References of "Nazé, Yaël"
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See detailHot gas distribution in the wind of ζ Pup and ζ Ori
Herve, A.; Rauw, Grégor ULg; Nazé, Yaël ULg

Poster (2013, June 01)

We have developped a new X-ray modelling code based on embedded shocks which computes synthetic spectra as a function of plasma temperature, abundances and localization of the X-ray emitting shell in the ... [more ▼]

We have developped a new X-ray modelling code based on embedded shocks which computes synthetic spectra as a function of plasma temperature, abundances and localization of the X-ray emitting shell in the wind. We have also included a proper treatment of the radial dependence of the X-ray opacity of the cool matter as well as a treatment forthe Forbiden Inter combination Resonance (FIR) lines of He-like ions. Our code combines several synthetic spectra in order to fit all the lines of an X-ray spectrum simultaneously and coherently. Our results on two O-type stars ζ Pup and ζ Ori reveal non-porous winds with a mass loss rate consistent with studies in the optical domain as well as non-solar abundances for the CNO elements as expected for evolved stars. More important, the X-ray plasma starts emitting close to the stellarsurface. An improved version of our code allowing an analysis of the radial dependence of the hot gas filling factor reveals for ζ Ori a non continuity of the X-ray emission regions associated to high values of the hot gas filling factor. [less ▲]

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See detailThe Chandra Delta Ori Large Project: Occultation Measurements of the Shocked Gas in the Nearest Eclipsing O-Star Binary
Corcoran, Michael; Nichols, Joy; Leutenegger, Maurice et al

Poster (2013, June 01)

Delta Ori is the nearest massive, single-lined eclipsing binary (O9.5 II+OB, P=5.7324d). High resolution X-ray spectrometry offers a unique opportunity to geometrically measure the dynamics of the shocked ... [more ▼]

Delta Ori is the nearest massive, single-lined eclipsing binary (O9.5 II+OB, P=5.7324d). High resolution X-ray spectrometry offers a unique opportunity to geometrically measure the dynamics of the shocked gas around the primary star. We summarize our recent campaign of phase-constrained high-resolution X-ray spectra obtained with the CHANDRA/HETGS plus high-precision photometry with MOST. These observations provide local measurement of the distribution of the embedded, X-ray emitting shocks in the wind of an O star via radial velocity variations and occultation effects, along with standard f/i ratio diagnostics, and enable us to look for correlations with the broad-band photometric variability. We discuss how these observations can help determine the primary star's clumping-corrected mass loss rate, and resolve critical uncertainties in our understanding of the connection between stellar and mass loss parameters. [less ▲]

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See detailThe Nebula around the Luminous Blue Variable WRAY 15-751 as seen by Herschel
Vamvatira-Nakou, Chloi ULg; Hutsemekers, Damien ULg; Royer, P. et al

in Massive Stars: From alpha to Omega (2013, June 01)

To understand the evolution of massive stars it is crucial to study the nebulae associated to Luminous Blue Variables which can reveal the star mass-loss history. We obtained far-infrared Herschel PACS ... [more ▼]

To understand the evolution of massive stars it is crucial to study the nebulae associated to Luminous Blue Variables which can reveal the star mass-loss history. We obtained far-infrared Herschel PACS imaging and spectroscopic observations of the nebula associated with the Luminous Blue Variable star WRAY 15-751. These images revealed a second nebula, bigger and cooler, lying in an empty cavity that probably delineates the remnant of the O-star bubble formed when the star was on the Main Sequence. The dust mass and temperature were derived from the modeling of the far-infrared SED. The analysis of the emission line spectrum revealed that the main nebula consists of a region of photoionised gas surrounded by a thin photodissociation region. Both regions are mixed with dust. The calculated C, N, O abundances, together with the estimated mass-loss rate, show that the nebula was ejected from the star during a Red Supergiant phase. This is compatible with the latest evolutionary tracks for a ~40 Mo star with little rotation. [less ▲]

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See detailSimultaneous X-ray and Optical Variability Study of the O-star Binary delta Orionis with Chandra and MOST
Nichols, Joy; Moffat, Anthony F. J.; Ignace, Richard et al

in Massive Stars: From alpha to Omega (2013, June 01)

We report preliminary results from variability analysis of delta Ori in Chandra high-resolution X-ray spectroscopy and concurrent MOST high-precision optical photometry. With nearly complete phase ... [more ▼]

We report preliminary results from variability analysis of delta Ori in Chandra high-resolution X-ray spectroscopy and concurrent MOST high-precision optical photometry. With nearly complete phase coverage of the 5-day eclipsing binary orbit, it is possible to measure directly radial velocity and flux variations as a function of phase, leading to a mapping of the stellar wind distribution for the massive primary star. The phase dependence of the X-ray overall intensity and the comparative behavior of the emission lines are also presented. [less ▲]

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See detailBuilding galaxies, stars, planets and the ingredients for life between the stars. A scientific proposal for a European Ultraviolet-Visible Observatory (EUVO)
Gómez de Castro, Ana I.; Appourchaux, Thierry; Barstow, Martin et al

Report (2013)

The growth of luminous structures and the building blocks of life in the Universe began as primordial gas was processed in stars and mixed at galactic scales. The mechanisms responsible for this ... [more ▼]

The growth of luminous structures and the building blocks of life in the Universe began as primordial gas was processed in stars and mixed at galactic scales. The mechanisms responsible for this development are not well understood and have changed over the intervening 13 billion years. To follow the evolution of matter over cosmic time, it is necessary to study the strongest (resonance) transitions of the most abundant species in the Universe. Most of them are in the ultraviolet (UV; 950A-3000A) spectral range that is unobservable from the ground. A versatile space observatory with UV sensitivity a factor of 50-100 greater than existing facilities will revolutionize our understanding of the Universe. Habitable planets grow in protostellar discs under ultraviolet irradiation, a by-product of the star-disk interaction that drives the physical and chemical evolution of discs and young planetary systems. The electronic transitions of the most abundant molecules are pumped by the UV field, providing unique diagnostics of the planet-forming environment that cannot be accessed from the ground. Earth's atmosphere is in constant interaction with the interplanetary medium and the solar UV radiation field. A 50-100 times improvement in sensitivity would enable the observation of the key atmospheric ingredients of Earth-like exoplanets (carbon, oxygen, ozone), provide crucial input for models of biologically active worlds outside the solar system, and provide the phenomenological baseline to understand the Earth atmosphere in context. In this white paper, we outline the key science that such a facility would make possible and outline the instrumentation to be implemented. [less ▲]

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See detailThe Hot and Energetic Universe: Star formation and evolution
Sciortino, S.; Rauw, Grégor ULg; Audard, M. et al

Report (2013)

Stars over a wide range of masses and evolutionary stages are nowadays known to emit X-rays. This X-ray emission is a unique probe of the most energetic phenomena occurring in the circumstellar ... [more ▼]

Stars over a wide range of masses and evolutionary stages are nowadays known to emit X-rays. This X-ray emission is a unique probe of the most energetic phenomena occurring in the circumstellar environment of these stars, and provides precious insight on magnetic phenomena or hydrodynamic shocks. Owing to its large collecting area, Athena+ will open up an entirely new window on these phenomena. Indeed, Athena+ will not only allow us to study many more objects with an unprecedented spectral resolution, but will also pioneer the study of the dynamics of these objects via time-resolved high-resolution spectroscopy. In this way, Athena+ will be a unique tool to study accretion processes in TTauri stars, flaring activity in young stars, dynamos in ultra-cool dwarfs, small and large-scale structures in the winds of single massive stars, wind interactions in massive binary systems, hot bubbles in planetary nebula... All these studies will lead to a deeper understanding of yet poorly understood processes which have profound impact in star and planetary system formation as well as in feedback processes on Galactic scale. [less ▲]

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See detailThe Hot and Energetic Universe: A White Paper presenting the science theme motivating the Athena+ mission
Nandra, Kirpal; Barret, Didier; Barcons, Xavier et al

Report (2013)

This White Paper, submitted to the recent ESA call for science themes to define its future large missions, advocates the need for a transformational leap in our understanding of two key questions in ... [more ▼]

This White Paper, submitted to the recent ESA call for science themes to define its future large missions, advocates the need for a transformational leap in our understanding of two key questions in astrophysics: 1) How does ordinary matter assemble into the large scale structures that we see today? 2) How do black holes grow and shape the Universe? Hot gas in clusters, groups and the intergalactic medium dominates the baryonic content of the local Universe. To understand the astrophysical processes responsible for the formation and assembly of these large structures, it is necessary to measure their physical properties and evolution. This requires spatially resolved X-ray spectroscopy with a factor 10 increase in both telescope throughput and spatial resolving power compared to currently planned facilities. Feedback from supermassive black holes is an essential ingredient in this process and in most galaxy evolution models, but it is not well understood. X-ray observations can uniquely reveal the mechanisms launching winds close to black holes and determine the coupling of the energy and matter flows on larger scales. Due to the effects of feedback, a complete understanding of galaxy evolution requires knowledge of the obscured growth of supermassive black holes through cosmic time, out to the redshifts where the first galaxies form. X-ray emission is the most reliable way to reveal accreting black holes, but deep survey speed must improve by a factor ~100 over current facilities to perform a full census into the early Universe. The Advanced Telescope for High Energy Astrophysics (Athena+) mission provides the necessary performance (e.g. angular resolution, spectral resolution, survey grasp) to address these questions and revolutionize our understanding of the Hot and Energetic Universe. These capabilities will also provide a powerful observatory to be used in all areas of astrophysics. [less ▲]

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See detail(G)astronomie - Soufflé structurel
Nazé, Yaël ULg

Article for general public (2013)

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See detailLes instruments anciens - cadrans de hauteur
Nazé, Yaël ULg

Article for general public (2013)

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See detailDiscovery of X-Ray Emission from Young Suns in the Small Magellanic Cloud
Oskinova, L. M.; Sun, W.; Evans, C. J. et al

in Astrophysical Journal (2013), 765

We report the discovery of extended X-ray emission within the young star cluster NGC 602a in the Wing of the Small Magellanic Cloud (SMC) based on observations obtained with the Chandra X-Ray Observatory ... [more ▼]

We report the discovery of extended X-ray emission within the young star cluster NGC 602a in the Wing of the Small Magellanic Cloud (SMC) based on observations obtained with the Chandra X-Ray Observatory. X-ray emission is detected from the cluster core area with the highest stellar density and from a dusty ridge surrounding the H II region. We use a census of massive stars in the cluster to demonstrate that a cluster wind or wind-blown bubble is unlikely to provide a significant contribution to the X-ray emission detected from the central area of the cluster. We therefore suggest that X-ray emission at the cluster core originates from an ensemble of low- and solar-mass pre-main-sequence (PMS) stars, each of which would be too weak in X-rays to be detected individually. We attribute the X-ray emission from the dusty ridge to the embedded tight cluster of the newborn stars known in this area from infrared studies. Assuming that the levels of X-ray activity in young stars in the low-metallicity environment of NGC 602a are comparable to their Galactic counterparts, then the detected spatial distribution, spectral properties, and level of X-ray emission are largely consistent with those expected from low- and solar-mass PMS stars and young stellar objects (YSOs). This is the first discovery of X-ray emission attributable to PMS stars and YSOs in the SMC, which suggests that the accretion and dynamo processes in young, low-mass objects in the SMC resemble those in the Galaxy. [less ▲]

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See detailA detailed X-ray investigation of ζ Puppis. III. Spectral analysis of the whole RGS spectrum
Hervé, Anthony ULg; Rauw, Grégor ULg; Nazé, Yaël ULg

in Astronomy and Astrophysics (2013), 551

Context. ζ Pup is the X-ray brightest O-type star of the sky. This object was regularly observed with the RGS instrument onboard XMM-Newton for calibration purposes, which led to an unprecedented set of ... [more ▼]

Context. ζ Pup is the X-ray brightest O-type star of the sky. This object was regularly observed with the RGS instrument onboard XMM-Newton for calibration purposes, which led to an unprecedented set of high-quality spectra. <BR /> Aims: We have previously reduced and extracted this data set and integrated it into the most detailed high-resolution X-ray spectrum of any early-type star so far. Here we present the analysis of this spectrum, taking into account for the presence of structures in the stellar wind. <BR /> Methods: For this purpose, we used our new modeling tool that allows fitting the entire spectrum with a multi-temperature plasma. We illustrate the impact of a proper treatment of the radial dependence of the X-ray opacity of the cool wind on the best-fit radial distribution of the temperature of the X-ray plasma. <BR /> Results: The best-fit of the RGS spectrum of ζ Pup is obtained assuming no porosity. Four plasma components at temperatures between 0.10 and 0.69 keV are needed to adequately represent the observed spectrum. Whilst the hardest emission is concentrated between ~3 and 4 R[SUB]∗[/SUB], the softer emission starts already at 1.5 R[SUB]∗[/SUB] and extends to the outer regions of the wind. <BR /> Conclusions: The inferred radial distribution of the plasma temperatures agrees rather well with theoretical expectations. The mass-loss rate and CNO abundances corresponding to our best-fit model also agree quite well with the results of recent studies of ζ Pup in the UV and optical domain. 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). [less ▲]

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See detailLes instruments anciens - le nocturlabe
Nazé, Yaël ULg

Article for general public (2013)

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See detail(G)astronomie - Smoothie interstellaire
Nazé, Yaël ULg

Article for general public (2013)

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See detailX-ray emission of interacting wind binaries in Cyg OB2
Nazé, Yaël ULg; Cazorla, Constantin ULg; Rauw, Grégor ULg

in EAS Publications Series (2013, February 01)

Cyg OB2 #5, #8A, and #9 are binary or multiple massive stars in the Cyg OB2 association displaying several peculiarities, such as bright X-ray emission and non-thermal radio emission. Our X-ray monitoring ... [more ▼]

Cyg OB2 #5, #8A, and #9 are binary or multiple massive stars in the Cyg OB2 association displaying several peculiarities, such as bright X-ray emission and non-thermal radio emission. Our X-ray monitoring of these stars reveals the details of their behaviours at high energies, which can be directly linked to wind-wind collisions (WWCs). In addition, the X-ray emission of Cyg OB2 #12, an evolved massive star, shows a long-term decrease, which could hint at the presence of a companion (with associated colliding winds) or indicate the return to quiescence of the star following a recent eruption. [less ▲]

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See detailAn unexpected result for the V444 Cyg binary
Nazé, Yaël ULg; Lomax, J.; Hoffman, J.

in EAS Publications Series (2013, February 01)

V444 Cyg is a short-period (4 d) binary composed of two massive objects, a WN star and an O star. The winds of the two massive components collide, generating X-ray emission. A monitoring campaign in the ... [more ▼]

V444 Cyg is a short-period (4 d) binary composed of two massive objects, a WN star and an O star. The winds of the two massive components collide, generating X-ray emission. A monitoring campaign in the high-energy domain was performed using Swift and XMM-Newton, with surprising results on the collision geometry (wide shock opening angle, clear Coriolis deflection). Polarimetric data further help to understand the system properties. This new information places strong constraints on the physical parameters of the two stars. [less ▲]

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See detailA Detailed X-Ray Investigation of ζ Puppis. II. The Variability on Short and Long Timescales
Nazé, Yaël ULg; Oskinova, Lidia M.; Gosset, Eric ULg

in Astrophysical Journal (2013), 763

Stellar winds are a crucial component of massive stars, but their exact properties still remain uncertain. To shed some light on this subject, we have analyzed an exceptional set of X-ray observations of ... [more ▼]

Stellar winds are a crucial component of massive stars, but their exact properties still remain uncertain. To shed some light on this subject, we have analyzed an exceptional set of X-ray observations of ζ Puppis, one of the closest and brightest massive stars. The sensitive light curves that were derived reveal two major results. On the one hand, a slow modulation of the X-ray flux (with a relative amplitude of up to 15% over 16 hr in the 0.3-4.0 keV band) is detected. Its characteristic timescale cannot be determined with precision, but amounts from one to several days. It could be related to corotating interaction regions, known to exist in ζ Puppis from UV observations. Hour-long changes, linked to flares or to the pulsation activity, are not observed in the last decade covered by the XMM observations; the 17 hr tentative period, previously reported in a ROSAT analysis, is not confirmed either and is thus transient, at best. On the other hand, short-term changes are surprisingly small (<1% relative amplitude for the total energy band). In fact, they are compatible solely with the presence of Poisson noise in the data. This surprisingly low level of short-term variability, in view of the embedded wind-shock origin, requires a very high fragmentation of the stellar wind, for both absorbing and emitting features (>10[SUP]5[/SUP] parcels, comparing with a two-dimensional wind model). This is the first time that constraints have been placed on the number of clumps in an O-type star wind and from X-ray observations. 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). [less ▲]

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See detailThe 2.35 year itch of Cyg OB2 #9. II. Radio monitoring
Blomme, R.; Nazé, Yaël ULg; Volpi, D. et al

in Astronomy and Astrophysics (2013), 550

Cyg OB2 #9 is one of a small set of non-thermal radio emitting massive O-star binaries. The non-thermal radiation is due to synchrotron emission in the colliding-wind region. Cyg OB2 #9 was only recently ... [more ▼]

Cyg OB2 #9 is one of a small set of non-thermal radio emitting massive O-star binaries. The non-thermal radiation is due to synchrotron emission in the colliding-wind region. Cyg OB2 #9 was only recently discovered to be a binary system and a multiwavelength campaign was organized to study its 2011 periastron passage. We want to better determine the parameters of this system and model the wind-wind collision. This will lead to a better understanding of the Fermi mechanism that accelerates electrons up to relativistic speeds in shocks, and its occurrence in colliding-wind binaries. We report here on the results of the radio observations obtained in the monitoring campaign and present a simple model to interpret the data. We used the Expanded Very Large Array (EVLA) radio interferometer to obtain 6 and 20 cm continuum fluxes during the Cyg OB2 #9 periastron passage in 2011. We introduce a simple model to solve the radiative transfer in the stellar winds and the colliding-wind region, and thus determine the expected behaviour of the radio light curve. The observed radio light curve shows a steep drop in flux sometime before periastron. The fluxes drop to a level that is comparable to the expected free-free emission from the stellar winds, suggesting that the non-thermal emitting region is completely hidden at that time. After periastron passage, the fluxes slowly increase. We use the asymmetry of the light curve to show that the primary has the stronger wind. This is somewhat unexpected if we use the astrophysical parameters based on theoretical calibrations. But it becomes entirely feasible if we take into account that a given spectral type – luminosity class combination covers a range of astrophysical parameters. The colliding-wind region also contributes to the free-free emission, which can help to explain the high values of the spectral index seen after periastron passage. Combining our data with older Very Large Array (VLA) data allows us to derive a period P = 860:0 3:7 days for this system. With this period, we update the orbital parameters that were derived in the first paper of this series. A simple model introduced to explain only the radio data already allows some constraints to be put on the parameters of this binary system. Future, more sophisticated, modelling that will also include optical, X-ray and interferometric information will provide even better constraints. [less ▲]

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See detailX-Ray Plasma Temperature Distribution in the Wind of ζ Puppis
Hervé, Anthony ULg; Rauw, Grégor ULg; Nazé, Yaël ULg

in Astronomical Society of the Pacific Conference Series (2013, January 01)

Different scenarios try to explain the X-ray production in the O-type star wind (magnetic confinement, embedded shocks…) and their plasma temperature distribution. In this context, we have developed a new ... [more ▼]

Different scenarios try to explain the X-ray production in the O-type star wind (magnetic confinement, embedded shocks…) and their plasma temperature distribution. In this context, we have developed a new modeling code which computes synthetic spectra as a function of plasma temperature, abundances, and localization of the X-ray emitting shell in the wind. Then we combine several synthetic spectra in order to fit the observed high-resolution spectra. Our preliminary results on ζ Puppis reveal a non-porous wind as well as non-solar abundances for the CNO elements. More important, an extended region with a low temperature plasma begins to emit close to the star surface while small shells with hotter temperature plasmas emit farther in the wind. [less ▲]

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See detailMassive Non-Thermal Radio Emitters: New Data and their Modeling
Volpi, D.; Blomme, R.; De Becker, Michaël ULg et al

in Astronomical Society of the Pacific Conference Series (2013, January 01)

During recent years some non-thermal radio emitting OB stars have been discovered to be binary or multiple systems. The non-thermal emission is due to synchrotron radiation that is emitted by electrons ... [more ▼]

During recent years some non-thermal radio emitting OB stars have been discovered to be binary or multiple systems. The non-thermal emission is due to synchrotron radiation that is emitted by electrons accelerated up to high energies. The electron acceleration occurs at the strong shocks created by the collision of radiatively-driven winds. Here we summarize the available radio data and more recent observations for the binary Cyg OB2 No. 9. We also show a new emission model which is being developed to compare the theoretical total radio flux and the spectral index with the observed radio light curves. This comparison will be useful in order to solve fundamental questions, such as the determination of the stellar mass-loss rates, which are perturbed by clumping. [less ▲]

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See detailQuantitative NIR Spectroscopy of Massive Stars
Sana, H.; Stap, F. A.; de Koter, A. et al

in Astronomical Society of the Pacific Conference Series (2013, January 01)

Interest for near-infrared (NIR) spectroscopy of massive stars has been dramatically increasing over the last decade. Because it allows one to observe objects inaccessible at optical wavelengths due to ... [more ▼]

Interest for near-infrared (NIR) spectroscopy of massive stars has been dramatically increasing over the last decade. Because it allows one to observe objects inaccessible at optical wavelengths due to absorption, the infrared domain offers a privileged window to study highly extinguished objects. Yet, a detailed calibration of the massive star properties at NIR wavelength is still missing. Following the lines of the work of Repolust et al. (2005), we have acquired high resolution spectroscopy of several nearby massive stars using VLT/CRIRES, focusing on spectral lines of interest in the J, H, K, and L bands. In this work, we present the earliest results of our quantitative spectroscopic analysis of the main sequence stars in our sample. Using the unique combination of a genetic algorithm approach with the state-of-the-art non-LTE atmosphere model FASTWIND, we compare the stellar and wind properties as derived from the optical and the NIR regime. [less ▲]

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