References of "Moffat, A. F. J"      in Complete repository Arts & humanities   Archaeology   Art & art history   Classical & oriental studies   History   Languages & linguistics   Literature   Performing arts   Philosophy & ethics   Religion & theology   Multidisciplinary, general & others Business & economic sciences   Accounting & auditing   Production, distribution & supply chain management   Finance   General management & organizational theory   Human resources management   Management information systems   Marketing   Strategy & innovation   Quantitative methods in economics & management   General economics & history of economic thought   International economics   Macroeconomics & monetary economics   Microeconomics   Economic systems & public economics   Social economics   Special economic topics (health, labor, transportation…)   Multidisciplinary, general & others Engineering, computing & technology   Aerospace & aeronautics engineering   Architecture   Chemical engineering   Civil engineering   Computer science   Electrical & electronics engineering   Energy   Geological, petroleum & mining engineering   Materials science & engineering   Mechanical engineering   Multidisciplinary, general & others Human health sciences   Alternative medicine   Anesthesia & intensive care   Cardiovascular & respiratory systems   Dentistry & oral medicine   Dermatology   Endocrinology, metabolism & nutrition   Forensic medicine   Gastroenterology & hepatology   General & internal medicine   Geriatrics   Hematology   Immunology & infectious disease   Laboratory medicine & medical technology   Neurology   Oncology   Ophthalmology   Orthopedics, rehabilitation & sports medicine   Otolaryngology   Pediatrics   Pharmacy, pharmacology & toxicology   Psychiatry   Public health, health care sciences & services   Radiology, nuclear medicine & imaging   Reproductive medicine (gynecology, andrology, obstetrics)   Rheumatology   Surgery   Urology & nephrology   Multidisciplinary, general & others Law, criminology & political science   Civil law   Criminal law & procedure   Criminology   Economic & commercial law   European & international law   Judicial law   Metalaw, Roman law, history of law & comparative law   Political science, public administration & international relations   Public law   Social law   Tax law   Multidisciplinary, general & others Life sciences   Agriculture & agronomy   Anatomy (cytology, histology, embryology...) & physiology   Animal production & animal husbandry   Aquatic sciences & oceanology   Biochemistry, biophysics & molecular biology   Biotechnology   Entomology & pest control   Environmental sciences & ecology   Food science   Genetics & genetic processes   Microbiology   Phytobiology (plant sciences, forestry, mycology...)   Veterinary medicine & animal health   Zoology   Multidisciplinary, general & others Physical, chemical, mathematical & earth Sciences   Chemistry   Earth sciences & physical geography   Mathematics   Physics   Space science, astronomy & astrophysics   Multidisciplinary, general & others Social & behavioral sciences, psychology   Animal psychology, ethology & psychobiology   Anthropology   Communication & mass media   Education & instruction   Human geography & demography   Library & information sciences   Neurosciences & behavior   Regional & inter-regional studies   Social work & social policy   Sociology & social sciences   Social, industrial & organizational psychology   Theoretical & cognitive psychology   Treatment & clinical psychology   Multidisciplinary, general & others     Showing results 1 to 20 of 23 1 2     The MiMeS survey of magnetism in massive stars: introduction and overviewWade, G. A.; Neiner, C.; Alecian, E. et alin Monthly Notices of the Royal Astronomical Society (2016), 456The MiMeS (Magnetism in Massive Stars) project is a large-scale, high-resolution, sensitive spectropolarimetric investigation of the magnetic properties of O- and early B-type stars. Initiated in 2008 and ... [more ▼]The MiMeS (Magnetism in Massive Stars) project is a large-scale, high-resolution, sensitive spectropolarimetric investigation of the magnetic properties of O- and early B-type stars. Initiated in 2008 and completed in 2013, the project was supported by three Large Program allocations, as well as various programmes initiated by independent principal investigators, and archival resources. Ultimately, over 4800 circularly polarized spectra of 560 O and B stars were collected with the instruments ESPaDOnS (Echelle SpectroPolarimetric Device for the Observation of Stars) at the Canada-France-Hawaii Telescope, Narval at the Télescope Bernard Lyot and HARPSpol at the European Southern Observatory La Silla 3.6 m telescope, making MiMeS by far the largest systematic investigation of massive star magnetism ever undertaken. In this paper, the first in a series reporting the general results of the survey, we introduce the scientific motivation and goals, describe the sample of targets, review the instrumentation and observational techniques used, explain the exposure time calculation designed to provide sensitivity to surface dipole fields above approximately 100 G, discuss the polarimetric performance, stability and uncertainty of the instrumentation, and summarize the previous and forthcoming publications. [less ▲]Detailed reference viewed: 52 (9 ULiège) A Coordinated X-Ray and Optical Campaign of the Nearest Massive Eclipsing Binary, δ Orionis Aa. I. Overview of the X-Ray SpectrumCorcoran, M. F.; Nichols, J. S.; Pablo, H. et alin Astrophysical Journal (2015), 809We present an overview of four deep phase-constrained Chandra HETGS X-ray observations of δ Ori A. Delta Ori A is actually a triple system that includes the nearest massive eclipsing spectroscopic binary ... [more ▼]We present an overview of four deep phase-constrained Chandra HETGS X-ray observations of δ Ori A. Delta Ori A is actually a triple system that includes the nearest massive eclipsing spectroscopic binary, δ Ori Aa, the only such object that can be observed with little phase-smearing with the Chandra gratings. Since the fainter star, δ Ori Aa2, has a much lower X-ray luminosity than the brighter primary (δ Ori Aa1), δ Ori Aa provides a unique system with which to test the spatial distribution of the X-ray emitting gas around δ Ori Aa1 via occultation by the photosphere of, and wind cavity around, the X-ray dark secondary. Here we discuss the X-ray spectrum and X-ray line profiles for the combined observation, having an exposure time of nearly 500 ks and covering nearly the entire binary orbit. The companion papers discuss the X-ray variability seen in the Chandra spectra, present new space-based photometry and ground-based radial velocities obtained simultaneously with the X-ray data to better constrain the system parameters, and model the effects of X-rays on the optical and UV spectra. We find that the X-ray emission is dominated by embedded wind shock emission from star Aa1, with little contribution from the tertiary star Ab or the shocked gas produced by the collision of the wind of Aa1 against the surface of Aa2. We find a similar temperature distribution to previous X-ray spectrum analyses. We also show that the line half-widths are about 0.3‑0.5 times the terminal velocity of the wind of star Aa1. We find a strong anti-correlation between line widths and the line excitation energy, which suggests that longer-wavelength, lower-temperature lines form farther out in the wind. Our analysis also indicates that the ratio of the intensities of the strong and weak lines of Fe xvii and Ne x are inconsistent with model predictions, which may be an effect of resonance scattering. [less ▲]Detailed reference viewed: 15 (1 ULiège) A Coordinated X-Ray and Optical Campaign of the Nearest Massive Eclipsing Binary, δ Orionis Aa. IV. A Multiwavelength, Non-LTE Spectroscopic AnalysisShenar, T.; Oskinova, L.; Hamann, W.-R. et alin Astrophysical Journal (2015), 809Eclipsing systems of massive stars allow one to explore the properties of their components in great detail. We perform a multi-wavelength, non-LTE analysis of the three components of the massive multiple ... [more ▼]Eclipsing systems of massive stars allow one to explore the properties of their components in great detail. We perform a multi-wavelength, non-LTE analysis of the three components of the massive multiple system δ Ori A, focusing on the fundamental stellar properties, stellar winds, and X-ray characteristics of the system. The primary’s distance-independent parameters turn out to be characteristic for its spectral type (O9.5 II), but usage of the Hipparcos parallax yields surprisingly low values for the mass, radius, and luminosity. Consistent values follow only if δ Ori lies at about twice the Hipparcos distance, in the vicinity of the σ-Orionis cluster. The primary and tertiary dominate the spectrum and leave the secondary only marginally detectable. We estimate the V-band magnitude difference between primary and secondary to be {{Δ }}V≈ 2\buildrel{{m}}\over{.} 8. The inferred parameters suggest that the secondary is an early B-type dwarf (≈B1 V), while the tertiary is an early B-type subgiant (≈B0 IV). We find evidence for rapid turbulent velocities (∼200 km s[SUP]‑1[/SUP]) and wind inhomogeneities, partially optically thick, in the primary’s wind. The bulk of the X-ray emission likely emerges from the primary’s stellar wind ({log}{L}[SUB]{{X[/SUB]}}/{L}[SUB]{Bol[/SUB]}≈ -6.85), initiating close to the stellar surface at {R}[SUB]0[/SUB]∼ 1.1 {R}[SUB]*[/SUB]. Accounting for clumping, the mass-loss rate of the primary is found to be {log}\dot{M}≈ -6.4 ({M}[SUB]ȯ [/SUB] {{yr}}[SUP]-1[/SUP]), which agrees with hydrodynamic predictions, and provides a consistent picture along the X-ray, UV, optical, and radio spectral domains. [less ▲]Detailed reference viewed: 26 (1 ULiège) A Coordinated X-Ray and Optical Campaign of the Nearest Massive Eclipsing Binary, δ Orionis Aa. II. X-Ray VariabilityNichols, J.; Huenemoerder, D. P.; Corcoran, M. F. et alin Astrophysical Journal (2015), 809We present time-resolved and phase-resolved variability studies of an extensive X-ray high-resolution spectral data set of the δ Ori Aa binary system. The four observations, obtained with Chandra ACIS ... [more ▼]We present time-resolved and phase-resolved variability studies of an extensive X-ray high-resolution spectral data set of the δ Ori Aa binary system. The four observations, obtained with Chandra ACIS HETGS, have a total exposure time of ≈ 479 ks and provide nearly complete binary phase coverage. Variability of the total X-ray flux in the range of 5–25 Å is confirmed, with a maximum amplitude of about ±15% within a single ≈ 125 ks observation. Periods of 4.76 and 2.04 days are found in the total X-ray flux, as well as an apparent overall increase in the flux level throughout the nine-day observational campaign. Using 40 ks contiguous spectra derived from the original observations, we investigate the variability of emission line parameters and ratios. Several emission lines are shown to be variable, including S xv, Si xiii, and Ne ix. For the first time, variations of the X-ray emission line widths as a function of the binary phase are found in a binary system, with the smallest widths at ϕ = 0.0 when the secondary δ Ori Aa2 is at the inferior conjunction. Using 3D hydrodynamic modeling of the interacting winds, we relate the emission line width variability to the presence of a wind cavity created by a wind–wind collision, which is effectively void of embedded wind shocks and is carved out of the X-ray-producing primary wind, thus producing phase-locked X-ray variability. Based on data from the Chandra X-ray Observatory and the MOST satellite, a Canadian Space Agency mission, jointly operated by Dynacon Inc., the University of Toronto Institute of Aerospace Studies, and the University of British Columbia, with the assistance of the University of Vienna. [less ▲]Detailed reference viewed: 36 (1 ULiège) Spectroscopic variability of two Oe starsRauw, Grégor ; Morel, Thierry ; Nazé, Yaël et alin Astronomy and Astrophysics (2015), 575Context. The two Oe stars HD 45 314 and HD 60 848 have recently been found to exhibit very different X-ray properties: whilst HD 60 848 has an X-ray spectrum and the emission level typical of most OB ... [more ▼]Context. The two Oe stars HD 45 314 and HD 60 848 have recently been found to exhibit very different X-ray properties: whilst HD 60 848 has an X-ray spectrum and the emission level typical of most OB stars, HD 45 314 features a much harder and brighter X-ray emission, making it a so-called γ Cas analogue. Aims: Monitoring the optical spectra could provide hints towards the origin of these very different behaviours. Methods: We analyse a large set of spectroscopic observations of HD 45 314 and HD 60 848, extending over 20 years. We further attempt to fit the Hα line profiles of both stars with a simple model of emission line formation in a Keplerian disk. Results: Strong variations in the strengths of the Hα, Hβ, and He i λ 5876 emission lines are observed for both stars. In the case of HD 60 848, we find a time lag between the variations in the equivalent widths of these lines, which is currently not understood. The emission lines are double peaked with nearly identical strengths of the violet and red peaks. The Hα profile of this star can be successfully reproduced by our model of a disk seen under an inclination of 30°. In the case of HD 45 314, the emission lines are highly asymmetric and display strong line profile variations. We find a major change in behaviour between the 2002 outburst and the one observed in 2013. This concerns both the relationship between the equivalent widths of the various lines and their morphologies at maximum strength (double-peaked in 2002 versus single-peaked in 2013). Our simple disk model fails to reproduce the observed Hα line profiles of HD 45 314. Conclusions: Our results further support the interpretation that Oe stars do have decretion disks similar to those of Be stars. Whilst the emission lines of HD 60 848 are explained well by a disk with a Keplerian velocity field, the disk of HD 45 314 seems to have a significantly more complex velocity field that could be another signature of the phenomenon that produces its peculiar X-ray emission. [less ▲]Detailed reference viewed: 33 (6 ULiège) World-wide amateur observationsEversberg, T.; Aldoretta, E. J.; Knapen, J. H. et alin Hamann, Wolf-Rainer; Sander, Andreas; Todt, Helge (Eds.) Wolf-Rayet Stars: Proceedings of an International Workshop held in Potsdam, Germany, 1–5 June 2015. Edited by Wolf-Rainer Hamann, Andreas Sander, Helge Todt. Universitätsverlag Potsdam, 2015., p.71-74 (2015)For some years now, spectroscopic measurements of massive stars in the amateur domain have been fulfilling professional requirements. Various groups in the northern and southern hemispheres have been ... [more ▼]For some years now, spectroscopic measurements of massive stars in the amateur domain have been fulfilling professional requirements. Various groups in the northern and southern hemispheres have been established, running successful professional-amateur (ProAm) collaborative campaigns, e.g., on WR, O and B type stars. Today high quality data (echelle and long-slit) are regularly delivered and corresponding results published. Night-to-night long-term observations over months to years open a new opportunity for massive-star research. We introduce recent and ongoing sample campaigns (e.g. ɛ Aur, WR 134, ζ Pup), show respective results and highlight the vast amount of data collected in various data bases. Ultimately it is in the time-dependent domain where amateurs can shine most. [less ▲]Detailed reference viewed: 30 (1 ULiège) Massive Non-Thermal Radio Emitters: New Data and their ModelingVolpi, D.; Blomme, R.; De Becker, Michaël et alin Astronomical Society of the Pacific Conference Series (2013, January 01)During recent years some non-thermal radio emitting OB stars have been discovered to be binary or multiple systems. The non-thermal emission is due to synchrotron radiation that is emitted by electrons ... [more ▼]During recent years some non-thermal radio emitting OB stars have been discovered to be binary or multiple systems. The non-thermal emission is due to synchrotron radiation that is emitted by electrons accelerated up to high energies. The electron acceleration occurs at the strong shocks created by the collision of radiatively-driven winds. Here we summarize the available radio data and more recent observations for the binary Cyg OB2 No. 9. We also show a new emission model which is being developed to compare the theoretical total radio flux and the spectral index with the observed radio light curves. This comparison will be useful in order to solve fundamental questions, such as the determination of the stellar mass-loss rates, which are perturbed by clumping. [less ▲]Detailed reference viewed: 14 (3 ULiège) 2009: A Colliding-Wind OdysseyFahed, R.; Moffat, A. F. J.; Zorec, J. et alin Astronomical Society of the Pacific Conference Series (2013, January 01)We present the results from two optical spectroscopic campaigns on colliding-wind binaries (CWB) which both occurred in 2009. The first one was on WR 140 (WC7pd + O5.5fc), the archetype of CWB, which ... [more ▼]We present the results from two optical spectroscopic campaigns on colliding-wind binaries (CWB) which both occurred in 2009. The first one was on WR 140 (WC7pd + O5.5fc), the archetype of CWB, which experienced periastron passage of its highly elliptical 8-year orbit in January. The WR 140 campaign consisted of a unique and constructive collaboration between amateur and professional astronomers and took place at half a dozen locations, including Teide Observatory, Observatoire de Haute Provence, Dominion Astrophysical Observatory, Observatoire du Mont-Mégantic and at several small private observatories. The second campaign was on a selection of 5 short-period WR + O binaries not yet studied for colliding-wind effects: WR 12 (WN8h), WR 21 (WN5o + O7 V), WR 30 (WC6 + O7.5 V), WR 31 (WN4o + O8), and WR 47 (WN6o + O5). The campaign took place at Leoncito Observatory, Argentina, during 1 month. We provide updated values of most of these systems for the orbital parameters, new estimates for the WR and O star masses and new constraints on the mass-loss rates and colliding wind geometry. [less ▲]Detailed reference viewed: 11 (0 ULiège) Discovery of a magnetic field in the rapidly rotating O-type secondary of the colliding-wind binary HD 47129 (Plaskett's star)Grunhut, J. H.; Wade, G. A.; Leutenegger, M. et alin Monthly Notices of the Royal Astronomical Society (2013), 428We report the detection of a strong, organized magnetic field in the secondary component of the massive O8III/I+O7.5V/III double-lined spectroscopic binary system HD 47129 (Plaskett's star) in the context ... [more ▼]We report the detection of a strong, organized magnetic field in the secondary component of the massive O8III/I+O7.5V/III double-lined spectroscopic binary system HD 47129 (Plaskett's star) in the context of the Magnetism in Massive Stars survey. Eight independent Stokes V observations were acquired using the Echelle SpectroPolarimetric Device for the Observations of Stars (ESPaDOnS) spectropolarimeter at the Canada-France-Hawaii Telescope and the Narval spectropolarimeter at the Télescope Bernard Lyot. Using least-squares deconvolution we obtain definite detections of signal in Stokes V in three observations. No significant signal is detected in the diagnostic null (N) spectra. The Zeeman signatures are broad and track the radial velocity of the secondary component; we therefore conclude that the rapidly rotating secondary component is the magnetized star. Correcting the polarized spectra for the line and continuum of the (sharp-lined) primary, we measured the longitudinal magnetic field from each observation. The longitudinal field of the secondary is variable and exhibits extreme values of -810 ± 150 and +680 ± 190 G, implying a minimum surface dipole polar strength of 2850 ± 500 G. In contrast, we derive an upper limit (3σ) to the primary's surface magnetic field of 230 G. The combination of a strong magnetic field and rapid rotation leads us to conclude that the secondary hosts a centrifugal magnetosphere fed through a magnetically confined wind. We revisit the properties of the optical line profiles and X-ray emission - previously interpreted as a consequence of colliding stellar winds - in this context. We conclude that HD 47129 represents a heretofore unique stellar system - a close, massive binary with a rapidly rotating, magnetized component - that will be a rich target for further study. [less ▲]Detailed reference viewed: 28 (2 ULiège) NGC 1624-2: a slowly rotating, X-ray luminous Of?cp star with an extraordinarily strong magnetic fieldWade, G. A.; Maíz Apellániz, J.; Martins, F. et alin Monthly Notices of the Royal Astronomical Society (2012), 425This paper presents a first observational investigation of the faint Of?p star NGC 1624-2, yielding important new constraints on its spectral and physical characteristics, rotation, magnetic field ... [more ▼]This paper presents a first observational investigation of the faint Of?p star NGC 1624-2, yielding important new constraints on its spectral and physical characteristics, rotation, magnetic field strength, X-ray emission and magnetospheric properties. Modelling the spectrum and spectral energy distribution, we conclude that NGC 1624-2 is a main-sequence star of mass M ≃ 30 M[SUB]&sun;[/SUB], and infer an effective temperature of 35 ± 2 kK and log g = 4.0 ± 0.2. Based on an extensive time series of optical spectral observations we report significant variability of a large number of spectral lines, and infer a unique period of 157.99 ± 0.94 d which we interpret as the rotational period of the star. We report the detection of a very strong (5.35 ± 0.5 kG) longitudinal magnetic field , coupled with probable Zeeman splitting of the Stokes I profiles of metal lines confirming a surface field modulus of 14 ± 1 kG, consistent with a surface dipole of polar strength ≳20 kG. This is the largest magnetic field ever detected in an O-type star, and the first report of Zeeman splitting of Stokes I profiles in such an object. We also report the detection of reversed Stokes V profiles associated with weak, high-excitation emission lines of O III, which we propose may form in the close magnetosphere of the star. We analyse archival Chandra ACIS-I X-ray data, inferring a very hard spectrum with an X-ray efficiency of log L[SUB]x[/SUB]/L[SUB]bol[/SUB] = -6.4, a factor of 4 larger than the canonical value for O-type stars and comparable to that of the young magnetic O-type star θ[SUP]1[/SUP] Ori C and other Of?p stars. Finally, we examine the probable magnetospheric properties of the star, reporting in particular very strong magnetic confinement of the stellar wind, with η[SUB]*[/SUB] ≃ 1.5 × 10[SUP]4[/SUP], and a very large Alfvén radius, R[SUB]Alf[/SUB] = 11.4 R[SUB]*[/SUB]. Based on spectropolarimetric observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers (INSU) of the Centre National de la Recherche Scientifique of France, and the University of Hawaii, as well as on observations obtained using the Narval spectropolarimeter at the Observatoire du Pic du Midi (France), which is operated by the INSU. The spectroscopic data were gathered with five facilities: the 9.2-m Hobby-Eberly Telescope at McDonald Observatory (MDO), the 3.5-m Telescope at Calar Alto Observatory (CAHA), the 1.5-m Telescope at the Observatorio de Sierra Nevada (OSN), the 4.2-m William Herschel Telescope at the Observatorio del Roque de los Muchachos (ORM) and the 2-m Himalayan Chandra Telescope at Indian Astronomical Observatory (IAO). [less ▲]Detailed reference viewed: 66 (2 ULiège) Spectroscopy of the archetype colliding-wind binary WR 140 during the 2009 January periastron passageFahed, R.; Moffat, A. F. J.; Zorec, J. et alin Monthly Notices of the Royal Astronomical Society (2011), 418We present the results from the spectroscopic monitoring of WR 140 (WC7pd + O5.5fc) during its latest periastron passage in 2009 January. The observational campaign consisted of a constructive ... [more ▼]We present the results from the spectroscopic monitoring of WR 140 (WC7pd + O5.5fc) during its latest periastron passage in 2009 January. The observational campaign consisted of a constructive collaboration between amateur and professional astronomers. It took place at six locations, including Teide Observatory, Observatoire de Haute Provence, Dominion Astrophysical Observatory and Observatoire du Mont Mégantic. WR 140 is known as the archetype of colliding-wind binaries and it has a relatively long period (?8 yr) and high eccentricity (?0.9). We provide updated values for the orbital parameters, new estimates for the WR and O star masses and new constraints on the mass-loss rates and colliding-wind geometry. [less ▲]Detailed reference viewed: 21 (2 ULiège) X-ray Emission from the Double-binary OB-star System QZ Car (HD 93206)Parkin, E. R.; Broos, P. S.; Townsley, L. K. et alin Astrophysical Journal Supplement Series (2011), 194X-ray observations of the double-binary OB-star system QZ Car (HD 93206) obtained with the Chandra X-ray Observatory over a period of roughly 2 years are presented. The respective orbits of systems A (O9 ... [more ▼]X-ray observations of the double-binary OB-star system QZ Car (HD 93206) obtained with the Chandra X-ray Observatory over a period of roughly 2 years are presented. The respective orbits of systems A (O9.7 I+b2 v, P [SUB]A[/SUB] = 21 days) and B (O8 III+o9 v, P [SUB]B[/SUB] = 6 days) are reasonably well sampled by the observations, allowing the origin of the X-ray emission to be examined in detail. The X-ray spectra can be well fitted by an attenuated three-temperature thermal plasma model, characterized by cool, moderate, and hot plasma components at kT ~= 0.2, 0.7, and 2 keV, respectively, and a circumstellar absorption of sime0.2 × 10[SUP]22[/SUP] cm[SUP]-2[/SUP]. Although the hot plasma component could be indicating the presence of wind-wind collision shocks in the system, the model fluxes calculated from spectral fits, with an average value of sime7 × 10[SUP]-13[/SUP] erg s[SUP]-1[/SUP] cm[SUP]-2[/SUP], do not show a clear correlation with the orbits of the two constituent binaries. A semi-analytical model of QZ Car reveals that a stable momentum balance may not be established in either system A or B. Yet, despite this, system B is expected to produce an observed X-ray flux well in excess of the observations. If one considers the wind of the O8 III star to be disrupted by mass transfer, the model and observations are in far better agreement, which lends support to the previous suggestion of mass transfer in the O8 III + o9 v binary. We conclude that the X-ray emission from QZ Car can be reasonably well accounted for by a combination of contributions mainly from the single stars and the mutual wind-wind collision between systems A and B. [less ▲]Detailed reference viewed: 42 (4 ULiège) Global X-ray Properties of the O and B Stars in CarinaNazé, Yaël ; Broos, P. S.; Oskinova, L. et alin Astrophysical Journal Supplement Series (2011), 194The key empirical property of the X-ray emission from O stars is a strong correlation between the bolometric and X-ray luminosities. In the framework of the Chandra Carina Complex Project, 129 O and B ... [more ▼]The key empirical property of the X-ray emission from O stars is a strong correlation between the bolometric and X-ray luminosities. In the framework of the Chandra Carina Complex Project, 129 O and B stars have been detected as X-ray sources; 78 of those, all with spectral type earlier than B3, have enough counts for at least a rough X-ray spectral characterization. This leads to an estimate of the L [SUB]X[/SUB]-L [SUB]BOL[/SUB] ratio for an exceptional number of 60 O stars belonging to the same region and triples the number of Carina massive stars studied spectroscopically in X-rays. The derived log(L [SUB]X[/SUB]/L [SUB]BOL[/SUB]) is -7.26 for single objects, with a dispersion of only 0.21 dex. Using the properties of hot massive stars listed in the literature, we compare the X-ray luminosities of different types of objects. In the case of O stars, the L [SUB]X[/SUB]-L [SUB]BOL[/SUB] ratios are similar for bright and faint objects, as well as for stars of different luminosity classes or spectral types. Binaries appear only slightly harder and slightly more luminous in X-rays than single objects; the differences are not formally significant (at the 1% level), except for the L [SUB]X[/SUB]-L [SUB]BOL[/SUB] ratio in the medium (1.0-2.5 keV) energy band. Weak-wind objects have similar X-ray luminosities but they display slightly softer spectra compared with "normal" O stars with the same bolometric luminosity. Discarding three overluminous objects, we find a very shallow trend of harder emission in brighter objects. The properties of the few B stars bright enough to yield some spectral information appear to be different overall (constant X-ray luminosities, harder spectra), hinting that another mechanism for producing X-rays, besides wind shocks, might be at work. However, it must be stressed that the earliest and X-ray brightest among these few detected objects are similar to the latest O stars, suggesting a possibly smooth transition between the two processes. [less ▲]Detailed reference viewed: 19 (1 ULiège) The WR 140 periastron passage 2009: first results from MONS and other optical sourcesFahed, R.; Moffat, A. F. J.; Zorec, J. et alin Eversberg, Thomas; Knapen, Johan (Eds.) Stellar Winds in Interaction (2011, January 01)We present the results from the spectroscopic follow-up of WR140 (WC7 + O4-5) during its last periastron passage in January 2009. This object is known as the archetype of colliding wind binaries and has a ... [more ▼]We present the results from the spectroscopic follow-up of WR140 (WC7 + O4-5) during its last periastron passage in January 2009. This object is known as the archetype of colliding wind binaries and has a relatively large period (~ 8 years) and eccentricity (~ 0.89). We provide updated values for the orbital parameters, new estimates for the WR and O star masses and new constraints on the mass-loss rates. [less ▲]Detailed reference viewed: 16 (1 ULiège) Spectroscopic follow-up of the colliding-wind binary WR140 during the 2009 January periastron passageFahed, R.; Moffat, A. F. J.; Zorec, J. et alin Bulletin de la Societe Royale des Sciences de Liege (2011), 80We present the results from the spectroscopic follow-up of WR140 (WC7 + O4-5) during its last periastron passage in January 2009. This object is known as the archetype of colliding wind binaries and has a ... [more ▼]We present the results from the spectroscopic follow-up of WR140 (WC7 + O4-5) during its last periastron passage in January 2009. This object is known as the archetype of colliding wind binaries and has a relatively large period (≃8 years) and eccentricity (≃0.9). We provide updated values for the orbital parameters, new estimates for the WR and O star masses and new constraints on the mass-loss rates. [less ▲]Detailed reference viewed: 49 (2 ULiège) The Mons campaign on OB starsMorel, Thierry ; Rauw, Grégor ; Eversberg, T. et alin Bulletin de la Société Royale des Sciences de Liège (2011), 80Detailed reference viewed: 14 (3 ULiège) MOST reveals Spica as an Eclipsing BinaryDesmet, M.; Aerts, C.; Matthews, J. M. et alin AIP Conference Proceedings (2009, September 01)We present a unique observational study of Spica, a binary system with a primary component of the β Cephei type. We exploit simultaneous high-resolution spectroscopic observations and high-precision ... [more ▼]We present a unique observational study of Spica, a binary system with a primary component of the β Cephei type. We exploit simultaneous high-resolution spectroscopic observations and high-precision photometry obtained by the MOST satellite. An important result is that the MOST photometry reveals Spica as an eclipsing binary contrary to what was quoted in the literature. [less ▲]Detailed reference viewed: 6 (0 ULiège) New insights into the nature of the SMC WR/LBV binary HD 5980Foellmi, C.; Koenigsberger, G.; Georgiev, L. et alin Revista Mexicana de Astronomía y Astrofísica (2008), 44(1), 3-27We present the results of optical wavelength observations of the unusual SMC eclipsing binary system HD 5980 obtained in 1999 and 2004-2005. Radial velocity curves for the erupting LBV/WR object (star A ... [more ▼]We present the results of optical wavelength observations of the unusual SMC eclipsing binary system HD 5980 obtained in 1999 and 2004-2005. Radial velocity curves for the erupting LBV/WR object (star A) and its close WR-like companion (star B) are obtained by deblending the variable emission-line profiles of NIV and NV lines. The derived masses M-A = 58 - 79 M-circle dot and M-B = 51 - 67 M-circle dot, are more consistent with the the stars' location near the top of the HRD than previous estimates. The presence of a wind-wind interaction region is inferred from the orbital phase-dependent behavior of He I P Cygni absorption components. The emission-line intensities continued with the declining trend previously seen in UV spectra. The behavior of the photospheric absorption lines is consistent with the results of Schweickhardt (2000) who concludes that the third object in the combined spectrum, star C, is also a binary system with P-starC similar to 96.5 days, e=0.83. [less ▲]Detailed reference viewed: 27 (3 ULiège) The Quadruple Wolf-Rayet System GP Cephei: Spectral Types, Masses, Mass-Loss Rate, and Colliding WindsDemers, H.; Moffat, A. F. J.; Marchenko, S. V. et alin Astrophysical Journal (2002), 577We have reevaluated the orbital elements for each pair of the quadruple (W-R+O) + (O+O) stellar system GP Cep and propose new spectral types WN6o/WCE + O3-6, B0: I + B1: V-III. It is shown that there is ... [more ▼]We have reevaluated the orbital elements for each pair of the quadruple (W-R+O) + (O+O) stellar system GP Cep and propose new spectral types WN6o/WCE + O3-6, B0: I + B1: V-III. It is shown that there is only one Wolf-Rayet (W-R) star in GP Cep, contrary to a previous claim. A rate of change P=1.3+/-0.2 s yr[SUP]-1[/SUP] is determined for the W-R+O pair, which leads to a new period of 6.6887 days and to a W-R mass-loss rate of (0.8-3.0)Ã 10[SUP]-5[/SUP] M[SUB]solar[/SUB] yr[SUP]-1[/SUP]. Masses for this pair are estimated to be M[SUB]W-R[/SUB]>~6 M[SUB]solar[/SUB] and M[SUB]O[/SUB]>~21 M[SUB]solar[/SUB]. The effects of wind-wind collision in the W-R+O pair are studied. It is shown that even after allowing for dilution by the OB components of the quadruple system, these effects are not as strong as in the binary V444 Cygni (WN5+O6, P=4.212 days). In GP Cep, the phase-dependent, relatively weak excess emission does not originate in the arms of the bow shock cone. Rather, it emerges from the extra heated portion of the W-R wind facing the hot O companion. The trailing bow shock arm is clearly seen, however, as an enhanced He I absorption component near quadrature at phase ~0.73. An anomalous blueshifted He I absorption is present at phase ~0.9, as is also seen in V444 Cyg, in the WC8+O9 I/O8 III binary Î³ Velorum and in the LBV-cotype binary R81 (B2.5 Iab:e). A 3.5 day orbit for the eclipsing B star pair is confirmed. [less ▲]Detailed reference viewed: 38 (1 ULiège) Optical spectroscopy of X-Mega targets - II. The massive double-lined O-type binary HD 93205Morrell, N. I.; Barbá, R. H.; Niemela, V. S. et alin Monthly Notices of the Royal Astronomical Society (2001), 326A new high-quality set of orbital parameters for the O-type spectroscopic binary HD 93205 has been obtained combining échelle and coudé CCD observations. The radial velocity orbits derived from the Heii ... [more ▼]A new high-quality set of orbital parameters for the O-type spectroscopic binary HD 93205 has been obtained combining échelle and coudé CCD observations. The radial velocity orbits derived from the Heii lambda4686Å (primary component) and Hei lambda4471Å (secondary component) absorption lines yield semi-amplitudes of 133+/-2 and 314+/-2kms[SUP]-1[/SUP] for each binary component, resulting in minimum masses of 31 and 13M[SUB]solar[/SUB] (q=0.42). We also confirm for the binary components the spectral classification of O3V+O8V previously assigned. Assuming for the O8V component a normal' mass of 22-25M[SUB]solar[/SUB] we would derive for the primary O3V a mass of only' 52-60M[SUB]solar[/SUB] and an inclination of about 55° for the orbital plane. We have also determined for the first time a period of apsidal motion for this system, namely 185+/-16yr using all available radial velocity data sets of HD 93205 (from 1975 to 1999). Phase-locked variations of the X-ray emission of HD 93205 consisting of a rise of the observed X-ray flux near periastron passage are also discussed. [less ▲]Detailed reference viewed: 29 (3 ULiège) 1 2