Conclusions: These results corroborate our earlier statement that evolved objects in binary stars create a Keplerian dusty circumbinary disc. With the measured orbits and mass functions, we conclude that the circumbinary discs seem to have a major impact on the evolution of a significant fraction of binary systems. based on observations collected with the Flemish 1.2 m Mercator telescope at Roque de los Muchachos (Spain), the Swiss 1.2 m Euler telescope at La Silla (Chile) and the 0.5 m and 0.75 m telescopes at SAAO (South-Africa). Tables [see full textsee full text]-[see full textsee full text] are only available in electronic form at http://www.aanda.org Postdoctoral fellow of the Fund for Scientific Research, Flanders. Ph.D. student of the Fund for Scientific Research, Flanders. [less ▲]Detailed reference viewed: 11 (0 ULg) A multiwavelength investigation of the massive eclipsing binary Cyg OB2 #5Linder, Natacha ; Rauw, Grégor ; Manfroid, Jean et alin Astronomy and Astrophysics (2009), 495Context. The properties of the early-type binary Cyg OB2 #5 have been debated for many years and spectroscopic and photometric investigations yielded conflicting results. Aims. We have attempted to ... [more ▼]Context. The properties of the early-type binary Cyg OB2 #5 have been debated for many years and spectroscopic and photometric investigations yielded conflicting results. Aims. We have attempted to constrain the physical properties of the binary by collecting new optical and X-ray observations. Methods. The optical light curves obtained with narrow-band continuum and line-bearing filters are analysed and compared. Optical spectra are used to map the location of the He II $\lambda$ 4686 and H$\alpha$ line-emission regions in velocity space. New XMM-Newton as well as archive X-ray spectra are analysed to search for variability and constrain the properties of the hot plasma in this system. Results. We find that the orbital period of the system slowly changes though we are unable to discriminate between several possible explanations of this trend. The best fit solution of the continuum light curve reveals a contact configuration with the secondary star being significantly brighter and hotter on its leading side facing the primary. The mean temperature of the secondary star turns out to be only slightly lower than that of the primary, whilst the bolometric luminosity ratio is found to be 3.1. The solution of the light curve yields a distance of $925 \pm 25$ pc much lower than the usually assumed distance of the Cyg OB2 association. Whilst we confirm the existence of episodes of higher X-ray fluxes, the data reveal no phase-locked modulation with the 6.6 day period of the eclipsing binary nor any clear relation between the X-ray flux and the 6.7 yr radio cycle. Conclusions. The bright region of the secondary star is probably heated by energy transfer in a common envelope in this contact binary system as well as by the collision with the primary's wind. The existence of a common photosphere probably also explains the odd mass-luminosity relation of the stars in this system. Most of the X-ray, non-thermal radio, and possibly $\gamma$-ray emission of Cyg OB2 #5 is likely to arise from the interaction of the combined wind of the eclipsing binary with at least one additional star of this multiple system. [less ▲]Detailed reference viewed: 54 (10 ULg) The atypical emission-line star Hen 3-209Nazé, Yaël ; Rauw, Grégor ; Hutsemekers, Damien et alin Monthly Notices of the Royal Astronomical Society (2006), 371(4), 1594-1600We analyse observations, spanning 15 yr, dedicated to the extreme emission-line object Hen 3-209. Our photometric data indicate that the luminosity of the star undergoes marked variations with a peak-to ... [more ▼]We analyse observations, spanning 15 yr, dedicated to the extreme emission-line object Hen 3-209. Our photometric data indicate that the luminosity of the star undergoes marked variations with a peak-to-peak amplitude of 0.65 mag. These variations are recurrent, with a period of 16.093 +/- 0.005 d. The spectrum of Hen 3-209 is peculiar with many different lines (H I, He I, Fe II,. showing P Cygni profiles. The line profiles are apparently changing in harmony with the photometry. The spectrum also contains [O III] lines that display a saddle profile topped by three peaks, with a maximum separation of about 600 km s(-1). Hen 3-209 is most likely an evolved luminous object suffering from mass ejection events and maybe belonging to a binary system. [less ▲]Detailed reference viewed: 23 (2 ULg) CPD-41° 7742: an unusual wind interactionSana, H.; Gosset, Eric ; Rauw, Grégor et alin Massive Stars and High-Energy Emission in OB Associations (2005, November 01)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 ... [more ▼]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. [less ▲]Detailed reference viewed: 14 (0 ULg) The massive binary CPD-41 degrees 7742 - II. Optical light curve and X-ray observationsSana, H.; Antokhina, E.; Royer, P. et alin Astronomy and Astrophysics (2005), 441(1), 213-229In the first paper of this series, we presented a detailed high-resolution spectroscopic study of CPD - 41 degrees 7742, deriving for the first time an orbital solution for both components of the system ... [more ▼]In the first paper of this series, we presented a detailed high-resolution spectroscopic study of CPD - 41 degrees 7742, deriving for the first time an orbital solution for both components of the system. In this second paper, we focus on the analysis of the optical light curve and on recent XMM-Newton X-ray observations. In the optical, the system presents two eclipses, yielding an inclination i similar to 77 degrees. Combining the constraints from the photometry with the results of our previous work, we derive the absolute parameters of the system. We confirm that the two components of CPD- 41 degrees 7742 are main sequence stars (O9 V+ B1 - 1.5 V) with masses (M-1 similar to 18 M-. and M-2 similar to 10 M-.) and respective radii (R-1 similar to 7.5 R-. and R-2 similar to 5.4 R-.) close to the typical values expected for such stars. We also report an unprecedented set of X-ray observations that almost uniformly cover the 2.44-day orbital cycle. The X-ray emission from CPD-41 degrees 7742 is well described by a two-temperature thermal plasma model with energies close to 0.6 and 1.0 keV, thus slightly harder than typical early-type emission. The X-ray light curve shows clear signs of variability. The emission level is higher when the primary is in front of the secondary. During the high emission state, the system shows a drop of its X-ray emission that almost exactly matches the optical eclipse. We interpret the main features of the X-ray light curve as the signature of a wind-photosphere interaction, in which the overwhelming primary O9 star wind crashes into the secondary surface. Alternatively the light curve could result from a wind-wind interaction zone located near the secondary star surface. As a support to our interpretation, we provide a phenomenological geometric model that qualitatively reproduces the observed modulations of the X-ray emission. [less ▲]Detailed reference viewed: 18 (0 ULg) A first detailed study of the colliding wind WR+O binary WR 30aGosset, Eric ; Royer, P.; Rauw, Grégor et alin Monthly Notices of the Royal Astronomical Society (2001), 327We present a detailed, extensive investigation of the photometric and spectroscopic behaviour of WR 30a. This star is definitely a binary system with a period around 4.6d. We propose the value P=4.619d ... [more ▼]We present a detailed, extensive investigation of the photometric and spectroscopic behaviour of WR 30a. This star is definitely a binary system with a period around 4.6d. We propose the value P=4.619d (sigma=0.002d). The identification of the components as WO4+O5((f)) indicates a massive evolved binary system; the O5 component is a main-sequence or, more likely, a giant star. The radial velocities of the O star yield a circular orbit with an amplitude K[SUB]O[/SUB]=29.9 (sigma=2.1)kms[SUP]-1[/SUP] and a mass function of 0.013 (sigma=0.003)M[SUB]solar[/SUB]. The spectrum of WR 30a exhibits strong profile variations of the broad emission lines that are phase-locked with the orbital period. We report the detection of the orbital motion of the WO component with K[SUB]WO[/SUB]=189kms[SUP]-1[/SUP], but this should be confirmed by further observations. If correct, it implies a mass ratio M[SUB]WO[/SUB] /M[SUB]O[/SUB]=0.16. The star exhibits sinusoidal light variations of amplitude 0.024mag peak-to-peak with the minimum of light occurring slightly after the conjunction with the O star in front. On the basis of the phase-locked profile variations of the Civ lambda4658 blend in the spectrum of the WO, we conclude that a wind-wind collision phenomenon is present in the system. We discuss some possibilities for the geometry of the interaction region. [less ▲]Detailed reference viewed: 14 (6 ULg) The WR content of IC10 - first detection of WC9 stars in a low metallicity environment?Royer, P.; Smartt, S. J.; Manfroid, Jean et alin Astronomy and Astrophysics (2001), 366We present deep, narrow-band photometry of the Local Group starburst galaxy IC 10. Our dedicated photometric system provides detection of 13 new Wolf-Rayet (WR) stars and allows spectral subtypes to be ... [more ▼]We present deep, narrow-band photometry of the Local Group starburst galaxy IC 10. Our dedicated photometric system provides detection of 13 new Wolf-Rayet (WR) stars and allows spectral subtypes to be assigned. Three of these new stars appear to be WC9 subtypes. If confirmed, these would be the very first WC9 stars ever detected in a low metallicity environment, hence putting strong new constraints on the formation and evolution models of massive stars. Eight of the new WR stars are of the WC subtype, which does not significantly modify the anomalously high WC/WN ratio in IC 10. However it is likely that a number of Wolf-Rayet stars of the WNE and WC spectral subtypes are still to be discovered in the heart of the galaxy. Based on observations at the William Herschel Telescope on La Palma and at the Observatoire de Haute-Provence. [less ▲]Detailed reference viewed: 3 (0 ULg) Correction of Systematic Errors in Differential PhotometryManfroid, Jean ; Royer, P.; Rauw, Grégor et alin Astronomical Data Analysis Software and Systems X (2001)A common cause of errors in CCD differential photometry is an improper calibration of the array. The importance of these errors is evaluated for different cameras with fields between 3 and 30 arcminutes ... [more ▼]A common cause of errors in CCD differential photometry is an improper calibration of the array. The importance of these errors is evaluated for different cameras with fields between 3 and 30 arcminutes. The usual superflat illumination corrections based on night sky exposures are often found to be unsatisfactory. Photometric superflats'' based on stellar measurements are more reliable and should be used instead. [less ▲]Detailed reference viewed: 15 (1 ULg) QSO colors in the proposed GAIA photometric systemsClaeskens, Jean-François ; Royer, P.; Surdej, Jean in Proceedings of the GAIA Workshop (2001)Detailed reference viewed: 14 (6 ULg) Simulations of observations with the Optical Monitor of the X-ray Multi-Mirror SatelliteRoyer, P.; Manfroid, Jean ; Gosset, Eric et alin Astronomy and Astrophysics. Supplement Series (2000), 145This paper addresses the question of the observations to be performed with the Optical Monitor (OM) of the X-ray Multi-Mirror Satellite (XMM) under several aspects. First, we discuss XMM-OM's photometric ... [more ▼]This paper addresses the question of the observations to be performed with the Optical Monitor (OM) of the X-ray Multi-Mirror Satellite (XMM) under several aspects. First, we discuss XMM-OM's photometric system and its colour transformations towards the standard U BV system. Second, we establish a set of procedures to determine the temperature and the amount of interstellar absorption affecting the observed stars. Last, we address the possibility of isolating quasars in multidimensional colour diagrams based on the XMM-OM filter set. [less ▲]Detailed reference viewed: 7 (0 ULg) 1 2