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

Abstract

The discrepancy between the prediction of shock models and the observed characteristics of H2 emission in Orion is reduced in virtue of two results of a study based on high-resolution Fourier transform spectrometer spectra: (1) the data show that the extinction of the H2 emission in Orion is much less than previously derived, lying in the 1.2-2.0 mag range at peaks 1,3 and 5, and probably also at peak 2; and (2) while confirming the large total line widths found previously, it is found that the H2 lines are composite, with at least two large-scale emitting regions having line widths of less than 50 km/sec contributing to the profiles. It is also found that the systematic change in mean velocity across the nebula exhibited by the stronger emission, which is centered near the velocity of OMC-1, strongly supports the hypothesis that it lies at the interface between the expanding plateau source and OMC-1.