References of "Nazé, Yaël"
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See detailDossier presse - expo les horlogers du ciel
Champenois, Carole ULg; Moreau, Didier ULg; Nazé, Yaël ULg

Diverse speeche and writing (2011)

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See detailOf?p stars: a class of slowly rotating magnetic massive stars
Wade, Gregg A; Grunhut, Jason H; Marcolino, Wagner L F et al

(2011, July 01)

Only 5 Of?p stars have been identified in the Galaxy. Of these, 3 have been studied in detail, and within the past 5 years magnetic fields have been detected in each of them. The observed magnetic and ... [more ▼]

Only 5 Of?p stars have been identified in the Galaxy. Of these, 3 have been studied in detail, and within the past 5 years magnetic fields have been detected in each of them. The observed magnetic and spectral characteristics are indicative of organised magnetic fields, likely of fossil origin, confining their supersonic stellar winds into dense, structured magnetospheres. The systematic detection of magnetic fields in these stars strongly suggests that the Of?p stars represent a general class of magnetic O-type stars. [less ▲]

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See detailOverall properties of hot, massive stars in the X-ray domain
Nazé, Yaël ULg

(2011, July 01)

Despite the absence of large surveys, the recent X-ray observatories provide X-ray data for hundreds of massive stars (294 OB stars detected in the 2XMM catalog, 129 OB stars detected in the Chandra ... [more ▼]

Despite the absence of large surveys, the recent X-ray observatories provide X-ray data for hundreds of massive stars (294 OB stars detected in the 2XMM catalog, 129 OB stars detected in the Chandra Carina Complex Project). Analyzing medium-resolution spectra led to new results on the relationship between the X-ray luminosity and the bolometric luminosity, as well as on the typical properties (plasma temperature, variability) of these objects. [less ▲]

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See detailThe Chandra survey of Carina OB stars
Gagné, Marc; Fehon, Garrett; Savoy, Michael R et al

(2011, July 01)

We have combined 22 deep Chandra ACIS-I pointings to map over one square degree of the Carina complex. Our x-ray survey detects 69 of 70 known O-type stars and 61 of 130 known early B stars. The majority ... [more ▼]

We have combined 22 deep Chandra ACIS-I pointings to map over one square degree of the Carina complex. Our x-ray survey detects 69 of 70 known O-type stars and 61 of 130 known early B stars. The majority of single O stars display soft X-ray spectra and have a mean log L[SUB]X[/SUB]/L[SUB]bol[/SUB] ~ -7.5 suggesting shocks embedded in the O-star winds. Over OB stars show unusually high X-ray luminosities, high shock temperatures or time variability, not predicted for embedded wind shocks. [less ▲]

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See detailThe latest developments on Of?p stars
Nazé, Yaël ULg; ud-Doula, Asif; Spano, Maxime et al

in Neiner, Coralie; Wade, G.; Meynet, G. (Eds.) et al Active OB stars: structure, evolution, mass loss and critical limits (2011, July 01)

In recent years several in-depth investigations of the three prototypical Of?p stars were undertaken, revealing their peculiar properties. To clarify some of the remaining questions, we have continued our ... [more ▼]

In recent years several in-depth investigations of the three prototypical Of?p stars were undertaken, revealing their peculiar properties. To clarify some of the remaining questions, we have continued our monitoring of the prototypical Of?p trio. HD 108 has now reached its quiescent, minimum-emission state, for the first time in 50-60yrs, while new echelle spectra of HD 148937 confirm the presence in several H and He lines of the 7d variations detected previously only in the Hα line. A new XMM observation of HD 191612 clearly shows that its X-ray emission is not modulated by the orbital period of 1542d, but the high-energy variations are rather compatible with the 538d period of the optical changes - it is thus not of colliding-wind origin but linked to the phenomena responsible for the spectral/photometric variations, though our current MHD simulations remain at odds with the observational properties. [less ▲]

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See detailThe surprising X-ray emission of Oe stars
Nazé, Yaël ULg; Rauw, Grégor ULg; ud-Doula, Asif

in Neiner, Coralie; Wade, G.; Meynet, G. (Eds.) et al Active OB stars: structure, evolution, mass loss and critical limits (2011, July 01)

Oe stars are thought to represent an extension of the Be phenomenon to higher temperatures. Dedicated XMM observations of HD 155806 revealed a surprising X-ray spectrum: soft character, absence of ... [more ▼]

Oe stars are thought to represent an extension of the Be phenomenon to higher temperatures. Dedicated XMM observations of HD 155806 revealed a surprising X-ray spectrum: soft character, absence of overluminosity, broad X-ray lines. These properties are fully compatible with the wind-shock model, which usually explains the X-rays from ``normal'', single O-type stars. In contrast, some other Oe/Be stars display a completely different behaviour at high energies. [less ▲]

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See detailTrois recettes célestes
Nazé, Yaël ULg

Article for general public (2011)

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See detailThe Search for Low-mass Companions of B Stars in the Carina Nebula Cluster Trumpler 16
Evans, Nancy Remage; DeGioia-Eastwood, Kathleen; Gagné, Marc et al

in Astrophysical Journal. Supplement Series (2011), 194

We have developed lists of likely B3-A0 stars (called "late B" stars) in the young cluster Trumpler 16. The following criteria were used: location within 3' of η Car, an appropriate V and B - V ... [more ▼]

We have developed lists of likely B3-A0 stars (called "late B" stars) in the young cluster Trumpler 16. The following criteria were used: location within 3' of η Car, an appropriate V and B - V combination, and proper motion (where available). Color and magnitude cuts have been made assuming an E(B - V) = 0.55 mag ± 0.1, which is a good approximation close to the center of Trumpler 16. These lists have been cross-correlated with X-ray sources found in the Chandra Carina Complex Project. Previous studies have shown that only very rarely (if at all) do late main-sequence B stars produce X-rays. We present evidence that the X-ray-detected sources are binaries with low-mass companions, since stars less massive than 1.4 M [SUB]sun[/SUB] are strong X-ray sources at the age of the cluster. Both the median X-ray energies and X-ray luminosities of these sources are in good agreement with values for typical low-mass coronal X-ray sources. We find that 39% of the late B stars based on a list with proper motions have low-mass companions. Similarly, 32% of a sample without proper motions have low-mass companions. We discuss the X-ray detection completeness. These results on low-mass companions of intermediate-mass stars are complementary to spectroscopic and interferometric results and probe new parameter space of low-mass companions at all separations. They do not support a steeply rising distribution of mass ratios to low masses for intermediate-mass (5 M [SUB]sun[/SUB]) primaries, such as would be found by random pairing from the initial mass function. Based on observations made with the Chandra X-ray Observatory. [less ▲]

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See detailAn Introduction to the Chandra Carina Complex Project
Townsley, Leisa K; Broos, Patrick S; Corcoran, Michael F et al

in Astrophysical Journal. Supplement Series (2011), 194

The Great Nebula in Carina provides an exceptional view into the violent massive star formation and feedback that typifies giant H II regions and starburst galaxies. We have mapped the Carina star-forming ... [more ▼]

The Great Nebula in Carina provides an exceptional view into the violent massive star formation and feedback that typifies giant H II regions and starburst galaxies. We have mapped the Carina star-forming complex in X-rays, using archival Chandra data and a mosaic of 20 new 60 ks pointings using the Chandra X-ray Observatory's Advanced CCD Imaging Spectrometer, as a testbed for understanding recent and ongoing star formation and to probe Carina's regions of bright diffuse X-ray emission. This study has yielded a catalog of properties of >14,000 X-ray point sources; >9800 of them have multiwavelength counterparts. Using Chandra's unsurpassed X-ray spatial resolution, we have separated these point sources from the extensive, spatially-complex diffuse emission that pervades the region; X-ray properties of this diffuse emission suggest that it traces feedback from Carina's massive stars. In this introductory paper, we motivate the survey design, describe the Chandra observations, and present some simple results, providing a foundation for the 15 papers that follow in this special issue and that present detailed catalogs, methods, and science results. [less ▲]

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See detailThe Chandra Carina Complex Project: Deciphering the Enigma of Carina's Diffuse X-ray Emission
Townsley, Leisa K; Broos, Patrick S; Chu, You-Hua et al

in Astrophysical Journal. Supplement Series (2011), 194

We present a 1.42 deg[SUP]2[/SUP] mosaic of diffuse X-ray emission in the Great Nebula in Carina from the Chandra X-ray Observatory Advanced CCD Imaging Spectrometer camera. After removing >14,000 X-ray ... [more ▼]

We present a 1.42 deg[SUP]2[/SUP] mosaic of diffuse X-ray emission in the Great Nebula in Carina from the Chandra X-ray Observatory Advanced CCD Imaging Spectrometer camera. After removing >14,000 X-ray point sources from the field, we smooth the remaining unresolved emission, tessellate it into segments of similar apparent surface brightness, and perform X-ray spectral fitting on those tessellates to infer the intrinsic properties of the X-ray-emitting plasma. By modeling faint resolved point sources, we estimate the contribution to the extended X-ray emission from unresolved point sources and show that the vast majority of Carina's unresolved X-ray emission is truly diffuse. Line-like correlated residuals in the X-ray spectral fits suggest that substantial X-ray emission is generated by charge exchange at the interfaces between Carina's hot, rarefied plasma and its many cold neutral pillars, ridges, and clumps. [less ▲]

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See detailCarina OB Stars: X-ray Signatures of Wind Shocks and Magnetic Fields
Gagné, Marc; Fehon, Garrett; Savoy, Michael R et al

in Astrophysical Journal. Supplement Series (2011), 194

The Chandra Carina Complex contains 200 known O- and B-type stars. The Chandra survey detected 68 of the 70 O stars and 61 of 127 known B0-B3 stars. We have assembled a publicly available optical/X-ray ... [more ▼]

The Chandra Carina Complex contains 200 known O- and B-type stars. The Chandra survey detected 68 of the 70 O stars and 61 of 127 known B0-B3 stars. We have assembled a publicly available optical/X-ray database to identify OB stars that depart from the canonical L [SUB]X[/SUB]/L [SUB]bol[/SUB] relation or whose average X-ray temperatures exceed 1 keV. Among the single O stars with high kT we identify two candidate magnetically confined wind shock sources: Tr16-22, O8.5 V, and LS 1865, O8.5 V((f)). The O4 III(fc) star HD 93250 exhibits strong, hard, variable X-rays, suggesting that it may be a massive binary with a period of >30 days. The visual O2 If* binary HD 93129A shows soft 0.6 keV and hard 1.9 keV emission components, suggesting embedded wind shocks close to the O2 If* Aa primary and colliding wind shocks between Aa and Ab. Of the 11 known O-type spectroscopic binaries, the long orbital-period systems HD 93343, HD 93403, and QZ Car have higher shock temperatures than short-period systems such as HD 93205 and FO 15. Although the X-rays from most B stars may be produced in the coronae of unseen, low-mass pre-main-sequence companions, a dozen B stars with high L [SUB]X[/SUB] cannot be explained by a distribution of unseen companions. One of these, SS73 24 in the Treasure Chest cluster, is a new candidate Herbig Be star. [less ▲]

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See detailX-ray Emission from the Double-binary OB-star System QZ Car (HD 93206)
Parkin, E. R.; Broos, P. S.; Townsley, L. K. et al

in Astrophysical Journal. Supplement Series (2011), 194

X-ray observations of the double-binary OB-star system QZ Car (HD 93206) obtained with the Chandra X-ray Observatory over a period of roughly 2 years are presented. The respective orbits of systems A (O9 ... [more ▼]

X-ray observations of the double-binary OB-star system QZ Car (HD 93206) obtained with the Chandra X-ray Observatory over a period of roughly 2 years are presented. The respective orbits of systems A (O9.7 I+b2 v, P [SUB]A[/SUB] = 21 days) and B (O8 III+o9 v, P [SUB]B[/SUB] = 6 days) are reasonably well sampled by the observations, allowing the origin of the X-ray emission to be examined in detail. The X-ray spectra can be well fitted by an attenuated three-temperature thermal plasma model, characterized by cool, moderate, and hot plasma components at kT ~= 0.2, 0.7, and 2 keV, respectively, and a circumstellar absorption of sime0.2 × 10[SUP]22[/SUP] cm[SUP]-2[/SUP]. Although the hot plasma component could be indicating the presence of wind-wind collision shocks in the system, the model fluxes calculated from spectral fits, with an average value of sime7 × 10[SUP]-13[/SUP] erg s[SUP]-1[/SUP] cm[SUP]-2[/SUP], do not show a clear correlation with the orbits of the two constituent binaries. A semi-analytical model of QZ Car reveals that a stable momentum balance may not be established in either system A or B. Yet, despite this, system B is expected to produce an observed X-ray flux well in excess of the observations. If one considers the wind of the O8 III star to be disrupted by mass transfer, the model and observations are in far better agreement, which lends support to the previous suggestion of mass transfer in the O8 III + o9 v binary. We conclude that the X-ray emission from QZ Car can be reasonably well accounted for by a combination of contributions mainly from the single stars and the mutual wind-wind collision between systems A and B. [less ▲]

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See detailGlobal X-ray Properties of the O and B Stars in Carina
Nazé, Yaël ULg; Broos, P. S.; Oskinova, L. et al

in Astrophysical Journal. Supplement Series (2011), 194

The key empirical property of the X-ray emission from O stars is a strong correlation between the bolometric and X-ray luminosities. In the framework of the Chandra Carina Complex Project, 129 O and B ... [more ▼]

The key empirical property of the X-ray emission from O stars is a strong correlation between the bolometric and X-ray luminosities. In the framework of the Chandra Carina Complex Project, 129 O and B stars have been detected as X-ray sources; 78 of those, all with spectral type earlier than B3, have enough counts for at least a rough X-ray spectral characterization. This leads to an estimate of the L [SUB]X[/SUB]-L [SUB]BOL[/SUB] ratio for an exceptional number of 60 O stars belonging to the same region and triples the number of Carina massive stars studied spectroscopically in X-rays. The derived log(L [SUB]X[/SUB]/L [SUB]BOL[/SUB]) is -7.26 for single objects, with a dispersion of only 0.21 dex. Using the properties of hot massive stars listed in the literature, we compare the X-ray luminosities of different types of objects. In the case of O stars, the L [SUB]X[/SUB]-L [SUB]BOL[/SUB] ratios are similar for bright and faint objects, as well as for stars of different luminosity classes or spectral types. Binaries appear only slightly harder and slightly more luminous in X-rays than single objects; the differences are not formally significant (at the 1% level), except for the L [SUB]X[/SUB]-L [SUB]BOL[/SUB] ratio in the medium (1.0-2.5 keV) energy band. Weak-wind objects have similar X-ray luminosities but they display slightly softer spectra compared with "normal" O stars with the same bolometric luminosity. Discarding three overluminous objects, we find a very shallow trend of harder emission in brighter objects. The properties of the few B stars bright enough to yield some spectral information appear to be different overall (constant X-ray luminosities, harder spectra), hinting that another mechanism for producing X-rays, besides wind shocks, might be at work. However, it must be stressed that the earliest and X-ray brightest among these few detected objects are similar to the latest O stars, suggesting a possibly smooth transition between the two processes. [less ▲]

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See detailXMM-Newton observation of the enigmatic object WR 46
Gosset, Eric ULg; De Becker, Michaël ULg; Nazé, Yaël ULg et al

in Astronomy and Astrophysics (2011), 527

Aims: To further investigate the nature of the enigmatic object WR 46 and better understand the X-ray emission in massive stars and in their evolved descendants, we observed this variable object for more ... [more ▼]

Aims: To further investigate the nature of the enigmatic object WR 46 and better understand the X-ray emission in massive stars and in their evolved descendants, we observed this variable object for more than two of its supposed cycles. The X-ray emission characteristics are appropriate indicators of the difference between a genuine Wolf-Rayet star and a specimen of a super soft source as sometimes suggested in the literature. The X-ray emission analysis might contribute to understanding the origin of the emitting plasma (intrinsically shocked wind, magnetically confined wind, colliding winds, and accretion onto a white dwarf or a more compact object) and to substantiating the decision about the exact nature of the star. <BR /> Methods: The X-ray observations of WR 46 were performed with the XMM-Newton facility over an effective exposure time of about 70 ks. <BR /> Results: Both the X-ray luminosity of WR 46, typical of a Wolf-Rayet star, and the existence of a relatively hard component (including the Fe-K line) rule out the possibility that WR 46 could be classified as a super soft source, and instead favour the Wolf-Rayet hypothesis. The X-ray emission of the star turns out to be variable below 0.5 keV but constant at higher energies. The soft variability is associated to the Wolf-Rayet wind, but revealing its deep origin necessitates additional investigations. It is the first time that such a variability is reported for a Wolf-Rayet star. Indeed, the X-ray emission exhibits a single-wave variation with a typical timescale of 7.9 h which could be related to the period observed in the visible domain both in radial velocities (single-wave) and in photometry (double-wave). The global X-ray emission seems to be dominated by lines and is closely reproduced by a three-temperature, optically thin, thermal plasma model. The derived values are 0.1-0.2 keV, 0.6 keV, and ~4 keV, which indicates that a wide range of temperatures is actually present. The soft emission part could be related to a shocked-wind phenomenon. The hard tail of the spectrum cannot presently be explained by such an intrinsic phenomenon as a shocked wind and instead suggests there is a wind-wind collision zone, as does the relatively high L[SUB]X[/SUB]/L[SUB]bol[/SUB] ratio. We argue that this scenario implies the existence of an object farther away from the WN3 object than any possible companion in an orbit related to the short periodicity. Based on observations 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 detailMESS (Mass-loss of Evolved StarS), a Herschel Key Program
Groenewegen, M. A. T.; Waelkens, C.; Barlow, M. J. et al

in Astronomy and Astrophysics (2011), 526

MESS (Mass-loss of Evolved StarS) is a Guaranteed Time Key Program that uses the PACS and SPIRE instruments on board the Herschel Space Observatory to observe a representative sample of evolved stars ... [more ▼]

MESS (Mass-loss of Evolved StarS) is a Guaranteed Time Key Program that uses the PACS and SPIRE instruments on board the Herschel Space Observatory to observe a representative sample of evolved stars, that include asymptotic giant branch (AGB) and post-AGB stars, planetary nebulae and red supergiants, as well as luminous blue variables, Wolf-Rayet stars and supernova remnants. In total, of order 150 objects are observed in imaging and about 50 objects in spectroscopy. This paper describes the target selection and target list, and the observing strategy. Key science projects are described, and illustrated using results obtained during Herschel's science demonstration phase. Aperture photometry is given for the 70 AGB and post-AGB stars observed up to October 17, 2010, which constitutes the largest single uniform database of far-IR and sub-mm fluxes for late-type stars. [less ▲]

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See detailLes animaux du ciel
Nazé, Yaël ULg

Article for general public (2011)

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See detailHerschel-PACS observations of Nebulae Ejected by Massive Stars
Vamvatira Nakou, Chloi ULg; Royer, Pierre; Hutsemekers, Damien ULg et al

in Bulletin de la Société Royale des Sciences de Liège (2011), 80

The study of the nebulae ejected from Luminous Blue Variables and the circumstellar bubbles around Wolf-Rayet stars, which radiate strongly in the infrared due to the heating of dust, is crucial for the ... [more ▼]

The study of the nebulae ejected from Luminous Blue Variables and the circumstellar bubbles around Wolf-Rayet stars, which radiate strongly in the infrared due to the heating of dust, is crucial for the understanding of the massive stars evolution. With Herschel we are able to observe these objects in the far-infrared region. In the context of the Mass-loss from Evolved StarS guaranteed time key program, we obtained imaging and spectroscopic observations of nebulae associated with Luminous Blue Variable and Wolf-Rayet stars using PACS, one of the three instruments on-board Herschel. A description of these observations, data analysis and preliminary results are presented. [less ▲]

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See detailThe multiplicity of O-type stars in NGC 2244
Mahy, Laurent ULg; Rauw, Grégor ULg; Martins, F. et al

in Bulletin de la Societe Royale des Sciences de Liege (2011), 80

The investigation of the multiplicity of massive stars is crucial to determine a robust binary fraction but also for understanding the physical properties of these objects. In this contribution, we will ... [more ▼]

The investigation of the multiplicity of massive stars is crucial to determine a robust binary fraction but also for understanding the physical properties of these objects. In this contribution, we will present the main results from our long-term spectroscopic survey devoted to the young open cluster NGC 2244. We discuss the spectral classification, the projected rotational velocity (v sin{i}) and the multiplicity of O-stars. The stellar and wind parameters of each star, obtained using the CMFGEN atmosphere code, help us to better constrain the individual properties of these objects. Several of these stars were observed by the CoRoT satellite (SRa02) in the Asteroseismology channel. This intensive monitoring and the unprecedented quality of the light curves allow us to shed a new light on these objects. [less ▲]

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See detailA first orbital solution for the non-thermal radio emitter Cyg OB2 #9
Nazé, Yaël ULg; Damerdji, Yassine ULg; Rauw, Grégor ULg et al

in Bulletin de la Société Royale des Sciences de Liège (2011), 80

We reported in 2008 the first detection of the binary nature of Cyg OB2 #9. Since then, we have continued our spectroscopic monitoring of this object, doubling the number of available spectra of the star ... [more ▼]

We reported in 2008 the first detection of the binary nature of Cyg OB2 #9. Since then, we have continued our spectroscopic monitoring of this object, doubling the number of available spectra of the star while covering a second periastron passage. Using a variety of techniques, the radial velocities were estimated and a first, preliminary orbital solution was derived (P=2.4 yrs). The mass ratio appears close to unity and the eccentricity is large, 0.7-0.75. [less ▲]

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See detailThe X-ray emission of the colliding wind binary V444 Cyg
Fauchez, Thomas; De Becker, Michaël ULg; Nazé, Yaël ULg

in Bulletin de la Societe Royale des Sciences de Liege (2011), 80

This paper presents the analysis of six XMM-Newton observations of the colliding wind system V444 Cyg. Unlike what one might have expected at first, it appears that the O star wind most probably dominates ... [more ▼]

This paper presents the analysis of six XMM-Newton observations of the colliding wind system V444 Cyg. Unlike what one might have expected at first, it appears that the O star wind most probably dominates the WN wind: the bow shock is wide open, with the hard X-ray emission arising close to the WN star. An important radiative braking could partly explain this situation but revising the wind parameters may also prove necessary. Furthermore, we have probably observed for the first time an occultation of the colliding wind zone by the binary components. [less ▲]

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