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See detailNon-thermal processes in colliding-wind massive binaries: the contribution of Simbol-X to a multiwavelength investigation
De Becker, Michaël ULg; Blomme, Ronny; Micela, Giusi et al

in AIP Conference Proceedings (2009, May), 1126

Several colliding-wind massive binaries are known to be non-thermal emitters in the radio domain. This constitutes strong evidence for the fact that an efficient particle acceleration process is at work ... [more ▼]

Several colliding-wind massive binaries are known to be non-thermal emitters in the radio domain. This constitutes strong evidence for the fact that an efficient particle acceleration process is at work in these objects. The acceleration mechanism is most probably the Diffusive Shock Acceleration (DSA) process in the presence of strong hydrodynamic shocks due to the colliding-winds. In order to investigate the physics of this particle acceleration, we initiated a multiwavelength campaign covering a large part of the electromagnetic spectrum. In this context, the detailed study of the hard X-ray emission from these sources in the SIMBOL-X bandpass constitutes a crucial element in order to probe this still poorly known topic of astrophysics. It should be noted that colliding-wind massive binaries should be considered as very valuable targets for the investigation of particle acceleration in a similar way as supernova remnants, but in a different region of the parameter space. [less ▲]

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See detailLong baseline interferometry as a tool to investigate colliding-wind massive binaries
De Becker, Michaël ULg

Conference (2009, March 20)

Massive stars present the interesting property to generate strong stellar winds. In the particular case of binary systems made of two massive stars, the two stellar winds are likely to collide. In ... [more ▼]

Massive stars present the interesting property to generate strong stellar winds. In the particular case of binary systems made of two massive stars, the two stellar winds are likely to collide. In addition, in this scenario, interesting physics is occurring, such as strong high-energy emission, dust production or even particle acceleration. However, our capability to understand these "higher-level" processes relies intimately on our knowledge of stellar and orbital parameters of these binaries, and on our vision of the hydrodynamics that is taking place in these objects. In this context, the purpose of this presentation is to discuss the expected contribution of long baseline interferometry. [less ▲]

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See detailThe Simbol-X mission and the investigation of hard X-rays from massive stars
De Becker, Michaël ULg

Conference (2009, February 19)

Simbol-X is a mission initially driven by the French and Italian space agencies. This is a formation flying satellite whose main interest is an unprecedented imaging and spectral capability, with a high ... [more ▼]

Simbol-X is a mission initially driven by the French and Italian space agencies. This is a formation flying satellite whose main interest is an unprecedented imaging and spectral capability, with a high sensitivity at energies between 10 and 80 keV. This space observatory is especially designed to study acceleration processes in astrophysical sources, along with extreme physics under relativistic conditions. I will briefly present the current status of the mission. I will also discuss prospects for future observations of massive stars with Simbol-X, aiming at probing the physics of particle acceleration in colliding-wind massive binaries. [less ▲]

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See detailLong baseline interferometry applied to the study of massive stars: current observations and prospects for VSI
De Becker, Michaël ULg

Conference (2009, February 19)

Recent advances in the development of interferometric instruments coupled to long baseline facilities such as the VLTI allow us to observe astronomical targets at the milli-arcsecond scale. In the context ... [more ▼]

Recent advances in the development of interferometric instruments coupled to long baseline facilities such as the VLTI allow us to observe astronomical targets at the milli-arcsecond scale. In the context of the study of massive stars, this new tool is likely to provide crucial information on the multiplicity of massive stars, and on interactions in colliding-wind binaries. In this context, our group is leading observation campaigns with the VLTI aiming at investigating massive multiple systems. I will briefly present these campaigns and discuss prospects for observations with next generation instruments such as the VLTI-Spectro-Imager (VSI). [less ▲]

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See detailA multiwavelength investigation of the massive eclipsing binary Cyg OB2 #5
Linder, Natacha ULg; Rauw, Grégor ULg; Manfroid, Jean ULg et al

in Astronomy and Astrophysics (2009), 495

Context. The properties of the early-type binary Cyg OB2 #5 have been debated for many years and spectroscopic and photometric investigations yielded conflicting results. Aims. We have attempted to ... [more ▼]

Context. The properties of the early-type binary Cyg OB2 #5 have been debated for many years and spectroscopic and photometric investigations yielded conflicting results. Aims. We have attempted to constrain the physical properties of the binary by collecting new optical and X-ray observations. Methods. The optical light curves obtained with narrow-band continuum and line-bearing filters are analysed and compared. Optical spectra are used to map the location of the He II $\lambda $ 4686 and H$\alpha $ line-emission regions in velocity space. New XMM-Newton as well as archive X-ray spectra are analysed to search for variability and constrain the properties of the hot plasma in this system. Results. We find that the orbital period of the system slowly changes though we are unable to discriminate between several possible explanations of this trend. The best fit solution of the continuum light curve reveals a contact configuration with the secondary star being significantly brighter and hotter on its leading side facing the primary. The mean temperature of the secondary star turns out to be only slightly lower than that of the primary, whilst the bolometric luminosity ratio is found to be 3.1. The solution of the light curve yields a distance of $925 \pm 25$ pc much lower than the usually assumed distance of the Cyg OB2 association. Whilst we confirm the existence of episodes of higher X-ray fluxes, the data reveal no phase-locked modulation with the 6.6 day period of the eclipsing binary nor any clear relation between the X-ray flux and the 6.7 yr radio cycle. Conclusions. The bright region of the secondary star is probably heated by energy transfer in a common envelope in this contact binary system as well as by the collision with the primary's wind. The existence of a common photosphere probably also explains the odd mass-luminosity relation of the stars in this system. Most of the X-ray, non-thermal radio, and possibly $\gamma$-ray emission of Cyg OB2 #5 is likely to arise from the interaction of the combined wind of the eclipsing binary with at least one additional star of this multiple system. [less ▲]

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See detailThe Quiet HMXB Candidates HD 14633 and HD 15137
McSwain, M. V.; Roberts, M. S. E.; Boyajian, T. S. et al

Conference (2009)

The runaway O-type binaries HD 14633 and HD 15137 were likely ejected from the cluster of their birth by supernovae explosions in close binaries. Neither star is a known X-ray source, but they likely ... [more ▼]

The runaway O-type binaries HD 14633 and HD 15137 were likely ejected from the cluster of their birth by supernovae explosions in close binaries. Neither star is a known X-ray source, but they likely contain neutron stars and may be weak stellar wind accretion systems. Hence the two binaries have been classified as "quiet HMXBs". Here we present new optical spectra of these spectroscopic binaries and reassess their orbits. We also present preliminary results from recent XMM-Newton observations, intended to detect the hard power-law spectrum from accreting or quiescent neutron star companions and reveal the evolutionary history of these intriguing runaways. [less ▲]

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See detailMilli-arcsecond Astrophysics with VSI, the VLTI Spectro-imager in the ELT Era
Malbet, F.; Buscher, D.; Weigelt, G. et al

in Moorwood, Alan (Ed.) Science with the VLT in the ELT Era (2009)

Nowadays, compact sources relatively warm like surfaces of nearby stars, circumstellar environments of stars from early stages to the most evolved ones and surroundings of active galactic nuclei can be ... [more ▼]

Nowadays, compact sources relatively warm like surfaces of nearby stars, circumstellar environments of stars from early stages to the most evolved ones and surroundings of active galactic nuclei can be investigated at milli-arcsecond scales only with the VLT in its interferometric mode. We propose a spectro-imager, named VSI (VLTI spectro-imager), which is capable to probe these sources both over spatial and spectral scales in the near-infrared domain. This instrument will provide information complementary to what is obtained at the same time with ALMA at different wavelengths and the extreme large telescopes. [less ▲]

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See detailThe multiwavelength picture of star formation in the very young open cluster NGC6383
Rauw, Grégor ULg; De Becker, Michaël ULg

in Reipurth, Bo (Ed.) Handbook of Star Forming Region. Volume 2: The Southern Sky (2008)

We review the properties of the very young (˜ 2 Myr) open cluster NGC 6383. The cluster is dominated by the massive binary HD 159176 (O7 V + O7 V). The distance to NGC 6383 is consistently found to be 1.3 ... [more ▼]

We review the properties of the very young (˜ 2 Myr) open cluster NGC 6383. The cluster is dominated by the massive binary HD 159176 (O7 V + O7 V). The distance to NGC 6383 is consistently found to be 1.3 ± 0.1 kpc and the average reddening is determined to be E(bv) = 0.32 ± 0.02. Several pre-main sequence candidates have been identified using different criteria relying on the detection of emission lines, infrared excesses, photometric variability and X-ray emission. [less ▲]

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See detailScience case for 1 mas spectro-imagining in the near-infrared
Garcia, Paulo J V; Berger, Jean-Phillipe; Marconi, Alessandro et al

in Schöller, Markus; Danchi, William; Delplancke, Françoise (Eds.) Optical and Infrared Interferometry (2008, July 01)

We present the work developed within the science team of the Very Large Telescope Interferometer Spectro-Imager (VSI) during the Phase A studies. VSI aims at delivering ~ 1 milliarcsecond resolution data ... [more ▼]

We present the work developed within the science team of the Very Large Telescope Interferometer Spectro-Imager (VSI) during the Phase A studies. VSI aims at delivering ~ 1 milliarcsecond resolution data cubes in the near-infrared, with several spectral resolutions up to 12 000, by combining up to 8 VLTI telescopes. In the design of an instrument, the science case plays a central role by supporting the instrument construction decision, defining the top-level requirements and balancing design options. The overall science philosophy of VSI was that of a general user instrument serving a broad community. The science team addressed themes which included several areas of astrophysics and illustrated specific modes of operation of the instrument: a) YSO disks and winds; b) Multiplicity of young stars; c) Exoplanets; d) Debris disks; e) Stellar surface imaging; f) The environments of evolved stars; g) AGN tori; h) AGN's Broad Line Region; i) Supermassive black-holes; and j) Microlensing. The main conclusions can be summarized as follows: a) The accessible targets and related science are extremely sensitive to the instrument limiting magnitude; the instrument should be optimized for sensitivity and have its own fringe tracker. b) Most of the science cases are readily achievable with on-axis fringe tracking, off-axis fringe tracking enabling extra science. c) In most targets (YSOs, evolved stars and AGNs), the interpretation and analysis of circumstellar/nuclear dust morphology requires direct access to the gas via spectral resolved studies of emission lines, requiring at least a spectral resolution of 2 500. d) To routinely deliver images at the required sensitivity, the number of telescopes in determinant, with 6 telescopes being favored. e) The factorial increase in the number of closure phases and visibilities, gained in a single observation, makes massive surveys of parameters and related science for the first time possible. f) High dynamic range imaging and very high dynamic range differential closure phase are possible allowing the study of debris disks and characterization of pegasides. g) Spectro-imaging in the near-infrared is highly complementary to ALMA, adaptive optics and interferometric imaging in the thermal infrared. [less ▲]

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See detailVSI: the VLTI spectro-imager
Malbet, F.; Buscher, D.; Weigelt, G. et al

in Schöller, Markus; Danchi, William; Delplancke, Françoise (Eds.) Optical and Infrared Interferometry (2008, July 01)

The VLTI Spectro Imager (VSI) was proposed as a second-generation instrument of the Very Large Telescope Interferometer providing the ESO community with spectrally-resolved, near-infrared images at ... [more ▼]

The VLTI Spectro Imager (VSI) was proposed as a second-generation instrument of the Very Large Telescope Interferometer providing the ESO community with spectrally-resolved, near-infrared images at angular resolutions down to 1.1 milliarcsecond and spectral resolutions up to R = 12000. Targets as faint as K = 13 will be imaged without requiring a brighter nearby reference object; fainter targets can be accessed if a suitable reference is available. The unique combination of high-dynamic-range imaging at high angular resolution and high spectral resolution enables a scientific program which serves a broad user community and at the same time provides the opportunity for breakthroughs in many areas of astrophysics. The high level specifications of the instrument are derived from a detailed science case based on the capability to obtain, for the first time, milliarcsecond-resolution images of a wide range of targets including: probing the initial conditions for planet formation in the AU-scale environments of young stars; imaging convective cells and other phenomena on the surfaces of stars; mapping the chemical and physical environments of evolved stars, stellar remnants, and stellar winds; and disentangling the central regions of active galactic nuclei and supermassive black holes. VSI will provide these new capabilities using technologies which have been extensively tested in the past and VSI requires little in terms of new infrastructure on the VLTI. At the same time, VSI will be able to make maximum use of new infrastructure as it becomes available; for example, by combining 4, 6 and eventually 8 telescopes, enabling rapid imaging through the measurement of up to 28 visibilities in every wavelength channel within a few minutes. The current studies are focused on a 4-telescope version with an upgrade to a 6-telescope one. The instrument contains its own fringe tracker and tip-tilt control in order to reduce the constraints on the VLTI infrastructure and maximize the scientific return. [less ▲]

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See detailPhase closure image reconstruction for future VLTI instrumentation
Filho, Mercedes E; Renard, Stephanie; Garcia, Paulo et al

in Schöller, Markus; Danchi, William; Delplancke, Françoise (Eds.) Optical and Infrared Interferometry (2008, July 01)

Classically, optical and near-infrared interferometry have relied on closure phase techniques to produce images. Such techniques allow us to achieve modest dynamic ranges. In order to test the feasibility ... [more ▼]

Classically, optical and near-infrared interferometry have relied on closure phase techniques to produce images. Such techniques allow us to achieve modest dynamic ranges. In order to test the feasibility of next generation optical interferometers in the context of the VLTI-spectro-imager (VSI), we have embarked on a study of image reconstruction and analysis. Our main aim was to test the influence of the number of telescopes, observing nights and distribution of the visibility points on the quality of the reconstructed images. Our results show that observations using six Auxiliary Telescopes (ATs) during one complete night yield the best results in general and is critical in most science cases; the number of telescopes is the determining factor in the image reconstruction outcome. In terms of imaging capabilities, an optical, six telescope VLTI-type configuration and ~200 meter baseline will achieve 4 mas spatial resolution, which is comparable to ALMA and almost 50 times better than JWST will achieve at 2.2 microns. Our results show that such an instrument will be capable of imaging, with unprecedented detail, a plethora of sources, ranging from complex stellar surfaces to microlensing events. [less ▲]

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See detailPhase referencing in optical interferometry
Filho, Mercedes E; Garcia, Paulo; Duvert, Gilles et al

in Schöller, Markus; Danchi, William; Delplancke, Françoise (Eds.) Optical and Infrared Interferometry (2008, July 01)

One of the aims of next generation optical interferometric instrumentation is to be able to make use of information contained in the visibility phase to construct high dynamic range images. Radio and ... [more ▼]

One of the aims of next generation optical interferometric instrumentation is to be able to make use of information contained in the visibility phase to construct high dynamic range images. Radio and optical interferometry are at the two extremes of phase corruption by the atmosphere. While in radio it is possible to obtain calibrated phases for the science objects, in the optical this is currently not possible. Instead, optical interferometry has relied on closure phase techniques to produce images. Such techniques allow only to achieve modest dynamic ranges. However, with high contrast objects, for faint targets or when structure detail is needed, phase referencing techniques as used in radio interferometry, should theoretically achieve higher dynamic ranges for the same number of telescopes. Our approach is not to provide evidence either for or against the hypothesis that phase referenced imaging gives better dynamic range than closure phase imaging. Instead we wish to explore the potential of this technique for future optical interferometry and also because image reconstruction in the optical using phase referencing techniques has only been performed with limited success. We have generated simulated, noisy, complex visibility data, analogous to the signal produced in radio interferometers, using the VLTI as a template. We proceeded with image reconstruction using the radio image reconstruction algorithms contained in aips imagr (clean algorithm). Our results show that image reconstruction is successful in most of our science cases, yielding images with a 4 milliarcsecond resolution in K band. We have also investigated the number of target candidates for optical phase referencing. Using the 2MASS point source catalog, we show that there are several hundred objects with phase reference sources less than 30 arcseconds away, allowing to apply this technique. [less ▲]

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See detailEvidence for short-term variations in two O-type stars
De Becker, Michaël ULg; Linder, Natacha ULg; Rauw, Grégor ULg

in Information Bulletin on Variable Stars (2008), 5841

Only a few O-type stars are known to display short-term (a fraction of a day) variations. Intense spectroscopic monitoring of the ON8V star HD 13268 revealed low amplitude variations with periods of ... [more ▼]

Only a few O-type stars are known to display short-term (a fraction of a day) variations. Intense spectroscopic monitoring of the ON8V star HD 13268 revealed low amplitude variations with periods of several hours. In addition, observations of the SB1 system HD 15137 revealed variations on a time scale of a few hours. We consider these stars to be a good candidates for non radial pulsations, even though variations related to inhomogeneities in a circumstellar disk can not be rejected. [less ▲]

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See detailThe XMM-Newton view of the rich cluster Cyg OB2
Rauw, Grégor ULg; De Becker, Michaël ULg; Nazé, Yaël ULg et al

Poster (2008, May)

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See detailA binary signature in the non-thermal radio-emitter Cyg OB2 #9
Nazé, Yaël ULg; De Becker, Michaël ULg; Rauw, Grégor ULg et al

in Astronomy and Astrophysics (2008), 483

Aims. Non-thermal radio emission associated with massive stars is believed to arise from a wind-wind collision in a binary system. However, the evidence of binarity is still lacking in some cases, notably ... [more ▼]

Aims. Non-thermal radio emission associated with massive stars is believed to arise from a wind-wind collision in a binary system. However, the evidence of binarity is still lacking in some cases, notably Cyg OB2 #9. Methods: For several years, we have been monitoring this heavily-reddened star from various observatories. This campaign allowed us to probe variations both on short and long timescales and constitutes the first in-depth study of the visible spectrum of this object. Results: Our observations provide the very first direct evidence of a companion in Cyg OB2 #9, confirming the theoretical wind-wind collision scenario. These data suggest a highly eccentric orbit with a period of a few years, compatible with the 2 yr-timescale measured in the radio range. In addition, the signature of the wind-wind collision is very likely reflected in the behaviour of some emission lines. [less ▲]

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See detailMultiplicity of O-type stars in NGC 2244
Mahy, Laurent ULg; Nazé, Yaël ULg; Rauw, Grégor ULg et al

Poster (2008)

We present the main results from our long‐term spectroscopic campaign devoted to the O‐type stars in the young open cluster NGC 2244. Previous works by our team on the O‐stars multiplicity in other young ... [more ▼]

We present the main results from our long‐term spectroscopic campaign devoted to the O‐type stars in the young open cluster NGC 2244. Previous works by our team on the O‐stars multiplicity in other young open clusters (IC 1805 and NGC 6231) showed that the number of binary systems in such clusters was larger than 40%. Until now, only two stars (HD 47129 and HD 48099) in the surroundings of NGC 2244 have been confirmed as spectroscopic binaries (SB) although Garcia & Mermilliod (2001) estimated the O‐type binary fraction at 50%. In this context, we revisited the spectral classification, the projected rotational velocity and the multiplicity of O‐type stars in NGC 2244. [less ▲]

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See detailThe investigation of particle acceleration in colliding-wind massive binaries with SIMBOL-X.
De Becker, Michaël ULg; Rauw, Grégor ULg; Pittard, J. M. et al

in Memorie della Società Astronomica Italiana : Journal of the Italian Astronomical Society (2008), 79

An increasing number of early-type (O and Wolf-Rayet) colliding wind binaries (CWBs) is known to accelerate particles up to relativistic energies. In this context, non-thermal emission processes such as ... [more ▼]

An increasing number of early-type (O and Wolf-Rayet) colliding wind binaries (CWBs) is known to accelerate particles up to relativistic energies. In this context, non-thermal emission processes such as inverse Compton (IC) scattering are expected to produce a high energy spectrum, in addition to the strong thermal emission from the shock-heated plasma. SIMBOL-X will be the ideal observatory to investigate the hard X-ray spectrum (above 10 keV) of these systems, i.e. where it is no longer dominated by the thermal emission. Such observations are strongly needed to constrain the models aimed at understanding the physics of particle acceleration in CWB. Such systems are important laboratories for investigating the underlying physics of particle acceleration at high Mach number shocks, and probe a different region of parameter space than studies of supernova remnants. [less ▲]

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See detailHigh-resolution optical spectroscopy of Plaskett's star
Linder, Natacha ULg; Rauw, Grégor ULg; Martins, Fabrice et al

in Astronomy and Astrophysics (2008), 489(2), 713-723

Context. Plaskett's star (HD 47 129) is a very massive O + O binary that belongs to the Mon OB2 association. Previous work suggests that this system displays the Struve-Sahade effect although the ... [more ▼]

Context. Plaskett's star (HD 47 129) is a very massive O + O binary that belongs to the Mon OB2 association. Previous work suggests that this system displays the Struve-Sahade effect although the measurements of the secondary radial velocities are very difficult and give controversial results. Both components have powerful stellar winds that collide and produce a strong X-ray emission. Aims. Our aim is to study the physical parameters of this system in detail and to investigate the relation between its spectral properties and its evolutionary status. Methods. We present here analysis of an extensive set of high-resolution optical spectra of HD 47 129. We used a disentangling method to separate the individual spectra of each star. We derived a new orbital solution and discuss the spectral classification of both components. A Doppler tomography technique applied to the emission lines H alpha and He II gamma 4686 yields a Doppler map that illustrates the wind interactions in the system. Finally, an atmosphere code is used to determine the different chemical abundances of the system components and the wind parameters. Results. HD 47 129 appears to be an O8 III/I + O7.5 III binary system in a post RLOF evolutionary stage, where matter has been transferred from the primary to the secondary star. The He overabundance of the secondary supports this scenario. In addition, the N overabundance and C underabundance of the primary component confirm previous results based on X-ray spectroscopy and indicate that the primary is an evolved massive star. We also determined a new orbital solution, with M-P sin(3) i = 45.4 +/- 2.4 M-circle dot and M-S sin(3) i = 47.3 +/- 0.3 M-circle dot. Furthermore, the secondary star has a high rotational velocity (nu sin i similar to 300 km s(-1)) that deforms its surface, leading to a non-uniform distribution in effective temperature. This could explain the variations in the equivalent widths of the secondary lines with phase. We suggest that the wind of the secondary star is confined near the equatorial plane because of its high rotational velocity, affecting the ram pressure equilibrium in the wind interaction zone. [less ▲]

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See detailSpectroscopic and photometric variability of the O9.5Vp star HD93521
Rauw, Grégor ULg; De Becker, Michaël ULg; van Winckel, Hans et al

in Astronomy and Astrophysics (2008), 487(2), 659-670

Aims. The line profile variability and photometric variability of the O9.5Vp star HD93521 are examined in order to establish the properties of the non-radial pulsations in this star. Methods. Fourier ... [more ▼]

Aims. The line profile variability and photometric variability of the O9.5Vp star HD93521 are examined in order to establish the properties of the non-radial pulsations in this star. Methods. Fourier techniques are used to characterize the modulations of the He I lambda lambda 5876, 6678 and H alpha lines in several spectroscopic time series and to search for variations in a photometric time series. Results. Our spectroscopic data confirm the existence of two periods of 1.75 and 2.89 h. The line profiles, especially those affected by emission wings, exhibit also modulations on longer time scales, but these are epoch-dependent and change from line to line. Unlike previous claims, we find no unambiguous signature of the rotational period in our data, nor of a third pulsation period (corresponding to a frequency of 2.66 d(-1)). Conclusions. HD93521 very likely exhibits non-radial pulsations with periods of 1.75 and 2.89 h with l similar or equal to 8 +/- 1 and l similar or equal to 4 +/- 1 respectively. No significant signal is found in the first harmonics of these two periods. The 2.89 h mode is seen at all epochs and in all lines investigated, while the visibility of the 1.75 h mode is clearly epoch-dependent. Whilst light variations are detected, their connection to these periodicities is not straightforward. [less ▲]

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See detailColliding-wind binaries as non-thermal X-ray emitters: an observational investigation from XMM-Newton to next generation X-ray observatories
De Becker, Michaël ULg

Poster (2007, December)

The investigation of massive stars in the radio domain revealed about 25 years ago that some of them are synchrotron emitters, showing that these objects are able to accelerate particles up to ... [more ▼]

The investigation of massive stars in the radio domain revealed about 25 years ago that some of them are synchrotron emitters, showing that these objects are able to accelerate particles up to relativistic velocities. In this context, non-thermal emission processes such as inverse Compton scattering are expected to be at work in the high-energy domain. For this reason, an observational campaign devoted to the X-ray investigation of non-thermal radio emitters has been carried out with XMM-Newton. However, considering the rather strong thermal X-ray emission from these systems below 10 keV, XMM-Newton does not appear to be the ideal observatory to detect their putative non-thermal X-rays. As a consequence, the advent of next generation X-ray observatories with a bandpass extending significantly above 10 keV (SIMBOL-X, XEUS, NEXT) is expected to provide important results related to the non-thermal high-energy emission from colliding-wind binaries and their capability to accelerate particles. [less ▲]

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