Detection of a vibration-rotation emission line of hydrogen deuteride toward Orion Peak 1: excitation coupling of HD to H_2

Abstract

The 2.46um v=1-0 R(5) line of deuterated molecular hydrogen, HD, has been detected in the Orion Peak~1 shock emission region, at a surface brightness of (8.5 +/- 2.1) x 10^(-9) W m^(-2)sr^(-1) over a 6 arcsec^2 area. Comparison of the column density of HD(v=1,J=6) with the column density of HD(v=0,J=6) previously observed from ISO and the H_2 level column densities toward the same region implies that the excitation of HD is similar to that of H_2 for these energy levels, despite much higher spontaneous transition rates for HD. We suggest that this rough equality is caused by the coupling of the HD levels to those of H_2, due to strong reactive collisions, HD + H -> H_2 + D, in warm, partially dissociated gas. The deuterium abundance implied by the combined ISO and UKIRT measurements toward Orion Peak 1 is [D]/[H] = (5.1 +/- 1.9)x10^(-6).

15 pages, 2 figures, accepted for publication in ApJ

References in corpus (1)

• Spatial Variability in the Ratio of Interstellar Atomic Deuterium to Hydrogen. II. Observations toward Gamma2 Velorum and Zeta Puppis by the Interstellar Medium Absorption Profile Spectrograph

Cited by in corpus (5)

• HD far infrared emission as a measure of protoplanetary disk mass
• Spitzer observations of hydrogen deuteride
• Mapping the Universe in HD
• PDRs4All XVII: Formation and excitation of HD in photodissociation regions. Application to the Orion Bar
• Ground-based detection of a vibration-rotation line of HD in Orion