High-Resolution Ultraviolet Observations of the Interstellar Diffuse Clouds toward MU Columbae

Abstract

Data obtained from the Goddard High Resolution spectrograph (GHRS) are used to study differences in gas-phase abundances of ions occurring in the diffuse neutral clouds toward mu Col. The sight-line characteristics determined in previous studies are reviewed and results for the cloud velocities, absorption equivalent widths, ion column densities, and depletions are presented. It is found that interstellar features from four distinct absorption regions with low-ionization gas are apparent in the GHRS data at heliocentric velocities of 23, 41, 53, and 62 km/s. Absorption by Mg II, Si II, and possibly Al II also occurs over the heliocentric velocity range from -17 to 0 km/s. The presence of stronger Si III absorption over this velocity region indicates that the absorption arises from an ionized gas region.