Publications of Yaël Nazé
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See detailHot stars observed by XMM-Newton. II. A survey of Oe and Be stars
Nazé, Yaël ULiege; Motch, Christian

in Astronomy and Astrophysics (2018), 619

We perform a survey of Oe and Be stars in the X-ray range. To this aim, we cross-correlated XMM-Newton and Chandra catalogs of X-ray sources with a list of Be stars, finding 84 matches in total. Of these ... [more ▼]

We perform a survey of Oe and Be stars in the X-ray range. To this aim, we cross-correlated XMM-Newton and Chandra catalogs of X-ray sources with a list of Be stars, finding 84 matches in total. Of these, 51 objects had enough counts for a spectral analysis. This paper provides the derived X-ray properties (X-ray luminosities, and whenever possible, hardness ratios, plasma temperatures, and variability assessment) of this largest ever sample of Oe and Be stars. The targets display a wide range in luminosity and hardness. In particular, the significant presence of very bright and hard sources is atypical for X-ray surveys of OB stars. Several types of sources are identified. A subset of stars display the typical characteristics of O-stars, magnetic OB stars, or pre-main-sequence (PMS) objects: their Be nature does not seem to play an important role. However, another subset comprises γ Cas analogs, which are responsible for the luminous and hard detections. Our sample contains seven known γ Cas analogs, but we also identify eight new γ Cas analogs and one γ Cas candidate. This nearly doubles the sample of such stars. Based on observations collected with NASA missions Chandra and Swift as well as the ESA observatory XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA).All tables are 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/619/A148">http://cdsarc. u-strasbg.fr/viz-bin/qcat?J/A+A/619/A148</A> [less ▲]

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See detailThe Of?p Stars of the Magellanic Clouds: Are They Strongly Magnetic?
Munoz, Melissa; Wade, Gregg A.; Nazé, Yaël ULiege et al

in proceedings of 3rd BRITE Science Conference (2018, August 01)

All known Galactic Of?p stars have been shown to host strong, organized, magnetic fields. Recently, five Of?p stars have been discovered in the Magellanic Clouds. They posses photometric (Naze et al.) and ... [more ▼]

All known Galactic Of?p stars have been shown to host strong, organized, magnetic fields. Recently, five Of?p stars have been discovered in the Magellanic Clouds. They posses photometric (Naze et al.) and spectroscopic (Walborn et al) variability compatible with the Oblique Rotator Model (ORM). However, their magnetic fields have yet to be directly detected. We have developed an algorithm allowing for the synthesis of photometric observables based on the Analytic Dynamical Magnetosphere (ADM) model of Owocki et al.. We apply our model to OGLE photometry in order to constrain their magnetic geometries and surface dipole strengths. We predict that the field strengths for some of these candidate extra-Galactic magnetic stars may be within the detection limits of the FORS2 instrument. [less ▲]

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See detailIntriguing X-ray and optical variations of the γ Cassiopeiae analog HD 45314
Rauw, Grégor ULiege; Nazé, Yaël ULiege; Smith, M. A. et al

in Astronomy and Astrophysics (2018), 615(A44), 1-19

Context. A growing number of Be and Oe stars, named the γ Cas stars, are known for their unusually hard and intense X-ray emission. This emission could either trace accretion by a compact companion or ... [more ▼]

Context. A growing number of Be and Oe stars, named the γ Cas stars, are known for their unusually hard and intense X-ray emission. This emission could either trace accretion by a compact companion or magnetic interaction between the star and its decretion disk. <BR /> Aims: To test these scenarios, we carried out a detailed optical monitoring of HD 45314, the hottest member of the class of γ Cas stars, along with dedicated X-ray observations on specific dates. <BR /> Methods: High-resolution optical spectra were taken to monitor the emission lines formed in the disk, while X-ray spectroscopy was obtained at epochs when the optical spectrum of the Oe star was displaying peculiar properties. <BR /> Results: Over the last four years, HD 45314 has entered a phase of spectacular variations. The optical emission lines have undergone important morphology and intensity changes including transitions between single- and multiple-peaked emission lines as well as shell events, and phases of (partial) disk dissipation. Photometric variations are found to be anti-correlated with the equivalent width of the Hα emission. Whilst the star preserved its hard and bright X-ray emission during the shell phase, the X-ray spectrum during the phase of (partial) disk dissipation was significantly softer and weaker. <BR /> Conclusions: The observed behaviour of HD 45314 suggests a direct association between the level of X-ray emission and the amount of material simultaneously present in the Oe disk as expected in the magnetic star-disk interaction scenario. 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), and with the TIGRE telescope (La Luz, Mexico). [less ▲]

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See detailThe ATHENA X-ray Integral Field Unit (X-IFU)
Barret, Didier; Lam Trong, Thien; den Herder, Jan-Willem et al

in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series (2018, July 01)

The X-ray Integral Field Unit (X-IFU) is the high resolution X-ray spectrometer of the ESA Athena X-ray observatory. Over a field of view of 5' equivalent diameter, it will deliver X-ray spectra from 0.2 ... [more ▼]

The X-ray Integral Field Unit (X-IFU) is the high resolution X-ray spectrometer of the ESA Athena X-ray observatory. Over a field of view of 5' equivalent diameter, it will deliver X-ray spectra from 0.2 to 12 keV with a spectral resolution of 2.5 eV up to 7 keV on ˜ 5" pixels. The X-IFU is based on a large format array of super-conducting molybdenum-gold Transition Edge Sensors cooled at ˜ 90 mK, each coupled with an absorber made of gold and bismuth with a pitch of 249 μm. A cryogenic anti-coincidence detector located underneath the prime TES array enables the non X-ray background to be reduced. A bath temperature of ˜ 50 mK is obtained by a series of mechanical coolers combining 15K Pulse Tubes, 4K and 2K Joule-Thomson coolers which pre-cool a sub Kelvin cooler made of a 3He sorption cooler coupled with an Adiabatic Demagnetization Refrigerator. Frequency domain multiplexing enables to read out 40 pixels in one single channel. A photon interacting with an absorber leads to a current pulse, amplified by the readout electronics and whose shape is reconstructed on board to recover its energy with high accuracy. The defocusing capability offered by the Athena movable mirror assembly enables the X-IFU to observe the brightest X-ray sources of the sky (up to Crab-like intensities) by spreading the telescope point spread function over hundreds of pixels. Thus the X-IFU delivers low pile-up, high throughput (< 50%), and typically 10 eV spectral resolution at 1 Crab intensities, i.e. a factor of 10 or more better than Silicon based X-ray detectors. In this paper, the current X-IFU baseline is presented, together with an assessment of its anticipated performance in terms of spectral resolution, background, and count rate capability. The X-IFU baseline configuration will be subject to a preliminary requirement review that is scheduled at the end of 2018. [less ▲]

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See detailA doctoral dissertation on a geocentric flat earth - "zetetic" astronomy at the university level
Nazé, Yaël ULiege

Article for general public (2018)

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See detail1543 : Des révolutions des orbes célestes
Nazé, Yaël ULiege

Article for general public (2018)

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See detailA Changing Wind Collision
Nazé, Yaël ULiege; Koenigsberger, Gloria; Pittard, Julian M. et al

in Astrophysical Journal (2018), 853

We report on the first detection of a global change in the X-ray emitting properties of a wind–wind collision, thanks to XMM-Newton observations of the massive Small Magellenic Cloud (SMC) system HD 5980 ... [more ▼]

We report on the first detection of a global change in the X-ray emitting properties of a wind–wind collision, thanks to XMM-Newton observations of the massive Small Magellenic Cloud (SMC) system HD 5980. While its light curve had remained unchanged between 2000 and 2005, the X-ray flux has now increased by a factor of ∼2.5, and slightly hardened. The new observations also extend the observational coverage over the entire orbit, pinpointing the light-curve shape. It has not varied much despite the large overall brightening, and a tight correlation of fluxes with orbital separation is found without any hysteresis effect. Moreover, the absence of eclipses and of absorption effects related to orientation suggests a large size for the X-ray emitting region. Simple analytical models of the wind–wind collision, considering the varying wind properties of the eruptive component in HD 5980, are able to reproduce the recent hardening and the flux-separation relationship, at least qualitatively, but they predict a hardening at apastron and little change in mean flux, contrary to observations. The brightness change could then possibly be related to a recently theorized phenomenon linked to the varying strength of thin-shell instabilities in shocked wind regions. Based on XMM-Newton and Chandra data. [less ▲]

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See detailMagnetic fields in intermediate- and high-mass binary systems with short periods
Nazé, Yaël ULiege; Alecian, E.

in Contributions of the Astronomical Observatory Skalnaté Pleso (2018), 48

Most stars of the upper HRD live in multiple systems. When the separation is small, interactions may occur, affecting the stellar evolution and feedback. The presence of magnetic fields here opens the ... [more ▼]

Most stars of the upper HRD live in multiple systems. When the separation is small, interactions may occur, affecting the stellar evolution and feedback. The presence of magnetic fields here opens the door to phenomena beyond the "usual" ones (mass transfer, wind collisions, tidal interactions,...) but it also put strong constraints on models of stellar evolution and magnetic field generation. This is why surveys of intermediate- and high-mass binaries with short periods have been undertaken. We will review results in this domain, including the properties of the (rare) detected cases such as Plaskett's star. [less ▲]

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See detailThe Of?p stars of the Magellanic Clouds: Are they strongly magnetic?
Munoz, M.; Wade, G. A.; Nazé, Yaël ULiege et al

in Contributions of the Astronomical Observatory Skalnaté Pleso (2018), 48

All known Galactic Of?p stars have been shown to host strong, organized, magnetic fields. Recently, five Of?p stars have been discovered in the Magellanic Clouds. They posses photometric (Nazé et al ... [more ▼]

All known Galactic Of?p stars have been shown to host strong, organized, magnetic fields. Recently, five Of?p stars have been discovered in the Magellanic Clouds. They posses photometric (Nazé et al., 2015) and spectroscopic (Walborn et al., 2015) variability compatible with the Oblique Rotator Model (ORM). However, their magnetic fields have yet to be directly detected. We have developed an algorithm allowing for the synthesis of photometric observables based on the Analytic Dynamical Magnetosphere (ADM) model by Owocki et al. (2016). We apply our model to OGLE photometry in order to constrain their magnetic geometries and surface dipole strengths. We predict that the field strengths for some of theses candidate extra-Galactic magnetic stars may be within the detection limits of the FORS2 instrument [less ▲]

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See detailA detailed X-ray investigation of ζ Puppis. IV. Further characterization of the variability
Nazé, Yaël ULiege; Ramiaramanantsoa, Tahina; Stevens, Ian R. et al

in Astronomy and Astrophysics (2018), 609

Context. One of the optically brightest and closest massive stars, ζ Pup, is also a bright X-ray source. Previously, its X-ray emission was found to be variable with light curves harbouring "trends" with ... [more ▼]

Context. One of the optically brightest and closest massive stars, ζ Pup, is also a bright X-ray source. Previously, its X-ray emission was found to be variable with light curves harbouring "trends" with a typical timescale longer than the exposure length, i.e. >1 d. The origin of these changes was proposed to be linked to large-scale structures in the wind of ζ Pup, but further characterization of the variability at high energies was needed to investigate this scenario. <BR /> Aims: Since the previous papers of this series, a number of new X-ray observations have become available. Furthermore, a cyclic behaviour with a 1.78 d period was identified in long optical photometric runs, which is thought to be associated with the launching mechanism of large-scale wind structures. <BR /> Methods: We analysed these new X-ray data, revisited the old data, and compared the X-ray light curves with the optical data, notably those taken simultaneously. <BR /> Results: The behaviour of ζ Pup in X-rays cannot be explained in terms of a perfect clock because the amplitude and shape of its variations change with time. For example, ζ Pup was much more strongly variable between 2007 and 2011 than before and after this interval. Comparing the X-ray spectra of the star at maximum and minimum brightness yields no compelling difference beyond the overall flux change: the temperatures, absorptions, and line shapes seem to remain constant, well within errors. The only common feature between X-ray datasets is that the variation amplitudes appear maximum in the medium (0.6-1.2 keV) energy band. Finally, no clear and coherent correlation can be found between simultaneous X-ray and optical data. Only a subgroup of observations may be combined coherently with the optical period of 1.78 d, although the simultaneous optical behaviour is unknown. <BR /> Conclusions: The currently available data do not reveal any obvious, permanent, and direct correlation between X-ray and optical variations. The origin of the X-ray variability therefore still needs to be ascertained, highlighting the need for long-term monitoring in multiwavelengths, i.e. X-ray, UV, and optical. [less ▲]

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See detailNicolas Copernic. De revolutionibus orbium coelestium, Nuremberg, Johann Petreius, 1543, 4° (Liège, Bibliothèques ULiège, R69C).
Nazé, Yaël ULiege

in Oger, Cécile; Simon, Stéphanie; Thirion, Paul (Eds.) Empreintes. Patrimoine écrit, témoin de l’Histoire (2018)

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See detailEuroplanet Prize 2012 : still committed to outreach
Nazé, Yaël ULiege

Poster (2018)

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See detailAstronomies du passé
Nazé, Yaël ULiege

Book published by Belin (2018)

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See detailExtended main sequence turn-off originating from a broad range of stellar rotational velocities
Lim, Beomdu; Rauw, Grégor ULiege; Nazé, Yaël ULiege et al

E-print/Working paper (2018)

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See detailX-ray spectroscopy of massive stellar winds: zeta Pup current and future
Miller, Nathan; Nichols, Joy; Huenemoerder, David et al

Poster (2018)

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See detailB stars seen at high resolution by XMM-Newton
Cazorla, Constantin ULiege; Nazé, Yaël ULiege

in Astronomy and Astrophysics (2017), 608(A54), 1-15

We report on the properties of 11 early B stars observed with gratings on board XMM-Newton and Chandra, thereby doubling the number of B stars analysed at high resolution. The spectra typically appear ... [more ▼]

We report on the properties of 11 early B stars observed with gratings on board XMM-Newton and Chandra, thereby doubling the number of B stars analysed at high resolution. The spectra typically appear soft, with temperatures of 0.2-0.6 keV, and moderately bright (log [L[SUB]X[/SUB]/L[SUB]BOL[/SUB]] -7) with lower values for later type stars. In line with previous studies, we also find an absence of circumstellar absorption, negligible line broadening, no line shift, and formation radii in the range 2-7 R[SUB]⋆[/SUB]. From the X-ray brightnesses, we derived the hot mass-loss rate for each of our targets and compared these values to predictions or values derived in the optical domain: in some cases, the hot fraction of the wind can be non-negligible. The derived X-ray abundances were compared to values obtained from the optical data, with a fair agreement found between them. Finally, half of the sample presents temporal variations, either in the long-term, short-term, or both. In particular, HD 44743 is found to be the second example of an X-ray pulsator, and we detect a flare-like activity in the binary HD 79351, which also displays a high-energy tail and one of the brightest X-ray emissions in the sample. Based on observations collected with the ESA science mission 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 detailA 3U CubeSat to Collect UV Photometry of Bright Massive Stars
Desselle, Richard ULiege; Kintziger, Christian ULiege; Rochus, Pierre ULiege et al

in Journal of Small Satellites (2017), 6(3), 635-650

Following the amazing progresses in miniaturizing essential components of spacecraft, the last decade has witnessed an important development of nano- and micro-satellites. Beyond the mere technological ... [more ▼]

Following the amazing progresses in miniaturizing essential components of spacecraft, the last decade has witnessed an important development of nano- and micro-satellites. Beyond the mere technological experiment, these small satellites are now considered as important complements of much larger and more sophisticated probes to do scientific research. In this context we have conducted a feasibility study of a near-UV telescope on-board a 3U CubeSat. The scientific purpose of this payload will be to collect time series of photometric measurements of bright, mainly massive, stars down to an optical magnitude of V=5. This paper presents the optimized optical design of the payload and its associated detector. We further discuss the system accommodation and integration as well as a preliminary mission analysis. A photometric budget taking into account the characteristics of the target stars and the payload performances is also presented. With this feasibility study we demonstrate that it is possible to do a robust science mission using a very small satellite and for a limited cost. [less ▲]

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See detailX-rays from colliding winds in massive binaries
Nazé, Yaël ULiege; Rauw, Grégor ULiege

in The Lives and Death-Throes of Massive Stars (2017, November 01)

In a massive binary, the strong shock between the stellar winds may lead to the generation of bright X-ray emission. While this phenomenon was detected decades ago, the detailed study of this emission was ... [more ▼]

In a massive binary, the strong shock between the stellar winds may lead to the generation of bright X-ray emission. While this phenomenon was detected decades ago, the detailed study of this emission was only made possible by the current generation of X-ray observatories. Through dedicated monitoring and observations at high resolution, unprecedented information was revealed, putting strong constraints on the amount and structure of stellar mass-loss. [less ▲]

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See detailUp and downs of a magnetic oblique rotator viewed at high resolution
Nazé, Yaël ULiege; Zhekov, S. A.; Ud-Doula, A.

in The Lives and Death-Throes of Massive Stars (2017, November 01)

In 2006, the Of?p star HD191612 became the second O-star where a magnetic field was discovered. It provided a benchmark to understand the Of?p phenomenon as a whole. Ten years later, an X-ray monitoring ... [more ▼]

In 2006, the Of?p star HD191612 became the second O-star where a magnetic field was discovered. It provided a benchmark to understand the Of?p phenomenon as a whole. Ten years later, an X-ray monitoring performed at high-resolution reveals the behaviour of the hottest magnetospheric plasma: it is located at ~ 2R [SUB]⊙[/SUB], hot but not extreme (log(T) ~ 7), producing unshifted lines, and displaying a very repetitive variability. A direct comparison with simulations yields an overall good agreement, with only a few further improvements needed. [less ▲]

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See detailAn X-ray view of HD 166734, a massive supergiant system
Nazé, Yaël ULiege; Gosset, Eric ULiege; Mahy, Laurent ULiege et al

in Astronomy and Astrophysics (2017), 607(A97), 1-10

The X-ray emission of the O+O binary HD 166734 was monitored using Swift and XMM-Newton observatories, leading to the discovery of phase-locked variations. The presence of an f line in the He-like ... [more ▼]

The X-ray emission of the O+O binary HD 166734 was monitored using Swift and XMM-Newton observatories, leading to the discovery of phase-locked variations. The presence of an f line in the He-like triplets further supports a wind-wind collision as the main source of the X-rays in HD 166734. While temperature and absorption do not vary significantly along the orbit, the X-ray emission strength varies by one order of magnitude, with a long minimum state (Δ(φ) 0.1) occurring after a steep decrease. The flux at minimum is compatible with the intrinsic emission of the O-stars in the system, suggesting a possible disappearance of colliding wind emission. While this minimum cannot be explained by eclipse or occultation effects, a shock collapse may occur at periastron in view of the wind properties. Afterwards, the recovery is long, with an X-ray flux proportional to the separation d (in hard band) or to d[SUP]2[/SUP] (in soft band). This is incompatible with an adiabatic nature for the collision (which would instead lead to F[SUB]X[/SUB] ∝ 1 /d), but could be reconciled with a radiative character of the collision, though predicted temperatures are lower and more variable than in observations. An increase in flux around φ 0.65 and the global asymmetry of the light curve remain unexplained, however. Based on observations collected with Swift and the ESA science mission 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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