Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992apj...392..571h&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 392, no. 2, June 20, 1992, p. 571-581.
Astronomy and Astrophysics
Astrophysics
22
Interstellar Chemistry, Interstellar Matter, Lyman Alpha Radiation, Molecular Clouds, Carbon 12, Carbon 13, Line Of Sight, Molecular Gases, Radio Emission, Ultraviolet Spectra
Scientific paper
An analysis of the diffuse interstellar cloud complex in front of HD 179406 (20 Aql) is presented. Along this sight line, multispectral absortion- and emission-line studies have uncovered at least three distinct velocity components due to individual clouds. A dominant velocity component is seen in both the absorption and emission-line data sets at 3 +/- 1 km/s. It is argued that the cloud associated with this velocity component is responsible for most of the atomic and all of the molecular gas in front of 20 Aql. The present chemical and physical analysis of the cloud combines the diagnostic tools of radio emission-line data with those of UV and optical absorption data. Using non-LTE models to synthesize the observed absorption profiles, (C-12)O and (C-13)O column densities along this line of sight are determined. The (C-12)O/(C-13)O abundance ratio was found to be 50 +/- 15, similar to that found by Wannier et al. toward Zeta Oph. The physical conditions of the cloud have been investigated using ultraviolet absorption lines. Measurements indicate that the dominant absorption cloud has a gas pressure similar to that found in the local diffuse molecular cloud in Ophiuchus with nT = 20,000/cu cm K.
Black John Harry
Hanson Margaret Murray
Snow Theodore P.
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