References of "Moffat, A. F. J"
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See detailMassive Non-Thermal Radio Emitters: New Data and their Modeling
Volpi, D.; Blomme, R.; De Becker, Michaël ULg et al

in 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 ▲]

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See detail2009: A Colliding-Wind Odyssey
Fahed, R.; Moffat, A. F. J.; Zorec, J. et al

in 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 ▲]

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See detailDiscovery 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 al

in Monthly Notices of the Royal Astronomical Society (2013), 428

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 ... [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 ▲]

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See detailNGC 1624-2: a slowly rotating, X-ray luminous Of?cp star with an extraordinarily strong magnetic field
Wade, G. A.; Maíz Apellániz, J.; Martins, F. et al

in Monthly Notices of the Royal Astronomical Society (2012), 425

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 ... [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 <B[SUB]z[/SUB]>, 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 ▲]

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See detailSpectroscopy of the archetype colliding-wind binary WR 140 during the 2009 January periastron passage
Fahed, R.; Moffat, A. F. J.; Zorec, J. et al

in Monthly Notices of the Royal Astronomical Society (2011), 418

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 ... [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 ▲]

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See detailX-ray Emission from the Double-binary OB-star System QZ Car (HD 93206)
Parkin, E. R.; Broos, P. S.; Townsley, L. K. et al

in Astrophysical Journal Supplement Series (2011), 194

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 ... [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 ▲]

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See detailGlobal X-ray Properties of the O and B Stars in Carina
Nazé, Yaël ULg; Broos, P. S.; Oskinova, L. et al

in Astrophysical Journal Supplement Series (2011), 194

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 ... [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 ▲]

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See detailThe WR 140 periastron passage 2009: first results from MONS and other optical sources
Fahed, R.; Moffat, A. F. J.; Zorec, J. et al

in 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 ▲]

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See detailSpectroscopic follow-up of the colliding-wind binary WR140 during the 2009 January periastron passage
Fahed, R.; Moffat, A. F. J.; Zorec, J. et al

in Bulletin de la Societe Royale des Sciences de Liege (2011), 80

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 (≃0.9). 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 ▲]

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See detailThe Mons campaign on OB stars
Morel, Thierry ULg; Rauw, Grégor ULg; Eversberg, T. et al

in Bulletin de la Société Royale des Sciences de Liège (2011), 80

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See detailMOST reveals Spica as an Eclipsing Binary
Desmet, M.; Aerts, C.; Matthews, J. M. et al

in 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 ▲]

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See detailNew insights into the nature of the SMC WR/LBV binary HD 5980
Foellmi, C.; Koenigsberger, G.; Georgiev, L. et al

in Revista Mexicana de Astronomía y Astrofísica (2008), 44(1), 3-27

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 ... [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 ▲]

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See detailThe Quadruple Wolf-Rayet System GP Cephei: Spectral Types, Masses, Mass-Loss Rate, and Colliding Winds
Demers, H.; Moffat, A. F. J.; Marchenko, S. V. et al

in Astrophysical Journal (2002), 577

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 ... [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)à 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 γ 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 ▲]

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See detailOptical spectroscopy of X-Mega targets - II. The massive double-lined O-type binary HD 93205
Morrell, N. I.; Barbá, R. H.; Niemela, V. S. et al

in Monthly Notices of the Royal Astronomical Society (2001), 326

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 ... [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 ▲]

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See detailCyclical Spectral and Photometric Variations of the Apparently Single Wolf-Rayet Star WR 134
Morel, Thierry ULg; Marchenko, S. V.; Eenens, P. R. J. et al

in Astrophysics & Space Science (1998), 260

Evidence is presented for the existence of a 2.3 day periodicity in the line-profile changes of the apparently singleWolf-Rayet star WR 134. This cyclical variability may be induced either by the presence ... [more ▼]

Evidence is presented for the existence of a 2.3 day periodicity in the line-profile changes of the apparently singleWolf-Rayet star WR 134. This cyclical variability may be induced either by the presence of an orbiting collapsed companion, or by the rotational modulation of a largely inhomogeneous outflow. [less ▲]

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See detailA comprehensive variability study of the enigmatic WN8 stars - Final results
Marchenko, S. V.; Moffat, A. F. J.; Eversberg, T. et al

in Monthly Notices of the Royal Astronomical Society (1998), 294

As a conclusion of our all-sky variability survey of the 'enigmatic' variable WN8 stars, we have carried out coordinated multisite photometric and spectroscopic observations of WN8 stars in 1989 and 1994 ... [more ▼]

As a conclusion of our all-sky variability survey of the 'enigmatic' variable WN8 stars, we have carried out coordinated multisite photometric and spectroscopic observations of WN8 stars in 1989 and 1994-1995. We confirm the leading role of the stellar core in restructuring the whole wind. This emerges as a statistical trend: the higher the level of the continuum (i.e., core) light variations, the higher the variability of the P Cygni edges of the optical emission lines. However, the form of the correlation between the light and profile variations is generally different for each individual star. The high level of activity of WN8 stars may be supported/induced by pulsational instability. [less ▲]

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See detailConfirmation of a 2.3-DAY Periodicity in the Wolf-Rayet Star WR 134: a Twin of EZ Cma?
Morel, Thierry ULg; Marchenko, S. V.; Eenens, P. R. J. et al

in Cyclical Variability in Stellar Winds (1998)

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