Looking for Pure Rotational H_2 Emission from Protoplanetary Disks

We report on a limited search for pure rotational molecular hydrogen emission associated with young, pre-main-sequence stars. We looked for H_2 v = 0, J = 3 → 1 and 4 → 2 emission in the mid-infrared using the Texas Echelon Cross Echelle Spectrograph at NASA's 3 m Infrared Telescope Facility. The high spectral and spatial resolutions of our observations lead to more stringent limits on narrow-line emission close to the source than previously achieved. One star, AB Aur, shows a possible (2 σ) H_2 detection, but further observations are required to make a confident statement. Our nondetections suggest that a significant fraction, perhaps all, of previously reported H_2 emission toward these objects could be extended on scales of 5" or more.