References of "Rauw, Grégor"
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See detailQuest for the tertiary component in Cyg OB2 #5
Rauw, Grégor ULiege; Nazé, Yaël ULiege; Campos, Fran

in Astronomy and Astrophysics (2019), 627

Aims: The Cyg OB2 #5 system is thought to consist of a short- period (6.6 d) eclipsing massive binary orbited by an OB-star with a period of 6.7 yr; these stars in turn are orbited by a distant early B ... [more ▼]

Aims: The Cyg OB2 #5 system is thought to consist of a short- period (6.6 d) eclipsing massive binary orbited by an OB-star with a period of 6.7 yr; these stars in turn are orbited by a distant early B-star with a period of thousands of years. However, while the inner binary has been studied many times, information is missing on the other stars, in particular the third star whose presence was indirectly postulated from recurrent modulations in the radio domain. Besides, to this date, the X-ray light curve could not be fully interpreted, for example in the framework of colliding-wind emission linked to one of the systems. Methods: We obtained new optical and X-ray observations of Cyg OB2 #5, which we combined to archival data. We performed a thorough and homogeneous investigation of all available data, notably revisiting the times of primary minimum in photometry. Results: In the X-ray domain, XMM-Newton provides scattered exposures over 5000 d whilst Swift provides a nearly continuous monitoring for the last couple of years. Although the X-ray light curve reveals clear variability, no significant period can be found hence the high-energy emission cannot be explained solely in terms of colliding winds varying along either the short or intermediate orbits. The optical data reveal for the first time clear signs of reflex motion. The photometry indicates the presence of a 2366 d (i.e. 6.5 yr) period while the associated radial velocity changes are detected at the 3σ level in the systemic velocity of the He II λ 4686 emission line. With the revised period, the radio light curve is interpreted consistently in terms of a wind interaction between the inner binary and the tertiary star. From these optical and radio data, we derive constraints on the physical properties of the tertiary star and its orbit. Table 1 is 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/627/A2">http://cdsarc.u-strasbg.fr/viz- bin/qcat?J/A+A/627/A2</A>Based on spectra obtained with the TIGRE telescope, located at La Luz observatory, Mexico (TIGRE is a collaboration of the Hamburger Sternwarte, the Universities of Hamburg, Guanajuato, and Liège), as well as data collected at the Observatoire de Haute Provence, with the Neil Gehrels Swift Observatory, and 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 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 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 detailNƎSIE: a fiber-fed near-infrared spectrograph for TIGRE telescope
Kintziger, Christian ULiege; Rauw, Grégor ULiege; Desselle, Richard ULiege et al

in Evans, Christopher; Simard, Luc; Takami, Hideki (Eds.) Proceedings Volume 10702, Ground-based and Airborne Instrumentation for Astronomy VII (2018, July 06)

Our contribution intends to present the obtained performances of the NƎSIE instrument, a new near-infrared fiber-fed spectrograph developed at the University of Liège. This instrument was developed ... [more ▼]

Our contribution intends to present the obtained performances of the NƎSIE instrument, a new near-infrared fiber-fed spectrograph developed at the University of Liège. This instrument was developed, aligned and tested at the Centre Spatial de Liège and first light was achieved in October 2017. This paper will go through the alignment process and optical performance verification to eventually introduce the first light observations. The final location of NƎSIE will be the TIGRE telescope located in La Luz, Mexico. The observational data provided by this instrument will help several research groups from the University of Liège to study massive stars. In particularly, evolution models will be improved through the comparison of the collected spectra with theoretical models. This collaboration will therefore contribute to a better understanding of massive stars and the mechanisms that take place within these extraordinary objects. [less ▲]

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See detailATHENA X-IFU thermal filters development status toward the end of the instrument phase-A
Barbera, Marco; Lo Cicero, Ugo; Sciortino, Luisa et al

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

The X-ray Integral Field Unit (X-IFU) is one of the two instruments of the Athena astrophysics space mission approved by ESA in the Cosmic Vision 2015-2025 Science Programme. The X-IFU consists of a large ... [more ▼]

The X-ray Integral Field Unit (X-IFU) is one of the two instruments of the Athena astrophysics space mission approved by ESA in the Cosmic Vision 2015-2025 Science Programme. The X-IFU consists of a large array of transition edge sensor micro-calorimeters that will operate at 100 mK inside a sophisticated cryostat. A set of thin filters, highly transparent to X-rays, will be mounted on the opening windows of the cryostat thermal shields in order to attenuate the IR radiative load, to attenuate radio frequency electromagnetic interferences, and to protect the detector from contamination. Thermal filters are critical items in the proper operation of the X-IFU detector in space. They need to be strong enough to survive the launch stresses but very thin to be highly transparent to X-rays. They essentially define the detector quantum efficiency at low energies and are fundamental to make the photon shot noise a negligible contribution to the energy resolution budget. In this paper, we review the main results of modeling and characterization tests of the thermal filters performed during the phase A study to identify the suitable materials, optimize the design, and demonstrate that the chosen technology can reach the proper readiness before mission adoption. [less ▲]

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See detailATHENA WFI optical blocking filters development status toward the end of the instrument phase-A
Barbera, Marco; Lo Cicero, Ugo; Sciortino, Luisa et al

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

The Wide Field Imager (WFI) is one of the two instruments of the ATHENA astrophysics space mission approved by ESA as the second large mission in the Cosmic Vision 2015-2025 Science Programme. The WFI ... [more ▼]

The Wide Field Imager (WFI) is one of the two instruments of the ATHENA astrophysics space mission approved by ESA as the second large mission in the Cosmic Vision 2015-2025 Science Programme. The WFI, based on a large array of depleted field effect transistors (DEPFET), will provide imaging in the 0.2-15 keV band over a 40'x40' field of view, simultaneously with spectrally and time resolved photon counting. The WFI detector is also sensitive to UV/Vis photons, with an electron-hole pair production efficiency in the UV/VIS larger than that for X-ray photons. Optically generated photo-electrons may degrade the spectral resolution as well as change the energy scale by introducing a signal offset. For this reason, the use of X-ray transparent optical blocking filters (OBFs) are needed to allow the observation of X-ray sources that present a UV/Vis bright counterpart. The OBFs design is challenging since one of the two required filters is quite large ( 160 mm × 160 mm), very thin (< 200 nm), and shall survive the mechanical load during the launch. In this paper, we review the main results of modeling and characterization tests of OBF partially representative samples, performed during the phase A study, to identify the suitable materials, optimize the design, prove that the filters can be launched in atmospheric pressure, and thus demonstrate that the chosen technology can reach the proper technical readiness before mission adoption. [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 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 THESEUS space mission concept: science case, design and expected performances
Amati, L.; O'Brien, P.; Götz, D. et al

in Advances in Space Research (2018), 62

THESEUS is a space mission concept aimed at exploiting Gamma-Ray Bursts for investigating the early Universe and at providing a substantial advancement of multi-messenger and time-domain astrophysics ... [more ▼]

THESEUS is a space mission concept aimed at exploiting Gamma-Ray Bursts for investigating the early Universe and at providing a substantial advancement of multi-messenger and time-domain astrophysics. These goals will be achieved through a unique combination of instruments allowing GRB and X-ray transient detection over a broad field of view (more than 1sr) with 0.5-1 arcmin localization, an energy band extending from several MeV down to 0.3 keV and high sensitivity to transient sources in the soft X-ray domain, as well as on-board prompt (few minutes) follow-up with a 0.7 m class IR telescope with both imaging and spectroscopic capabilities. THESEUS will be perfectly suited for addressing the main open issues in cosmology such as, e.g., star formation rate and metallicity evolution of the inter-stellar and intra-galactic medium up to redshift ∼ 10, signatures of Pop III stars, sources and physics of re-ionization, and the faint end of the galaxy luminosity function. In addition, it will provide unprecedented capability to monitor the X-ray variable sky, thus detecting, localizing, and identifying the electromagnetic counterparts to sources of gravitational radiation, which may be routinely detected in the late '20s/early '30s by next generation facilities like aLIGO/ aVirgo, eLISA, KAGRA, and Einstein Telescope. THESEUS will also provide powerful synergies with the next generation of multi-wavelength observatories (e.g., LSST, ELT, SKA, CTA, ATHENA). [less ▲]

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See detailThe long-period massive binary HD 54662 revisited
Mossoux, Enmanuelle ULiege; Mahy, Laurent ULiege; Rauw, Grégor ULiege

in Astronomy and Astrophysics (2018), 615(A19), 1-11

Context. HD 54662 is an O-type binary star belonging to the CMa OB1 association. Because of its long-period orbit, this system is an interesting target to test the adiabatic wind shock model. Aims. The ... [more ▼]

Context. HD 54662 is an O-type binary star belonging to the CMa OB1 association. Because of its long-period orbit, this system is an interesting target to test the adiabatic wind shock model. Aims. The goal of this study is to improve our knowledge of the orbital and stellar parameters of HD 54662 and to analyze its X-ray emission to test the theoretical scaling of X-ray emission with orbital separation for adiabatic wind shocks. Methods. We applied a spectral disentangling code to a set of optical spectra to determine the radial velocities and the individual spectra of the primary and secondary stars. The orbital solution of the system was established and the reconstructed individual spectra were analyzed by means of the CMFGEN model atmosphere code. We fitted two X-ray spectra using a Markov Chain Monte Carlo algorithm and compared these spectra to the emission expected from adiabatic shocks. Results. We determine an orbital period of 2103.4 days, a surprisingly low orbital eccentricity of 0.11, and a mass ratio m2/m1 of 0.84. Combined with the orbital inclination inferred in a previous astrometric study, we obtain surprisingly low masses of 9.7 and 8.2 Msun. From the disentangled primary and secondary spectra, we infer O6.5 spectral types for both stars, of which the primary is about two times brighter than the secondary. The softness of the X-ray spectra for the two observations, the very small variation of best-fitting spectral parameters, and the comparison of the X-ray-to-bolometric luminosity ratio with the canonical value for O-type stars allow us to conclude that X-ray emission from the wind interaction region is quite low and that the observed emission is rather dominated by the intrinsic emission from the stars. We cannot confirm the runaway status previously attributed to HD 54662 by computing the peculiar radial and tangential velocities. We find no X-ray emission associated with the bow shock detected in the infrared. Conclusions. The lack of hard X-ray emission from the wind-shock region suggests that the mass-loss rates are lower than expected and/or that the pre-shock wind velocities are much lower than the terminal wind velocities. The bow shock associated with HD 54662 possibly corresponds to a wind-blown arc created by the interaction of the stellar winds with the ionized gas of the CMa OB1 association rather than by a large differential velocity between the binary and the surrounding interstellar medium. [less ▲]

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See detailThe co-existence of hot and cold gas in debris discs
Rebollido, I.; Eiroa, C.; Montesinos, B. et al

in Astronomy and Astrophysics (2018), 614

Context. Debris discs have often been described as gas-poor discs as the gas-to-dust ratio is expected to be considerably lower than in primordial, protoplanetary discs. However, recent observations have ... [more ▼]

Context. Debris discs have often been described as gas-poor discs as the gas-to-dust ratio is expected to be considerably lower than in primordial, protoplanetary discs. However, recent observations have confirmed the presence of a non-negligible amount of cold gas in the circumstellar (CS) debris discs around young main-sequence stars. This cold gas has been suggested to be related to the outgassing of planetesimals and cometary-like objects. <BR /> Aims: The goal of this paper is to investigate the presence of hot gas in the immediate surroundings of the cold-gas-bearing debris-disc central stars. <BR /> Methods: High-resolution optical spectra of all currently known cold-gas-bearing debris-disc systems, with the exception of β Pic and Fomalhaut, have been obtained from La Palma (Spain), La Silla (Chile), and La Luz (Mexico) observatories. To verify the presence of hot gas around the sample of stars, we have analysed the Ca II H&K and the Na I D lines searching for non-photospheric absorptions of CS origin, usually attributed to cometary-like activity. <BR /> Results: Narrow, stable Ca II and/or Na I absorption features have been detected superimposed to the photospheric lines in 10 out of the 15 observed cold-gas-bearing debris-disc stars. Features are found at the radial velocity of the stars, or slightly blue- or red-shifted, and/or at the velocity of the local interstellar medium (ISM). Some stars also present transient variable events or absorptions extended towards red wavelengths (red wings). These are the first detections of such Ca II features in 7 out of the 15 observed stars. Although an ISM origin cannot categorically be excluded, the results suggest that the stable and variable absorptions arise from relatively hot gas located in the CS close-in environment of the stars. This hot gas is detected in at least 80%, of edge-on cold-gas-bearing debris discs, while in only 10% of the discs seen close to face-on. We interpret this result as a geometrical effect, and suggest that the non-detection of hot gas absorptions in some face-on systems is due to the disc inclination and likely not to the absence of the hot-gas component. This gas is likely released in physical processes related in some way to the evaporation of exocomets, evaporation of dust grains, or grain-grain collisions close to the central star. The reduced spectra are only available at the CDS (ascii files) and at the FEROS archive (FITS files) via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (<A href="http://130.79.128.5">http://130.79.128.5</A>) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/614/A3">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/614/A3</A> [less ▲]

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See detailFundamental parameters of massive stars in multiple systems: The cases of HD 17505A and HD 206267A
Raucq, Françoise ULiege; Rauw, Grégor ULiege; Mahy, Laurent ULiege et al

in Astronomy and Astrophysics (2018), 614

Context. Many massive stars are part of binary or higher multiplicity systems. The present work focusses on two higher multiplicity systems: HD 17505A and HD 206267A. <BR /> Aims: Determining the ... [more ▼]

Context. Many massive stars are part of binary or higher multiplicity systems. The present work focusses on two higher multiplicity systems: HD 17505A and HD 206267A. <BR /> Aims: Determining the fundamental parameters of the components of the inner binary of these systems is mandatory to quantify the impact of binary or triple interactions on their evolution. <BR /> Methods: We analysed high-resolution optical spectra to determine new orbital solutions of the inner binary systems. After subtracting the spectrum of the tertiary component, a spectral disentangling code was applied to reconstruct the individual spectra of the primary and secondary. We then analysed these spectra with the non-LTE model atmosphere code CMFGEN to establish the stellar parameters and the CNO abundances of these stars. <BR /> Results: The inner binaries of these systems have eccentric orbits with e 0.13 despite their relatively short orbital periods of 8.6 and 3.7 days for HD 17505Aa and HD 206267Aa, respectively. Slight modifications of the CNO abundances are found in both components of each system. The components of HD 17505Aa are both well inside their Roche lobe, whilst the primary of HD 206267Aa nearly fills its Roche lobe around periastron passage. Whilst the rotation of the primary of HD 206267Aa is in pseudo-synchronization with the orbital motion, the secondary displays a rotation rate that is higher. <BR /> Conclusions: The CNO abundances and properties of HD 17505Aa can be explained by single star evolutionary models accounting for the effects of rotation, suggesting that this system has not yet experienced binary interaction. The properties of HD 206267Aa suggest that some intermittent binary interaction might have taken place during periastron passages, but is apparently not operating anymore. Based on observations collected with the TIGRE telescope (La Luz, Mexico), the 1.93 m telescope at Observatoire de Haute Provence (France), the Nordic Optical Telescope at the Observatorio del Roque de los Muchachos (La Palma, Spain), and the Canada-France-Hawaii telescope (Mauna Kea, Hawaii). [less ▲]

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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 detailResearch activities in Astronomy and Astrophysics in Belgium
Frémat, Y.; Van Eck, S.; Aerts, C. et al

in BPhy - Belgian Physical Society Magazine (2018), 1-2018

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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 detailEvidence for past Roche-lobe overflow in two O-type binaries
Rauw, Grégor ULiege; Raucq, Françoise ULiege; Mahy, Laurent ULiege et al

Conference (2017, July 05)

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See detailChemical abundances of fast-rotating massive stars. I. Description of the methods and individual results
Cazorla, Constantin ULiege; Morel, Thierry ULiege; Nazé, Yaël ULiege et al

in Astronomy and Astrophysics (2017), 603(A56),

Aims: Recent observations have challenged our understanding of rotational mixing in massive stars by revealing a population of fast- rotating objects with apparently normal surface nitrogen abundances ... [more ▼]

Aims: Recent observations have challenged our understanding of rotational mixing in massive stars by revealing a population of fast- rotating objects with apparently normal surface nitrogen abundances. However, several questions have arisen because of a number of issues, which have rendered a reinvestigation necessary; these issues include the presence of numerous upper limits for the nitrogen abundance, unknown multiplicity status, and a mix of stars with different physical properties, such as their mass and evolutionary state, which are known to control the amount of rotational mixing. Methods: We have carefully selected a large sample of bright, fast-rotating early-type stars of our Galaxy (40 objects with spectral types between B0.5 and O4). Their high-quality, high-resolution optical spectra were then analysed with the stellar atmosphere modelling codes DETAIL/SURFACE or CMFGEN, depending on the temperature of the target. Several internal and external checks were performed to validate our methods; notably, we compared our results with literature data for some well-known objects, studied the effect of gravity darkening, or confronted the results provided by the two codes for stars amenable to both analyses. Furthermore, we studied the radial velocities of the stars to assess their binarity. Results: This first part of our study presents our methods and provides the derived stellar parameters, He, CNO abundances, and the multiplicity status of every star of the sample. It is the first time that He and CNO abundances of such a large number of Galactic massive fast rotators are determined in a homogeneous way. [less ▲]

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See detailGaia Data Release 1. Open cluster astrometry: performance, limitations, and future prospects
Gaia Collaboration; van Leeuwen, F.; Vallenari, A. et al

in Astronomy and Astrophysics (2017), 601

Context. The first Gaia Data Release contains the Tycho-Gaia Astrometric Solution (TGAS). This is a subset of about 2 million stars for which, besides the position and photometry, the proper motion and ... [more ▼]

Context. The first Gaia Data Release contains the Tycho-Gaia Astrometric Solution (TGAS). This is a subset of about 2 million stars for which, besides the position and photometry, the proper motion and parallax are calculated using Hipparcos and Tycho-2 positions in 1991.25 as prior information. <BR /> Aims: We investigate the scientific potential and limitations of the TGAS component by means of the astrometric data for open clusters. <BR /> Methods: Mean cluster parallax and proper motion values are derived taking into account the error correlations within the astrometric solutions for individual stars, an estimate of the internal velocity dispersion in the cluster, and, where relevant, the effects of the depth of the cluster along the line of sight. Internal consistency of the TGAS data is assessed. <BR /> Results: Values given for standard uncertainties are still inaccurate and may lead to unrealistic unit-weight standard deviations of least squares solutions for cluster parameters. Reconstructed mean cluster parallax and proper motion values are generally in very good agreement with earlier Hipparcos-based determination, although the Gaia mean parallax for the Pleiades is a significant exception. We have no current explanation for that discrepancy. Most clusters are observed to extend to nearly 15 pc from the cluster centre, and it will be up to future Gaia releases to establish whether those potential cluster-member stars are still dynamically bound to the clusters. <BR /> Conclusions: The Gaia DR1 provides the means to examine open clusters far beyond their more easily visible cores, and can provide membership assessments based on proper motions and parallaxes. A combined HR diagram shows the same features as observed before using the Hipparcos data, with clearly increased luminosities for older A and F dwarfs. Tables D.1 to D.19 are also available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (<A href="http://130.79.128.5">http://130.79.128.5</A>) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/601/A19">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/601/A19</A> [less ▲]

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