AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 69. The Young Ones 2: T-Tauri Stars, H-H Objects and Modeling
Display, Wednesday, June 2, 1999, 10:00am-6:30pm, Southwest Exhibit Hall

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[69.02] The Discovery of X-ray Induced H2 Flourescence in the Disk of a T Tauri Star

J.S. Bary, D.A. Weintraub (Vanderbilt University), J.H. Kastner (Rochester Institute of Technology)

We present high resolution, near-IR spectroscopic observations of three T Tauri stars in the v = 1-0 S(1) 2.1218 \mum emission line of molecular hydrogen. Our data were collected using CSHELL on the IRTF on 1999, February 23, UT. All three stars searched for H2 (TW Hya, HD 98800, and CD-33\circ 7795) reside in the nearby (D ~0 pc) TW Hya Association (Kastner et al. 1997, Science, 277, 67). We find that one of the three, TW Hya, likely displays H2 emission in the 2.1218 \mum line. TW Hya is apparently surrounded by a circumstellar disk containing gas (Zuckerman et al. 1995, Nature 373, 494) and dust (Weintraub et al. 1989, ApJ, 340, L69), but shows no optical jets, molecular outflow, or other phenomena that would produce shocked H2 emission. In addition, the central velocity of the apparent H2 line falls, to within the measurement errors, at the velocity of disk molecular emission previously detected toward TW Hya (Kastner et al. 1997), and the H2 line is not obviously resolved. Thus, it appears that the H2 emission is not excited by shocks. Rather, the 2.1218 \mum emission likely originates in the disk of TW Hya and is excited via flourescence, due either to direct UV photoexcitation (e.g., Black and van Dishoeck 1987, ApJ, 322, 412) or to X-ray ionization of H2 (Maloney et al. 1996, ApJ, 466, 561; Tine et al. 1997, Ap J, 481, 282). The latter possibility is especially appealing, as TW Hya is a bright X-ray source (Kastner et al. 1997). Hence, we propose that our detection of H2 emission toward TW Hya demonstrates that X-ray induced flourescence can occur in gaseous disks around X-ray bright T Tauri stars.

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