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Over the last decade, large-scale, organized (generally dipolar) magnetic fields with a strength between 0.1 and 20 kG were detected in dozens of OB stars. This contribution reviews the impact of such magnetic fields on the stellar winds of O-stars, with emphasis on variability and X-ray emission., Invited review at "Putting A-stars into context" (June 2013 ; Moscow, Russia), proceedings of 10 pages

In the framework of our multiwavelength study of the open cluster NGC6231, we observed the colliding-wind WR+O binary WR79 at six different epochs with the XMM-Newton observatory. These pointings offer the possibility to study the X-ray spectrum of WR79 and its possible variability. Our results are briefly discussed and compared with the X-ray characteristics of other similar objects.

The investigation of the multiplicity of massive stars is crucial to determine a robust binary fraction but also for understanding the physical properties of these objects. In this contribution, we will present the main results from our long-term spectroscopic survey devoted to the young open cluster NGC 2244. We discuss the spectral classification, the projected rotational velocity (v sin{i}) and the multiplicity of O-stars. The stellar and wind parameters of each star, obtained using the CMFGEN atmosphere code, help us to better constrain the individual properties of these objects. Several of these stars were observed by the CoRoT satellite (SRa02) in the Asteroseismology channel. This intensive monitoring and the unprecedented quality of the light curves allow us to shed a new light on these objects.

In a recent paper, Vink et al. analyzed some spectropolarimetry data of O-type stars. Here we comment on our disagreement with some points presented in this paper, with the hope of helping to fully grasp the scientific implication of these measurements., Comment: 3 pages

International audience

The scientific method is often presented, e.g. to children, as a linear process, starting by a question and ending by the elaboration of a theory, with a few experiments in-between. The reality of the building of science is much more complex, with back-and-forth motions between theories and observations, with some intervention of technology and randomness. This complex process is not always correctly understood and assimilated, even amongst scientists. The hero cult, mixed with some revisionism, still exists despite in-depth historical studies. In this context, it may be useful to comparatively examine the reaction to crucial observations, their interpretation and their impact on the contemporaneous theory development. Four examples are presented here, all linked to the question of the 'construction of the heavens' but at different epochs., invited contribution, in French, published in Azimuth, vol II, nr. 4, p15-39 (2014), special issue "ratio mundi: possible cosmologies between narrative and logic"

Although rare, massive stars, being the main sources of ionizing radiation, chemical enrichment and mechanical energy in the Galaxy, are the most important objects of the stellar population. This review presents the many different aspects of the main tool used to study these stars, i.e. spectroscopy. The first part consists in an introduction on these objects and their physical properties (mass, wind, evolution, relation with their environment). Next, the spectral behaviour of single massive stars is investigated, in the visible as well as in the X-ray domain. Finally, the last part of this paper deals with massive binaries, especially those exhibiting a colliding wind phenomenon., review published by the Liege Royal Societey of Sciences, 31 pages - figures provided in jpg, a complete version (including figures) is available on http://www.chimiefs.ulg.ac.be/SRSL/newSRSL/modules/FCKeditor/upload/File/75_2006/Naze-V75-2006-p20-61.pdf On Dec. 6, a typo was corrected

We present the results of optical wavelength observations of the unusual SMC eclipsing binary system HD 5980 obtained in 1999 and 2004--2005. Radial velocity curves for the erupting LBV/WR object (star A) and its close WR-like companion (star B) are obtained by deblending the variable emission-line profiles of N IV and N V lines under the simplistic assumption that these lines originate primarily in the winds of star A and star B. The derived masses M_A=58--79 Mo and M_B=51--67 Mo, are more consistent with the stars' location near the top of the HRD than previous estimates. The presence of a wind-wind interaction region is inferred from the orbital phase-dependent behavior of He I P Cygni absorption components. The emission-line intensities continued with the declining trend previously seen in UV spectra. The behavior of the photospheric absorption lines is consistent with the results of Schweickhardt (2002) who concludes that the third object in the combined spectrum, star C, is also a binary system with P(starC)~96.5 days, e=0.83. The data used in this paper will be made publicly available for further analysis., Comment: 48 pages, 26 figures