Interstellar gas abundances from rocket observations of ultraviolet absorption lines

Absorption lines from the ground states of 0 I, C II, and Si II were observed in the ultraviolet spectra of 8, T, A, `c, and v Sco, Oph, and Per, which were photographed on three Aerobee sounding rocket flights. While the oxygen and silicon absorptions are purely interstellar, some of the C II absorption arises from the star's atmosphere and some presumably from gas in the H ii region near the star. In the analysis of the lines the absorption by C ii in the H I regions was isolated from the other two sources. Curves of growth for the ultraviolet lines were derived from visual absorption-line profiles, when available. Absorptions by C I were marginally registered in some spectra, and N I was observed toward 8 Sco. When compared with H I column densities from the La absorptions, the amounts of 0 I and Si ii are consistent with the cosmic abundance ratios. C ii, on the other hand, appears for various stars to be from 3 to 10 times overabundant, although in some cases the errors are large. If much of the interstellar hydrogen is ionized or in the form of H2, the observed amount of carbon would be easier to reconcile with the cosmic composition. In principle, overestimates of the element abundances could result if a very small percentage of the gas has an extraordinarily large velocity dispersion and anomalously broadens these highly saturated absorption lines. Subject headings: abundances - interstellar matter - spectra, ultraviolet