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.