References of "Gosset, Eric"
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See detailThe Struve-Sahade effect in the optical spectra of O-type binaries - I. Main-sequence systems
Linder, Natacha ULg; Rauw, Grégor ULg; Sana, H. et al

in Astronomy and Astrophysics (2007), 474(1), 193-204

Aims. We present a spectroscopic analysis of four massive binary systems that are known or are good candidates to display the Struve-Sahade effect (defined as the apparent strengthening of the secondary ... [more ▼]

Aims. We present a spectroscopic analysis of four massive binary systems that are known or are good candidates to display the Struve-Sahade effect (defined as the apparent strengthening of the secondary spectrum of the binary when the star is approaching, and the corresponding weakening of the lines when it is receding). Methods. We use high resolution optical spectra to determine new orbital solutions and spectral types of HD 165 052, HD 100 213, HD 159 176 and DH Cep. As good knowledge of the fundamental parameters of the considered systems is necessary to examine the Struve-Sahade effect. We then study equivalent width variations in the lines of both components of these binaries during their orbital cycle. Results. In the case of these four systems, variations appear in the equivalent widths of some lines during the orbital cycle, but the definition given above can any longer be valid, since it is now clear that the effect modifies the primary spectrum as much as the secondary spectrum. Furthermore, the lines affected, and the way in which they are affected, depend on the considered system. For at least two of them (HD 100 213 and HD 159 176) these variations probably reflect the ellipsoidal variable nature of the system. [less ▲]

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See detailAn XMM-Newton view of the young open cluster NGC 6231-III. Optically faint X-ray sources
Sana, H.; Rauw, Grégor ULg; Sung, H. et al

in Monthly Notices of the Royal Astronomical Society (2007), 377(3), 945-956

We discuss the properties of the X-ray sources with faint optical counterparts in the very young open cluster NGC 6231. From their positions in the Hertzsprung-Russell diagram, we find that the bulk of ... [more ▼]

We discuss the properties of the X-ray sources with faint optical counterparts in the very young open cluster NGC 6231. From their positions in the Hertzsprung-Russell diagram, we find that the bulk of these objects probably consists of low-mass pre-main-sequence (PMS) stars with masses in the range 0.3-3.0 M-circle dot. The age distribution of these objects indicates that low-mass star formation in NGC 6231 started more than 10 Myr ago and culminated in a starburst-like event about 1-4 Myr ago when the bulk of the low-mass PMS stars as well as the massive cluster members formed. We find no evidence for a spatial age gradient that could point towards a sequential star formation process. Only a few X-ray sources have counterparts with a reddening exceeding the average value of the cluster or with infrared colours indicating the presence of a moderate near-IR excess. The X-ray spectra of the brightest PMS sources are best fitted by rather hard thermal plasma models and a significant fraction of these sources display flares in their light curve. The X-ray brightest flaring sources have decay times between 2 and 16 ks. The X-ray selected PMS stars in NGC 6231 have log L-X/L-bol values that increase strongly with decreasing bolometric luminosity and can reach a saturation level (log L-X/L-bol similar to -2.4) for non-flaring sources and even more extreme values during flares. [less ▲]

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See detailConstraining the fundamental parameters of the O-type binary CPD-41 7733
Sana, H.; Rauw, Grégor ULg; Gosset, Eric ULg

in Astrophysical Journal (2007), 659(2, Part 1), 1582-1591

Using a set of high-resolution spectra, we studied the physical and orbital properties of the O-type binary CPD -41 7733, located in the core of NGC 6231. We report the unambiguous detection of a ... [more ▼]

Using a set of high-resolution spectra, we studied the physical and orbital properties of the O-type binary CPD -41 7733, located in the core of NGC 6231. We report the unambiguous detection of a secondary spectral signature and we derive the first SB2 orbital solution of the system. The period is 5.6815 + 0.0015 days, and the orbit has no significant eccentricity. CPD -41 7733 probably consists of stars of spectral types O8.5 and B3. As for other objects in the cluster, we observe discrepant luminosity classifications while using spectroscopic or brightness criteria. Still, the present analysis suggests that both components display physical parameters close to those of typical O8.5 and B3 dwarfs. We also analyze the X-ray light curves and spectra obtained during six 30 ks XMM-Newton pointings spread over the 5.7 day period. We find no significant variability between the different pointings, nor within the individual observations. The CPD - 41 7733 X- ray spectrum is well reproduced by a three-temperature thermal mekal model with temperatures of 0.3, 0.8, and 2.4 keV. No X-ray overluminosity, resulting, e. g., from a possible wind interaction, is observed. The emission of CPD -41 7733 is thus very representative of typical O-type star X- ray emission. [less ▲]

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See detailEarly-type stars in the core of the young open cluster Westerlund 2
Rauw, Grégor ULg; Manfroid, Jean ULg; Gosset, Eric ULg et al

in Astronomy and Astrophysics (2007), 463(3), 981-991

Aims. The properties of the early-type stars in the core of the Westerlund 2 cluster are examined in order to establish a link between the cluster and the very massive Wolf-Rayet binary WR 20a as well as ... [more ▼]

Aims. The properties of the early-type stars in the core of the Westerlund 2 cluster are examined in order to establish a link between the cluster and the very massive Wolf-Rayet binary WR 20a as well as the H II complex RCW 49. Methods. Photometric monitoring as well as spectroscopic observations of Westerlund 2 are used to search for light variability and to establish the spectral types of the early-type stars in the cluster core. Results. The first light curves of the eclipsing binary WR 20a in B and V filters are analysed and a distance of 8 kpc is inferred. Three additional eclipsing binaries, which are probable late O or early B-type cluster members, are discovered, but none of the known early O-type stars in the cluster displays significant photometric variability above 1% at the 1-sigma level. The twelve brightest O-type stars are found to have spectral types between O3 and O6.5, significantly earlier than previously thought. Conclusions. The distance of the early-type stars in Westerlund 2 is established to be in excellent agreement with the distance of WR20a, indicating that WR20a actually belongs to the cluster. Our best estimate of the cluster distance thus amounts to 8.0 +/- 1.4 kpc. Despite the earlier spectral types, the currently known population of early-type stars in Westerlund 2 does not provide enough ionizing photons to account for the radio emission of the RCW49 complex. This suggests that there might still exist a number of embedded early O-stars in RCW49. [less ▲]

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See detailEtudes d'étoiles massives de types spectraux O, Wolf-Rayet et apparentés
Gosset, Eric ULg

Post doctoral thesis (2007)

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See detailThe XMM-LSS Survey : properties and two-point angular correlations of point-like sources
Garcet, O.; Gandhi, P.; Disseau, L. et al

Poster (2007)

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See detailNGC6231: X-ray Properties of the Early-Type Star Population
Sana, H.; Nazé, Yaël ULg; Gosset, Eric ULg et al

in Massive Stars in Interactive Binaries (2007)

Based on a deep XMM-Newton observation of the young open cluster NGC6231, we derive the main X-ray properties of its early-type star population. Among the 610 X-ray sources detected in the field, 42 are ... [more ▼]

Based on a deep XMM-Newton observation of the young open cluster NGC6231, we derive the main X-ray properties of its early-type star population. Among the 610 X-ray sources detected in the field, 42 are associated with early-type stars. We investigate their L[SUB]X[/SUB]/L[SUB]bol[/SUB] relationship and confirm the clear dichotomy between O- and B-type stars. The cut-off line between the two behaviours occurs at L[SUB]bol[/SUB] ~ 10[SUP]38[/SUP] erg s[SUP]-1[/SUP] as previously proposed by Berghöfer et al. (1997). The distinction between single and binary stars is not clear cut, except for the colliding wind system HD152248. The X-ray detected B-stars in NGC6231 appear to be more luminous than predicted from the Berghöfer et al. relation. Though this suggests a bimodal distribution of the B-star X-ray emission, we caution however that these results might be biased by detection limits. Finally we investigate the X-ray variability of the detected sources and we find that about 40% of the X-ray emitters in the field of view present consistent signs of variability in the EPIC instruments. This fraction is much larger than previously thought. About one third of the early-type star population, either singles or binaries, further show variability. These variations do not seem to be exclusively related to binarity and could thus not be systematically interpreted in the framework of a wind-wind collision phenomenon. [less ▲]

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See detailThe XMM large scale structure survey: optical vs. X-ray classifications of active galactic nuclei and the unified scheme
Garcet, Olivier ULg; Gandhi, P.; Gosset, Eric ULg et al

in Astronomy and Astrophysics (2007), 474

Aims.Our goal is to characterize AGN populations by comparing their X-ray and optical classifications within the framework of the standard orientation-based unified scheme. Methods: We present a sample of ... [more ▼]

Aims.Our goal is to characterize AGN populations by comparing their X-ray and optical classifications within the framework of the standard orientation-based unified scheme. Methods: We present a sample of 99 spectroscopically identified (R <= 22 mag) X-ray selected point sources in the XMM-LSS survey which are significantly detected (>=3sigma) in the [ 2-10] keV band with fluxes between 8 × 10[SUP]-15[/SUP] and 8 × 10[SUP]-14[/SUP] erg s[SUP]-1[/SUP] cm[SUP]-2[/SUP], and which have more than 80 counts. We have compared their X-ray and optical classifications. To this end, we performed an X-ray spectral analysis for all of these 99 X-ray sources in order to assess whether they are intrinsically absorbed or not. The X-ray classification is based on the measured intrinsic column density. The optical classification is based on the measured FWHM of the permitted emission lines, the absence of broad lines being due to obscuration within the framework of the standard AGN unified scheme. Results: Introducing the fourfold point correlation coefficient r, we find a mild correlation between the X-ray and the optical classifications (r = 0.28), as up to 32 X-ray sources out of 99 have differing X-ray and optical classifications: on one hand, 10% of the type 1 sources (7/32) present broad emission lines in their optical spectra and strong absorption (N{H}[SUP]int[/SUP] >= 10[SUP]22[/SUP] cm[SUP]-2[/SUP]) in the X-rays. These objects are highly luminous AGN lying at high redshift and thus dilution effects by the host galaxy light are totally ruled out, their discrepant nature being an intrinsic property instead. Their X-ray luminosities and redshifts distributions are consistent with those of the unabsorbed X-ray sources with broad emission lines (L{2-10} 4 × 10[SUP]44[/SUP] erg s[SUP]-1[/SUP]; z 1.9). On the other hand, 25/32 are moderate luminosity (L{2-10} <= 5 × 10[SUP]43[/SUP] erg s[SUP]-1[/SUP]) AGN, which are both unabsorbed in the X-rays and only present narrow emission lines in their optical spectra. Based on their line ratios in the optical, the majority of them have an optical spectrum which is more representative of the host galaxy rather than of a reddened AGN. We finally infer that dilution of the AGN by the host galaxy seems to account for their nature. 5/25 have been defined as Seyfert 2 based on their optical spectra. In conclusion, most of these 32 discrepant cases can be accounted for by the standard AGN unified scheme, as its predictions are not met for only 12% of the 99 X-ray sources. Table 4 and Figs. [see full text]-[see full text] are only available in electronic form at http://www.aanda.org [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. et al

in Astronomy and Astrophysics (2006), 460(3), 777-782

Context. Since the discovery, with the EINSTEIN satellite, of strong X-ray emission associated with HD 93162 (equivalent to WR 25), this object has been predicted to be a colliding-wind binary system ... [more ▼]

Context. Since the discovery, with the EINSTEIN satellite, of strong X-ray emission associated with HD 93162 (equivalent to WR 25), this object has been predicted to be a colliding-wind binary system. However, radial-velocity variations that would prove the suspected binary nature have yet to be found. Aims. We spectroscopically monitored this object to investigate its possible variability to address this discordance. Methods. We compiled the largest available radial-velocity data set for this star to look for variations that might be due to binary motion. We derived radial velocities from spectroscopic data acquired mainly between 1994 and 2006, and searched these radial velocities for periodicities using different numerical methods. Results. For the first time, periodic radial-velocity variations are detected. Our analysis definitively shows that the Wolf-Rayet star WR 25 is an eccentric binary system with a probable period of about 208 days. [less ▲]

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See detailThe XMM Large-Scale Structure survey: the X-ray pipeline and survey selection function
Pacaud, F.; Pierre, M.; Refregier, A. et al

in Monthly Notices of the Royal Astronomical Society (2006), 372(2), 578-590

We present the X-ray pipeline developed for the purpose of the cluster search in the XMM Large-Scale Structure (XMM-LSS) survey. It is based on a two-stage procedure via a dedicated handling of the ... [more ▼]

We present the X-ray pipeline developed for the purpose of the cluster search in the XMM Large-Scale Structure (XMM-LSS) survey. It is based on a two-stage procedure via a dedicated handling of the Poisson nature of the signal: (i) source detection on multiresolution wavelet filtered images and (ii) source analysis by means of a maximum likelihood fit to the photon images. The source detection efficiency and characterization are studied through extensive Monte Carlo simulations. This led us to define two samples of extended sources: the C1 class that is uncontaminated, and the less restrictive C2 class that allows for 50 per cent contamination. The resulting predicted selection function is presented and the comparison to the current XMM-LSS confirmed cluster sample shows very good agreement. We arrive at average predicted source densities of about seven C1 and 12 C2 per deg(2), which is higher than any available wide field X-ray survey. We finally note a substantial deviation of the predicted redshift distribution for our samples from the one obtained using the usual assumption of a flux-limited sample. [less ▲]

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See detailThe XMM Large-Scale Structure survey: a well-controlled X-ray cluster sample over the D1 CFHTLS area
Pierre, M.; Pacaud, F.; Duc, P. A. et al

in Monthly Notices of the Royal Astronomical Society (2006), 372(2), 591-608

We present the XMM Large-Scale Structure Survey (XMM-LSS) cluster catalogue corresponding to the Canada-France-Hawaii Telescope Legacy Survey D1 area. The list contains 13 spectroscopically confirmed, X ... [more ▼]

We present the XMM Large-Scale Structure Survey (XMM-LSS) cluster catalogue corresponding to the Canada-France-Hawaii Telescope Legacy Survey D1 area. The list contains 13 spectroscopically confirmed, X-ray selected galaxy clusters over 0.8 deg(2) to a redshift of unity and so constitutes the highest density sample of clusters to date. Cluster X-ray bolometric luminosities range from 0.03 to 5 x 10(44) erg s(-1). In this study, we describe our catalogue construction procedure: from the detection of X-ray cluster candidates to the compilation of a spectroscopically confirmed cluster sample with an explicit selection function. The procedure further provides basic X-ray products such as cluster temperature, flux and luminosity. We detected slightly more clusters with (0.5-2.0 keV) X-ray fluxes of > 2 x 10(-14) erg s(-1) cm(-2) than we expected based on expectations from deep ROSAT surveys. We also present the luminosity-temperature relation for our nine brightest objects possessing a reliable temperature determination. The slope is in good agreement with the local relation, yet compatible with a luminosity enhancement for the 0.15 < z < 0.35 objects having 1 < T < 2 keV, a population that the XMM-LSS is identifying systematically for the first time. The present study permits the compilation of cluster samples from XMM images whose selection biases are understood. This allows, in addition to studies of large-scale structure, the systematic investigation of cluster scaling law evolution, especially for low mass X-ray groups which constitute the bulk of our observed cluster population. All cluster ancillary data (images, profiles, spectra) are made available in electronic form via the XMM-LSS cluster data base. [less ▲]

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See detailAn XMM-Newton view of the young open cluster NGC 6231 - II. The OB star population
Sana, H.; Rauw, Grégor ULg; Nazé, Yaël ULg et al

in Monthly Notices of the Royal Astronomical Society (2006), 372(2), 661-678

In this second paper of the series, we pursue the analysis of the 180-ks XMM-Newton campaign towards the young open cluster NGC 6231 and we focus on its rich OB star population. We present a literature ... [more ▼]

In this second paper of the series, we pursue the analysis of the 180-ks XMM-Newton campaign towards the young open cluster NGC 6231 and we focus on its rich OB star population. We present a literature-based census of the OB stars in the field of view with more than one hundred objects, among which 30 per cent can be associated with an X-ray source. All the O-type stars are detected in the X-ray domain as soft and reasonably strong emitters. In the 0.5-10.0 keV band, their X-ray luminosities scale with their bolometric luminosities as log L-X - log L-bol = -6.912 +/- 0.153. Such a scaling law holds in the soft (0.5-1.0 keV) and intermediate (1.0-2.5 keV) bands but breaks down in the hard band. While the two colliding wind binaries in our sample clearly deviate from this scheme, the remaining O-type objects show a very limited dispersion (40 or 20 per cent according to whether 'cool' dwarfs are included or not), much smaller than that obtained from previous studies. At our detection threshold and with our sample, the sole identified mechanism that produces significant modulations in the O star X-ray emission is related to wind interaction. We thus propose that the intrinsic X-ray emission of non-peculiar O-type stars can be considered as constant for a given star. In addition, the level of X-ray emission is accurately related to the star luminosity or, equivalently, to its wind properties. Among B-type stars, the detection rate is only about 25 per cent in the subtype range B0-B4 and remains mostly uniform throughout the different subpopulations while it drops significantly at later subtypes. The associated X-ray spectra are harder than those of O-type stars. Our analysis points towards the detected emission being associated with a physical (in a multiple system) PMS companion. However, we still observe a correlation between the bolometric luminosity of the B stars and the measured X-ray luminosity. The best-fitting power law in the 0.5-10.0 keV band yields log L-X = 0.22(+/- 0.06) log L-bol + 22.8(+/- 2.4). [less ▲]

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See detailThe atypical emission-line star Hen 3-209
Nazé, Yaël ULg; Rauw, Grégor ULg; Hutsemekers, Damien ULg et al

in Monthly Notices of the Royal Astronomical Society (2006), 371(4), 1594-1600

We analyse observations, spanning 15 yr, dedicated to the extreme emission-line object Hen 3-209. Our photometric data indicate that the luminosity of the star undergoes marked variations with a peak-to ... [more ▼]

We analyse observations, spanning 15 yr, dedicated to the extreme emission-line object Hen 3-209. Our photometric data indicate that the luminosity of the star undergoes marked variations with a peak-to-peak amplitude of 0.65 mag. These variations are recurrent, with a period of 16.093 +/- 0.005 d. The spectrum of Hen 3-209 is peculiar with many different lines (H I, He I, Fe II,. showing P Cygni profiles. The line profiles are apparently changing in harmony with the photometry. The spectrum also contains [O III] lines that display a saddle profile topped by three peaks, with a maximum separation of about 600 km s(-1). Hen 3-209 is most likely an evolved luminous object suffering from mass ejection events and maybe belonging to a binary system. [less ▲]

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See detailThe XMM large scale structure survey: properties and two-point angular correlations of point-like sources
Gandhi, P.; Garcet, Olivier ULg; Disseau, L. et al

in Astronomy and Astrophysics (2006), 457(2), 393-404

We analyze X-ray sources detected over 4.2 pseudo-contiguous sq. deg. in the 0.5-2 keV and 2-10 keV bands down to fluxes of 2× 10[SUP]-15[/SUP] and 8× 10[SUP]-15[/SUP] erg s[SUP]-1[/SUP] cm[SUP]-2[/SUP ... [more ▼]

We analyze X-ray sources detected over 4.2 pseudo-contiguous sq. deg. in the 0.5-2 keV and 2-10 keV bands down to fluxes of 2× 10[SUP]-15[/SUP] and 8× 10[SUP]-15[/SUP] erg s[SUP]-1[/SUP] cm[SUP]-2[/SUP] respectively, as part of the XMM-Newton Large Scale Structure Survey. The log N-log S in both bands shows a steep slope at bright fluxes, but agrees well with other determinations below ~2 × 10[SUP]-14[/SUP] erg s[SUP]-1[/SUP] cm[SUP]-2[/SUP]. The detected sources resolve close to 30 per cent of the X-ray background in the 2-10 keV band. We study the two-point angular clustering of point sources using nearest neighbours and correlation function statistics and find a weak, positive signal for ~1130 sources in the 0.5-2 keV band, but no correlation for ~400 sources in the 2-10 keV band below scales of 100 arcsec. A sub-sample of ~200 faint sources with hard X-ray count ratios, that is likely to be dominated by obscured AGN, does show a positive signal with the data allowing for a large angular correlation length, but only at the ~2 (3)sigma level, based on re-sampling (Poisson) statistics. We discuss possible implications and emphasize the importance of wider, complete surveys in order to fully understand the large scale structure of the X-ray sky. [less ▲]

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See detailAngular Clustering of Obscured Active Galactic Nuclei
Gandhi, Poshak; Garcet, O.; Disseau, L. et al

in Bulletin of the American Astronomical Society, Vol. 38 (2006, September 01)

We describe the properties of X-ray point-like sources detected over 4.2 sq. degs. of the largest contiguous survey with XMM-Newton to date (the XMM-LSS survey) to fluxes of F[SUB]2-10 keV[/SUB] 8x10[SUP ... [more ▼]

We describe the properties of X-ray point-like sources detected over 4.2 sq. degs. of the largest contiguous survey with XMM-Newton to date (the XMM-LSS survey) to fluxes of F[SUB]2-10 keV[/SUB] 8x10[SUP]-15[/SUP] erg/s/cm[SUP]2[/SUP] and F[SUB]0.5-2 keV[/SUB] 2x10[SUP]-15[/SUP] erg/s/cm[SUP]2[/SUP] respectively. For 1200 sources in the soft band, we find a two-point angular correlation function (ACF) signal similar to previous work, but no correlation for 400 sources in the hard band. A sample of 200 faint sources with hard X-ray spectra does show a 2-3 sigma positive signal with a power-law normalization theta[SUB]0[/SUB]>40 arcsec. We discuss implications, including the fact that a large correlation length for obscured AGN is inconsistent with simple AGN Unification based on orientation only. [less ▲]

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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 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 detailAngular Clustering of X-ray Point-Like Sources in the XMM Large Scale Structure Survey
Garcet, O.; Gandhi, P.; Gosset, Eric ULg et al

in Wilson, A. (Ed.) Proceedings of the ‘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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