[Previous] | [Session 76] | [Next]
J.S. Bary, D.A. Weintraub (Vanderbilt University), J.H. Kastner (Carslon Center for Imaging Science, RIT)
We have detected H2 emission in the v=1-0 S(1) line at 2.12183 um in the circumstellar environment of two classical T Tauri stars, GG Tau A and LkCa 15, and one weak-lined T Tauri star, DoAr 21, in high-resolution (R = 60,000) spectra. The equivalent widths of the H2 emission line lie in the range 0.05-0.10 Å and, in each case, the central velocity of the emission line is centered at the star's systemic velocity. The FWHM of the line range from ~ 9 to 14 km s-1, in agreement with line widths expected from gas experiencing Keplerian rotation in circumstellar disks surrounding K-type stars at distances > 10 AU from the sources. The near zero systemic velocities and the narrow line widths of the H2 line rule out shock excitation as the most likely stimulating mechanism. We suggest either UV fluorescence or X-ray heating as likely candidates responsible for producing the observed emission. We have calculated lower limits on the masses of H2 gas on the order of 10-8-10-9 Msun for each of these sources, assuming that the emission arises from optically thin reservoirs of gas in LTE at T ~ 2000 K. The high temperature required for significant emission in the S(1) line suggests that we have detected reservoirs of hot H2 gas distinct from the reservoirs of cooler H2 gas recently detected in pure rotational line emission with ISO. If, after further study, the H2 proves to be in the inner regions of the circumstellar disks of these sources and traces the presence of more gas remaining in the extended regions of the disks, the criteria leading to assumptions about the paucity of circumstellar material around weak-lined T Tauri stars will need to be reconsidered. Therefore, disks once thought to have been dissipated, may be evolved such that the emission from gas and dust in these disks falls below present detection limits.
The author(s) of this abstract have provided an email address for comments about the abstract: jeff.bary@vanderbilt.edu