Physics
Scientific paper
Jul 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999hst..prop.8352f&link_type=abstract
HST Proposal ID #8352
Physics
Hst Proposal Id #8352 Interstellar And Intergalactic Matter
Scientific paper
We propose to determine the physical conditions in interstellar sight lines from archival GHRS spectra showing absorption from C I. The choice of sight lines is based on the fact that observed molecular abundances are relatively low. Analysis of the relative populations among fine structure levels in neutral carbon will yield estimates for gas density and temperature. We will incorporate published results on rotational excitation in H_2 to help constrain the gas temperature. The high quality data on C I, examined with our refined self-consistent set of oscillator strengths, will provide accurate estimates of gas density. We will use the results from C I excitation to further our studies in two areas. We will examine the extent of a separation into low and moderately dense neutral material within a single cloud toward stars in Scorpius and Ophiuchus and whether such stratification is a common feature of interstellar clouds and therefore must be included in studies of interstellar material on galactic scales. We will also obtain information on the amount of CH associated with CH^+ synthesis as an aid to understanding CH^+ formation in the low density portions of interstellar clouds, an unsolved problem despite nearly fifty years of study.
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