The Deuterium, Oxygen, and Nitrogen Abundance toward LSE 44

Abstract

We present measurements of the column densities of interstellar D I, O I, N I, and H₂ made with the Far Ultraviolet Spectroscopic Explorer (FUSE) and of H I made with the International Ultraviolet Explorer (IUE) toward the sdO star LSE 44 [(l, b)=(313.37d, +13.49d) d=554+/-66 pc; z=+129+/-15 pc]. This target is among the seven most distant Galactic sight lines for which these abundance ratios have been measured. The H I column density was estimated by fitting the damping wings of interstellar Lyα. The column densities of the remaining species were determined with profile fitting analyses and supplemented with curve-of-growth analyses for O I and H₂. We find logN(D I)=15.87+/-0.08, logN(O I)=17.57^+0.21_-0.15, logN(N I)=16.43+/-0.14, and logN(H I)=20.52^+0.20_-0.36 (all errors 2 σ). This implies that D/H=(2.24^+1.39_-1.32)×10^-5, D/O=(1.99^+1.30_-0.67)×10^-2, D/N=(2.75^+1.19_-0.89)×10^-1, and O/H=(1.13^+0.96_-0.71)×10^-3. Of the most distant Galactic sight lines for which the deuterium abundance has been measured, LSE 44 is one of the few with D/H higher than the Local Bubble value, but D/O toward all these targets is below the Local Bubble value and more uniform than the D/H distribution.