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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 XMM large-scale structure survey: an initial sample of galaxy groups and clusters to a redshift z < 0.6
Willis, J. P.; Pacaud, F.; Valtchanov, I. et al

in Monthly Notices of the Royal Astronomical Society (2005), 363(2), 675-691

We present X-ray and optical spectroscopic observations of 12 galaxy groups and clusters identified within the X-ray Multi-Mirror (XMM) Large-Scale Structure (LSS) survey. Groups and clusters are selected ... [more ▼]

We present X-ray and optical spectroscopic observations of 12 galaxy groups and clusters identified within the X-ray Multi-Mirror (XMM) Large-Scale Structure (LSS) survey. Groups and clusters are selected as extended X-ray sources from a 3.5 deg(2) XMM image mosaic above a flux limit 8 x 10(-15) erg s(-1) cm(-2) in the [0.5-2] keV energy band. Deep BVRI images and multi-object spectroscopy confirm each source as a galaxy concentration located within the redshift interval 0.29 < z < 0.56. We combine line-of-sight velocity dispersions with the X-ray properties of each structure computed from a two-dimensional surface brightness model and a single temperature fit to the XMM spectral data. The resulting distribution of X-ray luminosity, temperature and velocity dispersion indicate that the XMM-LSS survey is detecting low-mass clusters and galaxy groups to redshifts z < 0.6. Confirmed systems display little or no evidence for X-ray luminosity evolution at a given X-ray temperature compared to lower-redshift X-ray group and cluster samples. A more complete understanding of these trends will be possible with the compilation of a statistically complete sample of galaxy groups and clusters anticipated within the continuing XMM-LSS survey. [less ▲]

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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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See detailThe XMM-LSS survey - The XMDS/VVDS 4 sigma catalogue
Chiappetti, L.; Tajer, M.; Trinchieri, G. et al

in Astronomy and Astrophysics (2005), 439(1), 413-425

We present a first catalogue of X-ray sources resulting from the central area of the XMM-LSS (Large Scale Structure survey). We describe the reduction procedures and the database tools we developed and ... [more ▼]

We present a first catalogue of X-ray sources resulting from the central area of the XMM-LSS (Large Scale Structure survey). We describe the reduction procedures and the database tools we developed and used to derive a well defined catalogue of X-ray sources. The present catalogue is limited to a sub-sample of 286 sources detected at 4 sigma in the 1 deg(2) area covered by the photometric VVDS (VIRMOS VLT Deep Survey), which allows us to provide optical and radio identifications. We also discuss the X-ray properties of a larger X-ray sample of 536 sources detected at > 4 sigma in the full 3 deg(2) area of the XMM Medium Deep Survey (XMDS) independently of the optical identification. We also derive the log N - log S relationship for a sample of more than one thousand sources that we discuss in the context of other surveys at similar fluxes. [less ▲]

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See detailOptical spectroscopy of X-Mega targets - V. The spectroscopic binary HD 93161 A and its visual companion HD 93161 B
Nazé, Yaël ULg; Antokhin, I. I.; Sana, H. et al

in Monthly Notices of the Royal Astronomical Society (2005), 359(2), 688-698

We present the analysis of an extensive set of high-resolution spectroscopic observations of HD 93161, a visual binary with a separation of 2 arcsec. HD 93161 A is a spectroscopic binary, with both ... [more ▼]

We present the analysis of an extensive set of high-resolution spectroscopic observations of HD 93161, a visual binary with a separation of 2 arcsec. HD 93161 A is a spectroscopic binary, with both components clearly detected throughout the orbit. The primary star is most probably of spectral type O8V, while the secondary is likely an O9V. We obtain the first orbital solution for this system, characterized by a period of 8.566 +/- 0.004 d. The minimum masses of the primary and secondary stars are 22.2 +/- 0.6 and 17.0 +/- 0.4 M-., respectively. These values are quite large, suggesting a high inclination of the orbit. The second object, HD 93161 B, displays an O6.5V(f) spectral type and is thus slightly hotter than its neighbour. This star is at first sight single but presents radial velocity variations. Finally, we study HD 93161 in the X-ray domain. No significant variability is detected. The X-ray spectrum is well described by a 2T model with kT(1) similar to 0.3 keV and kT(2) similar to 0.7 keV. The X-ray luminosity is rather moderate, without any large emission excess imputable to a wind interaction. [less ▲]

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See detailXMDS/VVDS 4{sigma} catalogue (Chiappetti+, 2005)
Chiappetti, L.; Tajer, M.; Trinchieri, G. et al

Textual, factual or bibliographical database (2005)

We present a catalogue of 286 X-ray sources with their optical identification taken from the XMDS survey (using the XMM-Newton EPIC instrument). This first version is limited to sources detected at 4 ... [more ▼]

We present a catalogue of 286 X-ray sources with their optical identification taken from the XMDS survey (using the XMM-Newton EPIC instrument). This first version is limited to sources detected at 4{sigma} at least in one energy band, AND falling in the area covered by the optical VVDS survey. (1 data file). [less ▲]

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See detailThe spectrum of the very massive binary system WR20a (WN6ha+WN6ha): Fundamental parameters and wind interactions
Rauw, Grégor ULg; Crowther, P. A.; De Becker, Michaël ULg et al

in Astronomy and Astrophysics (2005), 432(3), 985-998

We analyse the optical spectrum of the very massive binary system WR20a (WN6ha + WN6ha). The most prominent emission lines, Halpha and He II lambda4686, display strong phase-locked profile variability ... [more ▼]

We analyse the optical spectrum of the very massive binary system WR20a (WN6ha + WN6ha). The most prominent emission lines, Halpha and He II lambda4686, display strong phase-locked profile variability. From the variations of their equivalent widths and from a tomographic analysis, we find that part of the line emission probably arises in a wind interaction region between the stars. Our analysis of the optical spectrum of WR20a indicates a reddening of A(nu) similar or equal to 6.0 mag and a distance of similar to 7.9 kpc, suggesting that the star actually belongs to the open cluster Westerlund 2. The location of the system at similar to 1.1 pc from the cluster core could indicate that WR20a was gently ejected from the core via dynamical interactions. Using a non-LTE model atmosphere code, we derive the fundamental parameters of each component: T-eff = 43 000 +/- 2000 K, log L-bol/ L-. similar or equal to 6.0, (M) over dot = 8.5 x 10(-6) M-. yr(-1) (assuming a clumped wind with a volume filling factor f = 0.1). Nitrogen is enhanced in the atmospheres of the components of WR20a, while carbon is definitely depleted. Finally, the position of the binary components in the Hertzsprung-Russell diagram suggests that they are core hydrogen burning stars in a pre-LBV stage and their current atmospheric chemical composition probably results from rotational mixing that might be enhanced in a close binary compared to a single star of same age. [less ▲]

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See detailAn XMM-Newton look at the Wolf-Rayet star WR 40 - The star itself, its nebula and its neighbours
Gosset, Eric ULg; Nazé, Yaël ULg; Claeskens, Jean-François ULg et al

in Astronomy and Astrophysics (2005), 429(2), 685-704

We present the results of an XMM-Newton observation of the field of the Wolf-Rayet star WR 40. Despite a nominal exposure of 20 ks and the high sensitivity of the satellite, the star itself is not ... [more ▼]

We present the results of an XMM-Newton observation of the field of the Wolf-Rayet star WR 40. Despite a nominal exposure of 20 ks and the high sensitivity of the satellite, the star itself is not detected: we thus derive an upper limit on its X-ray flux and luminosity. Joining this result to recent reports of a non-detection of some WC stars, we suggest that the X-ray emission from single normal Wolf-Rayet stars could often be insignificant despite remarkable instabilities in the wind. On the basis of a simple modelling of the opacity of the Wolf-Rayet wind of WR 40, we show that any X-ray emission generated in the particular zone where the shocks are supposed to be numerous will indeed have little chance to emerge from the dense wind of the Wolf-Rayet star. We also report the non-detection of the ejecta nebula RCW 58 surrounding WR 40. Concerning the field around these objects, we detected 33 X-ray sources, most of them previously unknown: we establish a catalog of these sources and cross-correlate it with catalogs of optical/infrared sources. [less ▲]

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See detailThe XMM-LSS survey. Survey design and first results
Pierre, Marguerite; Valtchanov, Ivan; Altieri, Bruno et al

in Journal of Cosmology and Astroparticle Physics [= JCAP] (2004), 09

The XMM Large Scale Structure survey (XMM-LSS) is a medium deep large area X-ray survey. Its goal is to extend large scale structure investigations attempted using ROSAT cluster samples to two redshift ... [more ▼]

The XMM Large Scale Structure survey (XMM-LSS) is a medium deep large area X-ray survey. Its goal is to extend large scale structure investigations attempted using ROSAT cluster samples to two redshift bins between 0<z<1 while maintaining the precision of earlier studies. Two main goals have constrained the survey design: the evolutionary study of the cluster cluster correlation function and of the cluster number density. The adopted observing configuration consists of an equatorial mosaic of 10 ks pointings, separated by 20^\prime and covering 8° à 8°, giving a pointsource sensitivity of {\sim } 5\times 10^{-15}~{\mathrm {erg~cm^{-2}~s^{-1}}} in the 0.5 2 keV band. This will yield more than 800 clusters of galaxies and a sample of X-ray AGN with a space density of about 300 deg[SUP]-2[/SUP]. We present the expected cosmological implications of the survey in the context of LgrCDM models and cluster evolution. We give an overview of the first observational results. The XMM-LSS survey is associated with several other major surveys, ranging from the UV to the radio wavebands, which will provide the necessary resources for X-ray source identification and further statistical studies. In particular, the associated CFHTLS weak lensing and AMiBA Sunyaev Zel'dovich surveys over the entire XMM-LSS area will provide for the first time a comprehensive study of the mass distribution and of cluster physics in the universe on scales of a few hundred Mpc. We describe the main characteristics of our wavelet-based X-ray pipeline and source identification procedures, including the classification of the cluster candidates by means of a photometric redshift analysis. This permits the selection of suitable targets for spectroscopic follow-up. We present preliminary results from the first 25 XMM-LSS pointings: X-ray source properties, optical counterparts, and highlights from the first Magellan and VLT/FORS2 spectroscopic runs as well as preliminary results from the NIR search for z>1 clusters. The results are promising and, so far, in accordance with our predictions. In particular: (1) we reproduce the logN logS distribution for point sources obtained from deeper surveys at our sensitivity; (2) we find a cluster number density of 15 20 deg[SUP]-2[/SUP] (3) for the first time, we statistically sample the group mass regime at a redshift out to {\sim } 0.5 . Paper based on observations obtained with the XMM,CFH, ESO (Prg: P70. A-0283 .A-0733), VLA, CTIO and Las Campanas observatories. [less ▲]

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See detailThe XMM-LSS survey - First high redshift galaxy clusters: Relaxed and collapsing systems
Valtchanov, I.; Pierre, M.; Willis, J. et al

in Astronomy and Astrophysics (2004), 423(1), 75-85

We present five newly found galaxy clusters at z > 0.6 from the XMM Large-Scale Structure Survey (XMM-LSS). All five objects are extended X-ray sources in the XMM images. For three of them we have ... [more ▼]

We present five newly found galaxy clusters at z > 0.6 from the XMM Large-Scale Structure Survey (XMM-LSS). All five objects are extended X-ray sources in the XMM images. For three of them we have sufficient spectroscopically confirmed member galaxies that an estimate of the velocity dispersion is possible: XLSSC 001 at z = 0.613 and sigma(nu) = 867(-60)(+80) km s(-1), XLSSC 002 at z = 0.772 and sigma(nu) = 524(-116)(+267) km s(-1) and XLSSC 003 at z = 0.839 and sigma(V) = 780(-75)(+137) km s(-1). These three clusters have X-ray bolometric luminosities L-X similar to 1-3 x 10(44) erg s(-1) and temperatures 2-4 keV, and consequently are less massive than previously known clusters at similar redshifts, but nevertheless they follow the low redshift scaling relations between L-X, T and sigma(upsilon), within the limits of the measurement errors. One of the clusters, XLSSC 004, is detected independently as an over-density of galaxies of a colour R - z' = 1.4 that matches the redshift of the central galaxy z = 0.87, although it cannot unambiguously be confirmed by the spectroscopic observations alone. The highest redshift candidate cluster pertaining to this paper, XLSSC 005, is most likely a double cluster complex at a redshift around unity, associated with an extended X-ray source with probable substructure. [less ▲]

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See detailWR 20a: A massive cornerstone binary system comprising two extreme early-type stars
Rauw, Grégor ULg; De Becker, Michaël ULg; Nazé, Yaël ULg et al

in Astronomy and Astrophysics (2004), 420(2), 9-13

We analyse spectroscopic observations of WR20a revealing that this star is a massive early-type binary system with a most probable orbital period of similar to3.675 days. Our spectra indicate that both ... [more ▼]

We analyse spectroscopic observations of WR20a revealing that this star is a massive early-type binary system with a most probable orbital period of similar to3.675 days. Our spectra indicate that both components are most likely of WN6ha or 031f*/WN6ha spectral type. The orbital solution for a period of 3.675 days yields extremely large minimum masses of 70.7 +/- 4.0 and 68.8 +/- 3.8 M. for the two stars. These properties make WR 20a a cornerstone system for the study of massive star evolution. [less ▲]

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See detailA phase-resolved XMM-Newton campaign on the colliding-wind binary HD 152248
Sana, H.; Stevens, I. R.; Gosset, Eric ULg et al

in Monthly Notices of the Royal Astronomical Society (2004), 350(3), 809-828

We report the first results of an XMM-Newton monitoring campaign of the open cluster NGC 6231 in the Sco OB 1 association. This first paper focuses on the massive colliding-wind binary HD 152248, which is ... [more ▼]

We report the first results of an XMM-Newton monitoring campaign of the open cluster NGC 6231 in the Sco OB 1 association. This first paper focuses on the massive colliding-wind binary HD 152248, which is the brightest X-ray source of the cluster. The campaign, with a total duration of 180 ks, was split into six separate observations, following the orbital motion of HD 152248. The X-ray flux from this system presents a clear, asymmetric modulation with the phase and ranges from 0.73 to 1.18 x 10(-12) erg s(-1) cm(-2) in the 0.5-10.0 keV energy band. The maximum of the emission is reached slightly after apastron. The EPIC spectra are quite soft, and peak around 0.8-0.9 keV. We characterize their shape using several combinations Of MEKAL models and power-law spectra and we detect significant spectral variability in the 0.5-2.5 keV energy band. We also perform 2D hydrodynamical simulations using different sets of parameters that closely reproduce the physical and orbital configuration of the HD 152248 system at the time of the six XMM-Newton pointings. This allows a direct confrontation of the model predictions with the constraints deduced from the X-ray observations of the system. We show that the observed variation of the flux can be explained by a variation of the X-ray emission from the colliding-wind zone, diluted by the softer X-ray contribution of the two O-type stars of the system. Our simulations also reveal that the interaction region of HD 152248 should be highly unstable, giving rise to shells of dense gas that are separated by low-density regions. Finally, we perform a search for short-term variability in the light curves of the system and we show that trends are present within several of the 30-ks exposures of our campaign. Further, most of these trends are in good agreement with the orbital motion and provide a direct constraint on the first-order derivative of the flux. In the same context, we also search for long-range correlations in the X-ray data of the system, but we only marginally detect them in the high-energy tail of the signal. [less ▲]

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See detailXMM-Newton observations of the giant H II region N 11 in the LMC
Nazé, Yaël ULg; Antokhin, I. I.; Rauw, Grégor ULg et al

in Astronomy and Astrophysics (2004), 418(3), 841-855

Using the sensitive XMM-Newton observatory, we have observed the giant H II region N11 in the LMC for similar to30 ks. We have detected several large areas of soft diffuse X-ray emission along with 37 ... [more ▼]

Using the sensitive XMM-Newton observatory, we have observed the giant H II region N11 in the LMC for similar to30 ks. We have detected several large areas of soft diffuse X-ray emission along with 37 point sources. One of the most interesting results is the possible association of a faint X-ray source with BSDL 188, a small extended object of uncertain nature, The OB associations in the field-of-view (LH9, LH10 and LH13) are all detected with XMM-Newton, but they appear very different from one another. The diffuse soft X-ray emission associated with LH9 peaks near HD 32228, a dense cluster of massive stars. The combined emission of all individual massive stars of LH9 and of the superbubble they have created is not sufficient to explain the high level of emission observed: hidden SNRs, colliding-wind binaries and the numerous pre-main sequence stars of the cluster are most likely the cause of this discrepancy. The superbubble may also be leaking some hot gas in the ISM since faint, soft emission can be observed to the south of the cluster. The X-ray emission from LH10 consists of three pointlike sources and a soft extended emission of low intensity. The two brightest point sources are clearly associated with the fastest expanding bubbles blown by hot stars in the SW part of the cluster. The total X-ray emission from LH10 is rather soft, although it presents a higher temperature than the other soft emissions of the field. The discrepancy between the combined emission of the stars and the observed luminosity is here less severe than for LH9 and could be explained in terms of hot gas filling the wind-blown bubbles. On the other hand, the case of LH13 is different: it does not harbour any extended emission and its X-ray emission could most probably be explained by the Sk -66degrees41 cluster alone. Finally, our XMM-Newton observation included simultaneous observations with the OM camera that provide us with unique UV photometry of more than 6000 sources and enable the discovery of the UV emission from the SNR N11L. [less ▲]

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See detailAn XMM-Newton observation of the massive binary HD 159176
De Becker, Michaël ULg; Rauw, Grégor ULg; Pittard, J. M. et al

in Astronomy and Astrophysics (2004), 416(1), 221-233

We report the analysis of an XMM-Newton observation of the close binary HD 159176 (O7 V + O7 V). The observed L-x/L-bol ratio reveals an X-ray luminosity exceeding by a factor similar to7 the expected ... [more ▼]

We report the analysis of an XMM-Newton observation of the close binary HD 159176 (O7 V + O7 V). The observed L-x/L-bol ratio reveals an X-ray luminosity exceeding by a factor similar to7 the expected value for X-ray emission from single O-stars. therefore suggesting a wind-wind interaction scenario. EPIC and RGS spectra are fitted consistently with a two temperature mekal optically thin thermal plasma model, with temperatures ranging from similar to2 to 6 x 10(6) K. At first sight, these rather low temperatures are consistent with the expectations for a close binary system where the winds collide well before reaching their terminal velocities. We also investigate the variability of the X-ray light curve of HD,159176 on various short time scales. No significant variability is found and we-conclude that if hydrodynamical instabilities exist in the wind interaction region of HD 159176, they are not sufficient to produce an observable signature in the X-ray emission. Hydrodynamic simulations using wind parameters from the literature reveal some puzzling discrepancies. The most-striking one concerns the predicted X-ray luminosity which is one or more orders of magnitude larger than the observed one. A significant reduction of the mass loss rate of the components compared to the values quoted in the literature alleviates the discrepancy but is not sufficient to fully account for the observed luminosity. Because hydrodynamical models are best for the adiabatic case whereas the colliding winds in HD 159176 are most likely highly radiative, a totally new approach has been envisaged, using a geometrical steady-state colliding wind model suitable for the case of radiative winds. This model successfully reproduces the spectral shape of the EPIC spectrum, but further developments are still needed to alleviate the disagreement between theoretical and observed X-ray luminosities. [less ▲]

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See detailAn XMM-Newton observation of the very young open cluster NGC 6383
Rauw, Grégor ULg; De Becker, Michaël ULg; Gosset, Eric ULg et al

in Astronomy and Astrophysics (2003), 407(3), 925-15

We report the detection of a number of X-ray sources associated with the very young open cluster NGC6383. About two thirds of these objects are correlated with a rather faint optical source and all but ... [more ▼]

We report the detection of a number of X-ray sources associated with the very young open cluster NGC6383. About two thirds of these objects are correlated with a rather faint optical source and all but one have at least one infrared counterpart within a correlation radius of 8 arcsec. Although NGC6383 is not associated with a prominent star forming region, the overall properties of many of the X-ray sources suggest that they may be candidates for low-mass pre-main sequence stars. The number of X-ray sources increases towards the cluster center suggesting that there exists a close relation between the massive O-star binary system HD159176 in the cluster core and the population of X-ray bright low-mass objects in NGC 6383. [less ▲]

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See detailThe massive binary CPD-41°7742 - I. High-resolution optical spectroscopy
Sana, H.; Hensberge, H.; Rauw, Grégor ULg et al

in Astronomy and Astrophysics (2003), 405(3), 1063-1074

We present the results of a spectroscopic campaign on the early-type binary CPD-41degrees 7742. For the first time, we unambiguously detect the secondary's spectral signature and derive an accurate ... [more ▼]

We present the results of a spectroscopic campaign on the early-type binary CPD-41degrees 7742. For the first time, we unambiguously detect the secondary's spectral signature and derive an accurate orbital solution for both components of the system. We confirm that the orbit displays a slight but definite eccentricity (e=0.027+/-0.006) despite the short period (P=2.44070+/-0.00043 days). Previous radial velocity measurements available in the literature constitute together with our new observations a data set that spans more than 30 years. The combined primary orbital solution inferred is in excellent agreement with our solution and gives a period P=2.44062+/-0.00005 days. Based on spectroscopic criteria, we derive a spectral and luminosity classification of O9 III + B1 III. However, the luminosities and radii inferred from the membership of NGC6231 rather indicate lower luminosity classes. We show that the equivalent widths of well isolated primary lines display variations that suggest that CPD-41degrees 7742 is an eclipsing binary. This makes CPD-41degrees 7742 the second known SB2 eclipsing early-type binary of the NGC 6231 cluster. We approximately constrain the inclination of the system i(min) approximate to 60degrees. This may indicate that the system does not offer enough room for two stars with radii typical of giant stars and lends further support to a less evolved luminosity classification for at least one of the objects. [less ▲]

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See detailPreliminary results from XMM-Newton observations of the massive Wolf-Rayet binary WR 22 (WN7h+O9III-V)
Gosset, Eric ULg; Rauw, Grégor ULg; Vreux, Jean-Marie ULg et al

in A Massive Star Odyssey: From Main Sequence to Supernova (2003)

We present preliminary results from observations of the massive WR+O binary WR 22 performed with the XMM observatory. The star is brighter in the X-ray domain near apastron and fainter at periastron. The ... [more ▼]

We present preliminary results from observations of the massive WR+O binary WR 22 performed with the XMM observatory. The star is brighter in the X-ray domain near apastron and fainter at periastron. The change in brightness is very progressive and mainly corresponds to a lowering of the soft part of the spectrum. [less ▲]

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See detailAn XMM-Newton observation of the Lagoon Nebula and the very young open cluster NGC 6530
Rauw, Grégor ULg; Nazé, Yaël ULg; Gosset, Eric ULg et al

in Astronomy and Astrophysics (2002), 395(2), 499-513

We report the results of an XMM-Newton observation of the Lagoon Nebula (M8). Our EPIC images of this region reveal a cluster of point sources, most of which have optical counterparts inside the very ... [more ▼]

We report the results of an XMM-Newton observation of the Lagoon Nebula (M8). Our EPIC images of this region reveal a cluster of point sources, most of which have optical counterparts inside the very young open cluster NGC6530. The bulk of these X-ray sources are probably associated with low and intermediate mass pre-main sequence stars. One of the sources experienced a flare-like increase of its X-ray flux making it the second brightest source in M8 after the O4 star 9 Sgr. The X-ray spectra of most of the brightest sources can be fitted with thermal plasma models with temperatures of kT similar to a few keV. Only a few of the X-ray selected PMS candidates are known to display Halpha emission and were previously classified as classical T Tauri stars. This suggests that most of the X-ray emitting PMS stars in NGC6530 are weak-line T Tauri stars. In addition to 9 Sgr, our EPIC field of view contains also a few early-type stars. The X-ray emission from HD 164816 is found to be typical for an O9.5 III-IV star. At least one of the known Herbig Be stars in NGC6530 ( LkHalpha 115) exhibits a relatively strong X-ray emission, while most of the main sequence stars of spectral type B1 and later are not detected. We also detect ( probably) diffuse X-ray emission from the Hourglass Region that might reveal a hot bubble blown by the stellar wind of Herschel 36, the ionizing star of the Hourglass Region. [less ▲]

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See detailPhase-resolved X-ray and optical spectroscopy of the massive binary HD 93403
Rauw, Grégor ULg; Vreux, Jean-Marie ULg; Stevens, I. R. et al

in Astronomy and Astrophysics (2002), 388(2), 552-562

We report the first results of a campaign aimed at the study of early-type binaries with the XMM-Newton observatory. Phase-resolved EPIC spectroscopy of the eccentric binary HD93403 reveals a clear ... [more ▼]

We report the first results of a campaign aimed at the study of early-type binaries with the XMM-Newton observatory. Phase-resolved EPIC spectroscopy of the eccentric binary HD93403 reveals a clear orbital modulation of the X-ray luminosity as a function of the orbital phase. Below 1.0 keV, the observed X-ray flux is modulated by the opacity of the primary wind. Above 1.0 keV, the observed variation of the X-ray flux is roughly consistent with a 1/r dependence expected for an adiabatic colliding wind interaction. HD93403 appears less overluminuous in X-rays than previously thought and a significant fraction of the total X-ray emission arises probably within the winds of the individual components of the binary. Optical monitoring of the system reveals strong variability of the He II lambda 4686 and Halpha line profiles. The He II lambda 4686 line displays a broad asymmetrical emission component which is found to be significantly stronger between phases 0.80 and 0.15 than around apastron. This suggests that part of the emission arises in the interaction region and most probably in the trailing arm of a shock cone wrapped around the secondary. Some absorption lines of the secondary's spectrum display equivalent width variations reminiscent of the so-called Struve-Sahade effect. The differences in behaviour between individual lines suggest that the temperature may not be the only relevant parameter that controls this effect. [less ▲]

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See detailV4741 Sagittarii
Gosset, Eric ULg

in International Astronomical Union Circular (2002), 7887

IAUC 7887 available at Central Bureau for Astronomical Telegrams.

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