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Title:
Cloud Structure and Physical Conditions in Star-forming Regions from Optical Observations. II. Analysis
Authors:
Pan, K.; Federman, S. R.; Sheffer, Y.; Andersson, B.-G.
Affiliation:
AA(Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606; ; .; Current address: Department of Physics and Astronomy, Bowling Green State University, 104 Overman Hall, Bowling Green, OH 43403; .), AB(Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606; ; .), AC(Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606; ; .), AD(Department of Physics and Astronomy, Johns Hopkins University, Charles and 34th Street, Baltimore, MD 21218; .)
Publication:
The Astrophysical Journal, Volume 633, Issue 2, pp. 986-1004. (ApJ Homepage)
Publication Date:
11/2005
Origin:
UCP
ApJ Keywords:
ISM: Abundances, ISM: Atoms, ISM: Clouds, ISM: Molecules, ISM: Structure, Stars: Formation
DOI:
10.1086/491466
Bibliographic Code:
2005ApJ...633..986P

Abstract

To complement the optical absorption line survey of diffuse molecular gas in Paper I, we obtained and analyzed far-ultraviolet H2 and CO data on lines of sight toward stars in Cep OB2 and Cep OB3. Possible correlations between column densities of different species for individual velocity components, not total columns along a line of sight as in the past, were examined and were interpreted in terms of cloud structure. The analysis reveals that there are two kinds of CH in diffuse molecular gas: CN-like CH and CH+-like CH. Evidence is provided that CO is also associated with CN in diffuse molecular clouds. Different species are distributed according to gas density in the diffuse molecular gas. Both calcium and potassium may be depleted onto grains in high-density gas, but with different dependencies on local gas density. Gas densities for components where CN was detected were inferred from a chemical model. Analysis of cloud structure indicates that our data are generally consistent with the large-scale structure suggested by maps of CO millimeter-wave emission. On small scales, the gas density is seen to vary by factors greater than 5.0 over scales of ~10,000 AU. The relationships between column densities of CO and CH with that of H2 along a line of sight show similar slopes for the gas toward Cep OB2 and Cep OB3, but the CO/H2 and CH/H2 ratios tend to differ, which we ascribe to variation in average density along the line of sight.

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