References of "Rauw, Grégor"
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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 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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See detailAn Optical and Infrared Photometric Study of the Young Open Cluster IC 1805 in the Giant H ii Region W4 †
Sung, Hwankyung; Bessell, Michael S.; Chun, Moo-Young et al

in Astrophysical Journal Supplement Series (2017), 230

We present deep wide-field optical CCD photometry and mid-infrared Spitzer/IRAC and MIPS 24 μm data for about 100,000 stars in the young open cluster IC 1805. The members of IC 1805 were selected from ... [more ▼]

We present deep wide-field optical CCD photometry and mid-infrared Spitzer/IRAC and MIPS 24 μm data for about 100,000 stars in the young open cluster IC 1805. The members of IC 1805 were selected from their location in the various color–color and color–magnitude diagrams, and the presence of Hα emission, mid-infrared excess emission, and X-ray emission. The reddening law toward IC 1805 is nearly normal (R [SUB] V [/SUB] = 3.05 ± 0.06). However, the distance modulus of the cluster is estimated to be 11.9 ± 0.2 mag (d=2.4+/- 0.2 kpc) from the reddening-free color–magnitude diagrams, which is larger than the distance to the nearby massive star-forming region W3(OH) measured from the radio VLBA astrometry. We also determined the age of IC 1805 ({τ }[SUB]{MSTO[/SUB]}=3.5 Myr). In addition, we critically compared the age and mass scale from two pre-main-sequence evolution models. The initial mass function with a Salpeter-type slope of Γ = ‑1.3 ± 0.2 was obtained and the total mass of IC 1805 was estimated to be about 2700 ± 200 {M}[SUB]ȯ [/SUB]. Finally, we found our distance determination to be statistically consistent with the Tycho-Gaia Astrometric Solution Data Release 1, within the errors. The proper motion of the B-type stars shows an elongated distribution along the Galactic plane, which could be explained by some of the B-type stars being formed in small clouds dispersed by previous episodes of star formation or supernova explosions. The optical imaging data in this article were gathered with two facilities: the AZT-22 1.5 m telescope at Maidanak Astronomical Observatory in Uzbekistan and the Canada–France–Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. [less ▲]

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See detailπ Aquarii is another γ Cassiopeiae object
Nazé, Yaël ULiege; Rauw, Grégor ULiege; Cazorla, Constantin ULiege

in Astronomy and Astrophysics (2017), 602

The γ Cas category is a subgroup of Be stars displaying a strong, hard, and variable thermal X-ray emission. An XMM-Newton observation of π Aqr reveals spectral and temporal characteristics that clearly ... [more ▼]

The γ Cas category is a subgroup of Be stars displaying a strong, hard, and variable thermal X-ray emission. An XMM-Newton observation of π Aqr reveals spectral and temporal characteristics that clearly make this Be star another member of the γ Cas category. Furthermore, π Aqr is a binary but, contrary to γ Cas, the nature of the companion to the Be star is known; it is a non-degenerate (stellar) object and its small separation from the Be star does not leave much room for a putative compact object close to the Be disk. This renders the accretion scenario difficult to apply in this system, and, hence, this discovery favors a disk-related origin for the γ Cas phenomenon. Based on observations collected with the ESA science mission XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). [less ▲]

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See detailHow unique is Plaskett's star? A search for organized magnetic fields in short period, interacting or post-interaction massive binary systems★
Nazé, Yaël ULiege; Neiner, Coralie; Grunhut, Jason et al

in Monthly Notices of the Royal Astronomical Society (2017), 467

Amongst O-type stars with detected magnetic fields, the fast rotator in the close binary called Plaskett's star shows a variety of unusual properties. Since strong binary interactions are believed to have ... [more ▼]

Amongst O-type stars with detected magnetic fields, the fast rotator in the close binary called Plaskett's star shows a variety of unusual properties. Since strong binary interactions are believed to have occurred in this system, one may wonder about their potential role in generating magnetic fields. Stokes V spectra collected with the low-resolution FORS2 and high-resolution ESPaDOnS and Narval spectropolarimeters were therefore used to search for magnetic fields in 15 interacting or post-interaction massive binaries. No magnetic field was detected in any of them, with 0 G always being within 2σ of the derived values. For 17 out of 25 stars in the systems observed at high resolution, the 90 per cent upper limit on the individual dipolar fields is below the dipolar field strength of Plaskett's secondary; a similar result is found for five out of six systems observed at low resolution. If our sample is considered to form a group of stars sharing similar magnetic properties, a global statistical analysis results in a stringent upper limit of ∼200 G on the dipolar field strength. Moreover, the magnetic incidence rate in the full sample of interacting or post-interaction systems (our targets + Plaskett's star) is compatible with that measured from large surveys, showing that they are not significantly different from the general O-star population. These results suggest that binary interactions play no systematic role in the magnetism of such massive systems. [less ▲]

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See detailPerspectives for observing hot massive stars with XMM-Newton in the years 2017-2027
Rauw, Grégor ULiege

in Astronomische Nachrichten (2017), 338

XMM-Newton has deeply changed our picture of X-ray emission of hot, massive stars. High-resolution X-ray spectroscopy as well as monitoring of these objects helped us gain a deeper insight into the ... [more ▼]

XMM-Newton has deeply changed our picture of X-ray emission of hot, massive stars. High-resolution X-ray spectroscopy as well as monitoring of these objects helped us gain a deeper insight into the physics of single massive stars with or without magnetic fields, as well as of massive binary systems, where the stellar winds of both stars interact. These observations also revealed a number of previously unexpected features that challenge our understanding of the dynamics of the stellar winds of massive stars. I briefly summarize the results obtained over the past 15 years and highlight the perspectives for the next decade. It is anticipated that coordinated (X-ray and optical or UV) monitoring and time-critical observations of either single or binary massive stars will become the most important topics in this field over the coming years. Synergies with existing or forthcoming X-ray observatories (NuSTAR, Swift, eROSITA) will also play a major role and will further enhance the importance of XMM-Newton in our quest for understanding the physics of hot, massive stars. [less ▲]

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See detailConception of a near-infrared spectrometer for ground-based observations of massive stars
Kintziger, Christian ULiege; Desselle, Richard ULiege; Loicq, Jerôme ULiege et al

in Journal of Astronomical Telescopes, Instruments, and Systems (2017), 3(1), 015002

In our contribution, we outline the different steps in the design of a fiber-fed spectrographic instrument for stellar astrophysics. Starting from the derivation of theoretical relationships from the ... [more ▼]

In our contribution, we outline the different steps in the design of a fiber-fed spectrographic instrument for stellar astrophysics. Starting from the derivation of theoretical relationships from the scientific requirements and telescope characteristics, the entire optical design of the spectrograph is presented. Specific optical elements, such as a toroidal lens, are introduced to improve the instrument’s efficiency. Then the verification of predicted optical performances is investigated through optical analyses, such as resolution checking. [less ▲]

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See detailXMM-Newton : en route vers une autre décennie de découvertes
Rauw, Grégor ULiege

Article for general public (2017)

Au mois de décembre 2016, cela faisait 17 ans que XMM-Newton fut lancé par une fusée Ariane V. Equipé de ses trois modules miroirs comportant chacun 58 miroirs imbriqués les uns dans les autres, XMM ... [more ▼]

Au mois de décembre 2016, cela faisait 17 ans que XMM-Newton fut lancé par une fusée Ariane V. Equipé de ses trois modules miroirs comportant chacun 58 miroirs imbriqués les uns dans les autres, XMM-Newton est à l’affût de l’émission X de sources cosmiques de tout genre. Malgré sa longévité, XMM-Newton reste à ce jour un des observatoires les plus sollicités au monde. Chaque année, les astrophysiciens proposent des programmes d’observation qui totalisent à peu près 6 fois le temps d’observation disponible! La compétition pour les observations avec XMM est donc très rude. Et a priori cela pourrait continuer encore comme cela pendant quelques années. De fait, les réserves de carburant et la performance des panneaux solaires indiquent que la mission pourrait encore fonctionner au moins 10 ans si les budgets le permettent1! [less ▲]

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See detailStudy of the variability of Nova V5668 Sgr, based on high-resolution spectroscopic monitoring
Jack, D.; Robles Pérez, J. De J.; De Gennaro Aquino, I. et al

in Astronomische Nachrichten (2017), 338

We present results of our dense spectroscopic monitoring of Nova V5668 Sgr. Starting on March 19 in 2015, only a few days after discovery, we have obtained a series of spectra with the TIGRE telescope and ... [more ▼]

We present results of our dense spectroscopic monitoring of Nova V5668 Sgr. Starting on March 19 in 2015, only a few days after discovery, we have obtained a series of spectra with the TIGRE telescope and its HEROS echelle spectrograph which offers a resolution of R = 20,000 and covers the optical wavelength range from 3800 to 8800 {\AA}. We performed a line identification of the discernible features for four spectra which are representative for the respective phases in the light curve evolution of that nova. By simultaneously analysing the variations in the visual light curve and the corresponding spectra of Nova V5668 Sgr, we found that during the declining phases of the nova the absorption features in all hydrogen and many other lines had shifted to higher expansion velocities of -2000 km s^-1. Conversely, during the rise towards the following maximum, these observed absorption features had returned to lower expansion velocities.We found that the absorption features of some Fe II lines displayed the same behaviour, but in addition disappeared for a few days during some declining phases. Features of several N I lines also disappeared while new N II lines appeared in emission for a few days during some of the declining phases of the light curve of Nova V5668 Sgr. The shape of the emission features is changing during the evolution and shows a clear double peak structure after the deep minimum. [less ▲]

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See detailA legacy survey of early B-stars using the RGS
Nazé, Yaël ULiege; Cazorla, C.; Rauw, Grégor ULiege et al

Poster (2017)

Despite their relatively large incidence among early-type stars, only a few B-stars have been observed with X-ray gratings. We therefore undertook a legacy project with XMM to gather high- resolution ... [more ▼]

Despite their relatively large incidence among early-type stars, only a few B-stars have been observed with X-ray gratings. We therefore undertook a legacy project with XMM to gather high- resolution spectra of a set of early B stars selected on the basis of their high RASS count rate. This poster presents the preliminary results of this project. [less ▲]

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See detailThe flaring activity of PMS in NGC6530
Rauw, Grégor ULiege; Nelissen, Marie; Nazé, Yaël ULiege

Poster (2017)

We have obtained XMM-Newton observations of the very young open cluster NGC6530 at four different epochs. The data reveal a wealth of relatively faint X-ray sources that are correlated with PMS members of ... [more ▼]

We have obtained XMM-Newton observations of the very young open cluster NGC6530 at four different epochs. The data reveal a wealth of relatively faint X-ray sources that are correlated with PMS members of NGC6530. We have investigated the X-ray properties of these sources with emphasis on their flaring activity. We compare our results with the properties of the sources (stellar masses, rotation rates,...) as inferred from optical studies. [less ▲]

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See detailObservational signatures of past mass-exchange episodes in massive binaries: the case of LSS 3074
Raucq, Françoise ULiege; Gosset, Eric ULiege; Rauw, Grégor ULiege et al

in Astronomy and Astrophysics (2017), 601

Context. The role of mass and momentum exchanges in close massive binaries is very important in the subsequent evolution of the components. Such exchanges produce several observational signatures such as ... [more ▼]

Context. The role of mass and momentum exchanges in close massive binaries is very important in the subsequent evolution of the components. Such exchanges produce several observational signatures such as asynchronous rotation and altered chemical compositions, that remain after the stars detach again. Aims. We investigated these effects for the close O-star binary LSS 3074 (O4 f + O6-7:(f):), which is a good candidate for a past Roche lobe overflow (RLOF) episode because of its very short orbital period, P = 2.185 days, and the luminosity classes of both components. Methods.We determined a new orbital solution for the system. We studied the photometric light curves to determine the inclination of the orbit and Roche lobe filling factors of both stars. Using phase-resolved spectroscopy, we performed the disentangling of the optical spectra of the two stars.We then analysed the reconstructed primary and secondary spectra with the CMFGEN model atmosphere code to determine stellar parameters, such as the effective temperatures and surface gravities, and to constrain the chemical composition of the components. Results. We confirm the apparent low stellar masses and radii reported in previous studies. We also find a strong overabundance in nitrogen and a strong carbon and oxygen depletion in both primary and secondary atmospheres, together with a strong enrichment in helium of the primary star. Conclusions. We propose several possible evolutionary pathways through a RLOF process to explain the current parameters of the system. We confirm that the system is apparently in overcontact configuration and has lost a significant portion of its mass to its surroundings. We suggest that some of the discrepancies between the spectroscopic and photometric properties of LSS 3074 could stem from the impact of a strong radiation pressure of the primary. [less ▲]

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See detailObservational signatures of past mass-exchange episodes in massive binaries : The cases of HD17505 and HD206267
Raucq, Françoise ULiege; Rauw, Grégor ULiege

Conference (2016, December 19)

Mass and angular momentum exchanges through Roche Lobe Overflow interactions within close massive binaries are known to play an important role in the subsequent evolution of the components of such systems ... [more ▼]

Mass and angular momentum exchanges through Roche Lobe Overflow interactions within close massive binaries are known to play an important role in the subsequent evolution of the components of such systems, and produce several observational signatures, such as asynchronous rotation and altered chemical compositions, that remain once the stars detach again. We have started to investigate these effects in a sample of massive O-star binaries that are thought to have previously experienced a Case A Roche Lobe Overflow episode. Using phase-resolved spectroscopy, we perform the disentangling of the optical spectra of the two stars. The reconstructed primary and secondary spectra are then analysed with the CMFGEN model atmosphere code to determine stellar parameters such as the effective temperatures, surface gravities and rotational velocities, and to constrain the chemical composition of the components. In this contribution, we present the results of our analyses of the triple system HD17505 ([O7V + O7V, P = 8.57 days] + O6.5III). We also present the first results of our analyses of the triple system HD206267 ([O6.5V + O9.5V,P = 3.71 days] + OB). [less ▲]

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See detailGaia Data Release 1. Summary of the astrometric, photometric, and survey properties
Gaia Collaboration; Brown, A. G. A.; Vallenari, A. et al

in Astronomy and Astrophysics (2016), 595

Context. At about 1000 days after the launch of Gaia we present the first Gaia data release, Gaia DR1, consisting of astrometry and photometry for over 1 billion sources brighter than magnitude 20.7. <BR ... [more ▼]

Context. At about 1000 days after the launch of Gaia we present the first Gaia data release, Gaia DR1, consisting of astrometry and photometry for over 1 billion sources brighter than magnitude 20.7. <BR /> Aims: A summary of Gaia DR1 is presented along with illustrations of the scientific quality of the data, followed by a discussion of the limitations due to the preliminary nature of this release. <BR /> Methods: The raw data collected by Gaia during the first 14 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into an astrometric and photometric catalogue. <BR /> Results: Gaia DR1 consists of three components: a primary astrometric data set which contains the positions, parallaxes, and mean proper motions for about 2 million of the brightest stars in common with the Hipparcos and Tycho-2 catalogues - a realisation of the Tycho-Gaia Astrometric Solution (TGAS) - and a secondary astrometric data set containing the positions for an additional 1.1 billion sources. The second component is the photometric data set, consisting of mean G-band magnitudes for all sources. The G-band light curves and the characteristics of 3000 Cepheid and RR Lyrae stars, observed at high cadence around the south ecliptic pole, form the third component. For the primary astrometric data set the typical uncertainty is about 0.3 mas for the positions and parallaxes, and about 1 mas yr[SUP]-1[/SUP] for the proper motions. A systematic component of 0.3 mas should be added to the parallax uncertainties. For the subset of 94 000 Hipparcos stars in the primary data set, the proper motions are much more precise at about 0.06 mas yr[SUP]-1[/SUP]. For the secondary astrometric data set, the typical uncertainty of the positions is 10 mas. The median uncertainties on the mean G-band magnitudes range from the mmag level to 0.03 mag over the magnitude range 5 to 20.7. <BR /> Conclusions: Gaia DR1 is an important milestone ahead of the next Gaia data release, which will feature five-parameter astrometry for all sources. Extensive validation shows that Gaia DR1 represents a major advance in the mapping of the heavens and the availability of basic stellar data that underpin observational astrophysics. Nevertheless, the very preliminary nature of this first Gaia data release does lead to a number of important limitations to the data quality which should be carefully considered before drawing conclusions from the data. [less ▲]

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See detailThe Gaia mission
Gaia Collaboration; Prusti, T.; de Bruijne, J. H. J. et al

in Astronomy and Astrophysics (2016), 595

Gaia is a cornerstone mission in the science programme of the EuropeanSpace Agency (ESA). The spacecraft construction was approved in 2006, following a study in which the original interferometric concept ... [more ▼]

Gaia is a cornerstone mission in the science programme of the EuropeanSpace Agency (ESA). The spacecraft construction was approved in 2006, following a study in which the original interferometric concept was changed to a direct-imaging approach. Both the spacecraft and the payload were built by European industry. The involvement of the scientific community focusses on data processing for which the international Gaia Data Processing and Analysis Consortium (DPAC) was selected in 2007. Gaia was launched on 19 December 2013 and arrived at its operating point, the second Lagrange point of the Sun-Earth-Moon system, a few weeks later. The commissioning of the spacecraft and payload was completed on 19 July 2014. The nominal five-year mission started with four weeks of special, ecliptic-pole scanning and subsequently transferred into full-sky scanning mode. We recall the scientific goals of Gaia and give a description of the as-built spacecraft that is currently (mid-2016) being operated to achieve these goals. We pay special attention to the payload module, the performance of which is closely related to the scientific performance of the mission. We provide a summary of the commissioning activities and findings, followed by a description of the routine operational mode. We summarise scientific performance estimates on the basis of in-orbit operations. Several intermediate Gaia data releases are planned and the data can be retrieved from the Gaia Archive, which is available through the Gaia home page. <A href="http://www.cosmos.esa.int/gaia">http://www.cosmos.esa.int/gaia</A> [less ▲]

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See detailApsidal motion in the massive binary HD 152218
Rauw, Grégor ULiege; Rosu, S.; Noels-Grötsch, Arlette ULiege et al

in Astronomy and Astrophysics (2016), 594(A33), 1-12

Massive binary systems are important laboratories in which to probe the properties of massive stars and stellar physics in general. In this context, we analysed optical spectroscopy and photometry of the ... [more ▼]

Massive binary systems are important laboratories in which to probe the properties of massive stars and stellar physics in general. In this context, we analysed optical spectroscopy and photometry of the eccentric short-period early-type binary HD 152218 in the young open cluster NGC 6231. We reconstructed the spectra of the individual stars using a disentangling code. The individual spectra were then compared with synthetic spectra obtained with the CMFGEN model atmosphere code. We furthermore analysed the light curve of the binary and used it to constrain the orbital inclination and to derive absolute masses of (19.8 ± 1.5) and (15.0 ± 1.1) M⊙. Combining radial velocity measurements from over 60 yr, we show that the system displays apsidal motion at a rate of (2.04 ± .24)°/yr. Solving the Clairaut-Radau equation, we used stellar evolution models, obtained with the CLES code, to compute the internal structure constants and to evaluate the theoretically predicted rate of apsidal motion as a function of stellar age and primary mass. In this way, we determine an age of 5.8 ± 0.6 Myr for HD 152218, which is towards the higher end of, but compatible with, the range of ages of the massive star population of NGC 6231 as determined from isochrone fitting. [less ▲]

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See detailX-ray and optical spectroscopy of the massive young open cluster IC 1805
Rauw, Grégor ULiege; Nazé, Yaël ULiege

in Astronomy and Astrophysics (2016), 594(A82), 19

Context. Very young open clusters are ideal places to study the X-ray properties of a homogeneous population of early-type stars. In this respect, the IC 1805 open cluster is very interesting as it hosts ... [more ▼]

Context. Very young open clusters are ideal places to study the X-ray properties of a homogeneous population of early-type stars. In this respect, the IC 1805 open cluster is very interesting as it hosts the O4 If+ star HD 15570 thought to be in an evolutionary stage intermediate between a normal O-star and a Wolf-Rayet star. Aims: Such a star could provide a test for theoretical models aiming at explaining the empirical scaling relation between the X-ray and bolometric luminosities of O-type stars. Methods: We have observed IC 1805 with XMM-Newton and further collected optical spectroscopy of some of the O-star members of the cluster. Results: The optical spectra allow us to revisit the orbital solutions of BD+60° 497 and HD 15558, and provide the first evidence of binarity for BD+60° 498. X-ray emission from colliding winds does not appear to play an important role among the O-stars of IC 1805. Notably, the X-ray fluxes do not vary significantly between archival X-ray observations and our XMM-Newton pointing. The very fast rotator BD+60° 513, and to a lesser extent the O4 If+ star HD 15570 appear somewhat underluminous. Whilst the underluminosity of HD 15570 is only marginally significant, its amplitude is found to be compatible with theoretical expectations based on its stellar and wind properties. A number of other X-ray sources are detected in the field, and the brightest objects, many of which are likely low-mass pre-main sequence stars, are analyzed in detail. [less ▲]

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See detailFeasibility study of a UV photometer on-board a 3 CubeSat for the study of bright massive stars
Desselle, Richard ULiege; Kintziger, Christian ULiege; Rauw, Grégor ULiege et al

Conference (2016, September 07)

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 are conducting a feasibility study of a UV photometer on-board a 3U CubeSat. The scientific purpose of this payload will be to collect time series of photometric measurements of bright massive stars. These massive stars are very hot and luminous objects emitting copious amounts of UV radiation. The properties of these stars during their life and their death in gigantic supernova explosions make them key players for the evolution of the Universe. The UV photometer will be used for imaging photometric observations of massive stars in the spectral range from 250 to 350 nm. The strength of space photometry is the absence of signal perturbation by the Earth’s atmosphere and the continuity of the time-series. Precisely measuring photometric variations allows studying radial and non-radial pulsations of stars. This discipline, called asteroseismology, is currently the most powerful technique for probing the physical conditions in the interiors of stars. An important problem in asteroseismology of massive stars is the mode identification. Simultaneous observations in the near UV (250-350 nm) and in the visible (600 nm) provide the best combination for precise and accurate mode identification based on amplitude ratios in massive stars. Data in the latter pass-band are currently covered by the satellites of the BRITE constellation. Combining the observations of our instrument with those of BRITE will hence result in unprecedented results for pulsating massive stars. The baseline for the UV photometer is a Ritchey-Chrétien telescope composed of two reflective hyperbolic mirrors that focalize the light coming from space onto a focal plane protected by an optical filter. We will present the optimized optical design of the payload and its associated optical sensor. A photometric budget taking into account the characteristics of the target’s stars and the payload performances will also be presented. We will further discuss the observation strategy. Finally, the accommodation of the payload in the spacecraft and its sub-units will be shown as well as mission and preliminary thermal analyses of the whole system obtained after accommodation. [less ▲]

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See detailLa malédiction X a encore frappé!
Rauw, Grégor ULiege

Article for general public (2016)

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