Velocity, reddening, and temperature structure of the H2 emission in Orion

We present high-resolution (ΔV = 20 km s-1) Fourier transform spectrometer spectra of the 2 μm He2 emission in the Orion molecular cloud (OMC) core. Using a 3. 75 aperture, we have mapped seven of the H2 transitions at twelve positions which include several of the H2 peaks and the continuum sources IRc2, IRS 2, and the BN object. The foreground extinction to the peaks of H2 emission is A/sub 2.1mum/roughly-equal1.2-2 mag, a value much less than the estimates derived from previous observations. There is a significant correlation between low H2 flux and high 2.1 μm extinction, suggesting that much of the clumpy structure in the S(1) line maps is attributable to variable OMC-1 foreground extinction which changes a factor of 2 on scales approx.411. The total luminosity and mass of emitting H2 are approx.150 L/sub sun/ and approx.2 x 10-2 M/sub sun/, again much lower than previous estimates. The kinematics inferred from the H2 line profiles are consistent with most of the emission arising from a shock-excited region at the interface between the near side of the plateau source and the surrounding molecular cloud. Separate, highly blueshifted (-50 to -100 km s -1) emission appears to originate from a more deeply embedded region. The identification of the line core and highly blueshifted emission with separate emitting regions reduces the discrepancy between the observed line profiles and the predictions of shock excitation models. Upper limits on Brγ emission away from the M42-contaminated line core require that H II is significantly less abundant than excited H2 at the shock fronts within OMC-1