Mariner 9 ultraviolet spectrometer experiment: interstellar absorption at Lyman alpha in OB stars

Column densities of neutral hydrogen NH toward 10 stars are derived from spectra obtained with the ultraviolet spectrometer (UVS) on the Mariner 9 Mars orbiter. The 7.5 A resolution is sufficient for a direct analysis of the data without assumptions about the strength of the lines that blend with the La profile at lower resolution. The deduced values of NH are systematically lower than those derived from OAO-2 data. Subject headings: abundances - early-type stars - interstellar matter - spectra, ultraviolet