Changes in interstellar atomic abundances from the galactic plane to the halo

A few, specially selected interstellar absorption lines were measured in the high resolution, far ultraviolet spectra of 200 O and B type stars observed by the International Ultraviolet Explorer (IUE). For lines of sight extending beyond about 500 pc from the galactic plane, the abundance of singly ionized iron atoms increases relative to singly ionized sulfur. However, the relative abundances of singly ionized sulfur, silicon and aluminum do not seem to change appreciably. An explanation for the apparent increase of iron is the partial sputtering of material off the surfaces of dust grains by interstellar shocks. Another possibility might be that the ejecta from type I supernovae enrich the low density medium in the halo with iron

Interpreting the convergence of Lyman series absorption lines

Spectra of quasars at high z often show absorption at the Lyman limit from intervening gas systems at intermediate z having N(H) approx. greater than 10(exp 7) cm(-2). In some circumstances, N(H) can be determined by measuring the strength of the Lyman limit absorption or the damping wings of Lyman - alpha. With a spectrum taken at low wavelength resolution, say, lambda/delta lambda approx. 10(exp 3), it is usually not possible to distinguish individual Lyman series lines near the limit, yet one can still discern how rapidly the average intensity drops off as the limit is approached from the long wavelength side. The purpose here is to point out the information which is available from measurements of this series convergence

Observations of interstellar lines using the IUE satellite, covering the years 1978 - 1988

The study of absorption lines produced by dispersed gases in front of various sources in the sky were addressed. Data was used from the IUE satellite. The results of the projects are summarized