TY - JOUR A1 - Richardson, Noel D. A1 - Russell, Christopher M. P. A1 - St-Jean, Lucas A1 - Moffat, Anthony F. J. A1 - St-Louis, Nicole A1 - Shenar, Tomer A1 - Pablo, Herbert A1 - Hill, Grant M. A1 - Ramiaramanantsoa, Tahina A1 - Corcoran, Michael A1 - Hamuguchi, Kenji A1 - Eversberg, Thomas A1 - Miszalski, Brent A1 - Chene, Andre-Nicolas A1 - Waldron, Wayne A1 - Kotze, Enrico J. A1 - Kotze, Marissa M. A1 - Luckas, Paul A1 - Cacella, Paulo A1 - Heathcote, Bernard A1 - Powles, Jonathan A1 - Bohlsen, Terry A1 - Locke, Malcolm A1 - Handler, Gerald A1 - Kuschnig, Rainer A1 - Pigulski, Andrzej A1 - Popowicz, Adam A1 - Wade, Gregg A. A1 - Weiss, Werner W. T1 - The variability of the BRITE-est Wolf-Rayet binary, gamma(2) Velorum-I. Photometric and spectroscopic evidence for colliding winds JF - Monthly notices of the Royal Astronomical Society N2 - We report on the first multi-colour precision light curve of the bright Wolf-Rayet binary gamma(2) Velorum, obtained over six months with the nanosatellites in the BRITE-Constellation fleet. In parallel, we obtained 488 high-resolution optical spectra of the system. In this first report on the data sets, we revise the spectroscopic orbit and report on the bulk properties of the colliding winds. We find a dependence of both the light curve and excess emission properties that scales with the inverse of the binary separation. When analysing the spectroscopic properties in combination with the photometry, we find that the phase dependence is caused only by excess emission in the lines, and not from a changing continuum. We also detect a narrow, high-velocity absorption component from the He perpendicular to lambda 5876 transition, which appears twice in the orbit. We calculate smoothed-particle hydrodynamical simulations of the colliding winds and can accurately associate the absorption from He perpendicular to to the leading and trailing arms of the wind shock cone passing tangentially through our line of sight. The simulations also explain the general strength and kinematics of the emission excess observed in wind lines such as C III lambda 5696 of the system. These results represent the first in a series of investigations into the winds and properties of gamma(2) Velorum through multi-technique and multi-wavelength observational campaigns. KW - stars: early type KW - stars: individual: gamma(2) Vel KW - stars: mass loss KW - stars: winds KW - outflows KW - stars: Wolf-Rayet Y1 - 2017 U6 - https://doi.org/10.1093/mnras/stx1731 SN - 0035-8711 SN - 1365-2966 VL - 471 SP - 2715 EP - 2729 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Oskinova, Lida A1 - Todt, Helge Tobias A1 - Ignace, Richard A1 - Brown, John C. A1 - Cassinelli, Joseph P. A1 - Hamann, Wolf-Rainer T1 - Early magnetic B-type stars X-ray emission and wind properties JF - Monthly notices of the Royal Astronomical Society N2 - We present a comprehensive study of X-ray emission by, and wind properties of, massive magnetic early B-type stars. Dedicated XMM-Newton observations were obtained for three early-type B-type stars, xi(1) CMa, V2052 Oph and zeta Cas, with recently discovered magnetic fields. We report the first detection of X-ray emission from V2052 Oph and zeta Cas. The latter is one the softest X-ray sources among the early-type stars, while the former is one of the X-ray faintest. The observations show that the X-ray spectra of our programme stars are quite soft with the bulk of X-ray emitting material having a temperature of about 1 MK. We compile the complete sample of early B-type stars with detected magnetic fields to date and existing X-ray measurements, in order to study whether the X-ray emission can be used as a general proxy for stellar magnetism. We find that the X-ray properties of early massive B-type magnetic stars are diverse, and that hard and strong X-ray emission does not necessarily correlate with the presence of a magnetic field, corroborating similar conclusions reached earlier for the classical chemically peculiar magnetic Bp-Ap stars. We analyse the ultraviolet (UV) spectra of five non-supergiant B stars with magnetic fields (tau Sco, beta Cep, xi(1) CMa, V2052 Oph and zeta Cas) by means of non-local thermodynamic equilibrium (non-LTE) iron-blanketed model atmospheres. The latter are calculated with the Potsdam Wolf-Rayet (PoWR) code, which treats the photosphere as well as the wind, and also accounts for X-rays. With the exception of t Sco, this is the first analysis of these stars by means of stellar wind models. Our models accurately fit the stellar photospheric spectra in the optical and the UV. The parameters of X-ray emission, temperature and flux are included in the model in accordance with observations. We confirm the earlier findings that the filling factors of X-ray emitting material are very high. Our analysis reveals that the magnetic early-type B stars studied here have weak winds with velocities not significantly exceeding upsilon(esc). The mass-loss rates inferred from the analysis of UV lines are significantly lower than predicted by hydrodynamically consistent models. We find that, although the X-rays strongly affect the ionization structure of the wind, this effect is not sufficient in reducing the total radiative acceleration. When the X-rays are accounted for at the intensity and temperatures observed, there is still sufficient radiative acceleration to drive a stronger mass-loss than we empirically infer from the UV spectral lines. KW - techniques: spectroscopic KW - stars: magnetic field KW - stars: massive KW - stars: mass loss KW - X-rays: stars Y1 - 2011 U6 - https://doi.org/10.1111/j.1365-2966.2011.19143.x SN - 0035-8711 VL - 416 IS - 2 SP - 1456 EP - 1474 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Massa, D. A1 - Oskinova, Lida A1 - Fullerton, A. W. A1 - Prinja, R. K. A1 - Bohlender, D. A. A1 - Morrison, N. D. A1 - Blake, M. A1 - Pych, W. T1 - CIR modulation of the X-ray flux from the O7.5 III(n)((f)) star xi Persei(a similar to...)? JF - Monthly notices of the Royal Astronomical Society N2 - We analyse a 162 ks high energy transmission grating Chandra observation of the O7.5 III(n)((f)) star xi Per, together with contemporaneous H alpha observations. The X-ray spectrum of this star is similar to other single O stars, and not pathological in any way. Its UV wind lines are known to display cyclical time variability, with a period of 2.086 d, which is thought to be associated with corotating interaction regions (CIRs). We examine the Chandra and H alpha data for variability on this time-scale. We find that the X-rays vary by similar to 15 per cent over the course of the observations and that this variability is out of phase with variable absorption on the blue wing of the H alpha profiles (assumed to be a surrogate for the UV absorption associated with CIRs). While not conclusive, both sets of data are consistent with models where the CIRs are either a source of X-rays or modulate them. KW - stars: early-type KW - stars: individual: xi Persei KW - stars: mass loss KW - stars: winds, outflows KW - X-rays: stars Y1 - 2014 U6 - https://doi.org/10.1093/mnras/stu565 SN - 0035-8711 SN - 1365-2966 VL - 441 IS - 3 SP - 2173 EP - 2180 PB - Oxford Univ. Press CY - Oxford ER -