@article{CorcoranNicholsPabloetal.2015,
  author    = {Corcoran, Michael F. and Nichols, Joy S. and Pablo, Herbert and Shenar, Tomer and Pollock, Andy M. T. and Waldron, Wayne L. and Moffat, Anthony F. J. and Richardson, Noel D. and Russell, Christopher M. P. and Hamaguchi, Kenji and Huenemoerder, David P. and Oskinova, Lida and Hamann, Wolf-Rainer and Naze, Yael and Ignace, Richard and Evans, Nancy Remage and Lomax, Jamie R. and Hoffman, Jennifer L. and Gayley, Kenneth and Owocki, Stanley P. and Leutenegger, Maurice and Gull, Theodore R. and Hole, Karen Tabetha and Lauer, Jennifer and Iping, Rosina C.},
  title     = {A coordinated X-Ray and optical campaign of the nearest massive eclipsing binary, delta ORIONIS Aa. I. Overview of thr X-Ray spectrum},
  series = {The astrophysical journal : an international review of spectroscopy and astronomical physics},
  volume    = {809},
  journal   = {The astrophysical journal : an international review of spectroscopy and astronomical physics},
  number    = {2},
  publisher = {IOP Publ. Ltd.},
  address   = {Bristol},
  issn      = {0004-637X},
  doi       = {10.1088/0004-637X/809/2/132},
  pages     = {15},
  year      = {2015},
  abstract  = {We present an overview of four deep phase-constrained Chandra HETGS X-ray observations of delta Ori A. Delta Ori A is actually a triple system that includes the nearest massive eclipsing spectroscopic binary, delta Ori Aa, the only such object that can be observed with little phase-smearing with the Chandra gratings. Since the fainter star, delta Ori Aa2, has a much lower X-ray luminosity than the brighter primary (delta Ori Aa1), delta Ori Aa provides a unique system with which to test the spatial distribution of the X-ray emitting gas around delta Ori Aa1 via occultation by the photosphere of, and wind cavity around, the X-ray dark secondary. Here we discuss the X-ray spectrum and X-ray line profiles for the combined observation, having an exposure time of nearly 500 ks and covering nearly the entire binary orbit. The companion papers discuss the X-ray variability seen in the Chandra spectra, present new space-based photometry and ground-based radial velocities obtained simultaneously with the X-ray data to better constrain the system parameters, and model the effects of X-rays on the optical and UV spectra. We find that the X-ray emission is dominated by embedded wind shock emission from star Aa1, with little contribution from the tertiary star Ab or the shocked gas produced by the collision of the wind of Aa1 against the surface of Aa2. We find a similar temperature distribution to previous X-ray spectrum analyses. We also show that the line half-widths are about 0.3-0.5 times the terminal velocity of the wind of star Aa1. We find a strong anti-correlation between line widths and the line excitation energy, which suggests that longer-wavelength, lower-temperature lines form farther out in the wind. Our analysis also indicates that the ratio of the intensities of the strong and weak lines of Fe XVII and Ne X are inconsistent with model predictions, which may be an effect of resonance scattering.},
  language  = {en}
}
@article{GvaramadzeCheneKniazevetal.2014,
  author    = {Gvaramadze, V. V. and Chene, A.-N. and Kniazev, A. Y. and Schnurr, O. and Shenar, Tomer and Sander, Andreas Alexander Christoph and Hainich, Rainer and Langer, N. and Hamann, Wolf-Rainer and Chu, Y.-H. and Gruendl, R. A.},
  title     = {Discovery of a new Wolf-Rayet star and a candidate star cluster in the Large Magellanic Cloud with Spitzer},
  series = {Monthly notices of the Royal Astronomical Society},
  volume    = {442},
  journal   = {Monthly notices of the Royal Astronomical Society},
  number    = {2},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0035-8711},
  doi       = {10.1093/mnras/stu909},
  pages     = {929 -- 945},
  year      = {2014},
  abstract  = {We report the first-ever discovery of a Wolf-Rayet (WR) star in the Large Magellanic Cloud via detection of a circular shell with the Spitzer Space Telescope. Follow-up observations with Gemini-South resolved the central star of the shell into two components separated from each other by a parts per thousand 2 arcsec (or a parts per thousand 0.5 pc in projection). One of these components turns out to be a WN3 star with H and He lines both in emission and absorption (we named it BAT99 3a using the numbering system based on extending the Breysacher et al. catalogue). Spectroscopy of the second component showed that it is a B0 V star. Subsequent spectroscopic observations of BAT99 3a with the du Pont 2.5-m telescope and the Southern African Large Telescope revealed that it is a close, eccentric binary system, and that the absorption lines are associated with an O companion star. We analysed the spectrum of the binary system using the non-LTE Potsdam WR (powr) code, confirming that the WR component is a very hot (a parts per thousand 90 kK) WN star. For this star, we derived a luminosity of log L/ L-aS (TM) = 5.45 and a mass-loss rate of 10(- 5.8) M-aS (TM) yr(- 1), and found that the stellar wind composition is dominated by helium with 20 per cent of hydrogen. Spectroscopy of the shell revealed an He iii region centred on BAT99 3a and having the same angular radius (a parts per thousand 15 arcsec) as the shell. We thereby add a new example to a rare class of high-excitation nebulae photoionized by WR stars. Analysis of the nebular spectrum showed that the shell is composed of unprocessed material, implying that the shell was swept-up from the local interstellar medium. We discuss the physical relationship between the newly identified massive stars and their possible membership of a previously unrecognized star cluster.},
  language  = {en}
}
@article{RichardsonShenarRoyLoubieretal.2016,
  author    = {Richardson, Noel D. and Shenar, Tomer and Roy-Loubier, Olivier and Schaefer, Gail and Moffat, Anthony F. J. and St-Louis, Nicole and Gies, Douglas R. and Farrington, Chris and Hill, Grant M. and Williams, Peredur M. and Gordon, Kathryn and Pablo, Herbert and Ramiaramanantsoa, Tahina},
  title     = {The CHARA Array resolves the long-period Wolf-Rayet binaries WR 137 and WR 138},
  series = {Monthly notices of the Royal Astronomical Society},
  volume    = {461},
  journal   = {Monthly notices of the Royal Astronomical Society},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0035-8711},
  doi       = {10.1093/mnras/stw1585},
  pages     = {4115 -- 4124},
  year      = {2016},
  abstract  = {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.},
  language  = {en}
}
@article{JaervinenHubrigIlyinetal.2017,
  author    = {Jaervinen, S. P. and Hubrig, Swetlana and Ilyin, Ilya and Shenar, Tomer and Schoeller, M.},
  title     = {A search for spectral variability in the highly magnetized O9.7 V star HD 54879},
  series = {Astronomische Nachrichten = Astronomical notes},
  volume    = {338},
  journal   = {Astronomische Nachrichten = Astronomical notes},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {0004-6337},
  doi       = {10.1002/asna.201713402},
  pages     = {952 -- 958},
  year      = {2017},
  abstract  = {The O9.7 V star HD 54879 possesses the second strongest magnetic field among the single, magnetic, O-type stars. In contrast to other magnetic O-type stars, the chemical abundance analysis of HD 54879 indicated a rather normal optical spectrum without obvious element enhancements or depletions. Furthermore, spectral variability was detected only in lines partly formed in the magnetosphere. As this star shows such a deviate, almost nonvariable, spectral behavior, we performed a deeper analysis of its spectral variability on different timescales using all currently available HARPSpol and FORS 2 spectropolarimetric observations. The longitudinal magnetic field strengths measured at different epochs indicate the presence of variability possibly related to stellar rotation, but the current data do not allow us yet to identify the periodicity of the field variation. As spectropolarimetric observations obtained at different epochs consist of subexposures with different integration times, we investigated spectral variability on timescales of minutes. The detected level of variability in line profiles of different elements is rather low, between 0.2 and 1.7\%, depending on the integration time of the exposures and the considered element.},
  language  = {en}
}
@article{MunozMoffatHilletal.2017,
  author    = {Munoz, Melissa and Moffat, Anthony F. J. and Hill, Grant M. and Shenar, Tomer and Richardson, Noel D. and Pablo, Herbert and St-Louis, Nicole and Ramiaramanantsoa, Tahina},
  title     = {WR 148: identifying the companion of an extreme runaway massive binary},
  series = {Monthly notices of the Royal Astronomical Society},
  volume    = {467},
  journal   = {Monthly notices of the Royal Astronomical Society},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0035-8711},
  doi       = {10.1093/mnras/stw2283},
  pages     = {3105 -- 3121},
  year      = {2017},
  abstract  = {WR 148 (HD 197406) is an extreme runaway system considered to be a potential candidate for a short-period (4.3173 d) rare WR + compact object binary. Provided with new high-resolution, high signal-to-noise spectra from the Keck observatory, we determine the orbital parameters for both the primary WR and the secondary, yielding respective projected orbital velocity amplitudes of 88.1 ± 3.8\&\#8201;km\&\#8201;s\&\#8722;1 and 79.2 ± 3.1\&\#8201;km\&\#8201;s\&\#8722;1 and implying a mass ratio of 1.1 ± 0.1. We then apply the shift-and-add technique to disentangle the spectra and obtain spectra compatible with a WN7ha and an O4-6 star. Considering an orbital inclination of \&\#8764;67°, derived from previous polarimetry observations, the system's total mass would be a mere 2-3M\&\#8857;\&\#8288;, an unprecedented result for a putative massive binary system. However, a system comprising a 37M\&\#8857; secondary (typical mass of an O5V star) and a 33M\&\#8857; primary (given the mass ratio) would infer an inclination of \&\#8764;18°. We therefore reconsider the previous methods of deriving the orbital inclination based on time-dependent polarimetry and photometry. While the polarimetric results are inconclusive requiring better data, the photometric results favour low inclinations. Finally, we compute WR 148's space velocity and retrace the runaway's trajectory back to the Galactic plane (GP). With an ejection velocity of 198 ± 27\&\#8201;km\&\#8201;s\&\#8722;1 and a travel time of 4.7 ± 0.8 Myr to reach its current location, WR 148 was most likely ejected via dynamical interactions in a young cluster.},
  language  = {en}
}
@article{ShenarHamannTodt2015,
  author    = {Shenar, Tomer and Hamann, Wolf-Rainer and Todt, Helge Tobias},
  title     = {The impact of rotation on the line profiles of Wolf-Rayet stars},
  series = {Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.-5. June 2015},
  journal   = {Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.-5. June 2015},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-88008},
  pages     = {193 -- 196},
  year      = {2015},
  abstract  = {The distribution of angular momentum in massive stars is a critical component of their evolution, yet not much is known on the rotation velocities of Wolf-Rayet stars. There are various indications that rapidly rotating Wolf-Rayet stars should exist. Unfortunately, due to their expanding atmospheres, rotational velocities of Wolf-Rayet stars are very difficult to measure. In this work, we model the effects of rotation on the atmospheres of Wolf-Rayet stars by implementing a 3D integration scheme in the PoWR code. We further investigate whether the peculiar spectra of five Wolf-Rayet stars may imply rapid rotation, infer the corresponding rotation parameters, and discuss the implications of our results. We find that rotation helps to reproduce the unique spectra analyzed here. However, if rotation is indeed involved, the inferred rotational velocities at the stellar surface are large (∼ 200 km/s), and the implied co-rotation radii (∼ 10R∗) suggest the existence of very strong photospheric magnetic fields (∼ 20 kG).},
  language  = {en}
}
@article{SanderHamannHainichetal.2015,
  author    = {Sander, A. and Hamann, Wolf-Rainer and Hainich, Rainer and Shenar, Tomer and Todt, Helge Tobias},
  title     = {Hydrodynamic modeling of massive star atmospheres},
  series = {Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.-5. June 2015},
  journal   = {Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.-5. June 2015},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-87857},
  pages     = {139 -- 142},
  year      = {2015},
  abstract  = {In the last decades, stellar atmosphere codes have become a key tool in understanding massive stars, including precise calculations of stellar and wind parameters, such as temperature, massloss rate, and terminal wind velocity. Nevertheless, for these models the hydrodynamic equation is not solved in the wind. Motivated by the results of the CAK theory, the models typically use a beta velocity law, which however turns out not to be adequate for stars with very strong winds, and treat the mass-loss rate as a free parameter. In a new branch of the Potsdam Wolf-Rayet model atmosphere (PoWR) code, we solve the hydrodynamic equation consistently throughout the stellar atmosphere. The PoWR code performs the calculation of the radiative force without approximations (e.g. Sobolev). We show the impact of hydrodynamically consistent modelling on OB and WR stars in comparison to conventional models and discuss the obtained velocity fields and their impact on the observed spectral lines.},
  language  = {en}
}
@article{KubatovaHamannTodtetal.2015,
  author    = {Kub{\´a}tov{\´a}, Brankica and Hamann, Wolf-Rainer and Todt, Helge Tobias and Sander, A. and Steinke, M. and Hainich, Rainer and Shenar, Tomer},
  title     = {Macroclumping in WR 136},
  series = {Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.-5. June 2015},
  journal   = {Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.-5. June 2015},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-87823},
  pages     = {125 -- 128},
  year      = {2015},
  abstract  = {Macroclumping proved to resolve the discordance between different mass-loss rate diagnostics for O-type stars, in particular between Hα and the P v resonance lines. In this paper, we report first results from a corresponding investigation for WR stars. We apply our detailed 3-D Monte Carlo (MC) line formation code to the P v resonance doublet and show, for the Galactic WNL star WR136, that macroclumping is require to bring this line in accordance with the mass-loss rate derived from the emission-line spectrum.},
  language  = {en}
}
@article{HainichPasemannTodtetal.2015,
  author    = {Hainich, Rainer and Pasemann, Diana and Todt, Helge Tobias and Shenar, Tomer and Sander, Andreas Alexander Christoph and Hamann, Wolf-Rainer},
  title     = {Wolf-Rayet stars in the Small Magellanic Cloud I. Analysis of the single WN stars},
  series = {Astronomy and astrophysics : an international weekly journal},
  volume    = {581},
  journal   = {Astronomy and astrophysics : an international weekly journal},
  publisher = {EDP Sciences},
  address   = {Les Ulis},
  issn      = {1432-0746},
  doi       = {10.1051/0004-6361/201526241},
  pages     = {30},
  year      = {2015},
  abstract  = {Context. Wolf-Rayet (WR) stars have a severe impact on their environments owing to their strong ionizing radiation fields and powerful stellar winds. Since these winds are considered to be driven by radiation pressure, it is theoretically expected that the degree of the wind mass-loss depends on the initial metallicity of WR stars. Aims. Following our comprehensive studies of WR stars in the Milky Way, M31, and the LMC, we derive stellar parameters and mass-loss rates for all seven putatively single WN stars known in the SMC. Based on these data, we discuss the impact of a low-metallicity environment on the mass loss and evolution of WR stars. Methods. The quantitative analysis of the WN stars is performed with the Potsdam Wolf-Rayet (PoWR) model atmosphere code. The physical properties of our program stars are obtained from fitting synthetic spectra to multi-band observations. Results. In all SMC WN stars, a considerable surface hydrogen abundance is detectable. The majority of these objects have stellar temperatures exceeding 75 kK, while their luminosities range from 10(5.5) to 10(6.1) L-circle dot. The WN stars in the SMC exhibit on average lower mass-loss rates and weaker winds than their counterparts in the Milky Way, M31, and the LMC. Conclusions. By comparing the mass-loss rates derived for WN stars in different Local Group galaxies, we conclude that a clear dependence of the wind mass-loss on the initial metallicity is evident, supporting the current paradigm that WR winds are driven by radiation. A metallicity effect on the evolution of massive stars is obvious from the HRD positions of the SMC WN stars at high temperatures and high luminosities. Standard evolution tracks are not able to reproduce these parameters and the observed surface hydrogen abundances. Homogeneous evolution might provide a better explanation for their evolutionary past.},
  language  = {en}
}
@article{ShenarHamannTodt2014,
  author    = {Shenar, Tomer and Hamann, Wolf-Rainer and Todt, Helge Tobias},
  title     = {The impact of rotation on the line profiles of Wolf-Rayet stars},
  series = {Astronomy and astrophysics : an international weekly journal},
  volume    = {562},
  journal   = {Astronomy and astrophysics : an international weekly journal},
  publisher = {EDP Sciences},
  address   = {Les Ulis},
  issn      = {0004-6361},
  doi       = {10.1051/0004-6361/201322496},
  pages     = {13},
  year      = {2014},
  abstract  = {Context. Massive Wolf-Rayet stars are recognized today to be in a very common, but short, evolutionary phase of massive stars. While our understanding of Wolf-Rayet stars has increased dramatically over the past decades, it remains unclear whether rapid rotators are among them. There are various indications that rapidly rotating Wolf-Rayet stars should exist. Unfortunately, due to their expanding atmospheres, rotational velocities of Wolf-Rayet stars are very difficult to measure. However, recently observed spectra of several Wolf-Rayet stars reveal peculiarly broad and round emission lines. Could these spectra imply rapid rotation? Aims. In this work, we model the effects of rotation on the atmospheres of Wolf-Rayet stars. We further investigate whether the peculiar spectra of five Wolf-Rayet stars may be explained with the help of stellar rotation, infer appropriate rotation parameters, and discuss the implications of our results. Methods. We make use of the Potsdam Wolf-Rayet (PoWR) non-LTE model atmosphere code. Since the observed spectra of WolfRayet stars are mainly formed in their expanding atmospheres, rotation must be accounted for with a 3D integration scheme of the formal integral. For this purpose, we assume a rotational velocity field consisting of an inner co-rotating domain and an outer domain, where the angular momentum is conserved. Results. We find that rotation can reproduce the unique spectra analyzed here. However, the inferred rotational velocities at the stellar surface are large (similar to 200 km s(-1)), and the inferred co-rotation radii (similar to 10R.) suggest the existence of very strong photospheric magnetic fields (similar to 20 kG).},
  language  = {en}
}