We present self-consistent models of gas in optically-thick dusty disks and calculate its thermal, density and chemical structure. The models focus on an accurate treatment of the upper layers where line emission originates, and at radii $\gtrsim 0.7$ AU.

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aLineEmissionfromGasinOpticallyThickDustDisksaroundYoungStarsU.Gorti1,2D.Hollenbach2ABSTRACTWepresentself-consistentmodelsofgasinoptically-thickdustydisksandcalculateitsthermal,densityandchemicalstructure.Themodelsfocusonanaccuratetreatmentoftheupperlayerswherelineemissionoriginates,andatradii 0.7AU.Althoughourmodelsareapplicabletostarsofanymass,wepresenthereonlyresultsaround～1M⊙starswherewehavevarieddustproper-ties,X-rayluminositiesandUVluminosities.Weseparatelytreatgasanddustthermalbalance,andcalculatelineluminositiesatinfraredandsub-millimeterwavelengthsfromalltransitionsoriginatinginthepredominantlyneutralgasthatliesbelowtheverytenuousandcompletelyionizedsurfaceofthedisk.We ndthatthe[ArII]7µm,[NeII]12.8µm,[FeI]24µm,[SI]25µm,[FeII]26µm,[SiII]35µm,[OI]63µmandpurerotationallinesofH2andCOcanbequitestrongandaregoodindicatorsofthepresenceanddistributionofgasindisks.Waterisanimportantcoolantinthediskandmanywateremissionlinescanbemoderatelystrong.CurrentandfutureobservationalfacilitiessuchastheSpitzerSpaceTele-scope,HerschelObservatoryandSOFIAarecapableofdetectinggasemissionfromyoungdisks.Weapplyourmodelstothediskaroundthenearbyyoungstar,TWHya,and ndgoodagreementbetweenourmodelcalculationsandobservations.WealsopredictstrongemissionlinesfromtheTWHyadiskthatarelikelytobedetectedbyfuturefacilities.AcomparisonofCOobservations

withourmodelssuggeststhatthegasdiskaroundTWHyamaybetruncatedto～120AU,comparedtoitsdustdiskof174AU.Wespeculatethatphotoevap-orationduetothestrongstellarFUV eldfromTWHyaisresponsibleforthegasdisktruncation.

Subjectheadings:infrared:ISM—line:formation—planetarysystems:proto-planetarydisks—radiativetransfer