A detailed X-ray investigation of ζ Puppis

III. Spectral analysis of the whole RGS spectrum^⋆

Groupe d’Astrophysique des Hautes Énergies, Institut d’Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août, Bât. B5c, 4000 Liège, Belgium
e-mail: herve@astro.ulg.ac.be

Received: 1 June 2012
Accepted: 16 January 2013

Abstract

Context. ζ Pup is the X-ray brightest O-type star of the sky. This object was regularly observed with the RGS instrument onboard XMM-Newton for calibration purposes, which led to an unprecedented set of high-quality spectra.

Aims. We have previously reduced and extracted this data set and integrated it into the most detailed high-resolution X-ray spectrum of any early-type star so far. Here we present the analysis of this spectrum, taking into account for the presence of structures in the stellar wind.

Methods. For this purpose, we used our new modeling tool that allows fitting the entire spectrum with a multi-temperature plasma. We illustrate the impact of a proper treatment of the radial dependence of the X-ray opacity of the cool wind on the best-fit radial distribution of the temperature of the X-ray plasma.

Results. The best-fit of the RGS spectrum of ζ Pup is obtained assuming no porosity. Four plasma components at temperatures between 0.10 and 0.69 keV are needed to adequately represent the observed spectrum. Whilst the hardest emission is concentrated between ~3 and 4 R_∗, the softer emission starts already at 1.5 R_∗ and extends to the outer regions of the wind.

Conclusions. The inferred radial distribution of the plasma temperatures agrees rather well with theoretical expectations. The mass-loss rate and CNO abundances corresponding to our best-fit model also agree quite well with the results of recent studies of ζ Pup in the UV and optical domain.