2004ApJ...614L.133B

We present new observations of the far-ultraviolet (FUV; 1100-2200 Å) radiation field and the near- to mid-IR (3-13.5 µm) spectral energy distribution (SED) of a sample of T Tauri stars selected on the basis of bright molecular disks (GM Aur, DM Tau, and LkCa 15). In each source we find evidence for Lyα-induced H₂fluorescence and an additional source of FUV continuum emission below 1700 Å. Comparison of the FUV spectra to a model of H₂excitation suggests that the strong continuum emission is due to electron impact excitation of H₂. The ultimate source of this excitation is likely X-ray irradiation that creates hot photoelectrons mixed in the molecular layer. Analysis of the SED of each object finds the presence of inner disk gaps with sizes of a few AU in each of these young (∼1 Myr) stellar systems. We propose that the presence of strong H₂continuum emission and inner disk clearing are related by the increased penetration power of high-energy photons in gas-rich regions with low grain opacity.