Infrared Emission from Gas in Optically Thick Disks
          David Hollenbach, NASA Ames Research Center
          Uma Gorti, University of California, Berkeley

          Gorti & Hollenbach (2004) presented models of the infrared emission from gas in optically thin disks, i.e., disks whose dust opacity (at optical wavelengths) radially outwards through the midplane is less than about 5. Here, we present preliminary results of models of young disks, whose dust is very optically thick to stellar photons. We focus on the separate calculation of dust and gas temperatures near the disk surface, where dust and gas decouple and their temperatures differ. We use a modified Chiang & Goldreich (1997) model to numerically determine the dust temperature. The gas temperature near the surface is determined by a thermal balance calculation, which includes a self-consistent computation of the chemistry. The disk spectrum is then computed, including the dust continuum as well as the gas emission lines. These preliminary models are for passive disks, with no heating due to viscous accretion, orbiting 1Myr old solar mass stars. We plan to present models of an optically thick disk with no inner hole, as well as models with inner holes of various radii.  Time permitting, we will also determine the photoevaporation mass loss fluxes as a function of radius for these models.  The heating sources for the photoevaporation include Xray, UV, and optical photons from the central star.