OPTICAL AND NEAR-INFRARED MODEL IMAGES OF THE CIRCUMSTELLAR ENVIRONMENTS OF CLASSICAL T-TAURI STARS

We describe model calculations of optical and near-infrared scattered light images expected from class II T Tauri stars-the star-plus-disk s ystems. The parameters controlling the disk shape, size, and mass are chosen to be within theoretically and observationally derived limits. We restrict our models to nearly edge-on disks, since for lower inclin ations the central starlight is many orders of magnitude greater than the radiation scattered in the disk. In addition to model flux images, we calculate spectral energy distributions for pole-on viewing using approximations for hat and flared disks. We find that direct imaging o f edge-on disks can provide only estimates of the scale height at larg e distances from the central star and an estimate of the disk mass. Th e images are rather insensitive to the inner disk radius and the degre e of Baring, provided the scale height is axed at large radii. Spectra l energy distribution modeling is required to constrain the inner disk radius and the degree of flaring.We apply our models to recent Hubble Space Telescope (HST) images of HH 30 IRS and investigate whether the scattered light images could have been produced by starlight scatteri ng off the walls of jet-carved cavities in infalling envelopes associa ted with the embedded class I sources. We find that while the class I infalling envelope plus cavity model qualitatively resembles the HST i mages, the spatial extent of the model images is too large. Edge-on di sk models appear to provide better fits to the data and enable us to d etermine the disk scale height at large distances from the central sta r. However, the assumption of axisymmetry and uniform illumination is clearly inadequate for this variable source. In addition to producing flux images, our radiation-transfer simulations predict the spatially resolved polarization structure of HH 30. We have also performed k'-ba nd simulations for HH 30 in anticipation of high-resolution infrared i maging polarimetry.