Spectral Energy Distributions of Passive T Tauri Disks: Inclination

Abstract

We compute spectral energy distributions (SEDs) for passive T Tauri disks viewed at arbitrary inclinations. Semianalytic models of disks in radiative and hydrostatic equilibrium are employed. Over viewing angles for which the flared disk does not occult the central star, the SED varies negligibly with inclination. For such aspects, the SED shortward of ~80 μm is particularly insensitive to orientation, since short wavelength disk emission is dominated by superheated surface layers, which are optically thin. The SED of a nearly edge-on disk is that of a class I source. The outer disk occults inner disk regions, and emission shortward of ~30 μm is dramatically extinguished. Spectral features from dust grains may appear in absorption. However, millimeter-wavelength fluxes decrease by at most a factor of 2 from face-on to edge-on orientations. We present illustrative applications of our SED models. The class I source 04108+2803B is considered a T Tauri star hidden from view by an inclined circumstellar disk. Fits to its observed SED yield model-dependent values for the disk mass of ~0.015 M_solar and a disk inclination of ~65 deg relative to face-on. The class II source GM Aur represents a T Tauri star only slightly obscured by its circumstellar disk. Fitted parameters include a disk mass of ~0.050 M_solar and an inclination of ~60 deg, where the viewing angle is chosen to reproduce the observed visual extinction of A_V=0.5 mag.