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J.S. Bary, D.A. Weintraub (Vanderbilt University), J.H. Kastner (Center for Imaging Science, RIT)
We present high resolution (R~q 60,000), near-IR spectroscopic observations of three T Tauri stars: GG Tau, LkCa 15, and DoAr 21. All three were detected in emission at the v=1-0 S(1) 2.12183 \mum line of molecular hydrogen using Phoenix on the 4-m telescope atop Kitt Peak on the nights of December 26--29, 1999 and June 20--23, 2000, UT. GG Tau and LkCa 15, with H\alpha equivalent widths of \approx40Åand \approx13Å, respectively, are both classified as classical T Tauri stars (cTTS). Both stars, found in the Taurus-Auriga star forming region (D~q 140pc), also have been detected in mm continuum emission (Guilloteau et al. 1999, A&A, 348, 570; Duvert et al. 2000, A&A, 355,165), indicating the presence of dust in the near circumstellar environments of these stars. On the other hand DoAr 21, located in the \rho Ophiuchus star forming region, is a weak-lined T Tauri star (wTTS) with a measured H\alpha EW<10Åthat remains undetected in mm continuum emission. We have detected H2 in the near circumstellar environment of an evolved T Tauri star with a significantly dust-depleted disk.
Of these three sources, none are known to drive outflows that might stimulate the H2 emission through shock excitation. Because the central velocity of the H2 emission line sits at the rest velocity for both LkCa 15 and DoAr 21, shocks can also be ruled out as the likely mechanism for exciting the H2 observed toward these two stars. The emission from GG Tau, on the other hand, is redshifted by simeq 25 km s-1, a velocity that could be representative of shock excitation; however, without a resolved image of the gas, no conclusions about its entrainment in an outflow or a ``streamer'' (Roddier et al. 1996, ApJ, 463, 326) can be made. The H2 emission from LkCa 15 and DoAr 21 likely originates within the circumstellar disks and would therefore have a different excitation mechanism. X-ray ionization (Maloney et al. 1996, ApJ, 466, 561) and UV photo-excitation (Black & van Dishoeck 1987, ApJ, 322, 412) are possible candidates for stimulating the detected H2 emission. Future observations are planned to help distinguish between the mechanisms.
Masses of H2 are determined from the measured line intensities assuming an appropriate density profile for the disk. Comparisons of our masses with those determined from dust continuum observations are presented.