Physics
Scientific paper
Mar 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999esasp.427..561r&link_type=abstract
The Universe as Seen by ISO. Eds. P. Cox & M. F. Kessler. ESA-SP 427., p. 561
Physics
2
Iso, Orion Peak 1, Shock Waves, H2, Hd
Scientific paper
Using the Short-Wavelength-Spectrometer on board of ISO we obtained near- and mid-infrared spectra of Orion Peak 1, the brightest H2 emission region in the sky. A wealth of emission and absorption features was detected, including some 80 H2 ro-vibrational and pure rotational lines, the latter reaching to 0-0 S(25). We speculated upon the nature of the observed high-excitation tail in the H2 level column density distribution, suggesting H2 formation or high-velocity collisional excitation in C-shocks as its cause. For the first time, an infrared emission line of HD was detected in the interstellar medium, the v=0-0 R(5) at 19.4305 μm. Assuming similar excitation conditions for H2 and HD, and accounting for the subthermal excitation of HD, we were able to derive an abundance ratio [HD]/[H2]=(9.0 +/- 2.5) x 10-6 in the Orion outflow. When we take into account that HD may be selectively depleted relative to H2 in the warm, partially dissociated layers of C-shocks, we find a deuterium abundance of [D]/[H] = (7.6 +/- 2.1)x 10-6, which is on the lower end of abundances derived recently through UV absorption measurements.
Bertoldi Frank
Drapatz Siegfried
Rosenthal David
Timmermann Ralf
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