Abundances of Deuterium, Nitrogen, and Oxygen toward HZ 43A: Results from the FUSE Mission

We present an analysis of interstellar absorption along the line of sight to the nearby white dwarf star HZ 43A. The distance to this star is 68 ± 13 pc, and the line of sight extends toward the north Galactic pole. Column densities of O I, N I, and N II were derived from spectra obtained by the Far Ultraviolet Spectroscopic Explorer (FUSE), the column density of D I was derived from a combination of our FUSE spectra and an archival Hubble Space Telescope (HST) GHRS spectrum, and the column density of H I was derived from a combination of the GHRS spectrum and values derived from Extreme Ultraviolet Explorer (EUVE) data obtained from the literature. We find the following abundance ratios (with 2 σ uncertainties): D /H = (1.66 ± 0.28) × 10-5, O /H = (3.63 ± 0.84) × 10-4, and N /H = (3.80 ± 0.74) × 10-5. The N II column density was slightly greater than that of N I, indicating that ionization corrections are important when deriving nitrogen abundances. Other interstellar species detected along the line of sight were C II, C III, O VI, Si II, Ar I, Mg II, and Fe II; an upper limit was determined for N III. No elements other than H I were detected in the stellar photosphere.