References of "Rauw, Grégor"
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See detailL'univers des Hautes Energies dévoilé par Integral
Nazé, Yaël ULg; Rauw, Grégor ULg

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See detailThe OB binary HD 152219: a detached, double-lined, eclipsing system
Sana, H.; Gosset, Eric ULg; Rauw, Grégor ULg

in Monthly Notices of the Royal Astronomical Society (2006), 371(1), 67-80

We present the results of an optical spectroscopic campaign on the massive binary HD 152219 located near the core of the NGC 6231 cluster. Though the primary to secondary optical brightness ratio is ... [more ▼]

We present the results of an optical spectroscopic campaign on the massive binary HD 152219 located near the core of the NGC 6231 cluster. Though the primary to secondary optical brightness ratio is probably about 10, we clearly detect the secondary spectral signature and we derive the first reliable SB2 orbital solution for the system. The orbital period is close to 4.2403 d and the orbit is slightly eccentric (e = 0.08 +/- 0.01). The system is most probably formed by an O9.5 giant and a B1-2 V-III star. We derive minimal masses of 18.6 +/- 0.3 and 7.3 +/- 0.1 M-circle dot for the primary and secondary, respectively, and we constrain the stellar radius at values about 11 and 5 R-circle dot. INTEGRAL-Optical Monitoring Camera (OMC) data reveal that HD 152219 is the third O-type eclipsing binary known in NGC 6231. In the Hertzsprung-Russell (HR) diagram, the primary component lies on the blue edge of the beta Cep-type instability strip and its spectral lines display clear profile variations that are reminiscent of those expected from non-radial pulsations. Finally, we report the analysis of XMM-Newton observations of the system. The X-ray spectrum is relatively soft and is well reproduced by a two-temperature mekal model with kT(1) = 0.26 keV and kT(2) = 0.67 keV. The X-ray flux is most probably variable on a time-scale of days. The average X-ray luminosity during our campaign is log(L-X) approximate to 31.8 (erg s(-1)), but shows fluctuations of about 10 per cent around this value. [less ▲]

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See detailEarly-type stars in the young open cluster IC 1805. II. The probably single stars HD 15570 and HD 15629, and the massive binary/triple system HD 15558
De Becker, Michaël ULg; Rauw, Grégor ULg; Manfroid, Jean ULg et al

in Astronomy and Astrophysics (2006), 456

Aims.We address the issue of the multiplicity of the three brightest early-type stars of the young open cluster IC 1805, namely HD 15570, HD 15629 and HD 15558. Methods: .For the three stars, we measured ... [more ▼]

Aims.We address the issue of the multiplicity of the three brightest early-type stars of the young open cluster IC 1805, namely HD 15570, HD 15629 and HD 15558. Methods: .For the three stars, we measured the radial velocity by fitting Gaussian curves to line profiles in the optical domain. In the case of the massive binary HD 15558, we also used a spectral disentangling method to separate the spectra of the primary and of the secondary in order to derive the radial velocities of the two components. These measurements were used to compute orbital solutions for HD 15558. Results: .For HD 15570 and HD 15629, the radial velocities do not present any significant trend attributable to a binary motion on time scales of a few days, nor from one year to the next. In the case of HD 15558 we obtained an improved SB1 orbital solution with a period of about 442 days, and we report for the first time on the detection of the spectral signature of its secondary star. We derive spectral types O5.5III(f) and O7V for the primary and the secondary of HD 15558. We tentatively compute a first SB2 orbital solution although the radial velocities from the secondary star should be considered with caution. The mass ratio is rather high, i.e. about 3, and leads to very extreme minimum masses, in particular for the primary object. Minimum masses of the order of 150 ± 50 and 50 ± 15 M_ȯ are found respectively for the primary and the secondary. Conclusions: .We propose that HD 15558 could be a triple system. This scenario could help to reconcile the very large minimum mass derived for the primary object with its spectral type. In addition, considering new and previously published results, we find that the binary frequency among O-stars in IC 1805 has a lower limit of 20%, and that previously published values (80%) are probably overestimated. [less ▲]

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See detailThe XMM-Newton view of Plaskett's star and its surroundings
Linder, Natacha ULg; Rauw, Grégor ULg; Pollock, A. M. T. et al

in Monthly Notices of the Royal Astronomical Society (2006), 370(4), 1623-1632

XMM-Newton 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 ... [more ▼]

XMM-Newton 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. Conventional models fail to provide a consistent fit of the European Photon Imaging Camera (EPIC) and Reflexion Grating Spectrometer (RGS) spectra. The lines seen in the RGS spectrum have a temperature of maximum emissivity between 0.18 and 1.4 keV. The EPIC and RGS spectra are best fitted by a non-equilibrium model consisting of a bremsstrahlung continuum at 2.2 +/- 0.1 keV and a number of independent emission lines. Our tests also suggest that an overabundance in nitrogen by a factor of similar to 6 might be indicated to best represent the RGS spectrum. On the other hand, a short-term variability study of the light curves of the system indicates that the X-ray flux of Plaskett's star did not display any significant variability during our observation. This result holds for all time-scales investigated here (from a few minutes to about one hour). Combining our XMM-Newton data with ROSAT archival observations, we find, however, a significant variability on the orbital time-scale. If this behaviour is indeed phase locked, it suggests a minimum in the X-ray flux when the primary star is in front. This might be attributed to an occultation of the colliding wind region by the body of the primary. Finally, 71 other X-ray sources have been detected in the field around Plaskett's star and most of them have a near-infrared (near-IR) counterpart with colours that are consistent with those of 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 detailHigh Resolution X-ray Spectroscopy of Early-Type Stars
Rauw, Grégor ULg; Pollock, A. M. T.; Nazé, Yaël ULg

in High Resolution X-ray Spectroscopy: towards XEUS and Con-X (2006, August 01)

Although X-ray emission from massive, early-type stars has been known for almost thirty years, it is only with the advent of the high-resolution spectrographs aboard Chandra and XMM-Newton that a detailed ... [more ▼]

Although X-ray emission from massive, early-type stars has been known for almost thirty years, it is only with the advent of the high-resolution spectrographs aboard Chandra and XMM-Newton that a detailed investigation of the X-ray spectra of these stars has become possible. The existing observations of both single and binary early-type stars have been used to study the properties of their stellar winds. While some results agree with the expectations from theoretical models, other spectra show unexpected features. In this contribution, we review our current knowledge on the X-ray emission of stars of spectral type O and Wolf-Rayet and discuss the possibilities to test some new ideas with future high-resolution X-ray observations. [less ▲]

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See detailAn XMM-Newton view of the young open cluster NGC 6231 - I. The catalogue
Sana, H.; Gosset, Eric ULg; Rauw, Grégor ULg et al

in Astronomy and Astrophysics (2006), 454(3), 1047-115

This paper is the first of a series dedicated to the X-ray properties of the young open cluster NGC 6231. Our data set relies on an XMM-Newton campaign of a nominal duration of 180 ks and reveals that NGC ... [more ▼]

This paper is the first of a series dedicated to the X-ray properties of the young open cluster NGC 6231. Our data set relies on an XMM-Newton campaign of a nominal duration of 180 ks and reveals that NGC 6231 is very rich in the X-ray domain too. Indeed, 610 X-ray sources are detected in the present field of view, centered on the cluster core. The limiting sensitivity of our survey is approximately 6 x 10(-15) erg cm(-2) s(-1) but clearly depends on the location in the field of view and on the source spectrum. Using different existing catalogues, over 85% of the X-ray sources could be associated with at least one optical and/or infrared counterpart within a limited cross-correlation radius of 3" at maximum. The surface density distribution of the X-ray sources presents a slight N-S elongation. Once corrected for the spatial sensitivity variation of the EPIC instruments, the radial profile of the source surface density is well described by a King profile with a central density of about 8 sources per arcmin(2) and a core radius close to 3.1 arcmin. The distribution of the X-ray sources seems closely related to the optical source distribution. The expected number of foreground and background sources should represent about 9% of the detected sources, thus strongly suggesting that most of the observed X-ray emitters are physically belonging to NGC 6231. Finally, beside a few bright but soft objects - corresponding to the early-type stars of the cluster - most of the sources are relatively faint (similar to 5 x 10(-15) erg cm(-2) s(-1)) with an energy distribution peaked around 1.0-2.0 keV. [less ▲]

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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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