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

Abstract

We present high-resolution (..delta..V = 20 km s/sup -1/) Fourier transform spectrometer spectra of the 2 ..mu..m He/sub 2/ emission in the Orion molecular cloud (OMC) core. Using a 3. 75 aperture, we have mapped seven of the H/sub 2/ transitions at twelve positions which include several of the H/sub 2/ peaks and the continuum sources IRc2, IRS 2, and the BN object. The foreground extinction to the peaks of H/sub 2/ 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 H/sub 2/ flux and high 2.1 ..mu..m 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.4/sup 11/. The total luminosity and mass of emitting H/sub 2/ are approx.150 L/sub sun/ and approx.2 x 10/sup -2/ M/sub sun/, again much lower than previous estimates. The kinematics inferred from the H/sub 2/ 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 tomore » -100 km s /sup -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 Br..gamma.. emission away from the M42-contaminated line core require that H II is significantly less abundant than excited H/sub 2/ at the shock fronts within OMC-1.« less