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 Å intersystem transition. We derive total hydrogen column densities [ N (H ) + 2 N (H 2 )] 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 (H 2 ) = 2 N (H 2 )/[ N (H ) + 2 N (H 2 )] = 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 10 6 (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 10 6 (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.