O/H in the Local Bubble

We present new measurements of the oxygen gas-phase abundance along four sight lines probing gas inside the Local Bubble, using data obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) and the Hubble Space Telescope (HST). Combining these with seven previously published N(O I) and N(H I) measurements, we determine a mean O/H ratio for the Local Bubble, (O/H)LB = (3.45 ± 0.19) × 10-4 (1 σ in the mean). Our result is virtually identical to O/H = (3.43 ± 0.15) × 10-4 derived from data for sight lines probing gas well outside the Local Bubble. In contrast to the D/O and D/H ratios, which seem to have different values beyond the Local Bubble, our results show that the O/H ratio is constant and single valued both inside and outside the Local Bubble for low-density sight lines with column densities up to log N(H) ≃ 21. In addition, the similarity of the two values above suggests that the net effect of the uncertain O I f-values in the FUSE bandpass is not significant. Taking into account the latest determinations of the solar abundance of oxygen, our result implies that ~25% of the oxygen in the Local Bubble is depleted onto dust grains. The similarity of the value for O/H along low average density sight lines in the Local Bubble with that of denser sight lines beyond may permit a limit on the diluting effects of infalling low-metallicity gas.