TY - JOUR A1 - Shenar, Tomer A1 - Hainich, Rainer A1 - Todt, Helge Tobias A1 - Sander, Andreas Alexander Christoph A1 - Hamann, Wolf-Rainer A1 - Moffat, Anthony F. J. A1 - Eldridge, J. J. A1 - Pablo, H. A1 - Oskinova, Lida A1 - Richardson, N. D. T1 - Wolf-Rayet stars in the Small Magellanic Cloud II. Analysis of the binaries JF - American mineralogist : an international journal of earth and planetary materials N2 - Context. Massive Wolf-Rayet (WR) stars are evolved massive stars (M-i greater than or similar to 20 M-circle dot) characterized by strong mass-loss. Hypothetically, they can form either as single stars or as mass donors in close binaries. About 40% of all known WR stars are confirmed binaries, raising the question as to the impact of binarity on the WR population. Studying WR binaries is crucial in this context, and furthermore enable one to reliably derive the elusive masses of their components, making them indispensable for the study of massive stars. Aims. By performing a spectral analysis of all multiple WR systems in the Small Magellanic Cloud (SMC), we obtain the full set of stellar parameters for each individual component. Mass-luminosity relations are tested, and the importance of the binary evolution channel is assessed. Methods. The spectral analysis is performed with the PotsdamWolf-Rayet (PoWR) model atmosphere code by superimposing model spectra that correspond to each component. Evolutionary channels are constrained using the Binary Population and Spectral Synthesis (BPASS) evolution tool. Results. Significant hydrogen mass fractions (0.1 < X-H < 0.4) are detected in all WN components. A comparison with mass-luminosity relations and evolutionary tracks implies that the majority of the WR stars in our sample are not chemically homogeneous. The WR component in the binary AB6 is found to be very luminous (log L approximate to 6.3 [L-circle dot]) given its orbital mass (approximate to 10 M-circle dot), presumably because of observational contamination by a third component. Evolutionary paths derived for our objects suggest that Roche lobe overflow had occurred in most systems, affecting their evolution. However, the implied initial masses (greater than or similar to 60 M-circle dot) are large enough for the primaries to have entered the WR phase, regardless of binary interaction. Conclusions. Together with the results for the putatively single SMC WR stars, our study suggests that the binary evolution channel does not dominate the formation of WR stars at SMC metallicity. KW - stars: massive KW - stars: Wolf-Rayet KW - stars: evolution KW - binaries: close KW - binaries: symbiotic KW - Magellanic Clouds Y1 - 2016 U6 - https://doi.org/10.1051/0004-6361/201527916 SN - 1432-0746 VL - 591 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Gimenez-Garcia, Ana A1 - Shenar, Tomer A1 - Torrejon, J. M. A1 - Oskinova, Lida A1 - Martinez-Nunez, S. A1 - Hamann, Wolf-Rainer A1 - Rodes-Roca, J. J. A1 - González-Galan, A. A1 - Alonso-Santiago, J. A1 - González-Fernández, C. A1 - Bernabeu, Guillermo A1 - Sander, Andreas Alexander Christoph T1 - Measuring the stellar wind parameters in IGR J17544-2619 and Vela X-1 constrains the accretion physics in supergiant fast X-ray transient and classical supergiant X-ray binaries JF - Siberian Mathematical Journal N2 - Aims. To close this gap, we perform a comparative analysis of the optical companion in two important systems: IGR J175442619 (SFXT) and Vela X-1 (SGXB). We analyze the spectra of each star in detail and derive their stellar and wind properties. As a next step, we compare the wind parameters, giving us an excellent chance of recognizing key differences between donor winds in SFXTs and SGXBs. Methods. We use archival infrared, optical and ultraviolet observations, and analyze them with the non-local thermodynamic equilibrium (NLTE) Potsdam Wolf-Rayet model atmosphere code. We derive the physical properties of the stars and their stellar winds, accounting for the influence of X-rays on the stellar winds. Results. We find that the stellar parameters derived from the analysis generally agree well with the spectral types of the two donors: O9I (IGR J17544-2619) and B0.5Iae (Vela X-1). The distance to the sources have been revised and also agree well with the estimations already available in the literature. In IGR J17544-2619 we are able to narrow the uncertainty to d = 3.0 +/- 0.2 kpc. From the stellar radius of the donor and its X-ray behavior, the eccentricity of IGR J17544-2619 is constrained to e < 0.25. The derived chemical abundances point to certain mixing during the lifetime of the donors. An important difference between the stellar winds of the two stars is their terminal velocities (v(infinity) = 1500 km s(-1) in IGR J17544-2619 and v(infinity) = 700 km s(-1) in Vela X-1), which have important consequences on the X-ray luminosity of these sources. Conclusions. The donors of IGR J17544-2619 and Vela X-1 have similar spectral types as well as similar parameters that physically characterize them and their spectra. In addition, the orbital parameters of the systems are similar too, with a nearly circular orbit and short orbital period. However, they show moderate differences in their stellar wind velocity and the spin period of their neutron star which has a strong impact on the X-ray luminosity of the sources. This specific combination of wind speed and pulsar spin favors an accretion regime with a persistently high luminosity in Vela X-1, while it favors an inhibiting accretion mechanism in IGR J17544-2619. Our study demonstrates that the relative wind velocity is critical in class determination for the HMXBs hosting a supergiant donor, given that it may shift the accretion mechanism from direct accretion to propeller regimes when combined with other parameters. KW - accretion, accretion disks KW - methods: observational KW - techniques: spectroscopic KW - stars: atmospheres KW - X-rays: binaries KW - stars: winds, outflows Y1 - 2016 U6 - https://doi.org/10.1051/0004-6361/201527551 SN - 1432-0746 VL - 591 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Aldoretta, E. J. A1 - St-Louis, N. A1 - Richardson, N. D. A1 - Moffat, Anthony F. J. A1 - Eversberg, T. A1 - Hill, G. M. A1 - Shenar, Tomer A1 - Artigau, E. A1 - Gauza, B. A1 - Knapen, J. H. A1 - Kubat, Jiří A1 - Kubatova, Brankica A1 - Maltais-Tariant, R. A1 - Munoz, M. A1 - Pablo, H. A1 - Ramiaramanantsoa, T. A1 - Richard-Laferriere, A. A1 - Sablowski, D. P. A1 - Simon-Diaz, S. A1 - St-Jean, L. A1 - Bolduan, F. A1 - Dias, F. M. A1 - Dubreuil, P. A1 - Fuchs, D. A1 - Garrel, T. A1 - Grutzeck, G. A1 - Hunger, T. A1 - Kuesters, D. A1 - Langenbrink, M. A1 - Leadbeater, R. A1 - Li, D. A1 - Lopez, A. A1 - Mauclaire, B. A1 - Moldenhawer, T. A1 - Potter, M. A1 - dos Santos, E. M. A1 - Schanne, L. A1 - Schmidt, J. A1 - Sieske, H. A1 - Strachan, J. A1 - Stinner, E. A1 - Stinner, P. A1 - Stober, B. A1 - Strandbaek, K. A1 - Syder, T. A1 - Verilhac, D. A1 - Waldschlaeger, U. A1 - Weiss, D. A1 - Wendt, A. T1 - An extensive spectroscopic time series of three Wolf-Rayet stars - I. The lifetime of large-scale structures in the wind of WR 134 JF - Monthly notices of the Royal Astronomical Society N2 - During the summer of 2013, a 4-month spectroscopic campaign took place to observe the variabilities in three Wolf-Rayet stars. The spectroscopic data have been analysed for WR 134 (WN6b), to better understand its behaviour and long-term periodicity, which we interpret as arising from corotating interaction regions (CIRs) in the wind. By analysing the variability of the He ii lambda 5411 emission line, the previously identified period was refined to P = 2.255 +/- 0.008 (s.d.) d. The coherency time of the variability, which we associate with the lifetime of the CIRs in the wind, was deduced to be 40 +/- 6 d, or similar to 18 cycles, by cross-correlating the variability patterns as a function of time. When comparing the phased observational grey-scale difference images with theoretical grey-scales previously calculated from models including CIRs in an optically thin stellar wind, we find that two CIRs were likely present. A separation in longitude of Delta I center dot a parts per thousand integral 90A degrees was determined between the two CIRs and we suggest that the different maximum velocities that they reach indicate that they emerge from different latitudes. We have also been able to detect observational signatures of the CIRs in other spectral lines (C iv lambda lambda 5802,5812 and He i lambda 5876). Furthermore, a DAC was found to be present simultaneously with the CIR signatures detected in the He i lambda 5876 emission line which is consistent with the proposed geometry of the large-scale structures in the wind. Small-scale structures also show a presence in the wind, simultaneously with the larger scale structures, showing that they do in fact co-exist. KW - instabilities KW - methods: data analysis KW - techniques: spectroscopic KW - stars: individual: WR 134 KW - stars: massive KW - stars: Wolf-Rayet Y1 - 2016 U6 - https://doi.org/10.1093/mnras/stw1188 SN - 0035-8711 SN - 1365-2966 VL - 460 SP - 3407 EP - 3417 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Richardson, Noel D. A1 - Shenar, Tomer A1 - Roy-Loubier, Olivier A1 - Schaefer, Gail A1 - Moffat, Anthony F. J. A1 - St-Louis, Nicole A1 - Gies, Douglas R. A1 - Farrington, Chris A1 - Hill, Grant M. A1 - Williams, Peredur M. A1 - Gordon, Kathryn A1 - Pablo, Herbert A1 - Ramiaramanantsoa, Tahina T1 - The CHARA Array resolves the long-period Wolf-Rayet binaries WR 137 and WR 138 JF - Monthly notices of the Royal Astronomical Society N2 - We report on interferometric observations with the CHARAArray of two classical Wolf-Rayet (WR) stars in suspected binary systems, namely WR 137 and WR 138. In both cases, we resolve the component stars to be separated by a few milliarcseconds. The data were collected in the H band, and provide a measure of the fractional flux for both stars in each system. We find that the WR star is the dominant H-band light source in both systems (fWR, 137 = 0.59 +/- 0.04; fWR, 138 = 0.67 +/- 0.01), which is confirmed through both comparisons with estimated fundamental parameters for WR stars and O dwarfs, as well as through spectral modelling of each system. Our spectral modelling also provides fundamental parameters for the stars and winds in these systems. The results on WR 138 provide evidence that it is a binary system which may have gone through a previous mass-transfer episode to create the WR star. The separation and position of the stars in the WR 137 system together with previous results from the IOTA interferometer provides evidence that the binary is seen nearly edgeon. The possible edge-on orbit of WR 137 aligns well with the dust production site imaged by the Hubble Space Telescope during a previous periastron passage, showing that the dust production may be concentrated in the orbital plane. KW - binaries: visual KW - stars: individual: WR 137 KW - stars: individual: WR 138 KW - stars: mass-loss KW - stars: winds, outflows KW - stars: Wolf-Rayet Y1 - 2016 U6 - https://doi.org/10.1093/mnras/stw1585 SN - 0035-8711 SN - 1365-2966 VL - 461 SP - 4115 EP - 4124 PB - Oxford Univ. Press CY - Oxford ER -