Deuterium Abundance toward WD 0621–376: Results from the FUSE Mission

Far Ultraviolet Spectroscopic Explorer observations are presented for WD 0621-376, a DA white dwarf star in the local interstellar medium (LISM) at a distance of about 78 pc. The data have a signal-to-noise ratio of ∼20-40 per 20 km s-1 resolution element and cover the wavelength range 905-1187 Å. LISM absorption is detected in the lines of D I, C II, C II*, C III, N I, N II, N III, O I, Ar I, and Fe II. This sight line is partially ionized, with an ionized nitrogen fraction of greater than 0.23. We determine the ratio D/O = × 10-2 (2 σ). Assuming a standard interstellar oxygen abundance, we derive D/H ≈ 1.3 × 10-5. Using the value of N(H I) derived from Extreme Ultraviolet Explorer data gives a similar D/H ratio. The D I/N I ratio is × 10-1 (2 σ).