  We present observations of pure rotational molecular hydrogen emission from
the Herbig Ae star, AB Aurigae. Our observations were made using the Texas
Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope
Facility and the Gemini North Observatory. We searched for H2 emission in the
S(1), S(2), and S(4) lines at high spectral resolution and detected all three.
By fitting a simple model for the emission in the three transitions, we derive
T = 670 +/- 40 K and M = 0.52 +/- 0.15 earth masses for the emitting gas. Based
on the 8.5 km/s FWHM of the S(2) line, assuming the emission comes from the
circumstellar disk, and with an inclination estimate of the AB Aur system taken
from the literature, we place the location for the emission near 18 AU.
Comparison of our derived temperature to a disk structure model suggests that
UV and X-ray heating are important in heating the disk atmosphere.
