IUE Observations of Hydrogen and Deuterium in the Local Interstellar Medium

Abstract

The authors present and analyze high-dispersion IUE observations of the interstellar hydrogen and deuterium Lyα absorption profiles toward the late-type stars ɛ Eri (3.3 pc), Procyon (3.5 pc), Altair (5.1 pc), Capella (13.2 pc), and HR 1099 (33 pc). They derive values for the density n_{H I}, the velocity dispersion b_{H I}, the bulk velocity v_{H I} and determine lower limits on the deuterium-to-hydrogen ratio (n_{D I}/n_{H I}). The results are compared with previous Copernicus data. Interstellar deuterium is detected toward every star except Altair. In particular, the strong lower limit of D/H ≥ 1.9×10^-5 from Copernicus is confirmed for the Capella sightline. A value of D/H = 2.0×10^-5 is consistent with all observations of late-type stars.