA calibration includes simultaneous observations ical composition of the planet-forming regions. So far, only a
ofthe183GHzwaterlinewithwatervaporradiometers,which few CS detectionsat lower frequencytransitionshave been re-
measure the water column in the antenna beam, later used portedindiskssurroundingK5toM0stars(Dutreyetal.2011;
to reduce the atmospheric phase noise. Amplitude calibration Kastneretal.2013).Herewe showforthefirsttimeaspatially
was done using Juno and Titan, and quasars J1256−057 and resolveddetectionoftheCS(7–6)transitionaroundaK0star.
J1147−6753were used to calibrate the bandpassand the com- The gas detected in the disk surrounding T Cha shows a
plex gain fluctuations respectively. Data reduction was per- velocity profile consistent with a Keplerian rotation pattern,
formedusing version4.1of the CommonAstronomySoftware whichcanbeseeninallthemoleculartransitionsobserved(see
Applications package (CASA). We applied self-calibration us- Figure 2). CO(3–2) emission is detected at velocities between
ingthecontinuumandweusedthetaskCLEANforimagingthe -5.0 to 16.5kms−1, 13CO(3–2) between -3.0 and 15.0 kms−1
self-calibratedvisibilities. The continuumimage was produced and the CS(7–6)between 0.0 to 11.0 kms−1. In Fig 4 we have
bycombiningalloftheline-freechannelsusinguniformweight- representedaposition-velocitydiagramalongthemajoraxisof
ing(synthesizedbeam0.52′′×0.34′′,P.A.∼29◦;rms=0.7mJy the gaseous disk traced by CO(3–2). The systemic velocity is
beam−1).FortheCO(3–2)lineweusedBriggsweighting(beam 5.95±0.22 kms−1. In that plot an absorption feature at veloci-
0.64′′×0.48′′,P.A.∼31◦;rmsperchannel=9mJybeam−1),and ties near 4.7kms−1 can be seen, which is verylikely produced
for the rest of the lines we used naturalweighting,providinga by a foreground molecular cloud in the same line of sight as
synthesizedbeam∼0.8′′×0.6′′,P.A.∼25◦andanrmsperchan- TCha(Nehme´etal.2008).Bycomparingtheposition-velocity
nelof11mJybeam−1forthe13COand7mJybeam−1fortheCS diagramwith a Keplerianvelocityprofile(Figure 4), we show
andtheSO2. that the emission is compatible with Keplerian rotation around
a 1.3 - 1.7 M object in a disk inclined at 67 degrees. This
⊙
mass range is in good agreementwith estimations from evolu-
3. Resultsanddiscussion tionarytracksforanageof∼10Myr(e.g.Schisanoetal.2009;
Murphyetal.2013).
3.1.Molecularemissionlinedetections
MolecularlineemissionisdetectedforthetransitionsCO(3–2),
3.2. Continuumemissionat850µm
13CO(3–2),andCS(7–6).Allofthemarespatiallyresolvedfor
thefirsttimeforTCha.NodetectionwasfoundforSO2(4(3,1)– Continuumemissionat850µmisdetectedcenteredattheposi-
3(2,2)),witha3σupperlimitof20mJy. tionR.A.(J2000)=11h57m13s.42,Dec(J2000)=−79◦21′31′′696.
Figure1showstheintegratedemissionmapsofthethreede- The flux density integrated over the disk structure above 5σ is
tectedmoleculeswhileFigure2displaystheintensity-weighted S =198±4mJy.
850µm
mean velocity maps. The CO(3–2) emission is spatially well Figure 1 shows the dusty outer disk around T Cha repre-
resolved along the major and the minor axis. The integrated sented by black contours. The disk is spatially resolved in its
intensity averaged over the whole emission area above 3σ is majoraxiswithaprojecteddiameterof1.50′′ (measuredatthe
12.46 ± 0.11 Jy kms−1, in agreement with the value reported 5σcontourlevel),whichcorrespondstoanouterdustdiskradius
bySaccoetal. (2014) fromthe fitwith a Kepleriandisk model ofR ∼ 80AUafterdeconvolutionwiththesynthesizedbeam,
out
profileto single-dishobservations.Consideringcontoursabove andadoptingadistanceof108pc.Twolocalpeaksareobserved
3σ, the outer radius extends to 2.1” which, after deconvolu- at a projected separation of 0.37” (40 AU at 108pc), which is
tion with the synthesized beam, correspondsto an outer radius closetothebeamsize,andsuggestthepresenceofagapinthe
R ∼ 230AU. The inclination (i) and the position angle (PA) innerregionsofthediskaspredictedbySEDmodeling.
CO
of the gaseous disk have been estimated by fitting a Gaussian InFigure3wehaverepresentedthecontinuumradialinten-
to the CO(3–2) integrated emission map, providing values of sity profilesatbothsidesof thedisk,togetherwith theaverage
i=67±5◦andPA=113±6◦. profile, includingonly datapointsabove 5-σ. As in the case of
13CO(3–2) emission line shows an integrated intensity of the gasmolecules,theyhavebeencomputedusingslices along
4.31±0.07 Jy kms−1 (above 3σ contour). The region of emis- thesemi-majoraxisofthedisk(dashedwhitelineinFig.1,left
2
Hue´lamoetal.:ALMAobservationsofTCha
Fig.1.Integratedemission mapsofthe CO(3–2),13CO(3–2),andthe CS(7–6)transitions(fromleftto right).The blackcontours
represent the continuum emission at 850 µm at 5, 15, 30, 45, 60, 75, 90, and 110 σ where 1 σ is 0.7 mJy beam−1. We detect
two emissionbumpsseparatedby40AU andanouterdustradiusof79AU. Thewhiteellipsesarethe synthesizedbeamsforthe
spectralemissionlinesandthegreenellipseisthesynthesizedbeamforthecontinuummap.Thewhitedashedlineintheleftpanel
representstheaxiswheretheposition-velocitydiagraminFigure4hasbeenobtained.
Fig.2.Intensity-weightedmeanvelocitymaps(first-ordermoment,2σcutforCO(3–2)and13CO(3–2),and1.5σcutforCS(7–6)).
panel) in the continuum emission maps. We can see a signifi- face density profile (with an exponentof α ≤ –2, for a power-
cantdifferencebetweentheprofilesatbothsides,withtheNW lawprescription).Thelargedegeneracybetweenthesetwodisk
sidebeingslightlylargerthantheSE one,suggestingasymme- parameters, R and α, did not allow them to choose between
out
trieswithinthedustydisk.Finally,theiand PA valuesthatwe thesetwoscenarios.Olofssonetal.(2013)usedMCFOSTtofit
derive using the continuum emission at 850 µm are similar to the SED togetherwith near-IRinterferometricdata.Theyfixed
thoseestimatedwiththeCO(3–2)observations. R =25AU,andα=-1,andfoundabestfitmodelwithanarrow
out
dustouterdisk(R =12±2AU).
in
OurALMAdatashowsthatmodelswithapower-lawsurface
3.3.Comparisonwithradiativetransfermodels
density,liketheonesusedinthesetwoworks,cannotreproduce
Our ALMA observations reveal that T Cha is surrounded by boththeCOandcontinuumdata.Weneverthelessfirstconsider
a compact dusty disk with a sharp outer edge at ∼80AU and thistypeofmodelstodiscusstheALMAdatainthecontextof
a larger gaseous disk with an outer radius of ∼230AU. This previousresults.
trend, a compact dust disk with a larger and more diffuse We have modeled the SED of T Cha with MCFOST, be-
gaseous disk, has already been observed in a significant num- ing the starting point the model grid presented by Ciezaetal.
ber of circumstellar disks (e.g. Isellaetal. 2007; Hughesetal. (2011)andrefinedbyOlofssonetal.(2013).Basically,thedisk
2008; Andrewsetal. 2012; deGregorio-Monsalvoetal. 2013; is composed of 2 sub-disks: an inner and an outer disk with a
Pie´tuetal.2014). density structure defined by a power law surface density pro-
Ciezaetal.(2011)usedtheradiativetransfercodeMCFOST file with exponent α, Σ(r) = Σ (r/r )α, and a scale height of
0 0
(Pinteetal. 2006, 2009) to model the SED of T Cha. They h(r) = h (r/r )β, with β being the disk flaring index, and h
0 0 0
showedthattherearetwofamiliesofdustdiskmodelsthatcan thescaleheightatareferenceradiusr =50AU.Eachdiskex-
0
reproduce equally well the SED: very small disks (a few AUs tendsfromaninnerradius,R toanouterradius,R .Thegrain
in out
width)ormuchlarger(R ∼300AU)butwithaverysteepsur- size distribution in each disk is defined by dn(a) ∝ apda, be-
out
3
Hue´lamoetal.:ALMAobservationsofTCha
0.10 CO(3−2)
m Intensity (Jy/beam)0.01 SE850 NNμWWm 0.01 SE 850 μm (NZWOOM)
Continuu ttarupnecraetde-de dpgoewer law
10 100 100
m) radius (AU) m) radius (AU)
m/s/bea CO (3-2) m/s/bea 13 CO(3-2)
Integrated Line Intensity (Jy.k01..10 10 radius (AU) 100 Integrated Line Intensity (Jy.k01..10 10 radius (AU) 100
10-12
Fig.4.Position-velocitydiagramalongthediskmajoraxis(see
10-14 exactaxisrepresentedinFig1leftpanel).Thedotted,solid,and
2m)
W / dashedblackcurvesrepresentthebestfits tothe data,thatcor-
λ . F (λ10-16 orefs5p.o9n5dktmo as−K1,eapnleirnicalninvaetilooncitoyfip(r◦o)fi=le67fo,ranadsayscteenmtriaclvmealoscsiotyf
10-18 1.3,1.5,and1.7M ,respectively.
⊙
10-20
1 10 100 1000 10000
λ (μm)
Fig.3.Topandmiddlepanels:Continuumandgasradialinten- observationaldatasetdisplayedinthatwork.Theadoptedstellar
sity profiles. The blue (SE) and red (NW) data points are the parametersareTeff=5400K,Av=1.5,andd=108pc(Torresetal.
ALMA data(over5-σ) atbothsidesof thedisk. Inthe case of 2008;Schisanoetal.2009).Thebestdiskmodel,thatis,theone
thecontinuumwehavealsoincludedtheaverageprofile(green withtheminimumχ2,providesparametersofα=-2.5,β=1.07,
data).Thesolidblacklinesshowthebestmodelusingatapered h0@50AU=6AU, Rin = 19AU, amax = 1000, and a disk dust
edgeprescriptionforthesurfacedensity,whilethedashedlines massofMdust∼1×10−5M⊙.
show the best model using a truncated power law. The upper SinceSEDmodelingishighlydegenerate,thebest-fitmodel
panelsshowthe continuumdata,includinga zoomoftheouter isunlikelytobeauniquesolution.Therefore,wehaveperformed
regions,whilethemiddlepanelsincludetheCOprofiles.Bottom aBayesiananalysistoestimatethevalidityrangeforeachofthe
panel:theobservedSEDandthefitfromthetaperededgemodel explored parameters (Pressetal. 1992; Pinteetal. 2007). The
presentedhere. result is displayed in Figure 5, where we show the Bayesian
probabilitydistributionsforthedifferentdiskparameters.While
M ,R andh seemwellconstrained,thisisnotthecaseforα:
dust in 0
itshowsalocalpeakatα=−2.5butarelativelyflatdistribution.
tween a and a . The temperature structure in the disk is
min max
Weconcludethat,evenfixingR ,αremainsunconstrainedby
calculatedbyconsideringthedustopacityonly.Thedustprop- out
theSEDmodeling.
erties are computedassuming the Mie theory.Finally, the total
dustmassinthedisk(includingallgrainsizes)isrepresentedby With ourALMA observationswe havepartially brokenthe
Mdust. (α,Rout)degeneracycommonlyencounteredwithSEDfittingby
TocalculatetheCOchannelmapsandsurfacebrightnessdis- measuringRout.Theresolutionreachedbyourobservationsdoes
tribution, we assume a constant gas-to-dust mass ratio of 100 notallow us to constrainaccuratelythe surface density profile.
throughout the disk (both radially and vertically). We adopted ButwithRin ∼20AUandadiskwidthof∼60AU,weexclude
a standard CO abundance with respect to H (10−4), set con- surface density profile shallower than -1. According to the ob-
2
stantthroughthediskwhereTdust>20Kandequaltozerowhere servedRout,wecanalsodiscardthefamilyofmodelswithvery
T <20KtomimictheeffectofCOfreezeout.The12CO/13CO narrow dusty rings, and the extreme case of a very large disk
dust
ratioissetto76.Thelevelpopulationsarecalculatedassuming (Rout∼300AU)withα∼-3.
T =T ateachpointinthedisk.Theradialandverticaltem- Ifwe take the gasemission intoaccount,themodelfails to
gas dust
peratureprofilesandtheradiationfieldestimatedbytheMonte fit simultaneously the gas and dust profiles (see Figure 3), as
Carlo simulationare used to calculatelevelpopulationsfor the alreadyobservedin other spatially resolvedcircumstellardisks
CO molecule and to producethe SED, continuumimages, and (e.g.Hughesetal. 2008).Asdiscussedbytheauthors,a power
line emission surface brightnessprofiles, as well as kinematics law density profile cannotreproducethe different extentof the
witharay-tracingmethod.Thekinematicsarecalculatedassum- gas and dust emission observed in circumstellar disks while
ingthediskisinpureKeplerianrotation. a tapered edge model, in which the surface density falls off
We have adopted the inner disk parameters from gradually, can in principle reconcile the observed profiles. We
Olofssonetal. (2013). For the outer disk, we have fixed have therefore run the MCFOST code, but using a tapered ex-
two parameters obtained from the ALMA data, R and i, se- ponential edge in the surface density distribution. In this case,
out
lectingthegridvaluesclosertotheALMAmeasurments(80AU the density profile is represented by a function defined by the
and 68◦, respectively). We have explored Rin, β, h◦@50AU, characteristicradius,Rc (theradiusoutofwhichthebrightness
a , α, and M , using the same parameter range shown drops towards zero) and γ, the surface density index: Σ(r) =
max dust
in Ciezaetal. (2011). For the SED, we have fitted the same Σ0(r/r0)−γexp(cid:16)−(r/r0)2−γ(cid:17).
4
Hue´lamoetal.:ALMAobservationsofTCha
CS(7–8). Using the CO(3-2) image we derive an outer ra-
0.4 0.4 0.6
0.5 diusofR ∼230AU,aninclinationofi(◦)=67±5,anda
0.3 0.3 gas,out
Probability00..12 00..12 000...234 aproesistiiomnilaanrgalteboofthPAsi(d◦)es=o1f13th±e6.dTishkeilninteheinCteOnsimtyolpercoufilleess,
0.1 consistentwithauniformdistributionofthegas.
0.0 0.0 0.0
100 1000 10000 -2.5 -1.5 -0.5 10-6 10-5 10-4 10-3 – The disk around T Cha is in Keplerian rotation, and
amax [µm] α Mdisk [MO • ] the estimated dynamical mass of the central object,
1.0 0.4 1.0 M∗=1.5±0.2M⊙, is in good agreement with previous esti-
Probability0000....2468 000...123 0000....2468 – mTadtihas8ekti5.od0Tnuµshsmetbyacsaodennidsdtkioninutisuesmhvreooswilnuosttleivoanensdsaitiriymynpitltrrahaorecfikilcseao.ndnditsipnPluaAuymstotwotbhoseeergmvaaisstesiooiounnss
0.0 0.0 0.0
4 5 6 7 8 10 100 bumps separated by 40AU, suggesting the presence of an
ho@50AU [AU] Rin [AU] Rout [AU]
innerdustgapaspredictedbySEDmodeling,andan outer
Fig.5.Bayesianprobabilitydistributionsofthediskparameters radiusof∼80AU.Theprofilesaredifferentatbothsidesof
of T Cha. The blue lines show the results without fixing any thedisk,whichpointstowardsasymmetriesinthe dustdis-
parameter, while the red lines show the results after fixing the tribution.Thesedataallowsustoruleoutboththeverysmall
outerdiskradiusandthediskinclination. andlargeR familiesofSEDmodels.
out
– Radiative transfer models including a truncated power law
prescriptionforthesurfacedensityprofilecannotreproduce
Forthismodel,wehavealsoadoptedtheinnerdiskparame-
simultaneously the gas and dust profiles. We can fit both
tersfromOlofssonetal.(2013),andvariedonlytheprescription
componentssimultaneouslyusingatapered-edgemodelpre-
fortheouterdisk.Wehavefixedthediskinclinationto68◦,the
scription for the surface density. The best model provides
dustmasstoMdust=9×10−5M⊙(deGregorio-Monsalvoetal.,in values of γ= 0.5, and R = 50AU, which is consistent with
c
prep.),andwehaveexploredtherestofthediskparameters:we
havingmostofthediskmasswithintheinner50AU.
havesampledarangeofγvaluesbetween0and2,R between
c
40 and 100AU, Rin between 12 and 30AU, the scale heightat Acknowledgements. This paper makes use of the following ALMA data:
50AU(h @50AU)between3and6AU,andtheflaringindex,β, ADS/JAO.ALMA#2011.0.00921.S.ALMAisapartnershipofESO(represent-
0
between1.0and1.1.Finally,totakeintoaccountthedifference ing its member states), NSF (USA) and NINS (Japan), together with NRC
(Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic
in brightness between both sides of the disk in the continuum,
ofChile. TheJointALMAObservatory isoperated byESO,AUI/NRAOand
weexploremodelsthatpassbetweenthetwoobservedprofiles. NAOJ.TheNRAOisafacilityoftheNationalScienceFoundationoperatedun-
The resultis displayedin Figure3 where we show the best der cooperative agreement by Associated Universities, Inc. This research has
modelthatcanfitsimultaneouslythetwodiskcomponentsand beenfundedbySpanishgrantsAYA2010-21161-C02-02andAYA2012-38897-
theobservedSED.Themodelshowsγ=0.5andR =50AUfor C02-01.IdGandEMacknowledge supportfromMICINN(Spain)AYA2011-
c 30228-C03grant(includingFEDERfunds).
boththegasandthedust.Wealsoderivetheseparameters:R =
in
20AU, h @50AU = 4AU, and β = 1.0. This model is consis-
0
tentwithhavingthegasandthedustwellmixedandmainlylo- References
catedataradiussmallerthan50AU,assuggestedbyCiezaetal.
Alcala,J.M.,Covino,E.,Franchini,M.,etal.1993,A&A,272,225
(2011) based on the steep drop of the SED at sub-mm wave-
Andrews,S.M.,Wilner,D.J.,Hughes,A.M.,etal.2012,ApJ,744,162
lengths.
Brown,J.M.,Blake,G.A.,Dullemond,C.P.,etal.2007,ApJ,664,L107
Figure3showsthatourbestmodeldoesnotperfectlyfitthe Cieza,L.A.,Olofsson,J.,Harvey,P.M.,etal.2011,ApJ,741,L25
CO line profiles, which can be related either with the underly- deGregorio-Monsalvo,I.,Me´nard,F.,Dent,W.,etal.2013,A&A,557,A133
Dutrey,A.,Wakelam,V.,Boehler,Y.,etal.2011,A&A,535,A104
ing chemistry (we assumed ISM abundances and very simple
Guilloteau,S.,Dutrey,A.,Wakelam,V.,etal.2012,A&A,548,A70
COfreeze-out)orwiththemodelprescriptions.Infact,tapered-
Hue´lamo,N.,Lacour,S.,Tuthill,P.,etal.2011,A&A,528,L7
edgemodelssometimesfailtoreproducesimultaneouslytheob- Hughes,A.M.,Wilner,D.J.,Qi,C.,&Hogerheijde,M.R.2008,ApJ,678,1119
serveddustandgasprofilesobtainedfromveryhighspatialres- Ikeda,M.,Kawaguchi,K.,Takakuwa,S.,etal.2002,A&A,390,363
olution and sensitivity observations (see Andrewsetal. 2012; Isella,A.,Testi,L.,Natta,A.,etal.2007,A&A,469,213
Kastner,J.,Punzi,K.,Rodriguez,D.,etal.2013,inProtostarsandPlanetsVI
deGregorio-Monsalvoetal.2013),andsuggeststhatotherpro-
Posters,22
cesseslikee.g.graingrowthandradialmigrationshouldbetaken Matthews,H.E.,Marten,A.,Moreno,R.,&Owen,T.2002,ApJ,580,598
intoaccount.Giventhatthediskisbarelyresolvedinourobser- Murphy,S.J.,Lawson,W.A.,&Bessell,M.S.2013,MNRAS,435,1325
vations,weexpectfuture,higherspatialresolutionobservations Nehme´,C.,Gry,C.,Boulanger,F.,etal.2008,A&A,483,471
Olofsson,J.,Benisty,M.,LeBouquin,J.-B.,etal.2013,A&A,552,A4
toprovidestrongerconstraintsontherelativelocationofthegas
Pascucci,I.&Sterzik,M.2009,ApJ,702,724
anddust,andthedeparturefrompoint-symmetry.
Pie´tu,V.,Guilloteau, S.,DiFolco,E.,Dutrey,A.,&Boehler, Y.2014,A&A,
564,A95
Pinte,C.,Fouchet,L.,Me´nard,F.,Gonzalez,J.-F.,&Ducheˆne,G.2007,A&A,
4. Conclusions 469,963
Pinte,C.,Harries,T.J.,Min,M.,etal.2009,A&A,498,967
HighspatialresolutionandhighsensitivityALMAobservations Pinte,C.,Me´nard,F.,Ducheˆne,G.,&Bastien,P.2006,A&A,459,797
have allowed us to spatially resolve the outer disk around the Press, W. H., Teukolsky, S. A., Vetterling, W. T., & Flannery, B. P.
1992, Numerical recipes in FORTRAN. The art of scientific computing
young and isolated object T Cha. The target is surrounded by
(Cambridge:UniversityPress,—c1992,2nded.)
a compact dusty disk and a ∼3 times larger gaseous disk. Our Sacco,G.G.,Kastner,J.H.,Forveille,T.,etal.2014,A&A,561,A42
mainresultscanbesummarizedasfollows: Schisano,E.,Covino,E.,Alcala´,J.M.,etal.2009,A&A,501,1013
Torres,C.A.O.,Quast,G.R.,Melo,C.H.F.,&Sterzik, M.F.2008,Young
– WehavespatiallyresolvedthegaseousdiskofTChainthree NearbyLooseAssociations,ed.Reipurth,B.,757–+
vanderPlas,G.,Casassus,S.,Me´nard,F.,etal.2014,ApJ,792,L25
differentmolecularemissionlines:CO(3–2),13CO(3-2)and
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