  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.
