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We present XMM-Newton observations of gamma^2 Velorum (WR 11, WC8+O7.5III, P= 78.53 d), a nearby Wolf-Ray binary system, at its X-ray high and low states.At high state, emission from a hot collisional plasma dominates from about 1 to8 keV. At low state, photons between 1 and 4 keV are absorbed. The hot plasmais identified with the shock zone between the winds of the primary Wolf-Rayetstar and the secondary O giant. The absorption at low state is interpreted asphotoelectric absorption in the Wolf-Rayet wind. This absorption allows us tomeasure the absorbing column density and to derive a mass loss rate 8x10^{-6}M_sun/yr for the WC8 star. This mass loss rate, in conjunction with a previousWolf-Rayet wind model, provides evidence for a clumped WR wind. A clumpingfactor of 16 is required. The X-ray spectra below 1 keV (12 Ang) show noabsorption and are essentially similar in both states. There is a rather clearseparation in that emission from a plasma hotter than 5 MK is heavily absorbedin low state while the cooler plasma is not. This cool plasma must come from amuch more extended region than the hot material. The Neon abundance in theX-ray emitting material is 2.5 times the solar value. The unexpected detectionof CV (25.3 Ang) and CVI (31.6 Ang) radiative recombination continua at bothphases indicates the presence of a cool (~40,000 K) recombination regionlocated far out in the binary system.Comment: 16 page

Wind clumping and the wind-wind collision zone in the Wolf-Rayet binaryγ2 Velorum

Wind clumping and the wind-wind collision zone in the Wolf-Rayet binaryγ² Velorum