Atomic oxygen abundance toward Sagittarius B2

A substantial fraction of oxygen in diffuse clouds is unaccounted for by observations and postulated to be an unknown refractory form, referred as unidentified depleted (UDO), which, depending on the local gas density, may contribute up 50% total content. Previous Infrared Space Observatory (ISO) suggest that a significant even denser, translucent atomic form. We have analyzed velocity-resolved archival SOFIA 63 μm fine-structure [O I ] transition toward high-mass star-forming region Sgr B2(M) Central Molecular Zone. The foreground spiral-arm well extended B2 envelope between Sun background dust continuum source produce multiple absorption components, spectrally separated velocity space. gas-phase column density correlated with hydrogen average abundance (2.51 ± 0.69) × 10 −4 respect nuclei. This value good agreement earlier ISO measurements same line sight, about 35% lower than interstellar medium low-density warm gas, measured UV. find no evidence sight Sagittarius form UDO.