Phosphorus in the diffuse interstellar medium

¹ Institut d'Astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98 bis boulevard Arago, 75014 Paris, France
² AZimov association, 14 rue Roger Moutte, 83270 St-Cyr sur Mer, France e-mail: leboutei@iap.fr

Received: 17 May 2005
Accepted: 18 July 2005

Abstract

We present FUSE and HST/STIS measurements of the P ii column density toward Galactic stars. We analyzed P ii 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 P ii 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.