Search for H₂ emission from disks around T Tauri and herbig AE stars

Preliminary results are presented of observations of the pure rotational lines of H₂ toward T Tauri and Herbig Ae stars using the Short Wavelength Spectrometer (SWS) on the Infrared Space Observatory (ISO). The sources are selected to be isolated low- and intermediate-mass young stellar objects, for which the presence of a circumstellar disk has been established by millimeter interferometry. The lowest H₂ S(0) and S(1) lines are detected in 3 out of 5 objects. The measured intensities indicate ∼ 0.01 M_⊙ of warm (T ≈ 150 K) gas in the ISO beam. It is argued that for at least one case (HD 163296), the emission is probably dominated by the warm gas in the circumstellar disk rather than by shocked- or photon-heated gas in the surrounding envelope. Such observations can provide important constraints on the radial and vertical temperature profiles in circumstellar disks.