Interstellar Abundances in Dense, Moderately Reddened Lines of Sight. I. Observational Evidence for Density-dependent Depletion

Abstract

The nature of dust-gas interactions, which are capable of modifying the size distribution of interstellar grains and thus causing changes in the selective extinction curve, are investigated through depletion studies. The gaseous abundances of 15 elements have been determined for several lines of sight toward moderately reddened stars, each having an anomalous extinction curve and a large abundance of cyanogen (CN). The basic result of this study is that certain elements appear to deplete preferentially in interstellar clouds having a large abundance of CN. The distinctly different signature of the element-to-element depletion pattern provides an important new diagnostic tool for determining the relative strengths of competing depletion processes in these denser clouds.