Oxygen gas-phase abundance revisited

We present new measurements of the interstellar gas-phase oxygen abundance along the sight lines toward 19 early-type Galactic stars at an average distance of 2.6 kpc. We derive O I column densities from Hubble Space Telescope/Space Telescope Imaging Spectrograph (HST/STIS) observations of the weak 1355 Åintersystem transition. We derive total hydrogen column densities [N(H I) + 2N(H₂)] using HST/STIS observations of Lyα and Far Ultraviolet Spectroscopic Explorer (FUSE) observations of molecular hydrogen. The molecular hydrogen content of these sight lines ranges from f(H₂) = 2N(H₂[N(H I) + 2N(H₂)] = 0.03 to 0.47. The average 〈H_tot/E_B-V〉 of 6.3 × 10 ²¹ cm^-2 mag^-1 with a standard deviation of 15% is consistent with previous surveys. The mean oxygen abundance along these sight lines, which probe a wide range of Galactic environments in the distant interstellar medium, is 10⁶ (O/H)_gas= 408 ± 13 (1 σ in the mean). We see no evidence for decreasing gas-phase oxygen abundance with increasing molecular hydrogen fraction, and the relative constancy of (O/H)_gas suggests that the component of dust containing the oxygen is not readily destroyed. We estimate that, if 60% of the dust grains are resilient against destruction by shocks, the distant interstellar total oxygen abundance can be reconciliated with the solar value derived from the most recent measurements of 10⁶ (O/H)_gas⊙= 517 ± 58 (1 σ). We note that the smaller oxygen abundances derived for the interstellar gas within 500 pc or from nearby B star surveys are consistent with a local elemental deficit.