Karl Stapelfeldt 1, Deborah Padgett 2, & Tim Brooke 1
1 Mail Stop 183-900 Jet Propulsion Laboratory 4800 Oak Grove Drive Pasadena CA 91109 USA
2 IPAC/Caltech
We have used ISO/SWS to search for molecular hydrogen S(0) and S(1) rotational emission toward 14 low mass pre-main sequence stars located in the nearby Chamaeleon, Ophiuchus, and Taurus-Auriga star forming regions. Eight classical T Tauri stars and six weak line T Tauri stars were observed. The survey was motivated by model calculations which indicate that there should be enough warm gas in a circumstellar/protoplanetary disk to produce H2 emission detectable by ISO. Emission was strongly detected toward the weak line T Tauri star SR 9, weakly detected toward the jet source Sz 68, and not detected at all in the other 12 objects. For SR 9, the observed rotational temperature is 80 K. Preliminary estimates indicate a much larger mass of circumstellar gas than has been inferred from the millimeter dust continuum brightness of this source. Interpretation of this result is complicated by the fact that SR 9 is a binary with projected separation of 80 AU, it is a strong X-ray source, and it is located in the dense core of the Rho Ophiuchus association where other sources may be present in the SWS aperture. Possible H2 excitation mechanisms and plans for follow-up observations will be discussed.