AAS Meeting #193 - Austin, Texas, January 1999
Session 65. Interstellar Dust and Gas
Display, Friday, January 8, 1999, 9:20am-6:30pm, Exhibit Hall 1

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[65.04] Neutral Carbon in Diffuse Clouds with Low Molecular Abundances

J. Zsarg\'{o}, S.R. Federman (U. Toledo), D.E. Welty (U. Chicago)

High quality archival spectra of interstellar absorption from C~{\small I} toward 9 stars, taken with the Goddard High Resolution Spectrograph on HST, were analyzed. The relative populations among the fine structure levels in the ground state of C~{\small I} were used to extract the thermal pressure for the clouds along these lines of sight. In the course of the analysis, oscillator strengths of C~{\small I} lines with wavelength below 1200 Å~were refined.

Profile synthesis of several multiplets yielded column densities and Doppler parameters for 7 of the 9 lines of sight. Very accurate values were deduced when high resolution spectra could be utilized, but the Doppler parameters were not well characterized when only medium resolution spectra were available. Oscillator strengths for lines below 1200 Å~toward \delta~Sco and \lambda~Ori were adjusted so that self-consistent results could be obtained. Equilibrium excitation analysis of the C~{\small I} fine structure levels, using the measured column densities as well as the temperature from H2 excitation, yielded values for density. These densities, in conjunction with measurements of CH, CH+ and CN column densities, provided estimates for the amount of CH associated with CH+ synthesis, which in turn set up constraints on the present theories for CH+ production in this environment.

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

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