References of "Rauw, Grégor"
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See detailNew light on the peculiar star HD108
Nazé, Yaël ULg; Barbieri, C.; Segafredo, A. et al

in Information Bulletin on Variable Stars (2006), 5693

HD 108 is a peculiar massive star of type Of?p, which present recurrent line profile variations. Archival data confirm the very long (50-60 yr) period of this star. Recent data show that the minimum state ... [more ▼]

HD 108 is a peculiar massive star of type Of?p, which present recurrent line profile variations. Archival data confirm the very long (50-60 yr) period of this star. Recent data show that the minimum state is not yet reached. [less ▲]

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See detailINTEGRAL detection of hard X-rays from NGC 6334: nonthermal emission from colliding winds or an AGN?
Bykov, A. M.; Krassilchtchikov, A. M.; Uvarov, Y. A. et al

in Astronomy and Astrophysics (2006), 449(3), 917-923

Aims. We report the detection of hard X-ray emission from the field of the star-forming region NGC 6334 with the International Gamma-Ray Astrophysics Laboratory INTEGRAL. Methods. The JEM-X monitor and ... [more ▼]

Aims. We report the detection of hard X-ray emission from the field of the star-forming region NGC 6334 with the International Gamma-Ray Astrophysics Laboratory INTEGRAL. Methods. The JEM-X monitor and ISGRI imager aboard INTEGRAL and Chandra ACIS imager were used to construct 3-80 keV images and spectra of NGC 6334. Results. The 3-10 keV and 10-35 keV images made with JEM-X show a complex structure of extended emission from NGC 6334. The ISGRI source detected in the energy ranges 20-40 keV, 40-80 keV, and 20-60 keV coincides with the NGC 6334 ridge. The 20-60 keV flux from the source is (1.8 +/- 0.37) x 10(-11) erg cm(-2) s(-1). Spectral analysis of the source revealed a hard power-law component with a photon index about 1. The observed X-ray fluxes are in agreement with extrapolations of X-ray imaging observations of NGC 6334 by Chandra ACIS and ASCAGIS. Conclusions. The X-ray data are consistent with two very different physical models. A probable scenario is emission from a heavily absorbed, compact and hard Chandra source that is associated with the AGN candidate radio source NGC 6334B. Another possible model is the extended Chandra source of nonthermal emission from NGC 6334 that can also account for the hard X-ray emission observed by INTEGRAL. The origin of the emission in this scenario is due to electron acceleration in energetic outflows from massive early type stars. The possibility of emission from a young supernova remnant, as suggested by earlier infrared observations of NGC 6334, is constrained by the non-detection of Ti-44 lines. [less ▲]

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See detailLe ciel selon XMM-Newton
Rauw, Grégor ULg; Nazé, Yaël ULg

Article for general public (2006)

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See detailX-ray Emission from Early-Type Stars: New Results and New Challenges
Rauw, Grégor ULg

in The X-ray Universe 2005 (2006, January 01)

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See detailAn Exceptional X-ray View of the Young Open Cluster NGC 6231: What XMM-Newton Has Taught Us
Sana, H.; Gosset, Eric ULg; Rauw, Grégor ULg et al

in The X-ray Universe 2005 (2006, January 01)

Considered as the core of the Sco OB1 association, the young open cluster NGC 6231 harbours a rich O-type star population. In 2001, the XMM-Newton satellite targeted the cluster for a nominal duration of ... [more ▼]

Considered as the core of the Sco OB1 association, the young open cluster NGC 6231 harbours a rich O-type star population. In 2001, the XMM-Newton satellite targeted the cluster for a nominal duration of about 180 ks. Thanks to the detector sensitivity, the EPIC cameras provided an unprecedented X-ray view of NGC 6231, revealing about 600 point-like sources. In this contribution, we review the main results that have been obtained thanks to this unprecedented data set. Concerning the O-type stars, we present the latest developments related to the so-called 'canonical' Lx-Lbol relation. The dispersion around this relation might actually be much smaller than previously thought. In our data set, the sole mechanism that yields a significant deviation from this scheme is wind interaction. It is also the sole mechanism that induces a significant variation of the early-type star X-ray flux. In a second part of this contribution, we probe the properties of the optically faint X-ray sources. Most of them are believed to be low mass pre-main sequence stars. Their analysis provides direct insight into the star formation history of the cluster. [less ▲]

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See detailThe Peculiar Of?p Stars HD 108 and HD 191612: The X-ray View
Nazé, Yaël ULg; Rauw, Grégor ULg; Walborn, N. R. et al

in The X-ray Universe 2005 (2006, January 01)

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See detailSearching for continuum gamma-ray emission from OB associations with INTEGRAL, some preliminary results
Leyder, Jean-Christophe ULg; Rauw, Grégor ULg

in Populations of High Energy Sources in Galaxies (2006)

Recent studies suggested that there might be a correlation between unidentified gamma-ray sources from the third EGRET catalogue and OB associations. Moreover, when extrapolating the fluxes measured by ... [more ▼]

Recent studies suggested that there might be a correlation between unidentified gamma-ray sources from the third EGRET catalogue and OB associations. Moreover, when extrapolating the fluxes measured by EGRET at energies above 100 MeV with a power-law down to the energy range of ISGRI, the expected count rates should be large enough to be detectable with INTEGRAL. Most of those OB associations being located in the Galactic plane, they are monitored by INTEGRAL as part of the Core Program during both the Galactic Plane Scans and the Galactic Center Deep Exposure. Combining public and CP data, we have performed a search for gamma-ray emission from OB associations and the first results are presented. [less ▲]

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See detailA spectroscopic investigation of the young open cluster IC 1805
De Becker, Michaël ULg; Rauw, Grégor ULg

in Rauw, Grégor; Nazé, Yaël; Blomme, R. (Eds.) et al Massive Stars and High-Energy Emission in OB Associations (2005, November 01)

We present the main results of a spectroscopic campaign devoted to the O-type stars in the young open cluster IC 1805. This study aims at the investigation of the multiplicity and the line profile ... [more ▼]

We present the main results of a spectroscopic campaign devoted to the O-type stars in the young open cluster IC 1805. This study aims at the investigation of the multiplicity and the line profile variability of its brightest massive members. We present new results concerning the line profile variability of He II 4686 and H-beta for HD 15570 and HD 15629. For these two stars, our radial velocity analysis does not reveal any variations compatible with a binary motion. We also significantly improve the orbital parameters of the long period binary HD 15558. For this latter system, we present for the first time evidence for the detection of the secondary, leading to spectral types of O5.5 and O7 respectively for the two components. [less ▲]

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See detailThe XMM-Newton view of Plaskett's star and its surroundings
Linder, N.; Rauw, Grégor ULg

in Massive Stars and High-Energy Emission in OB Associations (2005, November 01)

XMM data of Plaskett's star (HD 47129) are used in order to analyse its X-ray spectrum and variability and hence to derive further constraints on the wind interaction in this early-type binary (O6 I + O7 ... [more ▼]

XMM data of Plaskett's star (HD 47129) are used in order to analyse its X-ray spectrum and variability and hence to derive further constraints on the wind interaction in this early-type binary (O6 I + O7.5 I) system. Combining the information provided by the EPIC and RGS instruments, we find that the X-ray spectrum of Plaskett's star is dominated by thermal plasma at lower energies, whereas the higher energy part (> 3 keV) could probably best be represented by a featureless power law component since we do not detect a significant Fe-K line. Our tests also suggest that an overabundance in nitrogen by a factor Ë 6 might be indicated to best represent the RGS spectrum. On the other hand, 71 X-ray sources have been detected in Plaskett's star field of view and most of them have counterparts in near-IR colours that are consistent with slightly reddened main-sequence objects. Actually, a sizeable fraction of the X-ray sources in the EPIC images could be either foreground or background sources with no direct connection to HD 47129. [less ▲]

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See detailAre WC9 Wolf-Rayet stars in colliding-wind binaries?
Williams, P. M.; van der Hucht, K. A.; Rauw, Grégor ULg

in Massive Stars and High-Energy Emission in OB Associations (2005, November 01)

We present results from a spectroscopic search for massive companions to dust-making Galactic WC9 stars as a step to testing the paradigm that dust formation in these systems requires colliding winds to ... [more ▼]

We present results from a spectroscopic search for massive companions to dust-making Galactic WC9 stars as a step to testing the paradigm that dust formation in these systems requires colliding winds to produce over densities. We find evidence for OB companions to the WC9 stars WR 59 and WR 65, but not WR 121 or WR 117. We identify lines of N III-V and possibly N II in the spectrum of WR 88, one of the few Galactic WC9 stars which do not make circumstellar dust, and suggest that WR 88 is a transitional WN--WC9 object and less evolved than the other WC9 stars. On the other hand, the possible identification of a strong emission line at 4176 in the spectrum of WR 117 with Ne I suggests that this star is more evolved than other WC9 stars studied. [less ▲]

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See detailPreliminary results of an observational campaign aiming at the study of the binary system LSS3074
Gosset, Eric ULg; Rauw, Grégor ULg; Manfroid, Jean ULg et al

in Massive Stars and High-Energy Emission in OB Associations (2005, November 01)

We present preliminary results of an observational campaign aiming at the study of the binary system LSS3074. A new lightcurve clearly indicates that the system is in contact. Recent spectroscopy broadly ... [more ▼]

We present preliminary results of an observational campaign aiming at the study of the binary system LSS3074. A new lightcurve clearly indicates that the system is in contact. Recent spectroscopy broadly confirms the previous results and the rather low masses of both components (O4f[SUP]+[/SUP] and O6-7:(f):). We further analyse an XMM-Newton observation of the object that indicates a rather hard X-ray spectrum. This is partly due to the high interstellar extinction towards the object but also to the high plasma temperature (kT Ë 1.2-1.3 keV). [less ▲]

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See detailCPD-41° 7742: an unusual wind interaction
Sana, H.; Gosset, Eric ULg; Rauw, Grégor ULg et al

in 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 ▲]

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See detailThe young open cluster NGC 6231: five years of investigations
Sana, H.; Rauw, Grégor ULg; Gosset, Eric ULg

in Massive Stars and High-Energy Emission in OB Associations (2005, November 01)

In this contribution, we present an overview of the main results obtained by the Liège multiwavelength (in the X-ray and optical domains) campaign on the young open cluster NGC 6231. We probe the ... [more ▼]

In this contribution, we present an overview of the main results obtained by the Liège multiwavelength (in the X-ray and optical domains) campaign on the young open cluster NGC 6231. We probe the distribution of the O star properties, and especially their binary nature. In this regard, we revise the O-type binary fraction and we briefly discuss the distribution of the binary parameters. We then present the latest developments of the canonical L[SUB]X[/SUB]-L[SUB]bol[/SUB] relation. We discuss the causes of the observed deviations from this relation and of the X-ray variability among O-type stars. Probing the population of low mass pre-main sequence stars detected in the X-ray domain, we propose a scenario for the star formation history in NGC 6231. [less ▲]

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See detailThe peculiar Of?p stars HD 108 and HD 191612
Nazé, Yaël ULg; Rauw, Grégor ULg; Walborn, N. R. et al

in Massive Stars and High-Energy Emission in OB Associations (2005, November 01)

The Of?p spectral category was introduced by Walborn in 1972 to describe peculiar stars which possess intense emission lines of C III 4647,4650,4651. Recently, two of them, HD 108 and HD 191612, were ... [more ▼]

The Of?p spectral category was introduced by Walborn in 1972 to describe peculiar stars which possess intense emission lines of C III 4647,4650,4651. Recently, two of them, HD 108 and HD 191612, were found to display spectacular line profile variations in the visible domain: these stars apparently alternate between two different spectral states (O6-O8). To discover the origin of this intriguing behaviour, a multiwavelength campaign was undertaken. In this context, the analysis of the X-ray emission is especially important since it provides crucial information for constraining the nature of these peculiar objects and testing conflicting models. We are therefore carrying out high-quality XMM-Newton observations of these stars and we present the results of the data obtained up to now. [less ▲]

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See detailA survey for gamma-ray emission from OB associations with INTEGRAL: some preliminary results
Leyder, Jean-Christophe ULg; Rauw, Grégor ULg

in Massive Stars and High-Energy Emission in OB Associations (2005, November 01)

Recent studies indicated that there might be a correlation between OB associations and unidentified gamma-ray sources from the 3EG catalogue. Moreover, when extrapolating the fluxes measured by EGRET at ... [more ▼]

Recent studies indicated that there might be a correlation between OB associations and unidentified gamma-ray sources from the 3EG catalogue. Moreover, when extrapolating the fluxes measured by EGRET at energies higher than 100 MeV with a power-law down to the energy range of ISGRI, the expected count rates should be large enough to be detected with INTEGRAL. As most of these OB associations are located within the Galactic plane, they are being observed by INTEGRAL as part of the Core Program (CP) during both the Galactic Plane Scans (GPS) and the Galactic Center Deep Exposure (GCDE). Combining public and CP data, we have performed a survey for gamma-ray emission from OB associations and the first results are presented in this paper. [less ▲]

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See detailOn the multiplicity of the non-thermal radio emitters 9 Sgr and HD 168112
Rauw, Grégor ULg; Sana, H.; Gosset, Eric ULg et al

in Massive Stars and High-Energy Emission in OB Associations (2005, November)

We discuss the first results of our ongoing optical spectroscopic monitoring campaign of the two O-type stars 9 Sgr and HD 168112. Both objects display a non-thermal radio emission and were considered as ... [more ▼]

We discuss the first results of our ongoing optical spectroscopic monitoring campaign of the two O-type stars 9 Sgr and HD 168112. Both objects display a non-thermal radio emission and were considered as single stars. Based on a large set of high-resolution spectra, we find that 9 Sgr is clearly an eccentric SB2 binary with an orbital period of several years. On the other hand, no evidence for radial velocity variations attributable to binary motion is found in our spectra of HD 168112. [less ▲]

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See detailXMM-Newton observations of the Cyg OB2 association
Rauw, Grégor ULg; De Becker, Michaël ULg; Linder, Natacha ULg

in Massive Stars and High-Energy Emission in OB Associations (2005, November)

We present the first results of an observing campaign of the Cyg OB2 association with the XMM-Newton observatory. The brightest OB-type stars exhibit rather hard spectra suggesting that at least part of ... [more ▼]

We present the first results of an observing campaign of the Cyg OB2 association with the XMM-Newton observatory. The brightest OB-type stars exhibit rather hard spectra suggesting that at least part of their X-ray emission arises in a wind-wind interaction. The EPIC images reveal a large number of fainter X-ray sources most of which are probably low-mass pre-main sequence stars belonging to Cyg OB2. [less ▲]

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See detailEvidence for phase-locked X-ray variations from the colliding-wind massive binary Cyg OB2 #8A
De Becker, Michaël ULg; Rauw, Grégor ULg

in Rauw, G.; Nazé, Y.; Blomme, R. (Eds.) et al Massive Stars and High-Energy Emission in OB Associations (2005, November)

We report on preliminary results of a multi-observatory investigation of the X-ray emission from the massive colliding wind binary Cyg OB2 #8A (O6If + O5.5III(f)). On the basis of our new XMM-Newton-EPIC ... [more ▼]

We report on preliminary results of a multi-observatory investigation of the X-ray emission from the massive colliding wind binary Cyg OB2 #8A (O6If + O5.5III(f)). On the basis of our new XMM-Newton-EPIC observations, along with archive ASCA-SIS and ROSAT-PSPC data, we show strong evidence for a significant phase-locked variability of the X-ray emission from Cyg OB2 #8A with the period of 21.9 days determined by De Becker et al. (2004). These results lend further support to the colliding wind scenario that was already suggested by optical data (De Becker & Rauw 2005). We briefly discuss the behaviour of the X-ray emission from this binary system as a function of phase in the context of the colliding wind scenario. [less ▲]

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See detailMassive Stars and High-Energy Emission in OB Associations
Rauw, Grégor ULg; Nazé, Yaël ULg; Blomme, Ronny et al

Book (2005)

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See detailThe massive binary CPD-41 degrees 7742 - II. Optical light curve and X-ray observations
Sana, H.; Antokhina, E.; Royer, P. et al

in Astronomy and Astrophysics (2005), 441(1), 213-229

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 ... [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 ▲]

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