Phosphorus in the diffuse interstellar medium

Abstract

We present FUSE and HST/STIS measurements of the PII column density toward Galactic stars. We analyzed Pli through the profile fitting of the unsaturated λ1125 and λ1533 lines and derived column densities integrated along the sightlines as well as in individual resolved components. We find that phosphorus is not depleted along those sightlines sampling the diffuse neutral gas. We also investigate the correlation existing between PII and O I column densities and find that there is no differential depletion between these two specie. Furthermore, the ratio N(P II)/N(O I) is consistent with the solar P/O value, implying that P II and O I coexist in the same gaseous phase and are likely to evolve in parallel. We argue that phosphorus, as traced by P II, is an excellent neutral oxygen tracer in various physical environments, except when ionization corrections are a significant issue. Thus, P II lines (observable with FUSE, HST/STIS, or with VLT/UVES for the QSO sightlines) are particularly useful as a proxy for O I lines when these are saturated or blended. © ESO 2005.