Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989esasp.290..141b&link_type=abstract
In ESA, Infrared Spectroscopy in Astronomy p 141-147 (SEE N90-19084 11-89)
Astronomy and Astrophysics
Astronomy
7
Emission Spectra, Fine Structure, Infrared Spectroscopy, Line Spectra, Molecular Clouds, Photodissociation, Carbon Monoxide, Cosmic Dust, Hydrogen, Interstellar Gas, Molecular Spectra, Molecules
Scientific paper
The results of the study on the molecular and fine structure line emission, from dense photodissociation regions, are discussed. The work is focused on the prediction of the line emission from CO and H2 molecules. It is found that, when the gas density is sufficiently high, self-shielding of the molecules can move the C(+)/CO and H/H2 transitions close to the surfaces of the molecular cloud where they can feel the full effect of heating by the ultraviolet radiation field. Collisional de-excitation of the H2 can move the lower levels towards low temperature emission producing an apparently shocked line ratio for two low-J levels, while the high-J levels retain a fluorescent value. Appreciable emission in high-J CO molecules originates in this warm molecular gas. Comparison with observation suggests that high density clumps are a common phenomena in photodissociation regions.
Burton Marcia
Hollenbach David J.
Tielens Alexander G. G. M.
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