Deuterium toward the White Dwarf Wd0621−376: Results from the Far Ultraviolet Spectroscopic Explorer (fuse) Mission

Far Ultraviolet Spectroscopic Explorer observations are presented for WD0621−376, a DA white dwarf star in the local interstellar medium (LISM) at a distance of about 78 pc. The data have a signal-tonoise ratio of ∼20–40 per 20 km s 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 > 0.23. We determine the ratio D/O = (3.9 ± 1.3 1.0) × 10 −2 (2σ). Assuming a standard interstellar oxygen abundance, we derive D/H ≈ 1.3× 10. Using the value of N(H I) derived from EUVE data gives a similar D/H ratio. The D I/N I ratio is (3.3± 1.0 0.8)× 10 −1 (2σ). Subject headings: ISM: abundances – ultraviolet: ISM – ISM: structure – white dwarfs – stars: individual: WD0621−376