TY - JOUR A1 - Ramiaramanantsoa, Tahina A1 - Moffat, Anthony F. J. A1 - Harmon, Robert A1 - Ignace, R. A1 - St-Louis, Nicole A1 - Vanbeveren, Dany A1 - Shenar, Tomer A1 - Pablo, Herbert A1 - Richardson, Noel D. A1 - Howarth, Ian D. A1 - Stevens, Ian R. A1 - Piaulet, Caroline A1 - St-Jean, Lucas A1 - Eversberg, Thomas A1 - Pigulski, Andrzej A1 - Popowicz, Adam A1 - Kuschnig, Rainer A1 - Zoclonska, Elzbieta A1 - Buysschaert, Bram A1 - Handler, Gerald A1 - Weiss, Werner W. A1 - Wade, Gregg A. A1 - Rucinski, Slavek M. A1 - Zwintz, Konstanze A1 - Luckas, Paul A1 - Heathcote, Bernard A1 - Cacella, Paulo A1 - Powles, Jonathan A1 - Locke, Malcolm A1 - Bohlsen, Terry A1 - Chené, André-Nicolas A1 - Miszalski, Brent A1 - Waldron, Wayne L. A1 - Kotze, Marissa M. A1 - Kotze, Enrico J. A1 - Böhm, Torsten T1 - BRITE-Constellation high-precision time-dependent photometry of the early O-type supergiant zeta Puppis unveils the photospheric drivers of its small- and large-scale wind structures JF - Monthly notices of the Royal Astronomical Society N2 - From 5.5 months of dual-band optical photometric monitoring at the 1 mmag level, BRITE-Constellation has revealed two simultaneous types of variability in the O4I(n)fp star ζ Puppis: one single periodic non-sinusoidal component superimposed on a stochastic component. The monoperiodic component is the 1.78-d signal previously detected by Coriolis/Solar Mass Ejection Imager, but this time along with a prominent first harmonic. The shape of this signal changes over time, a behaviour that is incompatible with stellar oscillations but consistent with rotational modulation arising from evolving bright surface inhomogeneities. By means of a constrained non-linear light-curve inversion algorithm, we mapped the locations of the bright surface spots and traced their evolution. Our simultaneous ground-based multisite spectroscopic monitoring of the star unveiled cyclical modulation of its He ii λ4686 wind emission line with the 1.78-d rotation period, showing signatures of corotating interaction regions that turn out to be driven by the bright photospheric spots observed by BRITE. Traces of wind clumps are also observed in the He ii λ4686 line and are correlated with the amplitudes of the stochastic component of the light variations probed by BRITE at the photosphere, suggesting that the BRITE observations additionally unveiled the photospheric drivers of wind clumps in ζ Pup and that the clumping phenomenon starts at the very base of the wind. The origins of both the bright surface inhomogeneities and the stochastic light variations remain unknown, but a subsurface convective zone might play an important role in the generation of these two types of photospheric variability. KW - techniques: photometric KW - techniques: spectroscopic KW - stars: massive KW - stars: rotation KW - starspots KW - supergiants KW - stars: winds, outflows Y1 - 2017 U6 - https://doi.org/10.1093/mnras/stx2671 SN - 0035-8711 SN - 1365-2966 VL - 473 IS - 4 SP - 5532 EP - 5569 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Oskinova, Lida A1 - Huenemoerder, D. P. A1 - Hamann, Wolf-Rainer A1 - Shenar, Tomer A1 - Sander, Andreas Alexander Christoph A1 - Ignace, R. A1 - Todt, Helge Tobias A1 - Hainich, Rainer T1 - On the Binary Nature of Massive Blue Hypergiants: High-resolution X-Ray Spectroscopy Suggests That Cyg OB2 12 is a Colliding Wind Binary JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - The blue hypergiant Cyg OB2 12 (B3Ia(+)) is a representative member of the class of very massive stars in a poorly understood evolutionary stage. We obtained its high-resolution X-ray spectrum using the Chandra observatory. PoWR model atmospheres were calculated to provide realistic wind opacities and to establish the wind density structure. We find that collisional de-excitation is the dominant mechanism depopulating the metastable upper levels of the forbidden lines of the He-like ions Si XIV and Mg XII. Comparison between the model and observations reveals that X-ray emission is produced in a dense plasma, which could reside only at the photosphere or in a colliding wind zone between binary components. The observed X-ray spectra are well-fitted by thermal plasma models, with average temperatures in excess of 10 MK. The wind speed in Cyg OB2 12 is not high enough to power such high temperatures, but the collision of two winds in a binary system can be sufficient. We used archival data to investigate the X-ray properties of other blue hypergiants. In general, stars of this class are not detected as X-ray sources. We suggest that our new Chandra observations of Cyg OB2 12 can be best explained if Cyg OB2 12 is a colliding wind binary possessing a late O-type companion. This makes Cyg OB2 12 only the second binary system among the 16 known Galactic hypergiants. This low binary fraction indicates that the blue hypergiants are likely products of massive binary evolution during which they either accreted a significant amount of mass or already merged with their companions. KW - stars: individual (Cyg OB2 12) KW - stars: massive KW - stars: mass-loss KW - stars: winds, outflows KW - supergiants KW - X-rays: stars Y1 - 2017 U6 - https://doi.org/10.3847/1538-4357/aa7e79 SN - 0004-637X SN - 1538-4357 VL - 845 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Toala, Jesús Alberto A1 - Oskinova, Lida A1 - Ignace, R. T1 - On the Absence of Non-thermal X-Ray Emission around Runaway O Stars JF - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters N2 - Theoretical models predict that the compressed interstellar medium around runaway O stars can produce highenergy non-thermal diffuse emission, in particular, non-thermal X-ray and gamma-ray emission. So far, detection of nonthermal X-ray emission was claimed for only one runaway star, AE Aur. We present a search for non-thermal diffuse X-ray emission from bow shocks using archived XMM-Newton observations for a clean sample of six welldetermined runaway O stars. We find that none of these objects present diffuse X-ray emission associated with their bow shocks, similarly to previous X-ray studies toward. zeta ph and BD+ 43 degrees 3654. We carefully investigated multi-wavelength observations of AE Aur and could not confirm previous findings of non-thermal X-rays. We conclude that so far there is no clear evidence of non-thermal extended emission in bow shocks around runaway O stars. KW - stars: massive KW - stars: mass-loss KW - stars: winds, outflows KW - X-rays: ISM Y1 - 2017 U6 - https://doi.org/10.3847/2041-8213/aa667c SN - 2041-8205 SN - 2041-8213 VL - 838 SP - 1 EP - 32 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Toala, Jesús Alberto A1 - Oskinova, Lida A1 - Gonzalez-Galan, Ana A1 - Guerrero, Martín A. A1 - Ignace, R. A1 - Pohl, Martin T1 - X-RAY OBSERVATIONS OF BOW SHOCKS AROUND RUNAWAY O STARS. THE CASE OF zeta OPH AND BD+43 degrees 3654 JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - Non-thermal radiation has been predicted within bow shocks around runaway stars by recent theoretical works. We present X-ray observations toward the runaway stars zeta Oph by Chandra and Suzaku and of BD+43 degrees 3654 by XMM-Newton to search for the presence of non-thermal X-ray emission. We found no evidence of non-thermal emission spatially coincident with the bow shocks; nonetheless, diffuse emission was detected in the vicinity of zeta Oph. After a careful analysis of its spectral characteristics, we conclude that this emission has a thermal nature with a plasma temperature of T approximate to 2 x 10(6) K. The cometary shape of this emission seems to be in line with recent predictions of radiation-hydrodynamic models of runaway stars. The case of BD+43 degrees 3654 is puzzling, as non-thermal emission has been reported in a previous work for this source. KW - stars: individual (zeta Oph, BD+43 degrees 3654) KW - stars: winds, outflows Y1 - 2016 U6 - https://doi.org/10.3847/0004-637X/821/2/79 SN - 0004-637X SN - 1538-4357 VL - 821 PB - IOP Publ. Ltd. CY - Bristol ER -