Deuterium Abundance in the Local ISM and Possible Spatial Variations

Abstract

Excellent HST/GHRS spectra of interstellar hydrogen and deuterium Lyman-alpha absorption toward nearby stars allow us to identify systematic errors that have plagued earlier work and to measure accurate values of the D/H ratio in local interstellar gas. Analysis of 12 sightlines through the Local Interstellar Cloud leads to a mean value of D/H = (1.50 +/- 0.10) x 10-5 with all data points lying within +/- 1sigma of the mean. Whether or not the D/H ratio has different values elsewhere in the Galaxy and beyond is a very important open question that will be one of the major objectives of the Far Ultraviolet Spectroscopic Explorer (FUSE) mission.