A study of element depletions in interstellar gas.

Abstract

Optical and ultraviolet studies have shown that most elements in the gas phase of the interstellar medium are underabundant relative to the solar composition. The missing gas atoms are assumed to be contained in interstellar grains. The study of the depletion of interstellar elements in the gas phase provides, in this connection, a means for studying the composition of interstellar dust and possibly its formation/destruction mechanisms. The present investigation is concerned with ultraviolet observations of interstellar gas in the lines-of-sight toward seven stars. The high resolution ultraviolet spectra of the seven stars were obtained with the International Ultraviolet Explorer (IUE) satellite. The results of the investigation indicate that, at least for certain elements, the level of depletion depends on present densities in the interstellar medium. The implications of this conclusion are examined.