We present extensive optical spectroscopy of the early-type magnetic star HD 191612 (O6.5f?pe-O8fp). The Balmer and He I lines show strongly variable emission which is highly reproducible on a well-determined 538-d period. He II absorptions and metal lines (including many selective emission lines but excluding He II λ4686 Å emission) are essentially constant in line strength, but are variable in velocity, establishing a double-lined binary orbit with P orb = 1542 d, e = 0.45. We conduct a model-atmosphere analysis of the spectrum, and find that the system is consistent with a ∼O8 giant with a ∼B1 main-sequence secondary. Since the periodic 538-d changes are unrelated to orbital motion, rotational modulation of a magnetically constrained plasma is strongly favoured as the most likely underlying 'clock'. An upper limit on the equatorial rotation is consistent with this hypothesis, but is too weak to provide a strong constraint.

We present a practical, efficient, semianalytic formalism for computing steady state X-ray emission from radiative shocks between colliding stellar winds in relatively close (orbital period up to order tens of days) massive-star, binary systems. Our simplified approach idealizes the individual wind flows as smooth and steady, ignoring the intrinsic instabilities and associated structure thought to occur in such flows. By also suppressing thin-shell instabilities for wind-collision radiative shocks, our steady state approach avoids the extensive structure and mixing that has thus far precluded reliable computation of X-ray emission spectra from timedependent hydrodynamical simulations of close-binary, wind-collision systems; but in ignoring the unknown physical level of such mixing, the luminosity and hardness of X-ray spectra derived here represent upper limits to what is possible for a given set of wind and binary parameters. A key feature of our approach is the separation of calculations for the small-scale shock-emission from the ram-pressure-balance model for determining the largescale, geometric form of the wind-wind interaction front. Integrating the localized shock emission over the full interaction surface and using a warm-absorber opacity to take account of attenuation by both the smooth wind and the compressed, cooled material in the interaction front, the method can predict spectra for a distant observer at any arbitrary orbital inclination and phase. We illustrate results for a sample selection of wind, stellar, and binary parameters, providing both full X-ray light curves and detailed spectra at selected orbital phases. The derived spectra typically have a broad characteristic form, and by synthetic processing with the standard XSPEC package, we demonstrate that they simply cannot be satisfactorily fitted with the usual attenuated single-or twotemperature thermal-emission models. We conclude with a summary of the advantages and limitations of our approach and outline its potential application for interpreting detailed X-ray observations from close, massivestar binary systems.

Aims. X-ray properties of the stellar population in the Carina OB1 association are examined with special emphasis on early-type stars. Their spectral characteristics provide some clues to understanding the nature of X-ray formation mechanisms in the winds of single and binary early-type stars. Methods. A timing and spectral analysis of five observations with XMM-Newton is performed using various statistical tests and thermal spectral models. Results. 235 point sources have been detected within the field of view. Several of these sources are probably pre-main sequence stars with characteristic short-term variability. Seven sources are possible background AGNs. Spectral analysis of twenty four sources of type OB and WR 25 was performed. We derived spectral parameters of the sources and their fluxes in three energy bands. Estimating the interstellar absorption for every source and the distance to the nebula, we derived X-ray luminosities of these stars and compared them to their bolometric luminosities. We discuss possible reasons for the fact that, on average, the observed X-ray properties of binary and single early type stars are not very different, and give several possible explanations.

Abstract.We report the analysis of the first high-resolution X-ray spectra of the Wolf-Rayet (WR) object WR 25 (HD 93162, WN6ha+O4f) obtained with the eflection rating pectrometers () and the uropean hoton maging ameras (- and )  spectrometers on board the XMM-Newton satellite. The spectrum exhibits bright emission lines of the H-and Helike ions of Ne, Mg, Si and S, as well as Fe  to Fe  and Fe  lines. Line fluxes have been measured. The  and  spectra have been simultaneously fitted to obtain self-consistent temperatures, emission measures, and elemental abundances. Strong absorption by the dense WR stellar wind and the interstellar medium (ISM) is observed equivalent to N H = 7×10 21 cm −2 . Multi-temperature () fitting yields two dominant components around temperatures of 7.0 and 32 MK, respectively. The XMM intrinsic (i.e. unabsorbed, corrected for the stellar wind absorption and the absorption of ISM) X-ray luminosity of WR 25 is L x (0.5-10 keV) = 1.3 × 10 34 erg s −1 , and L x (0.5-10 keV) = 0.85 × 10 34 erg s −1 , (when correcting for the ISM only) assuming d = 3.24 kpc. The obtained chemical abundances are subsolar, except for S. This may be real, but could equally well be due to a weak coupling to the continuum, which is strongly influenced by the absorption column density and the subtracted background. The expected high N-abundance, as observed in the optical wavelength region, could not be confirmed due to the strong wind absorption, blocking out its spectral signature. The presence of the Fe  emission-line complex at ∼ 6.7 keV is argued as being indicative for colliding winds inside a WR+O binary system.