References of "Pittard, J. M"
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See detailThe 2.35 year itch of Cygnus OB2 #9. III. X-ray and radio emission analysis based on 3D hydrodynamical modelling
Parkin, E. R.; Pittard, J. M.; Nazé, Yaël ULg et al

in Astronomy and Astrophysics (2014), 570

Context. The wind-wind collision in a massive star binary system leads to the generation of high temperature shocks that emit at X-ray wavelengths and, if particle acceleration is effective, may exhibit ... [more ▼]

Context. The wind-wind collision in a massive star binary system leads to the generation of high temperature shocks that emit at X-ray wavelengths and, if particle acceleration is effective, may exhibit non-thermal radio emission. Cyg OB2#9 is one of a small number of massive star binary systems in this class. <BR /> Aims: X-ray and radio data recently acquired as part of a project to study Cyg OB2#9 are used to constrain physical models of the binary system, providing in-depth knowledge about the wind-wind collision and the thermal, and non-thermal, emission arising from the shocks. <BR /> Methods: We use a 3D, adaptive mesh refinement simulation (including wind acceleration, radiative cooling, and the orbital motion of the stars) to model the gas dynamics of the wind-wind collision. The simulation output is used as the basis for radiative transfer calculations considering the thermal X-ray emission and the thermal/non-thermal radio emission. <BR /> Results: The flow dynamics in the simulation show that wind acceleration (between the stars) is inhibited at all orbital phases by the opposing star's radiation field, reducing pre-shock velocities below terminal velocities. To obtain good agreement with the X-ray observations, our initial mass-loss rate estimates require a down-shift by a factor of ˜7.7 to 6.5 × 10[SUP]-7[/SUP] M[SUB]⊙[/SUB] yr[SUP]-1[/SUP] and 7.5 × 10[SUP]-7[/SUP] M[SUB]⊙[/SUB] yr[SUP]-1[/SUP] for the primary and secondary star, respectively. Furthermore, the low gas densities and high shock velocities in Cyg OB2 #9 are suggestive of unequal electron and ion temperatures, and the X-ray analysis indicates that an immediately post-shock electron-ion temperature ratio of ≃0.1 is also required. The radio emission is dominated by non-thermal synchrotron emission. A parameter space exploration provides evidence against models assuming equipartition between magnetic and relativistic energy densities. However, fits of comparable quality can be attained with models having stark contrasts in the ratio of magnetic-to-relativistic energy densities. Both X-ray and radio lightcurves are largely insensitive to viewing angle. The variations in X-ray emission with orbital phase can be traced back to an inverse relation with binary separation and pre-shock velocity. The radio emission also scales with pre-shock velocity and binary separation, but to positive powers (i.e. not inversely). The radio models also reveal a subtle effect whereby inverse Compton cooling leads to an increase in emissivity as a result of the synchrotron characteristic frequency being significantly reduced. Finally, using the results of the radio analysis, we estimate the surface magnetic field strengths to be ≈0.3 - 52G. [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 detailThe 2.35 year itch of Cygnus OB2 #9. I. Optical and X-ray monitoring
Nazé, Yaël ULg; Mahy, Laurent ULg; Damerdji, Yassine ULg et al

in Astronomy and Astrophysics (2012), 546

Context. Nonthermal radio emission in massive stars is expected to arise in wind-wind collisions occurring inside a binary system. One such case, the O-type star Cyg OB2 #9, was proven to be a binary only ... [more ▼]

Context. Nonthermal radio emission in massive stars is expected to arise in wind-wind collisions occurring inside a binary system. One such case, the O-type star Cyg OB2 #9, was proven to be a binary only four years ago, but the orbital parameters remained uncertain. The periastron passage of 2011 was the first one to be observable under good conditions since the discovery of binarity. <BR /> Aims: In this context, we have organized a large monitoring campaign to refine the orbital solution and to study the wind-wind collision. <BR /> Methods: This paper presents the analysis of optical spectroscopic data, as well as of a dedicated X-ray monitoring performed with Swift and XMM-Newton. <BR /> Results: In light of our refined orbital solution, Cyg OB2 #9 appears as a massive O+O binary with a long period and high eccentricity; its components (O5-5.5I for the primary and O3-4III for the secondary) have similar masses and similar luminosities. The new data also provide the first evidence that a wind-wind collision is present in the system. In the optical domain, the broad Hα line varies, displaying enhanced absorption and emission components at periastron. X-ray observations yield the unambiguous signature of an adiabatic collision, because as the stars approach periastron, the X-ray luminosity closely follows the 1/D variation expected in that case. The X-ray spectrum appears, however, slightly softer at periastron, which is probably related to winds colliding at slightly lower speeds at that time. <BR /> Conclusions: It is the first time that such a variation has been detected in O+O systems, and the first case where the wind-wind collision is found to remain adiabatic even at periastron passage. [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 detail3D modelling of the massive star binary systems Eta Carinae, WR 22, and WR 140
Parkin, E. R.; Pittard, J. M.; Corcoran, M. F. et al

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

Massive stars possess powerful stellar winds. Wind-wind collision in a massive star binary system generates a region of thermalized plasma which may emit prolifically at X-ray wavelengths. Results are ... [more ▼]

Massive stars possess powerful stellar winds. Wind-wind collision in a massive star binary system generates a region of thermalized plasma which may emit prolifically at X-ray wavelengths. Results are presented from 3D adaptive-mesh refinement (AMR) hydrodynamical models which include radiative cooling and the radiative driving of the stellar winds. The models provide an exceptional insight into the turbulent nature of the wind-wind interaction regions. The X-ray emission from the hydrodynamical models is then calculated, allowing detailed comparisons with observational data. Preliminary results from investigations of Eta Carinae, WR 22, and WR 140 are discussed. [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 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 detailAn XMM-Newton observation of the Lagoon Nebula and the very young open cluster NGC 6530
Rauw, Grégor ULg; Nazé, Yaël ULg; Gosset, Eric ULg et al

in Astronomy and Astrophysics (2002), 395(2), 499-513

We report the results of an XMM-Newton observation of the Lagoon Nebula (M8). Our EPIC images of this region reveal a cluster of point sources, most of which have optical counterparts inside the very ... [more ▼]

We report the results of an XMM-Newton observation of the Lagoon Nebula (M8). Our EPIC images of this region reveal a cluster of point sources, most of which have optical counterparts inside the very young open cluster NGC6530. The bulk of these X-ray sources are probably associated with low and intermediate mass pre-main sequence stars. One of the sources experienced a flare-like increase of its X-ray flux making it the second brightest source in M8 after the O4 star 9 Sgr. The X-ray spectra of most of the brightest sources can be fitted with thermal plasma models with temperatures of kT similar to a few keV. Only a few of the X-ray selected PMS candidates are known to display Halpha emission and were previously classified as classical T Tauri stars. This suggests that most of the X-ray emitting PMS stars in NGC6530 are weak-line T Tauri stars. In addition to 9 Sgr, our EPIC field of view contains also a few early-type stars. The X-ray emission from HD 164816 is found to be typical for an O9.5 III-IV star. At least one of the known Herbig Be stars in NGC6530 ( LkHalpha 115) exhibits a relatively strong X-ray emission, while most of the main sequence stars of spectral type B1 and later are not detected. We also detect ( probably) diffuse X-ray emission from the Hourglass Region that might reveal a hot bubble blown by the stellar wind of Herschel 36, the ionizing star of the Hourglass Region. [less ▲]

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See detailASCA spectroscopy of the hard X-ray emission from the colliding wind interaction in gamma[SUP]2[/SUP] Velorum
Rauw, Grégor ULg; Stevens, I. R.; Pittard, J. M. et al

in Monthly Notices of the Royal Astronomical Society (2000), 316

We discuss an ASCA observation of the eccentric WC8+O7.5III binary gamma[SUP]2[/SUP]Velorum near apastron. The X-ray spectrum is compared with two previous observations obtained when the system was near ... [more ▼]

We discuss an ASCA observation of the eccentric WC8+O7.5III binary gamma[SUP]2[/SUP]Velorum near apastron. The X-ray spectrum is compared with two previous observations obtained when the system was near periastron. All three spectra display a hard-emission component that undergoes strong variability over the orbital cycle. The properties of the hard X-ray emission of gamma[SUP]2[/SUP]Vel are constrained by taking into account the contribution from contaminating soft X-ray sources in the vicinity of gamma[SUP]2[/SUP]Vel. We find that the observed variations are in qualitative agreement with the predictions of colliding wind models. We investigate for the first time the effect of uncertainties in the chemical composition of the X-ray emitting plasma on our understanding of the high-energy properties of the wind interaction region. Our results indicate that these uncertainties significantly affect the derived shock temperature and absorption column, but play a smaller role in determining the intrinsic X-ray luminosity of the colliding wind zone. We further find that the intrinsic luminosity from the hard X-ray component in gamma[SUP]2[/SUP]Vel does not follow the 1/D distance relation expected from simple models of adiabatic shocks. [less ▲]

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