References of "Nazé, Yaël"
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See detailLe ciel pour tous
Nazé, Yaël ULg

Article for general public (2012)

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See detailThe first X-ray survey of Galactic Luminous Blue Variables
Nazé, Yaël ULg; Rauw, Grégor ULg; Hutsemekers, Damien ULg

in Astronomy and Astrophysics (2012), 538

Aims: The X-ray emission of massive stars has been studied when these objects are in their main-sequence phase, as well as in their Wolf-Rayet phase. However, the X-ray properties of the transitional ... [more ▼]

Aims: The X-ray emission of massive stars has been studied when these objects are in their main-sequence phase, as well as in their Wolf-Rayet phase. However, the X-ray properties of the transitional Luminous Blue Variable (LBV) phase remain unknown. Methods: Using a dedicated but limited XMM survey as well as archival XMM and Chandra observations, we performed the first X-ray survey of LBVs: about half of the known LBVs or candidate LBVs are studied. Results: Apart from the well known X-ray sources eta Car and Cyg OB2 #12, four additional LBVs are detected in this survey, though some doubt remains on the association with the X-ray source for two of these. For the other LBVs, upper limits on the flux were derived, down to $\log[L_{\rm X}/L_{\rm BOL}]-9.4$ for PCyg. This variety in the strength of the X-ray emission is discussed, with particular emphasis on the potential influence of binarity. [less ▲]

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See detailThe spectral variability and magnetic field characteristics of the Of?p star HD 148937
Wade, G. A.; Grunhut, J.; Gräfener, G. et al

in Monthly Notices of the Royal Astronomical Society (2012), 419

We report magnetic and spectroscopic observations and modelling of the Of?p star HD 148937 within the context of the Magnetism in Massive Stars (MiMeS) Large Program at the Canada-France-Hawaii Telescope ... [more ▼]

We report magnetic and spectroscopic observations and modelling of the Of?p star HD 148937 within the context of the Magnetism in Massive Stars (MiMeS) Large Program at the Canada-France-Hawaii Telescope. 32 high signal-to-noise ratio circularly polarized (Stokes V) spectra and 13 unpolarized (Stokes I) spectra of HD 148937 were acquired in 2009 and 2010. A definite detection of a Stokes V Zeeman signature is obtained in the grand mean of all observations [in both least-squares deconvolved (LSD) mean profiles and individual spectral lines]. The longitudinal magnetic field inferred from the Stokes V LSD profiles is consistently negative, in contrast to the essentially zero field strength measured from the diagnostic null profiles. A period search of new and archival equivalent width measurements confirms the previously reported 7.03 d variability period. The variation of equivalent widths is not strictly periodic: we present evidence for evolution of the amount or distribution of circumstellar plasma. Interpreting the 7.03 d period as the stellar rotational period within the context of the oblique rotator paradigm, we have phased the equivalent widths and longitudinal field measurements. The longitudinal field measurements show a weak sinusoidal variation of constant sign, with extrema out of phase with the Hα variation by about 0.25 cycles. From our constraint on v sin i≤ 45 km s[SUP]-1[/SUP], we infer that the rotational axis inclination i≤ 30°. Modelling the longitudinal field phase variation directly, we obtain the magnetic obliquity β= 38[SUP]+17[/SUP][SUB]-28[/SUB]° and dipole polar intensity B[SUB]d[/SUB]= 1020[SUP]-380[/SUP][SUB]+310[/SUB] G. Simple modelling of the Hα equivalent width variation supports the derived geometry. The inferred magnetic configuration confirms the suggestion of Nazé et al., who proposed that the weaker variability of HD 148937 as compared to other members of this class is a consequence of the stellar geometry. Based on the derived magnetic properties and published wind characteristics, we find a wind magnetic confinement parameter η[SUB]*[/SUB]≃ 20 and rotation parameter W= 0.12, supporting a picture in which the Hα emission and other line variability have their origin in an oblique, rigidly rotating magnetospheric structure resulting from a magnetically channelled wind. [less ▲]

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See detail(G)astronomie - Comète glacée
Nazé, Yaël ULg

Article for general public (2012)

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See detailCahier d'exploration du ciel II. Mesurer l'Univers
Nazé, Yaël ULg

Book published by Réjouisciences (2012)

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See detailLa cuisine du Cosmos. Traité de (G)astronomie
Nazé, Yaël ULg

Book published by Réjouisciences (2012)

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See detailCahier d'exploration du ciel I. découvrir l'Univers (réédition cahier 2009)
Nazé, Yaël ULg

Book published by Réjouisciences (2012)

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See detailFirst HARPSpol discoveries of magnetic fields in massive stars
Alecian, E.; Kochukhov, O.; Neiner, C. et al

in Astronomy and Astrophysics (2011), 536

In the framework of the Magnetism in Massive Stars (MiMeS) project, a HARPSpol Large Program at the 3.6m-ESO telescope has recently started to collect high-resolution spectropolarimetric data of a large ... [more ▼]

In the framework of the Magnetism in Massive Stars (MiMeS) project, a HARPSpol Large Program at the 3.6m-ESO telescope has recently started to collect high-resolution spectropolarimetric data of a large number of Southern massive OB stars in the field of the Galaxy and in many young clusters and associations. We report on the first discoveries of magnetic fields in two massive stars with HARPSpol - HD 130807 and HD 122451, and confirm the presence of a magnetic field at the surface of HD 105382 that was previously observed with a low spectral resolution device. The longitudinal magnetic field measurements strongly vary for HD 130807 from ~-100 G to ~700 G. Those of HD 122451 and HD 105382 are less variable with values ranging from ~-40 to -80 G, and from ~-300 to -600 G, respectively. The discovery and confirmation of three new magnetic massive stars, including at least two He-weak stars, is an important contribution to one of MiMeS objectives: the understanding of the origin of magnetic fields in massive stars and their impact on stellar structure and evolution. Based on observations collected at the European Southern Observatory, Chile (Program ID 187.D-0917). [less ▲]

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See detail(G)astronomie - Stoemp céleste
Nazé, Yaël ULg

Article for general public (2011)

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See detailA spectroscopic investigation of early-type stars in the young open cluster Westerlund 2
Rauw, Grégor ULg; Sana, H.; Nazé, Yaël ULg

in Astronomy and Astrophysics (2011), 535

Context. The distance of the very young open cluster <ASTROBJ>Westerlund 2</ASTROBJ>, which contains the very massive binary system <ASTROBJ>WR 20a</ASTROBJ> and is likely associated with a TeV source ... [more ▼]

Context. The distance of the very young open cluster <ASTROBJ>Westerlund 2</ASTROBJ>, which contains the very massive binary system <ASTROBJ>WR 20a</ASTROBJ> and is likely associated with a TeV source, has been the subject of much debate. <BR /> Aims: We attempt a joint analysis of spectroscopic and photometric data of eclipsing binaries in the cluster to constrain its distance. <BR /> Methods: A sample of 15 stars, including three eclipsing binaries (<ASTROBJ>MSP 44</ASTROBJ>, <ASTROBJ>MSP 96</ASTROBJ>, and <ASTROBJ>MSP 223</ASTROBJ>) was monitored with the FLAMES multi-object spectrograph. The spectroscopic data are analysed together with existing B V photometry. <BR /> Results: The analysis of the three eclipsing binaries clearly supports the larger values of the distance, around 8 kpc, and rules out values of about 2.4 - 2.8 kpc that have been suggested in the literature. Furthermore, our spectroscopic monitoring reveals no clear signature of binarity with periods shorter than 50 days in either the WN6ha star <ASTROBJ>WR 20b</ASTROBJ>, the early O-type stars <ASTROBJ>MSP 18</ASTROBJ>, <ASTROBJ>MSP 171</ASTROBJ>, <ASTROBJ>MSP 182</ASTROBJ>, <ASTROBJ>MSP 183</ASTROBJ>, <ASTROBJ>MSP 199</ASTROBJ>, and <ASTROBJ>MSP 203</ASTROBJ>, or three previously unknown mid O-type stars. The only newly identified candidate binary system is <ASTROBJ>MSP 167</ASTROBJ>. The absence of a binary signature is especially surprising for WR 20b and MSP 18, which were previously found to be bright X-ray sources. <BR /> Conclusions: The distance of Westerlund 2 is confirmed to be around 8 kpc as previously suggested based on the spectrophotometry of its population of O-type stars and the analysis of the light curve of WR 20a. Our results suggest that short-period binary systems are not likely to be common, at least not among the population of O-type stars in the cluster. Based on observations collected at the European Southern Observatory (Cerro Paranal, Chile).Appendix A is available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

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See detail(G)astronomie - Tarte Titan
Nazé, Yaël ULg

Article for general public (2011)

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See detailConfirmation of the magnetic oblique rotator model for the Of?p star HD 191612
Wade, G. A.; Howarth, I. D.; Townsend, R. H. D. et al

in Monthly Notices of the Royal Astronomical Society (2011), 416

This paper reports high-precision Stokes V spectra of HD 191612 acquired using the ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope, in the context of the Magnetism in Massive Stars ... [more ▼]

This paper reports high-precision Stokes V spectra of HD 191612 acquired using the ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope, in the context of the Magnetism in Massive Stars (MiMeS) Project. Using measurements of the equivalent width of the Hα line and radial velocities of various metallic lines, we have updated both the spectroscopic and orbital ephemerides of this star. We confirm the presence of a strong magnetic field in the photosphere of HD 191612, and detect its variability. We establish that the longitudinal field varies in a manner consistent with the spectroscopic period of 537.6 d, in an approximately sinusoidal fashion. The phases of minimum and maximum longitudinal field are, respectively, coincident with the phases of maximum and minimum Hα equivalent width and H[SUB]p[/SUB] magnitude. This demonstrates a firm connection between the magnetic field and the processes responsible for the line and continuum variability. Interpreting the variation of the longitudinal magnetic field within the context of the dipole oblique rotator model, and adopting an inclination i= 30° obtained assuming alignment of the orbital and rotational angular momenta, we obtain a best-fitting surface magnetic field model with obliquity β= 67°± 5° and polar strength B[SUB]d[/SUB]= 2450 ± 400 G. The inferred magnetic field strength implies an equatorial wind magnetic confinement parameter η[SUB]*[/SUB]≃ 50, supporting a picture in which the Hα emission and photometric variability have their origin in an oblique, rigidly rotating magnetospheric structure resulting from a magnetically channelled wind. This interpretation is supported by our successful Monte Carlo radiative transfer modelling of the photometric variation, which assumes the enhanced plasma densities in the magnetic equatorial plane above the star implied by such a picture, according to a geometry that is consistent with that derived from the magnetic field. Predictions of the continuum linear polarization resulting from Thompson scattering from the magnetospheric material indicate that the Stokes Q and U variations are highly sensitive to the magnetospheric geometry, and that expected amplitudes are in the range of current instrumentation. [less ▲]

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See detailLes secrets de l'astrolabe
Nazé, Yaël ULg

Article for general public (2011)

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See detailCCCP, une guerre stellaire plutot chaude - résumé
Nazé, Yaël ULg

Article for general public (2011)

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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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