Based on observations with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). Research Associate FNRS (Belgium). Postdoctoral Researcher FNRS (Belgium). [less ▲]Detailed reference viewed: 14 (5 ULg) Spectroscopic Study of the Variability of Three Northern Of+ SupergiantsDe Becker, Michaël ; Rauw, Grégor ; Linder, N.in Astrophysical Journal (2009), 704The transition from early Of stars to WN-type objects is poorly understood. O-type supergiants with emission lines (OIf+) are considered to be intermediate between these two classes. The scope of this ... [more ▼]The transition from early Of stars to WN-type objects is poorly understood. O-type supergiants with emission lines (OIf+) are considered to be intermediate between these two classes. The scope of this paper is to investigate the spectral variability of three Of+ supergiants. We constituted spectral time series of unprecedented quality for our targets (~200 spectra in total), essentially in the blue domain, covering timescales from a few hours up to a few years. Temporal Variance Spectrum and Fourier analyses were performed in order to characterize their spectral variability. We report on a correlated significant line profile variability in the prominent He II λ4686 and Hβ lines most likely related to the strong stellar winds. The variability pattern is similar for the three stars investigated (HD 14947, HD 15570, and HD 16691), and the main differences are more quantitative than qualitative. However, the reported timescales are somewhat different, and the most striking variability pattern is reported for HD 16691. We did not find any clear evidence for binarity, and we focus mainly on an interpretation based on a single-star scenario. We show that the behavior of the three stars investigated in this study present strong similarities, pointing to a putative common scenario, even though a few differences should be noted. Our preferred interpretation scheme is that of Large-Scale Corotating Structures modulating the profile of the lines that are produced in the strong stellar wind. [less ▲]Detailed reference viewed: 16 (5 ULg) Optical spectroscopy of X-Mega targets in the Carina nebula - VII. On the multiplicity of Tr16-112, HD93343 and HD93250Rauw, Grégor ; Nazé, Yaël ; Fernández Lajús, E. et alin Monthly Notices of the Royal Astronomical Society (2009), 398We present the results of a spectroscopic monitoring campaign devoted to three O-type stars in the Carina nebula. We derive the full SB2 orbital solution of the binary system Tr16-112, an exceptional ... [more ▼]We present the results of a spectroscopic monitoring campaign devoted to three O-type stars in the Carina nebula. We derive the full SB2 orbital solution of the binary system Tr16-112, an exceptional dissymmetrical system consisting of an O5.5-6V((f[SUP]+[/SUP]?p)) primary and a B2V-III secondary. We also report on low-amplitude brightness variations in Tr16-112 that are likely due to the ellipsoidal shape of the O5.5-6 primary revolving in an eccentric orbit around the system's centre of mass. We detect for the first time a clear SB2 binary signature in the spectrum of HD93343 (O8 + O8), although our data are not sufficient to establish an orbital solution. This system also displays low-amplitude photometric modulations. On the other hand, no indication of multiplicity is found in the optical spectra of HD93250. Finally, we discuss the general properties of multiple massive stars in the Carina OB1 association. Based on observations collected at the European Southern Observatory (La Silla, Chile), at Complejo Astronómico El Leoncito (Argentina), at the Cerro Tololo Inter-American Observatory (CTIO) and with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). E-mail: rauw@astro.ulg.ac.be â ¡ Research Associate FRS/FNRS (Belgium). § Postdoctoral Researcher FRS/FNRS (Belgium). ¶ Senior Research Associate FRS/FNRS (Belgium). [less ▲]Detailed reference viewed: 37 (10 ULg) Decoding of the light changes in eclipsing Wolf-Rayet binaries. I. A non-classical approach to the solution of light curvesPerrier, C.; Breysacher, J.; Rauw, Grégor in Astronomy and Astrophysics (2009), 503Aims. We present a technique to determine the orbital and physical parameters of eclipsing eccentric Wolf-Rayet + O-star binaries, where one eclipse is produced by the absorption of the O-star light by ... [more ▼]Aims. We present a technique to determine the orbital and physical parameters of eclipsing eccentric Wolf-Rayet + O-star binaries, where one eclipse is produced by the absorption of the O-star light by the stellar wind of the W-R star. Methods: Our method is based on the use of the empirical moments of the light curve that are integral transforms evaluated from the observed light curves. The optical depth along the line of sight and the limb darkening of the W-R star are modelled by simple mathematical functions, and we derive analytical expressions for the moments of the light curve as a function of the orbital parameters and the key parameters of the transparency and limb-darkening functions. These analytical expressions are then inverted in order to derive the values of the orbital inclination, the stellar radii, the fractional luminosities, and the parameters of the wind transparency and limb-darkening laws. Results: The method is applied to the SMC W-R eclipsing binary HD 5980, a remarkable object that underwent an LBV-like event in August 1994. The analysis refers to the pre-outburst observational data. A synthetic light curve based on the elements derived for the system allows a quality assessment of the results obtained. [less ▲]Detailed reference viewed: 14 (8 ULg) Early-type stars in the young open cluster NGC 2244 and in the Monoceros OB2 association. I. The multiplicity of O-type starsMahy, Laurent ; Nazé, Yaël ; Rauw, Grégor et alin Astronomy and Astrophysics (2009), 502Aims. We present the results obtained from a long-term spectroscopic campaign to study the multiplicity of O-type stars in both the young open cluster NGC 2244 and the Mon OB2 association. Methods: Our ... [more ▼]Aims. We present the results obtained from a long-term spectroscopic campaign to study the multiplicity of O-type stars in both the young open cluster NGC 2244 and the Mon OB2 association. Methods: Our spectroscopic monitoring was performed over several years, allowing us to investigate different timescales. For each star, several spectral diagnostic tools were applied to search for line shifts and profile variations. We also measured the projected rotational velocity and revisited the spectral classification. Results: Several stars in our sample have been previously considered to be spectroscopic binaries, although only a few scattered observations were available. Our results now have identified a more complex situation for two new spectroscopic binaries (HD 46 149 in NGC 2244 and HD 46 573 in Mon OB2). The first object is a long-period double-lined spectroscopic binary, although the exact value of its period remains uncertain and the second object is classified as an SB1 system with a period of about 10.67 days but the time series of our observations do not enable us to derive a unique orbital solution for this system. We also find another star to be variable in radial velocity (HD 46 150) and detect line profile variations in two rapid rotators (HD 46 056 and HD 46 485). Conclusions: This spectroscopic investigation places a firm lower limit (17%) on the binary fraction of O-stars in NGC 2244 and reveals the lack of short-period O+OB systems in this cluster. In addition, a comparison of these new results with two other well-studied clusters (NGC 6231 and IC 1805) puts forward possible hints of a relation between stellar density and binarity, which could provide constraints on the theories of the formation and early evolution of hot stars. Table 2 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/502/937 Based on observations collected at Observatoire de Haute-Provence (France), San Pedro Màrtir Observatory (Mexico), La Silla Observatory (European Southern Observatory), and Asiago Observatory (Italy). [less ▲]Detailed reference viewed: 47 (8 ULg) Spectroscopic and photometric variability of O and Wolf-Rayet starsGosset, Eric ; Rauw, Grégor in Communications in Asteroseismology (2009, July 01), 158Low-level line profile variability in the optical domain is a ubiquitous feature of O, Of and Wolf-Rayet type stars. This variability can arise from pulsations, from magnetic fields or wind structures ... [more ▼]Low-level line profile variability in the optical domain is a ubiquitous feature of O, Of and Wolf-Rayet type stars. This variability can arise from pulsations, from magnetic fields or wind structures (both small and large scales). For main-sequence O-type stars, the spectra display many absorption lines that provide stringent diagnostics of photospheric features. However, as the stars evolve off the main-sequence towards the Of and Wolf-Rayet stage, the stellar wind densities (and hence the wind optical depths) increase dramatically. The wind eventually dominates the formation of the entire spectrum rendering the investigation of photospheric structures more ambiguous. We discuss the observational analyses of the spectroscopic and photometric variability of massive stars of spectral type O, Of and WR. In particular, we highlight the search for a connection between the photospheric and the wind variability. [less ▲]Detailed reference viewed: 11 (3 ULg) Evidence for line-profile variability in the spectrum of the O supergiant HD 152249: preliminary resultsGosset, Eric ; Sana, H.; Linder, N. et alin Communications in Asteroseismology (2009, July 01), 158Already suspected to be variable, the O9Ib((f)) supergiant HD 152249 has been the subject of a dedicated follow-up spectroscopic run. We report here on the preliminary results. This star is definitely ... [more ▼]Already suspected to be variable, the O9Ib((f)) supergiant HD 152249 has been the subject of a dedicated follow-up spectroscopic run. We report here on the preliminary results. This star is definitely exhibiting significant line-profile variations which are most probably a sign of the existence of non-radial pulsations. HD 152249 could thus belong to the newly identified group of pulsating OB supergiants. [less ▲]Detailed reference viewed: 8 (3 ULg) Dust formation by the colliding wind WC5+O9 binary WR19 at periastron passageWilliams, P. M.; Rauw, Grégor ; van der Hucht, K. A.in Monthly Notices of the Royal Astronomical Society (2009), 395We present infrared photometry of the episodic dust-making Wolf-Rayet system WR19 (LS3), tracking its fading from a third observed dust formation episode in 2007 and strengthening the view that these ... [more ▼]We present infrared photometry of the episodic dust-making Wolf-Rayet system WR19 (LS3), tracking its fading from a third observed dust formation episode in 2007 and strengthening the view that these episodes are periodic (P = 10.1 +/- 0.1y). Radial velocities (RVs) of the O9 component observed between 2001 and 2008 show RV variations consistent with WR19 being a spectroscopic binary of high eccentricity (e = 0.8), having periastron passage in 2007.14, shortly before the phase of dust formation. In this respect, WR19 resembles the archetypical episodic dust-making colliding wind binary system WR140. Based on observations collected at the European Southern Observatory, La Silla, Chile, in allocations 67.D-0043, 70.D-0266, 72.D-0070, 73.D-0027, 74.D-0116, 76.D-0029, 78.D-0001, 79.D-0092 and 80.D-0198. E-mail: pmw@roe.ac.uk [less ▲]Detailed reference viewed: 54 (0 ULg) Non-thermal processes in colliding-wind massive binaries: the contribution of Simbol-X to a multiwavelength investigationDe Becker, Michaël ; Blomme, Ronny; Micela, Giusi et alin AIP Conference Proceedings (2009, May), 1126Several colliding-wind massive binaries are known to be non-thermal emitters in the radio domain. This constitutes strong evidence for the fact that an efficient particle acceleration process is at work ... [more ▼]Several colliding-wind massive binaries are known to be non-thermal emitters in the radio domain. This constitutes strong evidence for the fact that an efficient particle acceleration process is at work in these objects. The acceleration mechanism is most probably the Diffusive Shock Acceleration (DSA) process in the presence of strong hydrodynamic shocks due to the colliding-winds. In order to investigate the physics of this particle acceleration, we initiated a multiwavelength campaign covering a large part of the electromagnetic spectrum. In this context, the detailed study of the hard X-ray emission from these sources in the SIMBOL-X bandpass constitutes a crucial element in order to probe this still poorly known topic of astrophysics. It should be noted that colliding-wind massive binaries should be considered as very valuable targets for the investigation of particle acceleration in a similar way as supernova remnants, but in a different region of the parameter space. [less ▲]Detailed reference viewed: 39 (8 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 strange case of the Of?p starsNazé, Yaël ; Walborn, N. R.; Martins, F. et alPoster (2009)Detailed reference viewed: 5 (2 ULg) Hot stars survey with the GAIA space missionLobel, A.; Liu, C.; Frémat, Y. et alPoster (2009)Detailed reference viewed: 18 (8 ULg) The multiwavelength picture of star formation in the very young open cluster NGC6383Rauw, Grégor ; De Becker, Michaël in Reipurth, Bo (Ed.) Handbook of Star Forming Region. Volume 2: The Southern Sky (2008)We review the properties of the very young (˜ 2 Myr) open cluster NGC 6383. The cluster is dominated by the massive binary HD 159176 (O7 V + O7 V). The distance to NGC 6383 is consistently found to be 1.3 ... [more ▼]We review the properties of the very young (˜ 2 Myr) open cluster NGC 6383. The cluster is dominated by the massive binary HD 159176 (O7 V + O7 V). The distance to NGC 6383 is consistently found to be 1.3 ± 0.1 kpc and the average reddening is determined to be E(bv) = 0.32 ± 0.02. Several pre-main sequence candidates have been identified using different criteria relying on the detection of emission lines, infrared excesses, photometric variability and X-ray emission. [less ▲]Detailed reference viewed: 12 (1 ULg) The first orbital solution for the massive colliding-wind binary HD 93162 (=WR 25)Gamen, R.; Gosset, Eric ; Morrell, N. I. et alin Revista Mexicana de Astronomia y Astrofisica Conference Series (2008, August 01)Since the discovery, with EINSTEIN, of strong X-ray emission associated with HD 93162, this object was recurrently predicted by some authors to be a colliding-wind binary system. However, radial-velocity ... [more ▼]Since the discovery, with EINSTEIN, of strong X-ray emission associated with HD 93162, this object was recurrently predicted by some authors to be a colliding-wind binary system. However, radial-velocity variations that would prove the suspected binary nature have never been found so far. We spectroscopically monitored this object in order to investigate its possible variability and to provide an answer to the above-mentioned discordance. We derived radial velocities from spectroscopic data acquired mainly between 1994 and 2006, and searched for periodicities. For the first time, periodic radial-velocity variations are detected. Our analysis definitively shows that the Wolf-Rayet star WR 25 is actually an eccentric binary system with a probable period of about 208 days. [less ▲]Detailed reference viewed: 10 (0 ULg) Colliding Wind Signatures in Early-Type BinariesRauw, Grégor in Revista Mexicana de Astronomia y Astrofisica Conference Series (2008, August 01)Observations of early-type binaries not only allow us to establish the fundamental properties of massive stars in a model-independent fashion, but furthermore provide important information on the ... [more ▼]Observations of early-type binaries not only allow us to establish the fundamental properties of massive stars in a model-independent fashion, but furthermore provide important information on the interactions of their stellar winds. The signatures of wind-wind interactions have been found over a broad range of wavelengths and energies, from the radio domain to X-rays and possibly gamma-rays. In this review, I discuss some results of the study of wind interactions in Wolf-Rayet and O-star binaries. [less ▲]Detailed reference viewed: 10 (2 ULg) Evidence for short-term variations in two O-type starsDe Becker, Michaël ; Linder, Natacha ; Rauw, Grégor in Information Bulletin on Variable Stars (2008), 5841Only a few O-type stars are known to display short-term (a fraction of a day) variations. Intense spectroscopic monitoring of the ON8V star HD 13268 revealed low amplitude variations with periods of ... [more ▼]Only a few O-type stars are known to display short-term (a fraction of a day) variations. Intense spectroscopic monitoring of the ON8V star HD 13268 revealed low amplitude variations with periods of several hours. In addition, observations of the SB1 system HD 15137 revealed variations on a time scale of a few hours. We consider these stars to be a good candidates for non radial pulsations, even though variations related to inhomogeneities in a circumstellar disk can not be rejected. [less ▲]Detailed reference viewed: 25 (4 ULg)