References of "Gosset, Eric"
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See detailObservational signatures of past mass-exchange episodes in massive binaries
Raucq, Françoise ULg; Rauw, Grégor ULg; Gosset, Eric ULg et al

Poster (2014, September 05)

Mass and momentum exchanges in massive binaries can produce several observational signatures, such as asynchronous rotation and altered chemical compositions, which remain once the stars detach again. We ... [more ▼]

Mass and momentum exchanges in massive binaries can produce several observational signatures, such as asynchronous rotation and altered chemical compositions, which remain once the stars detach again. We have started to investigate these effects for a sample of detached massive O-star binaries that are thought to have previously experienced a Case A Roche lobe overflow. Using phase-resolved spectroscopy, we perform the disentangling of the spectra of the two stars. The reconstructed primary and secondary spectra are then analyzed to determine a range of stellar effective temperatures and gravity, as well as rotational velocities. Using model atmosphere codes we also constrain the chemical composition of the components. In this contribution, we present the first results of our analyses of HD149404 (O7.5If + ON9.5I, P = 9.81 days). [less ▲]

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See detailNIR interferometric observations of massive hierarchical triple systems: Tr16-104 and HD150136
Gosset, Eric ULg; Le Bouquin, Jean-Baptiste; Absil, Olivier ULg et al

in de Grijs, Richard (Ed.) Binary Systems: their Evolution and Environments (2014, September)

We report on an observational astrometric study of the orbit of the tertiary stars in two massive hierarchical triple systems. The work is complemented by radial velocity data with the aim of deriving the ... [more ▼]

We report on an observational astrometric study of the orbit of the tertiary stars in two massive hierarchical triple systems. The work is complemented by radial velocity data with the aim of deriving the full 3D orbit and constraints on the orbital planes. This is the first report of the tertiary star's detection for Tr16-104. The work is a natural extension of the search for binaries among massive O-stars. The basic motivation of the study of hierarchical triple systems is the determination of the masses of the individual components and the derivation of the relative orientation of the two orbital planes, with the ultimate aim of understanding the related star formation processes. [less ▲]

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See detailInvestigation of the stellar content in the western part of the Carina nebula
Kumar, Brajesh; Sharma, Saurabh; Manfroid, Jean ULg et al

in Astronomy and Astrophysics (2014), 567

Context. The low obscuration and proximity of the Carina nebula make it an ideal place to study the ongoing star formation process and impact of massive stars on low-mass stars in their surroundings. <BR ... [more ▼]

Context. The low obscuration and proximity of the Carina nebula make it an ideal place to study the ongoing star formation process and impact of massive stars on low-mass stars in their surroundings. <BR /> Aims: To investigate this process, we generated a new catalog of the pre-main-sequence stars in the Carina west (CrW) region and studied their nature and spatial distribution. We also determined various parameters (reddening, reddening law, age, mass), which are used further to estimate the initial mass function and K-band luminosity function for the region under study. <BR /> Methods: We obtained deep UBVRI Hα photometric data of the field situated to the west of the main Carina nebula and centered on WR 22. Medium-resolution optical spectroscopy of a subsample of X-ray selected objects along with archival data sets from Chandra, XMM-Newton and 2MASS surveys were used for the present study. Different sets of color-color and color-magnitude diagrams are used to determine reddening for the region and to identify young stellar objects (YSOs) and estimate their age and mass. <BR /> Results: Our spectroscopic results indicate that the majority of the X-ray sources are late spectral type stars. The region shows a large amount of differential reddening with minimum and maximum values of E(B - V) as 0.25 and 1.1 mag, respectively. Our analysis reveals that the total-to-selective absorption ratio R[SUB]V[/SUB] is ~3.7 ± 0.1, suggesting an abnormal grain size in the observed region. We identified 467 YSOs and studied their characteristics. The ages and masses of the 241 optically identified YSOs range from ~0.1 to 10 Myr and ~0.3 to 4.8 M[SUB]⊙[/SUB], respectively. However, the majority of them are younger than 1 Myr and have masses below 2 M[SUB]⊙[/SUB]. The high mass star WR 22 does not seem to have contributed to the formation of YSOs in the CrW region. The initial mass function slope, Γ, in this region is found to be -1.13 ± 0.20 in the mass range of 0.5 < M/M[SUB]⊙[/SUB] < 4.8. The K-band luminosity function slope (α) is also estimated as 0.31 ± 0.01. We also performed minimum spanning tree analysis of the YSOs in this region, which reveals that there are at least ten YSO cores associated with the molecular cloud, and that leads to an average core radius of 0.43 pc and a median branch length of 0.28 pc. Full Table 3 is only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/567/A109">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/567/A109</A> [less ▲]

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See detailThe X-ray properties of lambda Cep, a true twin of zeta Pup?
Rauw, Grégor ULg; Nazé, Yaël ULg; Gonzalez-Perez, Nicolas et al

Conference (2014, June)

Oef stars are O-stars that display a double-peaked He II λ 4686 line in their optical spectra, suggesting that the inner part of the stellar wind is co-rotating with the star. This hypothesis is also ... [more ▼]

Oef stars are O-stars that display a double-peaked He II λ 4686 line in their optical spectra, suggesting that the inner part of the stellar wind is co-rotating with the star. This hypothesis is also often used to explain their ubiquitous spectral variability in the optical domain. In this context, the fact that the high-resolution X-ray spectra of ζ Pup (O4Ief) meet the expectations of the wind-embedded shock model, assuming a spherically symmetric wind came as a surprise. To understand what is going on, we have obtained a 300 ksec observation of λ Cephei, the second brightest Oef star. This observation not only allows to collect the RGS high-resolution spectrum of the star, but further enables us to search for X-ray variability. To correlate the potential X-ray variability with that of the optical spectrum of λ Cep, we monitored the optical spectrum simultaneously with the TIGRE telescope. We present here the first results of this campaign, both in terms of the line profiles in the RGS spectrum and the search for X-ray variability in correlation with the optical variations. [less ▲]

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See detailThe XMM-Newton view of the yellow hypergiant IRC+10420 and its surroundings
De Becker, Michaël ULg; Hutsemekers, Damien ULg; Gosset, Eric ULg

in New Astronomy (2014), 29

Among evolved massive stars likely in transition to the Wolf-Rayet phase, IRC +10420 is probably one of the most enigmatic. It belongs to the category of yellow hypergiants and it is characterized by ... [more ▼]

Among evolved massive stars likely in transition to the Wolf-Rayet phase, IRC +10420 is probably one of the most enigmatic. It belongs to the category of yellow hypergiants and it is characterized by quite high mass loss episodes. Even though IRC+10420 benefited of many observations in several wavelength domains, it has never been a target for an X-ray observatory. We report here on the very first dedicated observation of IRC+10420 in X-rays, using the XMM-Newton satellite. Even though the target is not detected, we derive X-ray flux upper limits of the order of 1–3 ×10−14 erg cm−2 s−1 (between 0.3 and 10.0 keV), and we discuss the case of IRC+10420 in the framework of emission models likely to be adequate for such an object. Using the Optical/UV Monitor on board XMM-Newton, we present the very first upper limits of the flux density of IRC +10420 in the UV domain (between 1800 and 2250 Å and between 2050 and 2450 Å). Finally, we also report on the detection in this field of 10 X-ray and 7 UV point sources, and we briefly discuss their properties and potential counterparts at longer wavelengths. [less ▲]

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See detailEpoch-dependent absorption line profile variability in lambda Cep
Uuh-Sonda, J. M.; Rauw, Grégor ULg; Eenens, P. et al

in Revista Mexicana de Astronomia y Astrofisica (2014), 50

We present the analysis of a multi-epoch spectroscopic monitoring campaign of the O6 Ief star lambda Cep. Previous observations reported the existence of two modes of non-radial pulsations in this star ... [more ▼]

We present the analysis of a multi-epoch spectroscopic monitoring campaign of the O6 Ief star lambda Cep. Previous observations reported the existence of two modes of non-radial pulsations in this star. Our data reveal a much more complex situation. The frequency content of the power spectrum considerably changes from one epoch to the other. We find no stable frequency that can unambiguously be attributed to pulsations. The epoch-dependence of the frequencies and variability patterns are similar to what is seen in the wind emission lines of this and other Oef stars, suggesting that both phenomena likely have the same, currently still unknown, origin. [less ▲]

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See detailA multi-method approach to radial-velocity measurement for single-object spectra
David, M.; Blomme, R.; Frémat, Y. et al

in Astronomy and Astrophysics (2014), 562

Context. The derivation of radial velocities from large numbers of spectra that typically result from survey work, requires automation. However, except for the classical cases of slowly rotating late-type ... [more ▼]

Context. The derivation of radial velocities from large numbers of spectra that typically result from survey work, requires automation. However, except for the classical cases of slowly rotating late-type spectra, existing methods of measuring Doppler shifts require fine-tuning to avoid a loss of accuracy due to the idiosyncrasies of individual spectra. The radial velocity spectrometer (RVS) on the Gaia mission, which will start operating very soon, prompted a new attempt at creating a measurement pipeline to handle a wide variety of spectral types. <BR /> Aims: The present paper describes the theoretical background on which this software is based. However, apart from the assumption that only synthetic templates are used, we do not rely on any of the characteristics of this instrument, so our results should be relevant for most telescope-detector combinations. <BR /> Methods: We propose an approach based on the simultaneous use of several alternative measurement methods, each having its own merits and drawbacks, and conveying the spectral information in a different way, leading to different values for the measurement. A comparison or a combination of the various results either leads to a "best estimate" or indicates to the user that the observed spectrum is problematic and should be analysed manually. <BR /> Results: We selected three methods and analysed the relationships and differences between them from a unified point of view; with each method an appropriate estimator for the individual random error is chosen. We also develop a procedure for tackling the problem of template mismatch in a systematic way. Furthermore, we propose several tests for studying and comparing the performance of the various methods as a function of the atmospheric parameters of the observed objects. Finally, we describe a procedure for obtaining a knowledge-based combination of the various Doppler-shift measurements. [less ▲]

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See detailRecent results on the hierarchical triple system HD 150136
Gosset, Eric ULg; Berger, J. P.; Absil, Olivier ULg et al

in Bonanos, Alceste (Ed.) Massive Stars: From alpha to Omega (2013, June 01)

HD 150136 is a hierarchical triple system, non-thermal radio emitter, made of three O stars totalling some 130 solar masses. The 2.67-day inner orbit is rather well-known. Recent works derived a good ... [more ▼]

HD 150136 is a hierarchical triple system, non-thermal radio emitter, made of three O stars totalling some 130 solar masses. The 2.67-day inner orbit is rather well-known. Recent works derived a good approximation for the outer orbit with a period of 3000 days. We report here on interferometric observations that allow us to angularly resolve the outer orbit. First evidences for an astrometric displacement are given. The determination of the outer system orbit gives access to the inclinations of the systems and to the masses, including the one of the O3-O3.5 primary star. [less ▲]

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See detailThe Hot and Energetic Universe: Star formation and evolution
Sciortino, S.; Rauw, Grégor ULg; Audard, M. et al

Report (2013)

Stars over a wide range of masses and evolutionary stages are nowadays known to emit X-rays. This X-ray emission is a unique probe of the most energetic phenomena occurring in the circumstellar ... [more ▼]

Stars over a wide range of masses and evolutionary stages are nowadays known to emit X-rays. This X-ray emission is a unique probe of the most energetic phenomena occurring in the circumstellar environment of these stars, and provides precious insight on magnetic phenomena or hydrodynamic shocks. Owing to its large collecting area, Athena+ will open up an entirely new window on these phenomena. Indeed, Athena+ will not only allow us to study many more objects with an unprecedented spectral resolution, but will also pioneer the study of the dynamics of these objects via time-resolved high-resolution spectroscopy. In this way, Athena+ will be a unique tool to study accretion processes in TTauri stars, flaring activity in young stars, dynamos in ultra-cool dwarfs, small and large-scale structures in the winds of single massive stars, wind interactions in massive binary systems, hot bubbles in planetary nebula... All these studies will lead to a deeper understanding of yet poorly understood processes which have profound impact in star and planetary system formation as well as in feedback processes on Galactic scale. [less ▲]

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See detailThe Hot and Energetic Universe: A White Paper presenting the science theme motivating the Athena+ mission
Nandra, Kirpal; Barret, Didier; Barcons, Xavier et al

Report (2013)

This White Paper, submitted to the recent ESA call for science themes to define its future large missions, advocates the need for a transformational leap in our understanding of two key questions in ... [more ▼]

This White Paper, submitted to the recent ESA call for science themes to define its future large missions, advocates the need for a transformational leap in our understanding of two key questions in astrophysics: 1) How does ordinary matter assemble into the large scale structures that we see today? 2) How do black holes grow and shape the Universe? Hot gas in clusters, groups and the intergalactic medium dominates the baryonic content of the local Universe. To understand the astrophysical processes responsible for the formation and assembly of these large structures, it is necessary to measure their physical properties and evolution. This requires spatially resolved X-ray spectroscopy with a factor 10 increase in both telescope throughput and spatial resolving power compared to currently planned facilities. Feedback from supermassive black holes is an essential ingredient in this process and in most galaxy evolution models, but it is not well understood. X-ray observations can uniquely reveal the mechanisms launching winds close to black holes and determine the coupling of the energy and matter flows on larger scales. Due to the effects of feedback, a complete understanding of galaxy evolution requires knowledge of the obscured growth of supermassive black holes through cosmic time, out to the redshifts where the first galaxies form. X-ray emission is the most reliable way to reveal accreting black holes, but deep survey speed must improve by a factor ~100 over current facilities to perform a full census into the early Universe. The Advanced Telescope for High Energy Astrophysics (Athena+) mission provides the necessary performance (e.g. angular resolution, spectral resolution, survey grasp) to address these questions and revolutionize our understanding of the Hot and Energetic Universe. These capabilities will also provide a powerful observatory to be used in all areas of astrophysics. [less ▲]

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See detailThree-dimensional orbits of the triple-O stellar system HD 150136
Sana, H.; Le Bouquin, J.-B.; Mahy, Laurent et al

in Astronomy and Astrophysics (2013), 553

Context. HD 150136 is a triple hierarchical system and a non-thermal radio emitter. It is formed by an O3-3.5 V + O5.5-6 V close binary and a more distant O6.5-7 V tertiary. So far, only the inner orbital ... [more ▼]

Context. HD 150136 is a triple hierarchical system and a non-thermal radio emitter. It is formed by an O3-3.5 V + O5.5-6 V close binary and a more distant O6.5-7 V tertiary. So far, only the inner orbital properties have been reliably constrained. Aims. To quantitatively understand the non-thermal emission process, accurate knowledge of the physical and orbital properties of the object is crucial. Here, we aim to investigate the orbital properties of the wide system and to constrain the inclinations of the inner and outer binaries, and with these the absolute masses of the system components. Methods. We used the PIONIER combiner at the Very Large Telescope Interferometer to obtain the very first interferometric measurements of HD 150136. We combined the interferometric observations with new and existing high resolution spectroscopic data to derive the orbital solution of the outer companion in the three-dimensional space. Results. The wide system is clearly resolved by PIONIER, with a projected separation on the plane of the sky of about 9 milli-arcsec. The best-fit orbital period, eccentricity, and inclination are 8.2 yr, 0.73 and 108 degr. We constrain the masses of the three stars of the system to 63 +/- 10, 40 +/- 6, and 33 +/- 12 Msun for the O3-3.5 V, O5.5-6 V and O6.5-7 V components. Conclusions. The dynamical masses agree within errors with the evolutionary masses of the components. Future interferometric and spectroscopic monitoring of HD 150136 should allow one to reduce the uncertainties to a few per cent only and to accurately constrain the distance to the system. This makes HD 150136 an ideal system to quantitatively test evolutionary models of high-mass stars as well as the physics of non-thermal processes occurring in O-type systems. [less ▲]

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See detailA Detailed X-Ray Investigation of ζ Puppis. II. The Variability on Short and Long Timescales
Nazé, Yaël ULg; Oskinova, Lidia M.; Gosset, Eric ULg

in Astrophysical Journal (2013), 763

Stellar winds are a crucial component of massive stars, but their exact properties still remain uncertain. To shed some light on this subject, we have analyzed an exceptional set of X-ray observations of ... [more ▼]

Stellar winds are a crucial component of massive stars, but their exact properties still remain uncertain. To shed some light on this subject, we have analyzed an exceptional set of X-ray observations of ζ Puppis, one of the closest and brightest massive stars. The sensitive light curves that were derived reveal two major results. On the one hand, a slow modulation of the X-ray flux (with a relative amplitude of up to 15% over 16 hr in the 0.3-4.0 keV band) is detected. Its characteristic timescale cannot be determined with precision, but amounts from one to several days. It could be related to corotating interaction regions, known to exist in ζ Puppis from UV observations. Hour-long changes, linked to flares or to the pulsation activity, are not observed in the last decade covered by the XMM observations; the 17 hr tentative period, previously reported in a ROSAT analysis, is not confirmed either and is thus transient, at best. On the other hand, short-term changes are surprisingly small (<1% relative amplitude for the total energy band). In fact, they are compatible solely with the presence of Poisson noise in the data. This surprisingly low level of short-term variability, in view of the embedded wind-shock origin, requires a very high fragmentation of the stellar wind, for both absorbing and emitting features (>10[SUP]5[/SUP] parcels, comparing with a two-dimensional wind model). This is the first time that constraints have been placed on the number of clumps in an O-type star wind and from X-ray observations. Based on observations collected with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). [less ▲]

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See detailCoRoT Observations of O Stars: Diverse Origins of Variability
Blomme, R.; Briquet, Maryline ULg; Degroote, P. et al

in Astronomical Society of the Pacific Conference Series (2013, January 01)

Six O-type stars were observed continuously by the CoRoT satellite during a 34.3-day run. The unprecedented quality of the data allows us to detect even low-amplitude stellar pulsations in some of these ... [more ▼]

Six O-type stars were observed continuously by the CoRoT satellite during a 34.3-day run. The unprecedented quality of the data allows us to detect even low-amplitude stellar pulsations in some of these stars (HD 46202 and the binaries HD 46149 and Plaskett's star). These cover both opacity-driven modes and solar-like stochastic oscillations, both of importance to the asteroseismological modeling of O stars. Additional effects can be seen in the CoRoT light curves, such as binarity and rotational modulation. Some of the hottest O-type stars (HD 46223, HD 46150 and HD 46966) are dominated by the presence of red-noise: we speculate that this is related to a sub-surface convection zone. [less ▲]

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See detailSur l'histoire de l'astronomie à Liège
Gosset, Eric ULg; Nazé, Yaël ULg

Diverse speeche and writing (2012)

Cette série de posters s'intéresse à l'astronomie à Liège : (1) l'astronomie avant l'institut (Y. Nazé), (2) l'institut et les premiers directeurs (E. Gosset), et (3) l'astronomie au milieu du 20e siècle ... [more ▼]

Cette série de posters s'intéresse à l'astronomie à Liège : (1) l'astronomie avant l'institut (Y. Nazé), (2) l'institut et les premiers directeurs (E. Gosset), et (3) l'astronomie au milieu du 20e siècle (Y. Nazé). [less ▲]

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See detailBinary Interaction Dominates the Evolution of Massive Stars
Sana, H.; de Mink, S. E.; de Koter, A. et al

in Science (2012), 337(6093), 444-446

The presence of a nearby companion alters the evolution of massive stars in binary systems, leading to phenomena such as stellar mergers, x-ray binaries, and gamma-ray bursts. Unambiguous constraints on ... [more ▼]

The presence of a nearby companion alters the evolution of massive stars in binary systems, leading to phenomena such as stellar mergers, x-ray binaries, and gamma-ray bursts. Unambiguous constraints on the fraction of massive stars affected by binary interaction were lacking. We simultaneously measured all relevant binary characteristics in a sample of Galactic massive O stars and quantified the frequency and nature of binary interactions. More than 70% of all massive stars will exchange mass with a companion, leading to a binary merger in one-third of the cases. These numbers greatly exceed previous estimates and imply that binary interaction dominates the evolution of massive stars, with implications for populations of massive stars and their supernovae. [less ▲]

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See detail9 Sagittarii: uncovering an O-type spectroscopic binary with an 8.6 year period
Rauw, Grégor ULg; Sana, H.; Spano, M. et al

in Astronomy and Astrophysics (2012), 542

Context. The O-type object 9 Sgr is a well-known synchrotron radio emitter. This feature is usually attributed to colliding-wind binary systems, but 9 Sgr was long considered a single star. <BR /> Aims ... [more ▼]

Context. The O-type object 9 Sgr is a well-known synchrotron radio emitter. This feature is usually attributed to colliding-wind binary systems, but 9 Sgr was long considered a single star. <BR /> Aims: We have conducted a long-term spectroscopic monitoring of this star to investigate its multiplicity and search for evidence for wind-wind interactions. <BR /> Methods: Radial velocities are determined and analysed using various period search methods. Spectral disentangling is applied to separate the spectra of the components of the binary system. <BR /> Results: We derive the first ever orbital solution of 9 Sgr. The system is found to consist of an O3.5 V((f[SUP]+[/SUP])) primary and an O5-5.5 V((f)) secondary moving around each other on a highly eccentric (e = 0.7), 8.6 year orbit. The spectra reveal no variable emission lines that could be formed in the wind interaction zone in agreement with the expected properties of the interaction in such a wide system. <BR /> Conclusions: Our results provide further support to the paradigm of synchrotron radio emission from early-type stars being a manifestation of interacting winds in a binary system. Based on observations collected at the European Southern Observatory (La Silla, Chile and Cerro Paranal, Chile) and the San Pedro Mártir observatory (Mexico).Appendix A is available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A>The reduced spectra are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/542/A95">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/542/A95</A> [less ▲]

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See detailSpectroscopic binary processing within Gaia DPAC
Damerdji, Yassine ULg; Morel, Thierry ULg; Gosset, Eric ULg

in Orbital Couples: Pas de Deux in the Solar System and the Milky Way (2012, May 01)

Not Available

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See detailThe Struve-Sahade effect in the optical spectra of O-type binaries. I. Main-sequence systems (Corrigendum)
Linder, N.; Rauw, Grégor ULg; Sana, H. et al

in Astronomy and Astrophysics (2012), 541

Not Available.

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See detailEvidence for a physically bound third component in HD 150136
Mahy, Laurent ULg; Gosset, Eric ULg; Sana, H et al

in Astronomy and Astrophysics (2012), 540

Context. HD 150136 is one of the nearest systems harbouring an O3 star. Although this system was considered for a long time as a binary, more recent investigations have suggested the possible existence of ... [more ▼]

Context. HD 150136 is one of the nearest systems harbouring an O3 star. Although this system was considered for a long time as a binary, more recent investigations have suggested the possible existence of a third component. <BR /> Aims: We present a detailed analysis of HD 150136 to test its triple nature. In addition, we investigate the physical properties of the individual components of this system. <BR /> Methods: We analysed high-resolution, high signal-to-noise data collected through multi-epoch runs spread over ten years. We applied a disentangling program to refine the radial velocities and to obtain the individual spectra of each star. With the radial velocities, we computed the orbital solution of the inner system, and we describe the main properties of the orbit of the outer star such as the preliminary mass ratio, the eccentricity, and the orbital-period range. With the individual spectra, we determined the stellar parameters of each star by means of the CMFGEN atmosphere code. <BR /> Results: We offer clear evidence that HD 150136 is a triple system composed of an O3V((f[SUP]∗[/SUP]))-3.5V((f[SUP]+[/SUP])), an O5.5-6V((f)), and an O6.5-7V((f)) star. The three stars are between 0-3 Myr old. We derive dynamical masses of about 64, 40, and 35 M[SUB]&sun;[/SUB] for the primary, the secondary and the third components by assuming an inclination of 49° (sin[SUP]3[/SUP]i = 0.43). It currently corresponds to one of the most massive systems in our galaxy. The third star moves with a period in the range of 2950 to 5500 d on an outer orbit with an eccentricity of at least 0.3. However, because of the long orbital period, our dataset is not sufficient to constrain the orbital solution of the tertiary component with high accuracy. <BR /> Conclusions: We confirm there is a tertiary star in the spectrum of HD 150136 and show that it is physically bound to the inner binary system. This discovery makes HD 150136 the first confirmed triple system with an O3 primary star. Table 1 is available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

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See detailAngular correlation functions of X-ray point-like sources in the full exposure XMM-LSS field
Elyiv, Andrii ULg; Clerc, N.; Plionis, M. et al

in Astronomy and Astrophysics (2012), 537

<BR /> Aims: Our aim is to study the large-scale structure of different types of AGN using the medium-deep XMM-LSS survey. <BR /> Methods: We measure the two-point angular correlation function of 5700 and ... [more ▼]

<BR /> Aims: Our aim is to study the large-scale structure of different types of AGN using the medium-deep XMM-LSS survey. <BR /> Methods: We measure the two-point angular correlation function of 5700 and 2500 X-ray point-like sources over the 11 sq. deg. XMM-LSS field in the soft (0.5-2 keV) and hard (2-10 keV) bands. For the conversion from the angular to the spatial correlation function we used the Limber integral equation and the luminosity-dependent density evolution model of the AGN X-ray luminosity function. <BR /> Results: We have found significant angular correlations with the power-law parameters γ = 1.81 ± 0.02, θ[SUB]0[/SUB] = 1.3'' ± 0.2'' for the soft, and γ = 2.00 ± 0.04, θ[SUB]0[/SUB] = 7.3'' ± 1.0'' for the hard bands. The amplitude of the correlation function w(θ) is higher in the hard than in the soft band for f[SUB]x[/SUB] ≲ 10[SUP]-14[/SUP] erg s[SUP]-1[/SUP] cm[SUP]-2[/SUP] and lower above this flux limit. We confirm that the clustering strength θ[SUB]0[/SUB] grows with the flux limit of the sample, a trend which is also present in the amplitude of the spatial correlation function, but only for the soft band. In the hard band, it remains almost constant with r[SUB]0[/SUB] ≃ 10h[SUP]-1[/SUP] Mpc, irrespective of the flux limit. Our analysis of AGN subsamples with different hardness ratios shows that the sources with a hard-spectrum are more clustered than soft-spectrum ones. This result may be a hint that the two main types of AGN populate different environments. Finally, we find that our clustering results correspond to an X-ray selected AGN bias factor of 2.5 for the soft band sources (at a median <inline-formula>bar{z} ≃ 1.1) and 3.3 for the hard band sources (at a median <inline-formula>bar{z} ≃ 1), which translates into a host dark matter halo mass of 10[SUP]13[/SUP]h[SUP]-1[/SUP]M[SUB]&sun;[/SUB] and 10[SUP]13.7[/SUP]h[SUP]-1[/SUP]M[SUB]&sun;[/SUB] for the soft and hard bands, respectively. This paper is dedicated to the memory of Olivier Garcet who has initiated the present work just before his sudden death. [less ▲]

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