2003ApJ...587..235O

The interstellar abundances of D I, N I, and O I in the local ISM are studied using high-resolution spectra of four hot white dwarfs. The spectra of GD 246, WD 2331-475, HZ 21, and Lan 23 were obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) in the wavelength range 905-1187 Å. The line of sight to GD 246 probes the Local Interstellar Cloud and at least one other H I cloud inside the Local Bubble, which contains most of the gas seen along this line of sight. The column densities of H I, C II*, S II, and Si II are measured using archival Hubble Space Telescope STIS echelle-mode observations. The H I column density is determined by fitting the strong damping wings of interstellar Lyα and using a model atmosphere to account for the stellar continuum. The sight line-averaged ratios for GD 246 are DI/HI=1.51^+0.39_–0.33x10^–5, OI/HI=3.63^+0.77_–0.67x10^–4, and DI/OI=4.17^+1.20_–1.00x10^–2 (uncertainties are 2 σ). This line of sight provides the fourth reliable FUSE measurement of the Local Bubble D/H ratio. For the WD 2331-475 line of sight, we find sight line-averaged ratios DI/OI=5.13^+2.20_–1.69x10^–2 and DI/NI=4.57^+1.88_–1.45x10^–1. Toward HZ 21 the sight line-averaged ratios are DI/OI=4.57^+2.22_–1.63x10^–2 and DI/NI=4.27^+1.96_–1.44x10^–1. In the higher column density sight line to Lan 23, the sight line-averaged ratios are DI/OI=3.24^+3.27_–2.06x10^–2 and DI/NI=3.16^+1.56_–1.23x10^–1. Molecular hydrogen, corresponding to rotational levels J≤3, is clearly seen along this line of sight. No reliable H I measurements are available for WD 2331-475, HZ 21, or Lan 23. We combine the different abundance ratios computed here with previous published values to produce revised FUSE abundance ratios for D I/H I, O I/H I, N I/H I, D I/N I, D I/O I, and O I/N I.