An XMM-Newton look at the Wolf-Rayet star WR 40 - The star itself, its nebula and its neighbours

We present the results of an XMM-Newton observation of the field of the Wolf-Rayet star WR 40. Despite a nominal exposure of 20 ks and the high sensitivity of the satellite, the star itself is not detected: we thus derive an upper limit on its X-ray flux and luminosity. Joining this result to recent reports of a non-detection of some WC stars, we suggest that the X-ray emission from single normal Wolf-Rayet stars could often be insignificant despite remarkable instabilities in the wind. On the basis of a simple modelling of the opacity of the Wolf-Rayet wind of WR 40, we show that any X-ray emission generated in the particular zone where the shocks are supposed to be numerous will indeed have little chance to emerge from the dense wind of the Wolf-Rayet star. We also report the non-detection of the ejecta nebula RCW 58 surrounding WR 40. Concerning the field around these objects, we detected 33 X-ray sources, most of them previously unknown: we establish a catalog of these sources and cross-correlate it with catalogs of optical/infrared sources.status: publishe

Long-term Spectroscopic Variability of Two Oe Stars

HD 45314 and HD 60848 are poorly studied Oe-type stars. Spectroscopic monitoring over 5 years reveals strong variations in the strength of the emission lines and for HD 45314 in the V/R ratio of the double-peaked emissions. Part of these long-term variations could be recurrent.status: publishe

CPD-41° 7742: an unusual wind interaction

We summarize the results of a multiwavelength observing campaign on the massive eclipsing binary CPD-41° 7742, another remarkable object in the young open cluster NGC 6231. Our campaign relies on high resolution echelle spectroscopy, narrow-band optical photometry, and XMM-Newton X-ray observations. Combined with the spectroscopic analysis, the light curve analysis provides a direct measurement of the masses and sizes of the system components. However, the most outstanding results come from the XMM observations. Our 180 ks campaign towards NGC 6231, and CPD-41° 7742, provides an unprecedented phase coverage of such a close early-type binary. The EPIC-MOS light curves almost fully cover the 2.4 day period of the system and the brightness of the object is sufficient to yield a time resolution as tight as 1 ks. The X-ray flux presents clear variations along the orbit, that we interpret as the signature of an unusual wind interaction. We indeed expect that, in this O+B system, the dominant primary wind crashes into the secondary surface, leading to a wind-photosphere interaction. As a strong support to our interpretation, we provide a geometrical model that associates an extra X-ray emission to the secondary inner surface. Though quite simple, the present model matches the main features of the X-ray light curve.status: publishe