AAS 199th meeting, Washington, DC, January 2002
Session 11. Interstellar Medium - I
Display, Monday, January 7, 2002, 9:20am-6:30pm, Exhibit Hall

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[11.13] Density Variations over Subparsec Scales in Diffuse Molecular Gas

K. Pan, S.R. Federman (U. Toledo)

As part of a study on cloud structure in diffuse molecular gas, we obtained high-resolution observations of interstellar CN, CH, CH+, \ion{Ca}{1}, \ion{Ca}{2}, and \ion{K}{1} absorption lines toward the multiple star systems \rho Oph, HD206267, and HD217035. Optical depth profiles, corrected for instrumental function, were constructed for these absorption features. Optical depth profiles of different species may or may not have similar shapes for a given star, and the profiles for a given species sometimes vary among members of a system. Analysis shows that CN traces dense clouds well whereas CH+ traces less dense clouds. CH may trace dense clouds (CN-like CH) or less dense clouds (CH+-like CH). The optical depth profiles for \ion{Ca}{1} and \ion{Ca}{2} show that the absorption from these species primarily arises from low density gas.

Analysis of the physical conditions helps us understand the cloud structure inferred from the absorption lines and corresponding optical depth profiles. We focus on the conditions for the observed velocity components. The component structure for a specific sight line seen in different species matches very well. Gas densities for individual components are derived with the aid of a chemical model, independent of assumptions about cloud shape. Among the three systems, two of them, \rho Oph and HD206267, exhibit siginificant density contrasts between adjacent lines of sight separated by distances of order 1,000 to 10,000 AU. While the component densities can differ by factors of 5 over such scales, the derived densities are always less than 5000 cm-3. Calculations show that the derived density contrasts are not sensitive to the temperature or reaction rates used in the chemical model.

The author(s) of this abstract have provided an email address for comments about the abstract: kpan@astro1.panet.utoledo.edu

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