Spectrophotometric Results from the Copernicus Satellite. III. Ionization and Composition of the Intercloud Medium

Interstellar lines have been studied in the unreddened stars [E(B - V) 0.03] X Sco, v Sco, a Leo, and a Eri, which are located between 20 and 150 pc from the Sun. The lines are on the linear and saturated Doppler portions of the curve of growth. Preliminary analysis shows that processes producing large amounts of highly ionized species are not dominant. Doubly ionized C, N, Si, and S have been detected, but are all quite weak relative to the singly ionized species. Abundances relative to nitrogen are in the cosmic ratios or slightly lower, with some indication of general depletion of the heavier elements. Hydrogen number densities range from a measured value of 0.22 cm-3 for X Sco to a derived value of 0.02 cm-3 for a Leo assuming nitrogen to have its solar abundance relative to hydrogen. Subject headings:abundances - intersteflar matter - spectra, ultraviolet - spectrophotometry