A detailed X-ray investigation of {\zeta} Puppis III. A spectral analysis of the whole RGS spectrum

TL;DR

This study presents a detailed spectral analysis of Zeta Puppis using high-resolution X-ray data, revealing the plasma temperature distribution and wind structure, and confirming theoretical models and previous findings on mass-loss and elemental abundances.

Contribution

We developed a new modeling approach to fit the entire high-resolution X-ray spectrum of Zeta Puppis, accounting for wind structures and radial X-ray opacity variations.

Findings

Four plasma components are needed to fit the spectrum.

Hard X-ray emission is concentrated between 3 and 4 R*.

The plasma temperature distribution matches theoretical predictions.

Abstract

Context. Zeta Pup is the X-ray brightest O-type star of the sky. This object was regularly observed with the RGS instrument aboard XMM-Newton for calibration purposes, leading to an unprecedented set of high-quality spectra. Aims. We have previously reduced and extracted this data set and combined 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 accounting for the presence of structures in the stellar wind. Methods. For this purpose, we use 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 Zeta 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 Zeta Pup in the UV and optical domain.