A New Probe of the Planet-Forming Region in T Tauri Disks
AEROSPACE CORP LOS ANGELES CA
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We present new observations of the far-ultraviolet FUV 1100 2200 A radiation field and the near- to mid-IR 3-13.5 micron 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 Ly-alpha-induced H2 fluorescence and an additional source of FUV continuum emission below 1700 A. Comparison of the FUV spectra to a model of H2 excitation 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 H2 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.
- Atomic and Molecular Physics and Spectroscopy