The abundance of interstellar chlorine in the galaxy.

Abstract

The results of a large-scale survey of chlorine abundance in interstellar H I gas are presented. The abundances are derived from measurements of 40 interstellar-absorption-line equivalent widths in far-ultraviolet stellar spectra from the Copernicus and International Ultraviolet Explorer (IUE) satellites. It is found that the relative chlorine abundance shows no noticeable trend with either distance from the galactic plane of the background star, or with its color excess. A marked decrease in abundance was found with respect to increasing mean-line-of-sight hydrogen space density accordinig to an approximate relation. For low space densities, the chlorine abundance appears to approach the tentative solar value of about 5.5. Possible explanations for the correlations with hydrogen space density are discussed. A clear linear relation is found between the ratio of Cl II to Cl I column densities and that of H I to H2 (over the range 1-500 in the latter ratio) supporting simple models of interstellar chlorine chemistry.