Publications of Yaël Nazé
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See detailThe enigmatic binary system HD 5980
Hillier, D. John; Koenigsberger, Gloria; Nazé, Yaël ULiege et al

in Monthly Notices of the Royal Astronomical Society (2019), 486

The Small Magellanic Cloud multiple system HD 5980 contains a luminous blue variable (LBV) that underwent a major eruption in 1994, and whose current spectrum is that of a hydrogen-rich Wolf-Rayet (WR ... [more ▼]

The Small Magellanic Cloud multiple system HD 5980 contains a luminous blue variable (LBV) that underwent a major eruption in 1994, and whose current spectrum is that of a hydrogen-rich Wolf-Rayet (WR) star. Since the eruption, the wind mass-loss rate has been declining while wind speeds have been steadily increasing. Observations obtained in 2014 when Star A (the LBV) eclipses Star B indicate that the fitted mass-loss rate and luminosity have reached the lowest values ever determined for such spectra: \dot{M} = 4.5 × 10[SUP]-5[/SUP]M_⊙ yr^{-1}, L = 1.7 × 10[SUP]6 [/SUP]L[SUB]⊙[/SUB]. In addition, the radius of the LBV's continuum-emitting region is similar to that derived from the eclipse light curves of the late 1970s. Hence, it appears to have attained a similar `low' state to that of the late 1970s. While a good fit to the emission spectrum is obtained using a CMFGEN model, there are discrepancies in the UV. In particular, the extent of the observed absorption profiles is ˜1000 km s[SUP]-1[/SUP] greater than predicted by the emission-line intensities. Further, HST UV observations obtained in 2016, when Star A is eclipsed by Star B, show unusual P Cygni profiles that are not easily explained. Surprisingly the 2016 emission-line spectrum is similar to that at the opposite eclipse obtained in 2014. The complex UV profiles are likely to arise as a consequence of the dynamics of the wind-wind collision and radiative braking, both of which will cause significant departures from spherical symmetry, and have a strong orbital phase dependence. However, other scenarios, such as intrinsically aspherical winds, cannot be ruled out. [less ▲]

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See detailThe Athena X-ray observatory and the Liège contribution to the X-IFU instrument
Rauw, Grégor ULiege; Thibert, Tanguy ULiege; Jacques, Lionel ULiege et al

Scientific conference (2019, February 04)

Athena is ESA's next generation X-ray observatory that will address many science questions related to the hot and energetic Universe, but will also perform unprecedented observations of all kinds of ... [more ▼]

Athena is ESA's next generation X-ray observatory that will address many science questions related to the hot and energetic Universe, but will also perform unprecedented observations of all kinds of objects in the Universe. Athena will notably carry the X-ray Integral Field Unit (X-IFU), an X-ray calorimeter that will perform high-resolution X-ray spectroscopy of extended sources. STAR (CSL + GAPHE teams) contributes to the design of X-IFU. In this presentation, we will briefly highlight the anticipated science capabilities of Athena as well as the Liège contribution to the X-IFU consortium. [less ▲]

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See detailA remarkable change of the spectrum of the magnetic Of?p star HD 148937 reveals evidence of an eccentric, high-mass binary
Wade, G. A.; Smoker, J. V.; Evans, C. J. et al

in Monthly Notices of the Royal Astronomical Society (2019), 483

We report new spectroscopic observations of the magnetic Of?p star HD 148937 obtained since 2015 that differ qualitatively from its extensive historical record of weak, periodic spectral variations. This ... [more ▼]

We report new spectroscopic observations of the magnetic Of?p star HD 148937 obtained since 2015 that differ qualitatively from its extensive historical record of weak, periodic spectral variations. This remarkable behaviour represents clear evidence for an unprecedented change in the character of variability of the star. In this paper, we describe the new spectral properties and compare them to the previous line profiles. Based on measurements of the radial velocities of the C III/N III emission lines near 4640 Å and the C IV absorption lines near 5800 Å, we infer that HD 148937 is likely a high-mass, double-lined spectroscopic binary. Combining the spectroscopic orbit with an archival interferometric measurement of the apparent separation of the equal brightness components, we tentatively conclude that HD 148937 consists of two O-type stars with masses of approximately 34 and 49 M[SUB]⊙[/SUB], orbiting in an eccentric (e = 0.75), long-period (P[SUB]orb[/SUB] ˜ 26 yr) orbit. We discuss the potential relationship of the binary system to the peculiar properties of HD 148937, and propose future observations to refine the orbital and stellar properties. [less ▲]

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See detailExtreme resonance line profile variations in the ultraviolet spectra of NGC 1624-2: probing the giant magnetosphere of the most strongly magnetized known O-type star
David-Uraz, A.; Erba, C.; Petit, V. et al

in Monthly Notices of the Royal Astronomical Society (2019), 483

In this paper, we present high-resolution HST/COS observations of the extreme magnetic O star NGC 1624-2. These represent the first ultraviolet spectra of this archetypal object. We examine the ... [more ▼]

In this paper, we present high-resolution HST/COS observations of the extreme magnetic O star NGC 1624-2. These represent the first ultraviolet spectra of this archetypal object. We examine the variability of its wind-sensitive resonance lines, comparing it to that of other known magnetic O stars. In particular, the observed variations in the profiles of the C IV and Si IV doublets between low state and high state are the largest observed in any magnetic O-type star, consistent with the expected properties of NGC 1624-2's magnetosphere. We also observe a redshifted absorption component in the low state, a feature not seen in most stars. We present preliminary modelling efforts based on the Analytic Dynamical Magnetosphere (ADM) formalism, demonstrating the necessity of using non-spherically symmetric models to determine wind/magnetospheric properties of magnetic O stars. [less ▲]

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See detailBRITE photometry of the massive post-RLOF system HD149 404
Rauw, Grégor ULiege; Pigulski, A.; Nazé, Yaël ULiege et al

in Astronomy and Astrophysics (2019), 621

Context. HD 149 404 is an evolved non-eclipsing O-star binary that has previously undergone a Roche lobe overflow interaction. <BR /> Aims: Understanding some key properties of the system requires a ... [more ▼]

Context. HD 149 404 is an evolved non-eclipsing O-star binary that has previously undergone a Roche lobe overflow interaction. <BR /> Aims: Understanding some key properties of the system requires a determination of the orbital inclination and of the dimensions of the components. <BR /> Methods: The BRITE-Heweliusz satellite was used to collect photometric data of HD 149 404. Additional photometry was retrieved from the SMEI archive. These data were analysed using a suite of period search tools. The orbital part of the lightcurve was modelled with the nightfall binary star code. The Gaia-DR2 parallax of HD 149 404 was used to provide additional constraints. <BR /> Results: The periodograms reveal a clear orbital modulation of the lightcurve with a peak-to-peak amplitude near 0.04 mag. The remaining non-orbital part of the variability is consistent with red noise. The lightcurve folded with the orbital period reveals ellipsoidal variations, but no eclipses. The minimum when the secondary star is in inferior conjunction is deeper than the other minimum due to mutual reflection effects between the stars. Combined with the Gaia-DR2 parallaxes, the photometric data indicate an orbital inclination in the range of 23°-31° and a Roche lobe filling factor of the secondary larger than or equal to 0.96. <BR /> Conclusions: The luminosity of the primary star is consistent with its present-day mass, whereas the more evolved secondary appears overluminous for its mass. We confirm that the primary's rotation period is about half the orbital period. Both features most probably stem from the past Roche lobe overflow episode. Based on data collected by the BRITE-Constellation satellite mission, designed, built, launched, operated and supported by the Austrian Research Promotion Agency (FFG), the University of Vienna, the Technical University of Graz, the University of Innsbruck, the Canadian Space Agency (CSA), the University of Toronto Institute for Aerospace Studies (UTIAS), the Foundation for Polish Science & Technology (FNiTP MNiSW), and the National Science Centre (NCN). [less ▲]

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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

in Nature Astronomy (2019), 3

Star clusters have long been considered to comprise a simple stellar population, but this paradigm is being challenged, since in addition to multiple populations in Galactic globular clusters, a number of ... [more ▼]

Star clusters have long been considered to comprise a simple stellar population, but this paradigm is being challenged, since in addition to multiple populations in Galactic globular clusters, a number of younger star clusters exhibit a significant colour spread at the main sequence turn-off. A sequential evolution of multiple generations of stars formed over 100-200 Myr is a natural explanation of this colour spread. Another approach to explain this feature is to introduce the effect of stellar rotation. However, its effectiveness has not yet been proven due to the lack of direct measurements of rotational velocities. Here, we report the distribution of projected rotational velocities (Veqsin i) of stars in the Galactic open cluster M11, measured by Fourier transform analysis. Cluster members display a broad Veqsin i distribution, and fast rotators, including Be stars, have redder colours than slow rotators. Monte Carlo simulations infer that cluster members have highly aligned spin axes and a broad distribution of equatorial velocities biased towards high velocities. Our synthetic cluster simulation further demonstrates how stellar rotation affects the colours of cluster members, suggesting that the colour spread observed in populous clusters can be understood in the context of stellar evolution without introducing multiple stellar populations. [less ▲]

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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 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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