References of "Rauw, Grégor"
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See detailThe strange case of the Of?p stars
Nazé, Yaël ULg; Walborn, N. R.; Martins, F. et al

Poster (2009)

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See detailHot stars survey with the GAIA space mission
Lobel, A.; Liu, C.; Frémat, Y. et al

Poster (2009)

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See detailThe multiwavelength picture of star formation in the very young open cluster NGC6383
Rauw, Grégor ULg; De Becker, Michaël ULg

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 ▲]

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See detailThe first orbital solution for the massive colliding-wind binary HD 93162 (=WR 25)
Gamen, R.; Gosset, Eric ULg; Morrell, N. I. et al

in 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 ▲]

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See detailColliding Wind Signatures in Early-Type Binaries
Rauw, Grégor ULg

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 ▲]

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See detailEvidence for short-term variations in two O-type stars
De Becker, Michaël ULg; Linder, Natacha ULg; Rauw, Grégor ULg

in Information Bulletin on Variable Stars (2008), 5841

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 ... [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 ▲]

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See detailThe XMM-Newton view of the rich cluster Cyg OB2
Rauw, Grégor ULg; De Becker, Michaël ULg; Nazé, Yaël ULg et al

Poster (2008, May)

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See detailA binary signature in the non-thermal radio-emitter Cyg OB2 #9
Nazé, Yaël ULg; De Becker, Michaël ULg; Rauw, Grégor ULg et al

in Astronomy and Astrophysics (2008), 483

Aims. Non-thermal radio emission associated with massive stars is believed to arise from a wind-wind collision in a binary system. However, the evidence of binarity is still lacking in some cases, notably ... [more ▼]

Aims. Non-thermal radio emission associated with massive stars is believed to arise from a wind-wind collision in a binary system. However, the evidence of binarity is still lacking in some cases, notably Cyg OB2 #9. Methods: For several years, we have been monitoring this heavily-reddened star from various observatories. This campaign allowed us to probe variations both on short and long timescales and constitutes the first in-depth study of the visible spectrum of this object. Results: Our observations provide the very first direct evidence of a companion in Cyg OB2 #9, confirming the theoretical wind-wind collision scenario. These data suggest a highly eccentric orbit with a period of a few years, compatible with the 2 yr-timescale measured in the radio range. In addition, the signature of the wind-wind collision is very likely reflected in the behaviour of some emission lines. [less ▲]

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See detailHard X-ray emission from eta Carinae
Leyder, Jean-Christophe ULg; Walter, R.; Rauw, Grégor ULg

in Astronomy and Astrophysics (2008), 477

Context: If relativistic particle acceleration takes place in colliding-wind binaries, hard X-rays and gamma-rays are expected through inverse Compton emission, but to date these have never been ... [more ▼]

Context: If relativistic particle acceleration takes place in colliding-wind binaries, hard X-rays and gamma-rays are expected through inverse Compton emission, but to date these have never been unambiguously detected. Aims: To detect this emission, observations of eta Carinae were performed with INTEGRAL, leveraging its high spatial resolution. Methods: Deep hard X-ray images of the region of eta Car were constructed in several energy bands. Results: The hard X-ray emission previously detected by BeppoSax around eta Car originates from at least 3 different point sources. The emission of eta Car itself can be isolated for the first time, and its spectrum unambiguously analyzed. The X-ray emission of eta Car in the 22-100 keV energy range is very hard (Gamma ~= 1 ± 0.4) and its luminosity is 7 × 10^33 erg s^-1. Conclusions: The observed emission is in agreement with the predictions of inverse Compton models, and corresponds to about 0.1% of the energy available in the wind collision. eta Car is expected to be detected in the GeV energy range. [less ▲]

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See detailXMM-Newton X-ray study of early type stars in the Carina OB1 association
Antokhin, I. I.; Rauw, Grégor ULg; Vreux, Jean-Marie ULg et al

in Astronomy and Astrophysics (2008), 477(2), 593-609

Aims. X-ray properties of the stellar population in the Carina OB I association are examined with special emphasis on early-type stars. Their spectral characteristics provide some clues to understanding ... [more ▼]

Aims. X-ray properties of the stellar population in the Carina OB I association are examined with special emphasis on early-type stars. Their spectral characteristics provide some clues to understanding the nature of X-ray formation mechanisms in the winds of single and binary early-type stars. Methods. A timing and spectral analysis of five observations with XMM-Newton is performed using various statistical tests and thermal spectral models. Results. 235 point sources have been detected within the field of view. Several of these sources are probably pre-main sequence stars with characteristic short-term variability. Seven sources are possible background AGNs. Spectral analysis of twenty four sources of type OB and WR 25 was performed. We derived spectral parameters of the sources and their fluxes in three energy bands. Estimating the interstellar absorption for every source and the distance to the nebula, we derived X-ray luminosities of these stars and compared them to their bolometric luminosities. We discuss possible reasons for the fact that, on average, the observed X-ray properties of binary and single early type stars are not very different, and give several possible explanations. [less ▲]

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See detailMultiplicity of O-type stars in NGC 2244
Mahy, Laurent ULg; Nazé, Yaël ULg; Rauw, Grégor ULg et al

Poster (2008)

We present the main results from our long‐term spectroscopic campaign devoted to the O‐type stars in the young open cluster NGC 2244. Previous works by our team on the O‐stars multiplicity in other young ... [more ▼]

We present the main results from our long‐term spectroscopic campaign devoted to the O‐type stars in the young open cluster NGC 2244. Previous works by our team on the O‐stars multiplicity in other young open clusters (IC 1805 and NGC 6231) showed that the number of binary systems in such clusters was larger than 40%. Until now, only two stars (HD 47129 and HD 48099) in the surroundings of NGC 2244 have been confirmed as spectroscopic binaries (SB) although Garcia & Mermilliod (2001) estimated the O‐type binary fraction at 50%. In this context, we revisited the spectral classification, the projected rotational velocity and the multiplicity of O‐type stars in NGC 2244. [less ▲]

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See detailThe investigation of particle acceleration in colliding-wind massive binaries with SIMBOL-X.
De Becker, Michaël ULg; Rauw, Grégor ULg; Pittard, J. M. et al

in Memorie della Società Astronomica Italiana : Journal of the Italian Astronomical Society (2008), 79

An increasing number of early-type (O and Wolf-Rayet) colliding wind binaries (CWBs) is known to accelerate particles up to relativistic energies. In this context, non-thermal emission processes such as ... [more ▼]

An increasing number of early-type (O and Wolf-Rayet) colliding wind binaries (CWBs) is known to accelerate particles up to relativistic energies. In this context, non-thermal emission processes such as inverse Compton (IC) scattering are expected to produce a high energy spectrum, in addition to the strong thermal emission from the shock-heated plasma. SIMBOL-X will be the ideal observatory to investigate the hard X-ray spectrum (above 10 keV) of these systems, i.e. where it is no longer dominated by the thermal emission. Such observations are strongly needed to constrain the models aimed at understanding the physics of particle acceleration in CWB. Such systems are important laboratories for investigating the underlying physics of particle acceleration at high Mach number shocks, and probe a different region of parameter space than studies of supernova remnants. [less ▲]

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See detailThe massive binary HD 152218 revisited: A new colliding wind system in NGC 6231
Sana, H.; Nazé, Yaël ULg; O'Donnell, B. et al

in New Astronomy (2008), 13(4), 202-215

We present the results of an optical and X-ray monitoring campaign on the short-period massive SB2 binary HD 152218. Combining our HiRes spectroscopic data with previous observations, we unveil the ... [more ▼]

We present the results of an optical and X-ray monitoring campaign on the short-period massive SB2 binary HD 152218. Combining our HiRes spectroscopic data with previous observations, we unveil the contradictions between the published orbital solutions. In particular, we solve the aliasing on the period and derive a value close to 5.604 d. Our eccentricity e = 0.259 +/- 0.006 is slightly lower than previously admitted. We show that HD 152218 is probably undergoing a relatively rapid apsidal motion of about 3 degrees yr(-1) and we confirm the O9IV + O9.7V classification. We derive minimal masses of 15.82 +/- 0.26 M-circle dot and 12.00 +/- 0.19 M-circle dot and constrain the radius of the components to R-1 = 10.3 +/- 1.3 R-circle dot and R-2 = 7.8 +/- 1.7 R-circle dot. We also report the results of an XMM-Newton monitoring of the HD 152218 X-ray emission throughout its orbital motion. The averaged X-ray spectrum is relatively soft and it is well reproduced by a 2-T optically thin thermal plasma model with component temperatures about 0.3 and 0.7 keV. The system presents an increase of its X-ray flux by about 30% near apastron compared to periastron, which is interpreted as the signature of an ongoing wind-wind interaction process occurring within the wind acceleration region. (C) 2007 Elsevier B.V. All rights reserved. [less ▲]

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See detailX-ray spectroscopy of early-type stars: The present and the future
Rauw, Grégor ULg; Nazé, Yaël ULg; Oskinova, L. M.

in Astronomische Nachrichten (2008), 329(2), 222-225

XMM-Newton and Chandra have boosted our knowledge about the X-ray emission of early-type stars (spectral types OB and Wolf-Rayet). However, there are still a number of open questions that need to be ... [more ▼]

XMM-Newton and Chandra have boosted our knowledge about the X-ray emission of early-type stars (spectral types OB and Wolf-Rayet). However, there are still a number of open questions that need to be addressed in order to fully understand the X-ray spectra of these objects. Many of these issues require high-resolution spectroscopy or monitoring of a sample of massive stars. Given the moderate X-ray brightness of these targets, rather long exposure times are needed to achieve these goals. In this contribution, we review our current knowledge in this field and present some hot topics that could ideally be addressed with XMM-Newton over the next decade. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. [less ▲]

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See detailThe massive star binary fraction in young open clusters - I. NGC 6231 revisited
Sana, H.; Gosset, Eric ULg; Nazé, Yaël ULg et al

in Monthly Notices of the Royal Astronomical Society (2008), 386(1), 447-460

We present the results of a long-term high-resolution spectroscopy campaign on the O-type stars in NGC 6231. We revise the spectral classification and multiplicity of these objects and we constrain the ... [more ▼]

We present the results of a long-term high-resolution spectroscopy campaign on the O-type stars in NGC 6231. We revise the spectral classification and multiplicity of these objects and we constrain the fundamental properties of the O-star population. Almost three quarters of the O-type stars in the cluster are members of a binary system. The minimum binary fraction is 0.63, with half the O-type binaries having an orbital period of the order of a few days. The eccentricities of all the short-period binaries are revised downward, and henceforth match a normal period-eccentricity distribution. The mass ratio distribution shows a large preference for O + OB binaries, ruling out the possibility that, in NGC 6231, the companion of an O-type star is randomly drawn from a standard initial mass function. Obtained from a complete and homogeneous population of O-type stars, our conclusions provide interesting observational constraints to be confronted with the formation and early evolution theories of O-stars. [less ▲]

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See detailHD 148937: A multiwavelength study of the third galactic member of the Of?p class
Nazé, Yaël ULg; Walborn, Nolan R.; Rauw, Grégor ULg et al

in Astronomical Journal (The) (2008), 135(5), 1946-1957

Three Galactic O-type stars belong to the rare class of Of? p objects: HD 108, HD 191612, and HD 148937. The first two stars show a wealth of phenomena, including strong X-ray emission, light variability ... [more ▼]

Three Galactic O-type stars belong to the rare class of Of? p objects: HD 108, HD 191612, and HD 148937. The first two stars show a wealth of phenomena, including strong X-ray emission, light variability, and dramatic periodic spectral variability. We present here the first detailed optical and X-ray study of the third Galactic Of? p star, HD 148937. Spectroscopic monitoring has revealed low-level variability in the Balmer and He II lambda 4686 lines, but constancy at He I and C III lambda 4650. The H alpha line exhibits profile variations at a possible periodicity of similar to 7 days. Model atmosphere fits yield T-eff = 41000 +/- 2000 K, log(g) = 4.0 +/- 0.1, M-sph less than or similar to 10(-7) M-circle dot yr(-1), and an overabundance of nitrogen by a factor of 4. At X-ray wavelengths, HD 148937 resembles HD 108 and HD 191612 in having a thermal spectrum dominated by a relatively cool component (kT = 0.2 keV), broad lines (>= 1700 km s(-1)), and an order-of-magnitude overluminosity compared to normal O stars (log[L-X(unabs) / L-BOL]similar to -6). [less ▲]

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See detailChandra monitoring of the very massive binary WR20a and the young massive cluster Westerlund 2
Nazé, Yaël ULg; Rauw, Grégor ULg; Manfroid, Jean ULg

in Astronomy and Astrophysics (2008), 483(1), 171-182

Context. Westerlund 2 is a young and massive, obscured stellar cluster of our Galaxy. It harbors the most massive star with well-determined parameters, WR20a (82 + 83 M-circle dot), a dozen very early O ... [more ▼]

Context. Westerlund 2 is a young and massive, obscured stellar cluster of our Galaxy. It harbors the most massive star with well-determined parameters, WR20a (82 + 83 M-circle dot), a dozen very early O-type stars (O3-7), and a wealth of PMS stars. Although of clear significance, this star cluster has not been well-studied. Aims. The high-energy properties of this cluster, especially those of its early-type stars are examined in detail. The variability of the X-ray sources is investigated. Methods. A monitoring of the field was performed using three Chandra observations. This dataset probes daily as well as monthly to yearly timescales and provides the deepest X-ray view of the cluster to date. Results. The two Wolf-Rayet stars WR20a (WN6ha+WN6ha) and WR20b (WN6ha) were analyzed in detail. They are both luminous and display hard spectra, but WR20b does not appear to vary. In contrast, WR20a, a known eclipsing, colliding-wind binary, brightens in the X-ray domain during eclipses, i.e. when the collision is seen face-on. This can be explained by the properties of the wind-wind collision zone, whose high density leads to a large absorbing column (2 x 10(24) cm(-2)). All twelve O-type stars previously classified spectroscopically, two eclipsing binaries previously identified and nine newly-identified, O-type star candidates are detected in the high-energy domain; ten of those could be analyzed spectroscopically. Four are overluminous, but the others have typical LX/LBOL ratios, suggesting that several O-type objects are actually binaries. Variability at the similar to 2 sigma level is detected for a majority of the sources, of unknown origin for single objects. Faint, soft, diffuse emission pervades the entire field-of-view but no clear structure can be identified, even at the position of a blister proposed to correspond to the TeV source HESS J1023-575. The X-ray properties of PMS objects, in particular the brightest flaring ones, are also investigated. They provided an additional argument in favor of a large distance (similar to 8 kpc) for the cluster. [less ▲]

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See detailHigh-resolution X-ray spectroscopy of theta Carinae
Nazé, Yaël ULg; Rauw, Grégor ULg

in Astronomy and Astrophysics (2008), 490(2), 801-806

Context. The peculiar hot star. Car in the open cluster IC2602 is a blue straggler as well as a single-line binary with a short period (2.2d). Aims. Its high-energy properties are not well known, though X ... [more ▼]

Context. The peculiar hot star. Car in the open cluster IC2602 is a blue straggler as well as a single-line binary with a short period (2.2d). Aims. Its high-energy properties are not well known, though X-rays can provide useful constraints on the energetic processes at work in binaries as well as in peculiar, single objects. Methods. We present the analysis of a 50 ks exposure taken with the XMM-Newton observatory. It provides medium as well as high-resolution spectroscopy. Results. Our high-resolution spectroscopy analysis reveals a very soft spectrum with multiple temperature components (1-6 MK) and an X-ray flux slightly below the 'canonical' value (log [L-X(0.1-10.)/L-BOL]similar to -7). The X-ray lines appear surprisingly narrow and unshifted, reminiscent of those of beta Cru and tau Sco. Their relative intensities confirm the anomalous abundances detected in the optical domain (C strongly depleted, N strongly enriched, O slightly depleted). In addition, the X-ray data favor a slight depletion in neon and iron, but they are less conclusive for the magnesium abundance, which may be solar-like. While no significant changes occur during the XMM-Newton observation, variability in the X-ray domain is detected in the long-term range. The formation radius of the X-ray emission is loosely constrained to < 5 R-circle dot, which allows for a range of models (wind-shock, corona, magnetic confinement,...) though not all of them can be reconciled with the softness of the spectrum and the narrowness of the lines. [less ▲]

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See detailHigh-resolution optical spectroscopy of Plaskett's star
Linder, Natacha ULg; Rauw, Grégor ULg; Martins, Fabrice et al

in Astronomy and Astrophysics (2008), 489(2), 713-723

Context. Plaskett's star (HD 47 129) is a very massive O + O binary that belongs to the Mon OB2 association. Previous work suggests that this system displays the Struve-Sahade effect although the ... [more ▼]

Context. Plaskett's star (HD 47 129) is a very massive O + O binary that belongs to the Mon OB2 association. Previous work suggests that this system displays the Struve-Sahade effect although the measurements of the secondary radial velocities are very difficult and give controversial results. Both components have powerful stellar winds that collide and produce a strong X-ray emission. Aims. Our aim is to study the physical parameters of this system in detail and to investigate the relation between its spectral properties and its evolutionary status. Methods. We present here analysis of an extensive set of high-resolution optical spectra of HD 47 129. We used a disentangling method to separate the individual spectra of each star. We derived a new orbital solution and discuss the spectral classification of both components. A Doppler tomography technique applied to the emission lines H alpha and He II gamma 4686 yields a Doppler map that illustrates the wind interactions in the system. Finally, an atmosphere code is used to determine the different chemical abundances of the system components and the wind parameters. Results. HD 47 129 appears to be an O8 III/I + O7.5 III binary system in a post RLOF evolutionary stage, where matter has been transferred from the primary to the secondary star. The He overabundance of the secondary supports this scenario. In addition, the N overabundance and C underabundance of the primary component confirm previous results based on X-ray spectroscopy and indicate that the primary is an evolved massive star. We also determined a new orbital solution, with M-P sin(3) i = 45.4 +/- 2.4 M-circle dot and M-S sin(3) i = 47.3 +/- 0.3 M-circle dot. Furthermore, the secondary star has a high rotational velocity (nu sin i similar to 300 km s(-1)) that deforms its surface, leading to a non-uniform distribution in effective temperature. This could explain the variations in the equivalent widths of the secondary lines with phase. We suggest that the wind of the secondary star is confined near the equatorial plane because of its high rotational velocity, affecting the ram pressure equilibrium in the wind interaction zone. [less ▲]

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See detailSpectroscopic and photometric variability of the O9.5Vp star HD93521
Rauw, Grégor ULg; De Becker, Michaël ULg; van Winckel, Hans et al

in Astronomy and Astrophysics (2008), 487(2), 659-670

Aims. The line profile variability and photometric variability of the O9.5Vp star HD93521 are examined in order to establish the properties of the non-radial pulsations in this star. Methods. Fourier ... [more ▼]

Aims. The line profile variability and photometric variability of the O9.5Vp star HD93521 are examined in order to establish the properties of the non-radial pulsations in this star. Methods. Fourier techniques are used to characterize the modulations of the He I lambda lambda 5876, 6678 and H alpha lines in several spectroscopic time series and to search for variations in a photometric time series. Results. Our spectroscopic data confirm the existence of two periods of 1.75 and 2.89 h. The line profiles, especially those affected by emission wings, exhibit also modulations on longer time scales, but these are epoch-dependent and change from line to line. Unlike previous claims, we find no unambiguous signature of the rotational period in our data, nor of a third pulsation period (corresponding to a frequency of 2.66 d(-1)). Conclusions. HD93521 very likely exhibits non-radial pulsations with periods of 1.75 and 2.89 h with l similar or equal to 8 +/- 1 and l similar or equal to 4 +/- 1 respectively. No significant signal is found in the first harmonics of these two periods. The 2.89 h mode is seen at all epochs and in all lines investigated, while the visibility of the 1.75 h mode is clearly epoch-dependent. Whilst light variations are detected, their connection to these periodicities is not straightforward. [less ▲]

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