Observations of the extinction and excitation of the molecular hydrogen emission in Orion

We present the first observations of two quadrupole rotational transitions of molecular hydrogen, the J = 7→5 and 9→7 transitions, along with several previously observed vibration-rotation H2 lines in the Orion molecular cloud. The line ratios indicate a 2.1 μm extinction of approximately 2 mag. This extinction is intermediate between the earliest estimates of 4 mag and the more recent estimate of 1.2--2.0 mag. A comparison of the populations of three vibrational levels indicates a distribution of excitation temperatures between 1000 and 3000 K for the levels included; 1500 K best represents the temperature of the gas responsible for the v = 1→0 line emission. These results imply the total luminosity of the molecular hydrogen emission is 200 +- 80L/sub sun/, and the mass of the emitting gas is of order 0.05 M/sub sun/. The uncertainties in the structure of the extinction and the geometry of the emission region may make it impossible to determine the luminosity and mass of the hot H2 any more accurately. The mass and cooling time of the hot H2 indicates at least 10 M/sub sun/ of material has been heated over the lifetime of the outflow