THE TEMPERATURE PROFILE OF T-TAURI DISKS

This paper proposes that T Tauri stars are three-component systems, fo rmed by a star, its circumstellar disk and a tenuous, dusty envelope w hich surrounds both. The dust in the envelope scatters and reemits ste llar light in the direction of the disk, which is therefore significan tly hotter at large distance from the star than if direct heating alon e is considered. The overall behavior of the disk temperature is very sensitive to the envelope properties. For example, for spherically sym metric 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 de nsity in the envelope is-proportional-to r-1 and values Of T increasin g from 0 to approximately 0.4. In this context, stellar winds, disk wi nds, and infall models are discussed. Only disk winds seem able to rep roduce the observed flat TTS spectra.