Reversed far-infrared line emission from OH in Orion.
The fundamental OH rotational transition at 2514 GHz (119.2 micrometers) has been observed in the Orion IRc2 region at a spectral resolution of 0.6 km s-1.  The emission is spatially compact (< 25" FWHM) and centered near IRc2.  A comparison of the observed profile with spectra of other species known to exist in the region suggests that the entire blueshifted side of the OH profile has been "self-absorbed," leaving only a redshifted emission component.  In addition, there is pronounced absorption near 5 km s-1 VLSR indicative of the "hot core" source.  The presence of the 119 micrometers absorption provides a straightforward explanation for the high ratio of 163/119 micrometers integrated line intensities which was previously considered anomalous.
Betz
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Space Sciences Laboratory, University of California, USA.
Boreiko
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D055580:Astronomical Phenomena; D001256:Astronomy; D002248:Carbon Monoxide / Q000032:analysis; D005118:Extraterrestrial Environment; D005740:Gases / Q000032:analysis*; D017665:Hydroxyl Radical / Q000032:analysis*; D013055:Spectrophotometry, Infrared
D005740:Gases; D017665:Hydroxyl Radical; D002248:Carbon Monoxide