THE TEMPERATURE PROFILE OF T-TAURI DISKS

This paper proposes that T Tauri stars are three-component systems, formed by a star, its circumstellar disk and a tenuous, dusty envelope which surrounds both. The dust in the envelope scatters and reemits stellar light in the direction of the disk, which is therefore significantly hotter at large distance from the star than if direct heating alone is considered. The overall behavior of the disk temperature is very sensitive to the envelope properties. For example, for spherically symmetric envelopes, the whole observed range of spectral indices in the interval 5-100 mum, (4/3 to 0), can be accounted for by models with density in the envelope is-proportional-to r-1 and values Of T increasing from 0 to approximately 0.4. In this context, stellar winds, disk winds, and infall models are discussed. Only disk winds seem able to reproduce the observed flat TTS spectra.