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M. J. Richter, D.T. Jaffe (UT Austin), G.A. Blake (Caltech), J.H. Lacy (UT Austin)
We report on a limited search for low-level pure-rotational molecular hydrogen emission from young, pre-main sequence stars. In H2, the 0-0~S(1) line at 17~microns and the 0-0~S(2) line at 12~microns are sensitive to warm (T~>~175~K) gas. In contrast, near-infrared rotation-vibration transitions, such as are seen at 2~microns, typically arise in quite hot (T~\geq~2000~K) gas or through radiative pumping processes. Therefore, the pure rotation lines are likely to be more representative of the gas in a circumstellar disk.
Our search, at 17 and 12~microns, uses the Texas Echelon-Cross-Echelle Spectrograph (TEXES) at NASA's 3m Infrared Telescope Facility. The high spectral and high spatial resolution of our observations result in greater sensitivity to certain gas distributions than infrared satellite observations. In particular, our observations are best suited for detecting point sources with narrow line emission, as might be expected for gas in Keplerian orbit at a radius of ~1-50~AU from a solar-mass star. Analysis of the line profile using assumptions such as Keplerian rotation, the stellar mass, and the system inclination angle, constrains the location of the emitting gas. Thus, our search is a natural extention of satellite observations.
We observed 5 young stellar objects in November 2000 with TEXES and will conduct further observations in November 2001. In this poster, we present spectra and comparisons to ISO detections, where appropriate. To date, we detect no H2 emission. We discuss the implications of this as well as strategies for pursuing this research in the future.
MJR and TEXES are supported by grants from the NSF, NASA through the USRA SOFIA program, and the Texas Advanced Research Program (TARP).