References of "Rauw, Grégor"
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See detailEpoch-dependent absorption line profile variability in lambda Cep
Uuh-Sonda, J. M.; Rauw, Grégor ULg; Eenens, P. et al

in Revista Mexicana de Astronomia y Astrofisica (2014), 50

We present the analysis of a multi-epoch spectroscopic monitoring campaign of the O6 Ief star lambda Cep. Previous observations reported the existence of two modes of non-radial pulsations in this star ... [more ▼]

We present the analysis of a multi-epoch spectroscopic monitoring campaign of the O6 Ief star lambda Cep. Previous observations reported the existence of two modes of non-radial pulsations in this star. Our data reveal a much more complex situation. The frequency content of the power spectrum considerably changes from one epoch to the other. We find no stable frequency that can unambiguously be attributed to pulsations. The epoch-dependence of the frequencies and variability patterns are similar to what is seen in the wind emission lines of this and other Oef stars, suggesting that both phenomena likely have the same, currently still unknown, origin. [less ▲]

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See detailWind collisions in three massive stars of Cygnus OB2
Cazorla, Constantin ULg; Nazé, Yaël ULg; Rauw, Grégor ULg

in Astronomy and Astrophysics (2014), 561

Aims. We wish to study the origin of the X-ray emission of three massive stars in the CygOB2 association: CygOB2#5, Cyg OB2 #8A, and Cyg OB2 #12. Methods. To this aim, dedicated X-ray observations from ... [more ▼]

Aims. We wish to study the origin of the X-ray emission of three massive stars in the CygOB2 association: CygOB2#5, Cyg OB2 #8A, and Cyg OB2 #12. Methods. To this aim, dedicated X-ray observations from XMM-Newton and Swift are used, as well as archival ROSAT and Suzaku data. Results. Our results on Cyg OB2 #8A improve the phase coverage of the orbit and confirm previous studies: the signature of a wind- wind collision is conspicuous. In addition, signatures of a wind-wind collision are also detected in Cyg OB2 #5, but the X-ray emission appears to be associated with the collision between the inner binary and the tertiary component orbiting it with a 6.7 yr period, without a putative collision inside the binary. The X-ray properties strongly constrain the orbital parameters, notably allowing us to discard some proposed orbital solutions. To improve the knowledge of the orbit, we revisit the light curves and radial velocity of the inner binary, looking for reflex motion induced by the third star. Finally, the X-ray emission of Cyg OB2 #12 is also analyzed. It shows a marked decrease in recent years, compatible with either a wind-wind collision in a wide binary or the aftermath of a recent eruption. [less ▲]

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See detailWR 138: new results from X-ray and optical spectroscopy
Palate, Matthieu ULg; Rauw, Grégor ULg; De Becker, Michaël ULg et al

in Astronomy and Astrophysics (2013), 560

Massive-binary evolution models predict that some systems will go through an evolutionary phase where the original primary has become a supernova and left a compact object behind that then orbits a Wolf ... [more ▼]

Massive-binary evolution models predict that some systems will go through an evolutionary phase where the original primary has become a supernova and left a compact object behind that then orbits a Wolf-Rayet (WR) star. WR 138 is an X-ray bright WR star that has been described as a triple system, including a compact companion in a short-period orbit. Our goal is to search for spectroscopic evidence of a compact companion around WR 138. We used optical and X-ray spectra to search for signatures of a compact companion, which can be revealed by systematic variations in WR optical spectral lines induced by orbital motion of the compact companion or by hard, luminous X-rays from accretion onto this companion. The optical spectra display emission-line profile variations that are most probably caused by clumps inside the stellar winds. The radial velocities do not vary on a short time-scale compatible with the suggested orbital period of a putative compact companion. The X-ray spectra are found to be normal for a WN5-6+OB system with no indication of accretion by a compact companion. There is no evidence for the presence of a compact companion, and we therefore conclude that WR 138 is a normal long-period (P ~ 1521 d) eccentric WR+OB system. [less ▲]

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See detailL'ULg met un TIGRE dans son moteur
Rauw, Grégor ULg; Nazé, Yaël ULg

Article for general public (2013)

Ciel (Le)

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See detailAthena+: The first Deep Universe X-ray Observatory
Barret, D.; Nandra, K.; Barcons, X. et al

in Cambresy, L.; Martins, F.; Nuss, E. (Eds.) et al SF2A-2013: Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics (2013, November 01)

The Advanced Telescope for High-energy Astrophysics (Athena+) is being proposed to ESA as the L2 mission (for a launch in 2028) and is specifically designed to answer two of the most pressing questions ... [more ▼]

The Advanced Telescope for High-energy Astrophysics (Athena+) is being proposed to ESA as the L2 mission (for a launch in 2028) and is specifically designed to answer two of the most pressing questions for astrophysics in the forthcoming decade: How did ordinary matter assemble into the large scale structures we see today? and how do black holes grow and shape the Universe? For addressing these two issues, Athena+ will provide transformational capabilities in terms of angular resolution, effective area, spectral resolution, grasp, that will make it the most powerful X-ray observatory ever flown. Such an observatory, when opened to the astronomical community, will be used for virtually all classes of astrophysical objects, from high-z gamma-ray bursts to the closest planets in our solar neighborhood. In this paper, we briefly review the core science objectives of Athena+, present the science requirements and the foreseen implementation of the mission, and illustrate its transformational capabilities compared to existing facilities. [less ▲]

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

Poster (2013, September)

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 system following a recent eruption. [less ▲]

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See detailThe Hot and Energetic Universe: The X-ray Integral Field Unit (X-IFU) for Athena+
Barret, D.; den Herder, J. W.; Piro, L. et al

Report (2013)

The Athena+ mission concept is designed to implement the Hot and Energetic Universe science theme submitted to the European Space Agency in response to the call for White Papers for the definition of the ... [more ▼]

The Athena+ mission concept is designed to implement the Hot and Energetic Universe science theme submitted to the European Space Agency in response to the call for White Papers for the definition of the L2 and L3 missions of its science program. The Athena+ science payload consists of a large aperture high angular resolution X-ray optics and twelve meters away, two interchangeable focal plane instruments: the X-ray Integral Field Unit (X-IFU) and the Wide Field Imager (WFI). The X-IFU is a cryogenic X-ray spectrometer, based on a large array of Transition Edge Sensors (TES), offering 2.5 eV spectral resolution, with ~5" pixels, over a field of view of 5 arc minutes in diameter. In this paper, we briefly describe the Athena+ mission concept and the X-IFU performance requirements. We then present the X-IFU detector and readout electronics principles, the current design of the focal plane assembly, the cooling chain and review the global architecture design. Finally, we describe the current performance estimates, in terms of effective area, particle background rejection, count rate capability and velocity measurements. Finally, we emphasize on the latest technology developments concerning TES array fabrication, spectral resolution and readout performance achieved to show that significant progresses are being accomplished towards the demanding X-IFU requirements. [less ▲]

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See detailSpectral modelling of the α Virginis (Spica) binary system
Palate, Matthieu ULg; Koenigsberger, G.; Rauw, Grégor ULg et al

in Astronomy and Astrophysics (2013), 556

Context. The technique of matching synthetic spectra computed with theoretical stellar atmosphere models to the observations is widely used in deriving fundamental parameters of massive stars. When ... [more ▼]

Context. The technique of matching synthetic spectra computed with theoretical stellar atmosphere models to the observations is widely used in deriving fundamental parameters of massive stars. When applied to binaries, however, these models generally neglect the interaction effects present in these systems. <BR /> Aims: The aim of this paper is to explore the uncertainties in binary stellar parameters that are derived from single-star models. <BR /> Methods: Synthetic spectra that include the tidal perturbations and irradiation effects are computed for the binary system α Virginis (Spica) using our recently-developed CoMBiSpeC model. The synthetic spectra are compared to S/N ~ 2000 observations and optimum values of T[SUB]eff[/SUB] and log g are derived. <BR /> Results: The binary interactions have only a small effect on the strength of the photospheric absorption lines in Spica (<2% for the primary and <4% for the secondary). These differences are comparable to the uncertainties inherent to the process of matching synthetic spectra to the observations and thus the derived values of T[SUB]eff[/SUB] and log g are unaffected by the binary perturbations. On the other hand, the interactions do produce significant phase-dependent line profile variations in the primary star, leading to systematic distortions in the shape of its radial velocity curve. Migrating sub-features ("bumps") are predicted by our model to be present in the same photospheric lines as observed, and their appearance does not require any a priori assumptions regarding non-radial pulsation modes. Matching the strength of lines in which the most prominent "bumps" occur requires synthetic spectra computed with larger "microturbulence" than that required by other lines. [less ▲]

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See detailHD 45314: a new γ Cassiopeiae analog among Oe stars
Rauw, Grégor ULg; Nazé, Yaël ULg; Spano, M. et al

in Astronomy and Astrophysics (2013), 555

Context. Oe stars possibly form an extension to higher temperatures of the Be phenomenon, but it is still unclear whether these stars have disks. <BR /> Aims: X-ray spectra could provide hints for ... [more ▼]

Context. Oe stars possibly form an extension to higher temperatures of the Be phenomenon, but it is still unclear whether these stars have disks. <BR /> Aims: X-ray spectra could provide hints for interactions of the star with a putative surrounding disk. <BR /> Methods: We obtained XMM-Newton observations of two Oe stars, HD 45314 and HD 60848. Spectra and light curves were extracted and analysed. Optical spectra were also obtained to support the X-ray observations. <BR /> Results: We find that both stars display very different X-ray properties. Whilst HD 60848 has an X-ray spectrum and emission level typical for its spectral type, HD 45314 displays a very hard X-ray emission, dominated by a thermal plasma with kT ~ 21 keV. Furthermore, HD 45314 displays count rate variations by a factor 2 on timescales of ~ 10[SUP]3[/SUP] s and a high log (L[SUB]X[/SUB]/L[SUB]bol[/SUB]) = -6.10 ± 0.03. <BR /> Conclusions: The X-ray properties of HD 45314 indicate that this star is a new member of the class of γ Cas analogs, the first one among the original category of Oe stars. 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 observations collected at the European Southern Observatory (La Silla, Chile) and the Observatoire de Haute Provence (France). [less ▲]

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See detailX-ray properties of the young open clusters HM1 and IC 2944/2948
Nazé, Yaël ULg; Rauw, Grégor ULg; Sana, H. et al

in Astronomy and Astrophysics (2013), 555

Using XMM-Newton data, we study for the first time the X-ray emission of HM1 and IC 2944/2948. Low-mass, pre-main-sequence objects with an age of a few Myr are detected, as well as a few background or ... [more ▼]

Using XMM-Newton data, we study for the first time the X-ray emission of HM1 and IC 2944/2948. Low-mass, pre-main-sequence objects with an age of a few Myr are detected, as well as a few background or foreground objects. Most massive stars in both clusters display the usual high-energy properties of that type of objects, though with log [L[SUB]X[/SUB]/L[SUB]BOL[/SUB]] apparently lower in HM1 than in IC 2944/2948. Compared with studies of other clusters, it seems that a low signal-to-noise ratio at soft energies, due to the high extinction, may be the main cause of this difference. In HM1, the two Wolf-Rayet stars show contrasting behaviors: WR89 is extremely bright, but much softer than WR87. It remains to be seen whether wind-wind collisions or magnetically confined winds can explain these emissions. In IC 2944/2948, the X-ray sources concentrate around HD 101205; a group of massive stars to the north of this object is isolated, suggesting that there exist two subclusters in the field-of-view. Tables 2, 5, and Figs. 5, 9 are available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A>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).Tables 1, 3 and 4 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/555/A83">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/555/A83</A> [less ▲]

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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 detailAn Observational Study of Mixing in Fast-Rotating Massive Stars: Description of the Method and Very First Results
Morel, Thierry ULg; Palate, Matthieu ULg; Rauw, Grégor ULg

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

Collecting He and CNO abundances for a large sample of fast-rotating massive stars is crucial for addressing the efficiency of rotational mixing in these objects. This is becoming a pressing issue ... [more ▼]

Collecting He and CNO abundances for a large sample of fast-rotating massive stars is crucial for addressing the efficiency of rotational mixing in these objects. This is becoming a pressing issue following the recent recognition based on observations by the VLT-FLAMES Survey of massive stars that fast rotators can show no signs of deep mixing contrary to the predictions of models. We have embarked in a project aiming at determining the abundances of the key elements indicators of mixing in a sample of bright, Galactic OB dwarfs. We present here the method and the very first results for two of the fastest OB stars known vsin i = 400 km/s : HD 93521 and zeta Oph. [less ▲]

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See detailSpectral Modelling with Interaction Effect of the Binary System Spica
Palate, Matthieu ULg; Koenigsberger, G.; Harrington, D. et al

Poster (2013, June 01)

Massive binary systems are crucial to improve our knowledge of the fundamental properties of massive stars, and synthetic spectra modelling with theoretical stellar atmospheres is commonly used in ... [more ▼]

Massive binary systems are crucial to improve our knowledge of the fundamental properties of massive stars, and synthetic spectra modelling with theoretical stellar atmospheres is commonly used in deriving some of these properties. However, the current stellar atmosphere models are designed for single spherical stars and therefore neglect interaction effects that occur in close binaries. We have developed a combined model that uses the TIDES code for computing the surface and the velocity field and the CoMBiSpeC model for the synthetic spectrum computation. This 2-in-1 model allows us to account for the interactions between the stars. We can now simulate the impact of the binarity on the spectra and refine the physical parameters of the binary systems. This model is presented here through the example of the spectral computation of Spica. In this particular system, the strongest effects due to the binarity appear in the line profile variations and the shape of the radial velocity curve. [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 detailAn XMM-Newton view of the M 17 nebula
Mernier, François ULg; Rauw, Grégor ULg

in New Astronomy (2013), 20

We present the analysis of an XMM-Newton observation of the M 17 nebula. The X-ray point source population consists of massive O-type stars and a population of probable low-mass pre-main sequence stars ... [more ▼]

We present the analysis of an XMM-Newton observation of the M 17 nebula. The X-ray point source population consists of massive O-type stars and a population of probable low-mass pre-main sequence stars. CEN 1a,b and OI 352, the X-ray brightest O-type stars in M 17, display hard spectra (kT of 3.8 and 2.6 keV) consistent with a colliding wind origin in binary/multiple systems. We show that the strong interstellar reddening towards the O-type stars of M 17 yields huge uncertainties on their L[SUB]X[/SUB]/L[SUB]bol[/SUB] values. The low-mass pre-main sequence stars exhibit hard spectra resulting from a combination of high plasma temperatures and very large interstellar absorption. We find evidence for considerable long term (months to years) variability of these sources. M 17 is one of the few star formation complexes in our Galaxy producing diffuse X-ray emission. We analyze the spectrum of this emission and compare it with previous studies. Finally, we discuss the Optical Monitor UV data obtained simultaneously with the X-ray images. We find very little correspondence between the UV and X-ray sources, indicating that the majority of the UV sources are foreground stars, whilst the bulk of the X-ray sources are deeply embedded in the M 17 complex. [less ▲]

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See detailSpectral modelling of massive binary systems
Palate, Matthieu ULg; Rauw, Grégor ULg; Koenigsberger, Gloria et al

in Astronomy and Astrophysics (2013), 552

Context. The spectra of massive binaries may be affected by interactions between the stars in the system. These are believed to produce observational phenomena such as the Struve-Sahade effect. Aims: We ... [more ▼]

Context. The spectra of massive binaries may be affected by interactions between the stars in the system. These are believed to produce observational phenomena such as the Struve-Sahade effect. Aims: We simulate the spectra of massive binaries at different phases of the orbital cycle, accounting for the gravitational influence of the companion star on the shape and physical properties of the stellar surface. Methods: We used the Roche potential modified to account for radiation pressure to compute the stellar surface of close circular systems. We furthermore used the tidal interactions with dissipation of energy through shear code for surface computations of eccentric systems. In both cases, we accounted for gravity darkening and mutual heating generated by irradiation to compute the surface temperature. We then interpolated non-local thermodynamic equilibrium (NLTE) plane-parallel atmosphere model spectra in a grid to obtain the local spectrum at each surface point. We finally summed all contributions, accounting for the Doppler shift, limb-darkening, and visibility to obtain the total synthetic spectrum. We computed different orbital phases and different sets of physical and orbital parameters. Results: Our models predict line strength variations through the orbital cycle, but fail to completely reproduce the Struve-Sahade effect. Including radiation pressure allows us to reproduce a surface temperature distribution that is consistent with observations of semi-detached binary systems. Conclusions: Radiation pressure effects on the stellar surface are weak in (over)contact binaries and well-detached systems but can become very significant in semi-detached systems. The classical von Zeipel theorem is sufficient for the spectral computation. Broad-band light curves derived from the spectral computation are different from those computed with a model in which the stellar surfaces are equipotentials of the Roche potential scaled by the instantaneous orbital separation. In many cases, the fit of two Gaussian/Lorentzian profiles fails to properly measure the equivalent width of the lines and leads to apparent variations that could explain some of the effects reported in the literature. [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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