@article{ParkinBroosTownsleyetal.2011,
  author    = {Parkin, E. R. and Broos, Patrick S. and Townsley, L. K. and Pittard, J. M. and Moffat, Anthony F. J. and Naze, Y. and Rauw, G. and Oskinova, Lida and Waldron, W. L.},
  title     = {X-RAY EMISSION FROM THE DOUBLE-BINARY OB-STAR SYSTEM QZ CAR (HD 93206)},
  series = {ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES},
  volume    = {194},
  journal   = {ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES},
  number    = {1},
  publisher = {IOP PUBLISHING LTD},
  address   = {BRISTOL},
  issn      = {0067-0049},
  doi       = {10.1088/0067-0049/194/1/8},
  pages     = {11},
  year      = {2011},
  abstract  = {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-A = 21 days) and B (O8 III+o9 v, P-B = 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 similar or equal to 0.2, 0.7, and 2 keV, respectively, and a circumstellar absorption of similar or equal to 0.2 x 10(22) cm(-2). 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 similar or equal to 7x10(-13) erg s(-1) cm(-2), 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.},
  language  = {en}
}
@article{OskinovaHamannCassinellietal.2011,
  author    = {Oskinova, Lida and Hamann, Wolf-Rainer and Cassinelli, Joseph P. and Brown, John C. and Todt, Helge Tobias},
  title     = {X-ray emission from massive stars with magnetic fields},
  series = {Astronomische Nachrichten = Astronomical notes},
  volume    = {332},
  journal   = {Astronomische Nachrichten = Astronomical notes},
  number    = {9-10},
  publisher = {Wiley-Blackwell},
  address   = {Malden},
  issn      = {0004-6337},
  doi       = {10.1002/asna.201111602},
  pages     = {988 -- 993},
  year      = {2011},
  abstract  = {We investigate the connections between the magnetic fields and the X-ray emission from massive stars. Our study shows that the X-ray properties of known strongly magnetic stars are diverse: while some comply to the predictions of the magnetically confined wind model, others do not. We conclude that strong, hard, and variable X-ray emission may be a sufficient attribute of magnetic massive stars, but it is not a necessary one. We address the general properties of X-ray emission from "normal" massive stars, especially the long standing mystery about the correlations between the parameters of X-ray emission and fundamental stellar properties. The recent development in stellar structure modeling shows that small-scale surface magnetic fields may be common. We suggest a "hybrid" scenario which could explain the X-ray emission from massive stars by a combination of magnetic mechanisms on the surface and shocks in the stellar wind. The magnetic mechanisms and the wind shocks are triggered by convective motions in sub-photospheric layers. This scenario opens the door for a natural explanation of the well established correlation between bolometric and X-ray luminosities.},
  language  = {en}
}