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See detailGeneral X-ray properties of hot, massive stars
Nazé, Yaël ULg

in Bulletin de la Societe Royale des Sciences de Liege (2011), 80

The recent X-ray observatories have not yet provided a large survey comparable (in sky coverage) to that based upon the ROSAT All-Sky Survey (RASS). However, two limited surveys exist : the 2XMM catalog ... [more ▼]

The recent X-ray observatories have not yet provided a large survey comparable (in sky coverage) to that based upon the ROSAT All-Sky Survey (RASS). However, two limited surveys exist : the 2XMM catalog for XMM-Newton (294 OB stars detected) and the Carina large-scale survey from Chandra (129 OB stars detected). Medium-resolution (CCD) spectra were analyzed and led to new results on the relationship between the X-ray luminosity and the bolometric luminosity, as well as on the typical properties (plasma temperature, variability) of these objects. This contribution thus presents the results of the first high-sensitivity investigation of the overall high-energy properties of a sizeable sample of hot stars. [less ▲]

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See detailThe X-ray emission of the WR+O binary WR 79
Gosset, Eric ULg; Sana, Hugues; Rauw, Grégor ULg et al

in Bulletin de la Societe Royale des Sciences de Liege (2011), 80

In the framework of our multiwavelength study of the open cluster NGC 6231, we observed the colliding-wind WR+O binary WR 79 at six different epochs with the XMM-Newton observatory. These pointings offer ... [more ▼]

In the framework of our multiwavelength study of the open cluster NGC 6231, we observed the colliding-wind WR+O binary WR 79 at six different epochs with the XMM-Newton observatory. These pointings offer the possibility to study the X-ray spectrum of WR 79 and its possible variability. Our results are briefly discussed and compared with the X-ray characteristics of other similar objects. [less ▲]

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See detailMassive binaries as seen with Gaia
Palate, Matthieu ULg; Rauw, Grégor ULg; Gosset, Eric ULg et al

in Bulletin de la Societe Royale des Sciences de Liege (2011), 80

Gaia, ESA's forthcoming astrometric observatory, will observe a billion stars of our Galaxy, among which thousands of high-mass stars. In this contribution, we study the capabilities of Gaia's ... [more ▼]

Gaia, ESA's forthcoming astrometric observatory, will observe a billion stars of our Galaxy, among which thousands of high-mass stars. In this contribution, we study the capabilities of Gaia's spectrometer (RVS) in the context of massive stars, especially the detectability of lower-mass companions to O-type stars. This preliminary study enables us to estimate to what extent Gaia will constrain the distribution of the physical and orbital parameters of massive binaries (luminosity, period, mass ratio, eccentricity...). [less ▲]

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See detailThe X-ray emission of the colliding wind binary V444 Cyg
Fauchez, Thomas; De Becker, Michaël ULg; Nazé, Yaël ULg

in Bulletin de la Societe Royale des Sciences de Liege (2011), 80

This paper presents the analysis of six XMM-Newton observations of the colliding wind system V444 Cyg. Unlike what one might have expected at first, it appears that the O star wind most probably dominates ... [more ▼]

This paper presents the analysis of six XMM-Newton observations of the colliding wind system V444 Cyg. Unlike what one might have expected at first, it appears that the O star wind most probably dominates the WN wind: the bow shock is wide open, with the hard X-ray emission arising close to the WN star. An important radiative braking could partly explain this situation but revising the wind parameters may also prove necessary. Furthermore, we have probably observed for the first time an occultation of the colliding wind zone by the binary components. [less ▲]

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See detailA photometric study of the Carina nebula region around WR 22
Kumar, Brajesh ULg; Manfroid, Jean ULg; Gosset, Eric ULg et al

in Bulletin de la Societe Royale des Sciences de Liege (2011), 80

We performed the first photometric observations of a field situated around WR 22 in the Carina nebula region. We present and discuss the preliminary results of the study.

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See detailSpectroscopic follow-up of the colliding-wind binary WR140 during the 2009 January periastron passage
Fahed, R.; Moffat, A. F. J.; Zorec, J. et al

in Bulletin de la Societe Royale des Sciences de Liege (2011), 80

We present the results from the spectroscopic follow-up of WR140 (WC7 + O4-5) during its last periastron passage in January 2009. This object is known as the archetype of colliding wind binaries and has a ... [more ▼]

We present the results from the spectroscopic follow-up of WR140 (WC7 + O4-5) during its last periastron passage in January 2009. This object is known as the archetype of colliding wind binaries and has a relatively large period (≃8 years) and eccentricity (≃0.9). We provide updated values for the orbital parameters, new estimates for the WR and O star masses and new constraints on the mass-loss rates. [less ▲]

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See detailSpectroscopic binaries as observed by the future Gaia space mission
Damerdji, Yassine ULg; Delchambre, Ludovic ULg; Morel, Thierry ULg et al

in Bulletin de la Societe Royale des Sciences de Liege (2011), 80

The future Gaia satellite will observe a large number of stars through its three main channels: astrometric, photometric and, for the brightest stars, spectroscopic. The satellite is equipped with the RVS ... [more ▼]

The future Gaia satellite will observe a large number of stars through its three main channels: astrometric, photometric and, for the brightest stars, spectroscopic. The satellite is equipped with the RVS spectrograph, which will provide medium-resolution spectra over a small wavelength range. These spectra should allow us to identify stars exhibiting a composite spectrum, either because of a chance alignment or a true binarity. We discuss the various aspects related to the data treatment of the binary candidates and describe the algorithms that are intended to be included in the processing pipeline. [less ▲]

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See detailEffects of porosity on emergent synthetic spectra of massive stars in the X-ray domain
Hervé, Anthony ULg; Rauw, Grégor ULg

in Bulletin de la Societe Royale des Sciences de Liege (2011), 80

Massive stars possess powerful stellar winds. Studies over the last decade, including the analyses of X-ray emission-line profiles, revealed the importance of wind fragmentation and clumping and led to a ... [more ▼]

Massive stars possess powerful stellar winds. Studies over the last decade, including the analyses of X-ray emission-line profiles, revealed the importance of wind fragmentation and clumping and led to a downwards revision of the mass-loss rates. We present the first results of our code that allows to compare two models of wind fragmentation, and their consequences on the emergent X-ray spectra of massive stars. [less ▲]

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See detail3D modelling of the massive star binary systems Eta Carinae, WR 22, and WR 140
Parkin, E. R.; Pittard, J. M.; Corcoran, M. F. et al

in Bulletin de la Societe Royale des Sciences de Liege (2011), 80

Massive stars possess powerful stellar winds. Wind-wind collision in a massive star binary system generates a region of thermalized plasma which may emit prolifically at X-ray wavelengths. Results are ... [more ▼]

Massive stars possess powerful stellar winds. Wind-wind collision in a massive star binary system generates a region of thermalized plasma which may emit prolifically at X-ray wavelengths. Results are presented from 3D adaptive-mesh refinement (AMR) hydrodynamical models which include radiative cooling and the radiative driving of the stellar winds. The models provide an exceptional insight into the turbulent nature of the wind-wind interaction regions. The X-ray emission from the hydrodynamical models is then calculated, allowing detailed comparisons with observational data. Preliminary results from investigations of Eta Carinae, WR 22, and WR 140 are discussed. [less ▲]

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See detailStudying massive stars with the International X-ray Observatory
Rauw, Grégor ULg; Oskinova, Lida

in Bulletin de la Societe Royale des Sciences de Liege (2011), 80

Chandra and XMM-Newton have deeply changed our view of the X-ray emission of massive stars. However, the majority of the massive stars being rather faint sources, the number of high-resolution X-ray ... [more ▼]

Chandra and XMM-Newton have deeply changed our view of the X-ray emission of massive stars. However, the majority of the massive stars being rather faint sources, the number of high-resolution X-ray spectra of massive stars remains rather limited and obtaining these spectra requires rather long exposure times. ESA, NASA and JAXA are currently designing the International X-ray Observatory (IXO) that will provide a quantum leap in collecting area compared to the current missions. In this contribution, we highlight the capabilities of IXO and its instrumentation for the study of massive stars in our Galaxy and beyond. [less ▲]

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See detailThe XMM-Newton view of the X-ray spectrum of WR140 across periastron passage
De Becker, Michaël ULg; Pittard, Julian M; Williams, Peredur et al

in Bulletin de la Societe Royale des Sciences de Liege (2011), 80

An XMM-Newton campaign dedicated to the study of the X-ray emission of the colliding wind massive binary WR140 across its 2009 periastron passage has been undertaken. The high quality EPIC spectra ... [more ▼]

An XMM-Newton campaign dedicated to the study of the X-ray emission of the colliding wind massive binary WR140 across its 2009 periastron passage has been undertaken. The high quality EPIC spectra revealed a strong phase-locked variability both in flux and in spectral shape. The observed variations are consistently explained by the varying emission measure of the emitting plasma along the eccentric orbit, and by the changing absorption column density along the line of sight. Our results are first interpreted in the context of simple multi-temperature thermal emission models, and prospects for more sophisticated modelling are discussed. [less ▲]

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See detailA Multiwavelength Study of the Runaway Binaries HD 14633 and HD 15137
McSwain, M Virginia; De Becker, Michaël ULg; Roberts, Mallory S E et al

in Bulletin de la Societe Royale des Sciences de Liege (2011), 80

The runaway O-type binaries HD 14633 and HD 15137 were likely ejected from the cluster of their birth by supernovae explosions in close binaries. Here we present recent optical spectra to update the ... [more ▼]

The runaway O-type binaries HD 14633 and HD 15137 were likely ejected from the cluster of their birth by supernovae explosions in close binaries. Here we present recent optical spectra to update the orbital solutions of the binaries and study the physical parameters of the O star primaries. We also present XMM-Newton observations of both systems that attempt to detect hard power-law emission from compact companions. EPIC spectra of HD 14633 at periastron and apastron reveal a non-thermal X-ray flux component that is variable during the orbit. Our EPIC spectra of HD 15137 indicate thermal X-ray emission consistent with an isolated O star. We provide an upper limit on the emission from a compact companion in HD 15137. [less ▲]

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See detailFirst results on the optical campaign devoted to the gamma-ray binary candidate HD259440
De Becker, Michaël ULg; McSwain, M Virginia; Aragona, Christina

in Bulletin de la Societe Royale des Sciences de Liege (2011), 80

Quite recently, a very high-energy gamma-ray source has been detected in the Monoceros region. This source belongs to the category of TeV emitters with no identified counterpart at other wavelengths, even ... [more ▼]

Quite recently, a very high-energy gamma-ray source has been detected in the Monoceros region. This source belongs to the category of TeV emitters with no identified counterpart at other wavelengths, even though it may be coincident with other high-energy sources detected with other observatories (ROSAT, CGRO). However, it is interesting to note that the error box of this TeV source admits the possibility that the Be star HD259440 is at the origin of the high-energy emission. This may be possible only if that Be star is member of a still undetected binary system including a compact (neutron star or black hole) companion, therefore belonging to the very scarce category of gamma-ray binaries. We describe here the first results of the optical campaign devoted to HD 259440, with emphasis on the investigation of its multiplicity, using spectra obtained at the Observatoire de Haute-Provence (OHP) and at the Kitt Peak National Observatory (KPNO). [less ▲]

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See detailProspects for the multiplicity investigation of massive stars with the CARLINA interferometer
De Becker, Michaël ULg; Le Coroller, Hervé; Dejonghe, Julien

in Bulletin de la Societe Royale des Sciences de Liege (2011), 80

The multiwavelength study of massive stars has revealed many phenomena that are intimately related to their multiplicity. Colliding winds in massive binaries play indeed a significant role in thermal X ... [more ▼]

The multiwavelength study of massive stars has revealed many phenomena that are intimately related to their multiplicity. Colliding winds in massive binaries play indeed a significant role in thermal X-ray emission, particle acceleration, or even dust formation in such systems. In this context, the identification of binaries and the determination of their orbital parameters is a pivotal issue. We first briefly describe the CARLINA project. The sensitivity and imaging capability of Carlina are perfectly adapted for the study of binary systems. Considering its expected specifications, Carlina will operate in complementarity with ELTs and kilometer baseline interferometers. Then, we discuss some prospects for the multiplicity investigation of massive stars, on the basis of the expected performances of the prototype currently studied at the Observatoire de Haute-Provence (OHP). [less ▲]

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See detailThe multiplicity of O-type stars in NGC 2244
Mahy, Laurent ULg; Rauw, Grégor ULg; Martins, F. et al

in Bulletin de la Societe Royale des Sciences de Liege (2011), 80

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 ... [more ▼]

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. [less ▲]

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