Oxygen Gas‐Phase Abundance Revisited

Abstract

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 Ainter- system transition. We derive total hydrogen column densities (NðH i Þþ 2NðH2Þ) using HST/STIS observa- tions of Lyand Far Ultraviolet Spectroscopic Explorer (FUSE) observations of molecular hydrogen. The molecular hydrogen content of these sight lines ranges from f ðH2 Þ¼ 2NðH2Þ=½NðH i Þþ 2NðH2Þ� ¼ 0:03 to 0.47. The average hHtot=EBV i 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)gas¼ 408 � 13 (1 � in the mean). We see no evi- dence for decreasing gas-phase oxygen abundance with increasing molecular hydrogen fraction, and the rela- tive 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� ¼ 517 � 58 (1 � ). 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. Subject headings: dust, extinction — ISM: abundances — ultraviolet: ISM