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Page 1: High-resolution observations in T Cha: the ATCA and ALMA vie · High-resolution observations in T Cha: the ATCA and ALMA view Transitional protoplanetary disks are considered as the

High-resolution observations in T Cha: the ATCA and ALMA view

Transitionalprotoplanetarydisksareconsideredasthe"missing link" betweendiskssurroundingyoungstarsandplanetarysystems. Thesedisksshowlittleornoexcessemissionatλ<10μmandasigni?icantexcessatλ≥10μm.Thislackofnear-infraredexcesswasinterpretedasadiagnosticofinnerdiskclearingpossiblyconnectedtotheearlystagesofplanetformation(e.g.,Calvetetal.2002).Dustclearingcanberelatedwithgapsorholeswithinthedisks,whichcanbecreatedbyseveralmechanisms,suchasaclose companion,diskphotoevaporation,orgiantplanetformation.Untilrecently,noplanethadbeendetectedaroundstarswithtransitionaldisks,butthishaschangedwiththerecent?irstdirectdetectionofayoungaccretingplanetaroundLkCa15(Kraus&Ireland,2012;Sallumetal.2015)andayetuncon?irmedsubstellarcompanioninsidethegapofthetransitionaldiskthatsurroundsTChamaleontis(TCha,hereafter;Huelamoetal.2011). Thisopensavery interestingresearch line forstudying in-situ formationofplanets intransitionaldisks,beingauniqueopportunitytocaptureakeymomentofon-goingplanetaryformation.

I. de Gregorio-Monsalvo1, N.Huelamo2, M. Ireland3,4, C. Pinte5, E. Macias6, P. Tuthill3, H. Bouy2, S. Lacour7, A. Kraus8

(1) ESO-ALMA (Chile), (2) LAEX-Astrobiology Center (INTA-CSIC) (Spain), (3) Macquarie U. (Australia), (4) Australian Astronomical Observatory (Australia), (5) UMI-FCA, CNRS/INSU, France , (6) IAA-CSIC (Spain), (7) Observatoire de Paris (France), (8) Hawaii U. (USA)

REFERENCES: Calvet et al. 2002, ApJ, 568, 1008 Cieza et al. 2011, ApJL, 471, L25 De Gregorio-Monsalvo et al. 2013, A&A, 557, 133 Dullemond & Dominik, 2005, A&A, 434, 971 Huelamo et al. 2011, A&A, 528, L7 Huelamo et al. 2015, A&A, 575, L5 Kraus & Ireland, 2012, ApJ, 742, L5 Sallum et al. 2015, Nature 527, 324

Motivation

Fig2.ATCAmapat7mm.Thespatialresolutionis0.2”x0.2“

The case of T Chamaleontis: TChaisayoung(~7Myr)nearby(108pc)TTauristarwithaSpectralEnergyDistribution(SED)typicalofatransitionaldisk.Huelamoetal.(2011)reportedthepresenceofasubstellarcompanioncandidatewithinitsgap(TChab).TChaissurroundedbyanouterdiskwhosemainpropertieshavebeeninferredfromthemodelingofitsspectralenergydistribution(Ciezaetal.2011).Thosemodelsarehighlydegenerateandcan?ittheSEDequallywelleitherwithaverycompact(fewAUs)outerdiskormuchwidertenuousdiskwithaverysteepsurfacedensitypro?ile.ToshedlightonthepeculiardiskpropertiesofTCha,weperformedhighangularresolutionobservationsinthesubmillimeter,millimeter,andinthecentimeterregimes.

Unveiling the outer disk properties using ALMA HighspatialresolutionandhighsensitivityALMAobservations incontinuumandinCO(3-2)at850μmshowTChaissurroundedbyacompactdustydiskandathreetimeslargergaseousdisk(seeFig1).

UsingtheCO(3−2)imagewederiveanouterradiusofthegaseousdiskof230AU,aninclinationof67±5degreesandapositionangleofPA=113±6degrees. Thegasemission is inKeplerianrotation,and theestimated dynamical mass of the central object is 1.5±0.2 Msun, in good agreement with previousestimationsbasedonevolutionarytracks.

Thedustydiskisresolvedat850μmanditshowsasimilarinclinationandP.A.tothegaseousdisk.Thecontinuum intensity pro?ile displays two emission bumps separated by 40 AU, suggesting for the ?irsttime the presence of an inner dust gap as predicted by SEDmodeling, and an outer radius of ~80AU.These data allow us to rule out both the very small and large Rout families predicted by SEDmodels(Huelamoetal.2015).

Comparison with radiative transfer models WeusedtheradiativetransfercodeMCFOSTwithataperedexponentialedgeinthesurfacedensitydistributionforreproducingsimultaneouslythegasandthedustpro?iles(seeFig.3). Thebestmodelprovidesvaluesofγ=0.5,andcriticalradiusof50AU,whichisconsistentwithhavingmostofthediskmasswithintheinner50AU.Ourbestmodeldoesnotperfectly?ittheCOlinepro?iles,whichcanberelatedeithertotheunderlyingchemistry(weassumedISMabundances and very simple CO freeze-out) or to themodel prescriptions. In fact, tapered edgemodels sometimes fail to reproduce simultaneously theobserveddustandgaspro?ilesobtainedfromveryhighspatialresolutionandsensitivityobservations(e.g.deGregorio-Monsalvoetal.2013),andsuggeststhatotherprocessessuchasgraingrowthandradialmigrationshouldbetakenintoaccount.

Fig1. ALMACO(3-2) (colors)+continuumat850μm(contours)

Resolving the central gap using ATCA High-angular resolution continuumobservations using theAustraliaTelescope CompactArray at 7mmshowdustemissionasymmetricinbothaxiswithacleargapatthecenter(seeFig2).Wealsoperformedcontinuumobservationat1.7cm.Itshowsfaintemissionbarelyresolvedandtracingasimilarstructureinthemainaxisasobservedat7mm.

The spectral index between 3.3 mm (from literature) and 7 mm is ~2.6, consistent with thermal dustemission.Thisprovidesadustopacitylawβ=(2-α)<1,whichcanbenaturallyexplainedbygraingrowthtomm and cm size. Between 7 mm and 1.7 cm, the spectral index is ~1.5, which points to a possiblecombinationofthermalemissionfromdust(asrevealsthemapat1.7cm)andpossiblyfree-freeradiationfromwinds.

Fig3.Continuum(left,850μm)andgas(right,CO(3-2))radialintensityproJiles.Theblue(SE)andred(NW)datapointsaretheALMAdata(over5σ)atbothsidesofthedisk.InthecaseofthecontinuumwehavealsoincludedtheaverageproJile(greendata).Thesolidblacklinesshowthebestmodelusingataperededgeprescriptionforthesurfacedensity,whilethedashedlinesshowthebestmodelusingatruncatedpowerlaw.Centralpanelisazoomoftheouterregions.