Silicate Emission in T Tauri Stars: Evidence for Disk Atmospheres?

Abstract

We present low-resolution mid-infrared spectra of nine classical T Tauri stars associated with the Cha-maeleon I dark cloud. The data were obtained with the PHOT-S instrument on board the Infrared Space Observatory (ISO) in the two wavelength ranges 2.5È4.9 and 5.9È11.7 km. All nine stars show evi-dence of silicate emission at 10 km, which is the only prominent feature in the spectra. We discuss a model for the origin of these features in a hot, optically thin surface layer of the circumstellar disks surrounding the central young stars (i.e., a disk atmosphere). We report excellent agreement of our observations with predictions based upon this simple model for most stars in our sample, assuming that a mixture of amorphous silicates of radius km is the dominant source of opacity. These observations [1 support the notion that extended disk atmospheres contribute substantially to the mid-infrared Ñux of young stars.