References of "Nazé, Yaël"
     in
Bookmark and Share    
See detailMagnetic Massive Stars
Townsend, Rich; Cohen, David H; Dessart, Luc et al

in IAU Symposium (2008, June 01)

Magnetic fields are unexpected in massive stars, due to the absence of a sub-surface convective dynamo. However, advances in instrumentation over the past three decades have led to their detection in a ... [more ▼]

Magnetic fields are unexpected in massive stars, due to the absence of a sub-surface convective dynamo. However, advances in instrumentation over the past three decades have led to their detection in a small but growing subset of these stars. Moreover, complementary theoretical developments have highlighted their potentially significant influence over the structure, evolution and circumstellar environments of massive stars. Here, we summarize a special session convened prior to the main conference, focused on presenting recent developments in the study of massive-star magnetic fields. [less ▲]

Detailed reference viewed: 10 (0 ULg)
See detailThe XMM-Newton view of the rich cluster Cyg OB2
Rauw, Grégor ULg; De Becker, Michaël ULg; Nazé, Yaël ULg et al

Poster (2008, May)

Detailed reference viewed: 13 (5 ULg)
Full Text
Peer Reviewed
See detailA binary signature in the non-thermal radio-emitter Cyg OB2 #9
Nazé, Yaël ULg; De Becker, Michaël ULg; Rauw, Grégor ULg et al

in Astronomy and Astrophysics (2008), 483

Aims. Non-thermal radio emission associated with massive stars is believed to arise from a wind-wind collision in a binary system. However, the evidence of binarity is still lacking in some cases, notably ... [more ▼]

Aims. Non-thermal radio emission associated with massive stars is believed to arise from a wind-wind collision in a binary system. However, the evidence of binarity is still lacking in some cases, notably Cyg OB2 #9. Methods: For several years, we have been monitoring this heavily-reddened star from various observatories. This campaign allowed us to probe variations both on short and long timescales and constitutes the first in-depth study of the visible spectrum of this object. Results: Our observations provide the very first direct evidence of a companion in Cyg OB2 #9, confirming the theoretical wind-wind collision scenario. These data suggest a highly eccentric orbit with a period of a few years, compatible with the 2 yr-timescale measured in the radio range. In addition, the signature of the wind-wind collision is very likely reflected in the behaviour of some emission lines. [less ▲]

Detailed reference viewed: 29 (4 ULg)
See detailLa vie tourmentée des amas globulaires
Nazé, Yaël ULg

Article for general public (2008)

Not Available

Detailed reference viewed: 14 (1 ULg)
See detailPluralité des Mondes
Nazé, Yaël ULg

Article for general public (2008)

Not Available

Detailed reference viewed: 10 (1 ULg)
See detailA la Une du cosmos (rubrique mensuelle depuis 2008)
Nazé, Yaël ULg

in Athena (2008)

Detailed reference viewed: 8 (2 ULg)
See detailA la une du Cosmos (rubrique mensuelle)
Nazé, Yaël ULg

Article for general public (2008)

Detailed reference viewed: 9 (6 ULg)
Full Text
See detailMultiplicity of O-type stars in NGC 2244
Mahy, Laurent ULg; Nazé, Yaël ULg; Rauw, Grégor ULg et al

Poster (2008)

We present the main results from our long‐term spectroscopic campaign devoted to the O‐type stars in the young open cluster NGC 2244. Previous works by our team on the O‐stars multiplicity in other young ... [more ▼]

We present the main results from our long‐term spectroscopic campaign devoted to the O‐type stars in the young open cluster NGC 2244. Previous works by our team on the O‐stars multiplicity in other young open clusters (IC 1805 and NGC 6231) showed that the number of binary systems in such clusters was larger than 40%. Until now, only two stars (HD 47129 and HD 48099) in the surroundings of NGC 2244 have been confirmed as spectroscopic binaries (SB) although Garcia & Mermilliod (2001) estimated the O‐type binary fraction at 50%. In this context, we revisited the spectral classification, the projected rotational velocity and the multiplicity of O‐type stars in NGC 2244. [less ▲]

Detailed reference viewed: 14 (5 ULg)
Full Text
Peer Reviewed
See detailThe massive binary HD 152218 revisited: A new colliding wind system in NGC 6231
Sana, H.; Nazé, Yaël ULg; O'Donnell, B. et al

in New Astronomy (2008), 13(4), 202-215

We present the results of an optical and X-ray monitoring campaign on the short-period massive SB2 binary HD 152218. Combining our HiRes spectroscopic data with previous observations, we unveil the ... [more ▼]

We present the results of an optical and X-ray monitoring campaign on the short-period massive SB2 binary HD 152218. Combining our HiRes spectroscopic data with previous observations, we unveil the contradictions between the published orbital solutions. In particular, we solve the aliasing on the period and derive a value close to 5.604 d. Our eccentricity e = 0.259 +/- 0.006 is slightly lower than previously admitted. We show that HD 152218 is probably undergoing a relatively rapid apsidal motion of about 3 degrees yr(-1) and we confirm the O9IV + O9.7V classification. We derive minimal masses of 15.82 +/- 0.26 M-circle dot and 12.00 +/- 0.19 M-circle dot and constrain the radius of the components to R-1 = 10.3 +/- 1.3 R-circle dot and R-2 = 7.8 +/- 1.7 R-circle dot. We also report the results of an XMM-Newton monitoring of the HD 152218 X-ray emission throughout its orbital motion. The averaged X-ray spectrum is relatively soft and it is well reproduced by a 2-T optically thin thermal plasma model with component temperatures about 0.3 and 0.7 keV. The system presents an increase of its X-ray flux by about 30% near apastron compared to periastron, which is interpreted as the signature of an ongoing wind-wind interaction process occurring within the wind acceleration region. (C) 2007 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 42 (3 ULg)
Full Text
Peer Reviewed
See detailX-ray spectroscopy of early-type stars: The present and the future
Rauw, Grégor ULg; Nazé, Yaël ULg; Oskinova, L. M.

in Astronomische Nachrichten (2008), 329(2), 222-225

XMM-Newton and Chandra have boosted our knowledge about the X-ray emission of early-type stars (spectral types OB and Wolf-Rayet). However, there are still a number of open questions that need to be ... [more ▼]

XMM-Newton and Chandra have boosted our knowledge about the X-ray emission of early-type stars (spectral types OB and Wolf-Rayet). However, there are still a number of open questions that need to be addressed in order to fully understand the X-ray spectra of these objects. Many of these issues require high-resolution spectroscopy or monitoring of a sample of massive stars. Given the moderate X-ray brightness of these targets, rather long exposure times are needed to achieve these goals. In this contribution, we review our current knowledge in this field and present some hot topics that could ideally be addressed with XMM-Newton over the next decade. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. [less ▲]

Detailed reference viewed: 21 (5 ULg)
Full Text
Peer Reviewed
See detailNew insights into the nature of the SMC WR/LBV binary HD 5980
Foellmi, C.; Koenigsberger, G.; Georgiev, L. et al

in Revista Mexicana de Astronomía y Astrofísica (2008), 44(1), 3-27

We present the results of optical wavelength observations of the unusual SMC eclipsing binary system HD 5980 obtained in 1999 and 2004-2005. Radial velocity curves for the erupting LBV/WR object (star A ... [more ▼]

We present the results of optical wavelength observations of the unusual SMC eclipsing binary system HD 5980 obtained in 1999 and 2004-2005. Radial velocity curves for the erupting LBV/WR object (star A) and its close WR-like companion (star B) are obtained by deblending the variable emission-line profiles of NIV and NV lines. The derived masses M-A = 58 - 79 M-circle dot and M-B = 51 - 67 M-circle dot, are more consistent with the the stars' location near the top of the HRD than previous estimates. The presence of a wind-wind interaction region is inferred from the orbital phase-dependent behavior of He I P Cygni absorption components. The emission-line intensities continued with the declining trend previously seen in UV spectra. The behavior of the photospheric absorption lines is consistent with the results of Schweickhardt (2000) who concludes that the third object in the combined spectrum, star C, is also a binary system with P-starC similar to 96.5 days, e=0.83. [less ▲]

Detailed reference viewed: 26 (3 ULg)
Full Text
Peer Reviewed
See detailThe massive star binary fraction in young open clusters - I. NGC 6231 revisited
Sana, H.; Gosset, Eric ULg; Nazé, Yaël ULg et al

in Monthly Notices of the Royal Astronomical Society (2008), 386(1), 447-460

We present the results of a long-term high-resolution spectroscopy campaign on the O-type stars in NGC 6231. We revise the spectral classification and multiplicity of these objects and we constrain the ... [more ▼]

We present the results of a long-term high-resolution spectroscopy campaign on the O-type stars in NGC 6231. We revise the spectral classification and multiplicity of these objects and we constrain the fundamental properties of the O-star population. Almost three quarters of the O-type stars in the cluster are members of a binary system. The minimum binary fraction is 0.63, with half the O-type binaries having an orbital period of the order of a few days. The eccentricities of all the short-period binaries are revised downward, and henceforth match a normal period-eccentricity distribution. The mass ratio distribution shows a large preference for O + OB binaries, ruling out the possibility that, in NGC 6231, the companion of an O-type star is randomly drawn from a standard initial mass function. Obtained from a complete and homogeneous population of O-type stars, our conclusions provide interesting observational constraints to be confronted with the formation and early evolution theories of O-stars. [less ▲]

Detailed reference viewed: 30 (3 ULg)
Full Text
Peer Reviewed
See detailHD 148937: A multiwavelength study of the third galactic member of the Of?p class
Nazé, Yaël ULg; Walborn, Nolan R.; Rauw, Grégor ULg et al

in Astronomical Journal (The) (2008), 135(5), 1946-1957

Three Galactic O-type stars belong to the rare class of Of? p objects: HD 108, HD 191612, and HD 148937. The first two stars show a wealth of phenomena, including strong X-ray emission, light variability ... [more ▼]

Three Galactic O-type stars belong to the rare class of Of? p objects: HD 108, HD 191612, and HD 148937. The first two stars show a wealth of phenomena, including strong X-ray emission, light variability, and dramatic periodic spectral variability. We present here the first detailed optical and X-ray study of the third Galactic Of? p star, HD 148937. Spectroscopic monitoring has revealed low-level variability in the Balmer and He II lambda 4686 lines, but constancy at He I and C III lambda 4650. The H alpha line exhibits profile variations at a possible periodicity of similar to 7 days. Model atmosphere fits yield T-eff = 41000 +/- 2000 K, log(g) = 4.0 +/- 0.1, M-sph less than or similar to 10(-7) M-circle dot yr(-1), and an overabundance of nitrogen by a factor of 4. At X-ray wavelengths, HD 148937 resembles HD 108 and HD 191612 in having a thermal spectrum dominated by a relatively cool component (kT = 0.2 keV), broad lines (>= 1700 km s(-1)), and an order-of-magnitude overluminosity compared to normal O stars (log[L-X(unabs) / L-BOL]similar to -6). [less ▲]

Detailed reference viewed: 46 (6 ULg)
Full Text
Peer Reviewed
See detailChandra monitoring of the very massive binary WR20a and the young massive cluster Westerlund 2
Nazé, Yaël ULg; Rauw, Grégor ULg; Manfroid, Jean ULg

in Astronomy and Astrophysics (2008), 483(1), 171-182

Context. Westerlund 2 is a young and massive, obscured stellar cluster of our Galaxy. It harbors the most massive star with well-determined parameters, WR20a (82 + 83 M-circle dot), a dozen very early O ... [more ▼]

Context. Westerlund 2 is a young and massive, obscured stellar cluster of our Galaxy. It harbors the most massive star with well-determined parameters, WR20a (82 + 83 M-circle dot), a dozen very early O-type stars (O3-7), and a wealth of PMS stars. Although of clear significance, this star cluster has not been well-studied. Aims. The high-energy properties of this cluster, especially those of its early-type stars are examined in detail. The variability of the X-ray sources is investigated. Methods. A monitoring of the field was performed using three Chandra observations. This dataset probes daily as well as monthly to yearly timescales and provides the deepest X-ray view of the cluster to date. Results. The two Wolf-Rayet stars WR20a (WN6ha+WN6ha) and WR20b (WN6ha) were analyzed in detail. They are both luminous and display hard spectra, but WR20b does not appear to vary. In contrast, WR20a, a known eclipsing, colliding-wind binary, brightens in the X-ray domain during eclipses, i.e. when the collision is seen face-on. This can be explained by the properties of the wind-wind collision zone, whose high density leads to a large absorbing column (2 x 10(24) cm(-2)). All twelve O-type stars previously classified spectroscopically, two eclipsing binaries previously identified and nine newly-identified, O-type star candidates are detected in the high-energy domain; ten of those could be analyzed spectroscopically. Four are overluminous, but the others have typical LX/LBOL ratios, suggesting that several O-type objects are actually binaries. Variability at the similar to 2 sigma level is detected for a majority of the sources, of unknown origin for single objects. Faint, soft, diffuse emission pervades the entire field-of-view but no clear structure can be identified, even at the position of a blister proposed to correspond to the TeV source HESS J1023-575. The X-ray properties of PMS objects, in particular the brightest flaring ones, are also investigated. They provided an additional argument in favor of a large distance (similar to 8 kpc) for the cluster. [less ▲]

Detailed reference viewed: 32 (2 ULg)
Full Text
Peer Reviewed
See detailThe mysterious Of?p class and the magnetic O-star theta(1) Ori C: Confronting observations
Nazé, Yaël ULg; Walborn, Nolan R.; Martins, Fabrice

in Revista Mexicana de Astronomía y Astrofísica (2008), 44(2), 331-340

In recent years, the stars of the Of?p category have revealed a wealth of peculiar phenomena: varying line profiles, photometric changes, and X-ray over-luminosity are only a few of their characteristics ... [more ▼]

In recent years, the stars of the Of?p category have revealed a wealth of peculiar phenomena: varying line profiles, photometric changes, and X-ray over-luminosity are only a few of their characteristics. Here we review their physical properties to facilitate comparisons among the Galactic members of this class. As one of them his been proposed to resemble the magnetic oblique rotator theta(1) Ori C, though with a longer period, this latter object is also included in our study to illuminate its similarities and differences with the Of?p category. [less ▲]

Detailed reference viewed: 18 (2 ULg)
Full Text
Peer Reviewed
See detailHigh-resolution X-ray spectroscopy of theta Carinae
Nazé, Yaël ULg; Rauw, Grégor ULg

in Astronomy and Astrophysics (2008), 490(2), 801-806

Context. The peculiar hot star. Car in the open cluster IC2602 is a blue straggler as well as a single-line binary with a short period (2.2d). Aims. Its high-energy properties are not well known, though X ... [more ▼]

Context. The peculiar hot star. Car in the open cluster IC2602 is a blue straggler as well as a single-line binary with a short period (2.2d). Aims. Its high-energy properties are not well known, though X-rays can provide useful constraints on the energetic processes at work in binaries as well as in peculiar, single objects. Methods. We present the analysis of a 50 ks exposure taken with the XMM-Newton observatory. It provides medium as well as high-resolution spectroscopy. Results. Our high-resolution spectroscopy analysis reveals a very soft spectrum with multiple temperature components (1-6 MK) and an X-ray flux slightly below the 'canonical' value (log [L-X(0.1-10.)/L-BOL]similar to -7). The X-ray lines appear surprisingly narrow and unshifted, reminiscent of those of beta Cru and tau Sco. Their relative intensities confirm the anomalous abundances detected in the optical domain (C strongly depleted, N strongly enriched, O slightly depleted). In addition, the X-ray data favor a slight depletion in neon and iron, but they are less conclusive for the magnesium abundance, which may be solar-like. While no significant changes occur during the XMM-Newton observation, variability in the X-ray domain is detected in the long-term range. The formation radius of the X-ray emission is loosely constrained to < 5 R-circle dot, which allows for a range of models (wind-shock, corona, magnetic confinement,...) though not all of them can be reconciled with the softness of the spectrum and the narrowness of the lines. [less ▲]

Detailed reference viewed: 20 (1 ULg)
Full Text
Peer Reviewed
See detailSpectroscopic and photometric variability of the O9.5Vp star HD93521
Rauw, Grégor ULg; De Becker, Michaël ULg; van Winckel, Hans et al

in Astronomy and Astrophysics (2008), 487(2), 659-670

Aims. The line profile variability and photometric variability of the O9.5Vp star HD93521 are examined in order to establish the properties of the non-radial pulsations in this star. Methods. Fourier ... [more ▼]

Aims. The line profile variability and photometric variability of the O9.5Vp star HD93521 are examined in order to establish the properties of the non-radial pulsations in this star. Methods. Fourier techniques are used to characterize the modulations of the He I lambda lambda 5876, 6678 and H alpha lines in several spectroscopic time series and to search for variations in a photometric time series. Results. Our spectroscopic data confirm the existence of two periods of 1.75 and 2.89 h. The line profiles, especially those affected by emission wings, exhibit also modulations on longer time scales, but these are epoch-dependent and change from line to line. Unlike previous claims, we find no unambiguous signature of the rotational period in our data, nor of a third pulsation period (corresponding to a frequency of 2.66 d(-1)). Conclusions. HD93521 very likely exhibits non-radial pulsations with periods of 1.75 and 2.89 h with l similar or equal to 8 +/- 1 and l similar or equal to 4 +/- 1 respectively. No significant signal is found in the first harmonics of these two periods. The 2.89 h mode is seen at all epochs and in all lines investigated, while the visibility of the 1.75 h mode is clearly epoch-dependent. Whilst light variations are detected, their connection to these periodicities is not straightforward. [less ▲]

Detailed reference viewed: 35 (6 ULg)
See detailAstrobiologie
Javaux, Emmanuelle ULg; Claeys, Philippe; Dehant, Véronique et al

Learning material (2008)

powerpoint sur MyULg, notes partielles imprimées

Detailed reference viewed: 46 (11 ULg)
See detailPromenade céleste
Nazé, Yaël ULg

Article for general public (2007)

Detailed reference viewed: 3 (0 ULg)
See detailEntre les étoiles, voyage au coeur du milieu interstellaire
Nazé, Yaël ULg

Article for general public (2007)

Not Available

Detailed reference viewed: 11 (1 ULg)