A new probe of the planet-forming region in T Tauri disks

We present new observations of the far-ultraviolet (FUV; 1100-2200 Angstrom) radiation field and the near- to mid-A IR (3-13.5 mum) 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 Lyalpha-induced H(2) fluorescence and an additional source of FUV continuum emission below 1700 Angstrom. Comparison of the FUV spectra to a model of H(2) excitation suggests that the strong continuum emission is due to electron impact excitation of H(2). 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 (similar to1 Myr) stellar systems. We propose that the presence of strong H(2) continuum emission and inner disk clearing are related by the increased penetration power of high-energy photons in gas-rich regions with low grain opacity.