@article{ShenarSablowskiHainichetal.2019,
  author    = {Shenar, Tomer and Sablowski, D. P. and Hainich, Rainer and Todt, Helge Tobias and Moffat, Anthony F. J. and Oskinova, Lida and Ramachandran, Varsha and Sana, Hugues and Sander, Andreas Alexander Christoph and Schnurr, O. and St-Louis, N. and Vanbeveren, D. and Gotberg, Y. and Hamann, Wolf-Rainer},
  title     = {The Wolf-Rayet binaries of the nitrogen sequence in the Large Magellanic Cloud Spectroscopy, orbital analysis, formation, and evolution},
  series = {Astronomy and astrophysics : an international weekly journal},
  volume    = {627},
  journal   = {Astronomy and astrophysics : an international weekly journal},
  publisher = {EDP Sciences},
  address   = {Les Ulis},
  issn      = {0004-6361},
  doi       = {10.1051/0004-6361/201935684},
  pages     = {68},
  year      = {2019},
  abstract  = {Context. Massive Wolf-Rayet (WR) stars dominate the radiative and mechanical energy budget of galaxies and probe a critical phase in the evolution of massive stars prior to core collapse. It is not known whether core He-burning WR stars (classical WR; cWR) form predominantly through wind stripping (w-WR) or binary stripping (b-WR). Whereas spectroscopy of WR binaries has so-far largely been avoided because of its complexity, our study focuses on the 44 WR binaries and binary candidates of the Large Magellanic Cloud (LMC; metallicity Z approximate to 0.5 Z(circle dot)), which were identified on the basis of radial velocity variations, composite spectra, or high X-ray luminosities. Aims. Relying on a diverse spectroscopic database, we aim to derive the physical and orbital parameters of our targets, confronting evolution models of evolved massive stars at subsolar metallicity and constraining the impact of binary interaction in forming these stars. Methods. Spectroscopy was performed using the Potsdam Wolf-Rayet (PoWR) code and cross-correlation techniques. Disentanglement was performed using the code Spectangular or the shift-and-add algorithm. Evolutionary status was interpreted using the Binary Population and Spectral Synthesis (BPASS) code, exploring binary interaction and chemically homogeneous evolution. Results. Among our sample, 28/44 objects show composite spectra and are analyzed as such. An additional five targets show periodically moving WR primaries but no detected companions (SB1); two (BAT99 99 and 112) are potential WR + compact-object candidates owing to their high X-ray luminosities. We cannot confirm the binary nature of the remaining 11 candidates. About two-thirds of the WN components in binaries are identified as cWR, and one-third as hydrogen-burning WR stars. We establish metallicity-dependent mass-loss recipes, which broadly agree with those recently derived for single WN stars, and in which so-called WN3/O3 stars are clear outliers. We estimate that 45 +/- 30\% of the cWR stars in our sample have interacted with a companion via mass transfer. However, only approximate to 12 +/- 7\% of the cWR stars in our sample naively appear to have formed purely owing to stripping via a companion (12\% b-WR). Assuming that apparently single WR stars truly formed as single stars, this comprises approximate to 4\% of the whole LMC WN population, which is about ten times less than expected. No obvious differences in the properties of single and binary WN stars, whose luminosities extend down to log L approximate to 5.2 [L-circle dot], are apparent. With the exception of a few systems (BAT99 19, 49, and 103), the equatorial rotational velocities of the OB-type companions are moderate (v(eq) less than or similar to 250 km s(-1)) and challenge standard formalisms of angular-momentum accretion. For most objects, chemically homogeneous evolution can be rejected for the secondary, but not for the WR progenitor. Conclusions. No obvious dichotomy in the locations of apparently single and binary WN stars on the Hertzsprung-Russell diagram is apparent. According to commonly used stellar evolution models (BPASS, Geneva), most apparently single WN stars could not have formed as single stars, implying that they were stripped by an undetected companion. Otherwise, it must follow that pre-WR mass-loss/mixing (e.g., during the red supergiant phase) are strongly underestimated in standard stellar evolution models.},
  language  = {en}
}
@article{RamiaramanantsoaRatnasingamShenaretal.2018,
  author    = {Ramiaramanantsoa, Tahina and Ratnasingam, Rathish and Shenar, Tomer and Moffat, Anthony F. J. and Rogers, Tamara M. and Popowicz, Adam and Kuschnig, Rainer and Pigulski, Andrzej and Handler, Gerald and Wade, Gregg A. and Zwintz, Konstanze and Weiss, Werner W.},
  title     = {A BRITE view on the massive O-type supergiant V973 Scorpii},
  series = {Monthly notices of the Royal Astronomical Society},
  volume    = {480},
  journal   = {Monthly notices of the Royal Astronomical Society},
  number    = {1},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0035-8711},
  doi       = {10.1093/mnras/sty1897},
  pages     = {972 -- 986},
  year      = {2018},
  abstract  = {Stochastically triggered photospheric light variations reaching similar to 40 mmag peak-to-valley amplitudes have been detected in the O8 Iaf supergiant V973 Scorpii as the outcome of 2 months of high-precision time-resolved photometric observations with the BRIght Target Explorer (BRITE) nanosatellites. The amplitude spectrum of the time series photometry exhibits a pronounced broad bump in the low-frequency regime (less than or similar to 0.9 d(-1)) where several prominent frequencies are detected. A time-frequency analysis of the observations reveals typical mode lifetimes of the order of 5-10 d. The overall features of the observed brightness amplitude spectrum of V973 Sco match well with those extrapolated from two-dimensional hydrodynamical simulations of convectively driven internal gravity waves randomly excited from deep in the convective cores of massive stars. An alternative or additional possible source of excitation from a sub-surface convection zone needs to be explored in future theoretical investigations.},
  language  = {en}
}
@article{RamiaramanantsoaMoffatHarmonetal.2018,
  author    = {Ramiaramanantsoa, Tahina and Moffat, Anthony F. J. and Harmon, Robert and Ignace, R. and St-Louis, Nicole and Vanbeveren, Dany and Shenar, Tomer and Pablo, Herbert and Richardson, Noel D. and Howarth, Ian D. and Stevens, Ian R. and Piaulet, Caroline and St-Jean, Lucas and Eversberg, Thomas and Pigulski, Andrzej and Popowicz, Adam and Kuschnig, Rainer and Zoclonska, Elzbieta and Buysschaert, Bram and Handler, Gerald and Weiss, Werner W. and Wade, Gregg A. and Rucinski, Slavek M. and Zwintz, Konstanze and Luckas, Paul and Heathcote, Bernard and Cacella, Paulo and Powles, Jonathan and Locke, Malcolm and Bohlsen, Terry and Chen{\´e}, Andr{\´e}-Nicolas and Miszalski, Brent and Waldron, Wayne L. and Kotze, Marissa M. and Kotze, Enrico J. and B{\"o}hm, Torsten},
  title     = {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},
  series = {Monthly notices of the Royal Astronomical Society},
  volume    = {473},
  journal   = {Monthly notices of the Royal Astronomical Society},
  number    = {4},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0035-8711},
  doi       = {10.1093/mnras/stx2671},
  pages     = {5532 -- 5569},
  year      = {2018},
  abstract  = {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.},
  language  = {en}
}
@article{ShenarHainichTodtetal.2018,
  author    = {Shenar, Tomer and Hainich, Rainer and Todt, Helge Tobias and Moffat, Anthony F. J. and Sander, Andreas Alexander Christoph and Oskinova, Lida and Ramachandran, Varsha and Munoz, M. and Pablo, H. and Sana, Hugues and Hamann, Wolf-Rainer},
  title     = {The shortest-period Wolf-Rayet binary in the small magellanic cloud},
  series = {Astronomy and astrophysics : an international weekly journal},
  volume    = {616},
  journal   = {Astronomy and astrophysics : an international weekly journal},
  publisher = {EDP Sciences},
  address   = {Les Ulis},
  issn      = {1432-0746},
  doi       = {10.1051/0004-6361/201833006},
  pages     = {15},
  year      = {2018},
  abstract  = {Context. SMC AB6 is the shortest-period (P = 6.5 d) Wolf-Rayet (WR) binary in the Small Magellanic Cloud. This binary is therefore a key system in the study of binary interaction and formation of WR stars at low metallicity. The WR component in AB6 was previously found to be very luminous (log L = 6.3 [L-circle dot]) compared to its reported orbital mass (approximate to 8 M-circle dot), placing it significantly above the Eddington limit. Aims. Through spectroscopy and orbital analysis of newly acquired optical data taken with the Ultraviolet and Visual Echelle Spectrograph (UVES), we aim to understand the peculiar results reported for this system and explore its evolutionary history. Methods. We measured radial velocities via cross-correlation and performed a spectral analysis using the Potsdam Wolf-Rayet model atmosphere code. The evolution of the system was analyzed using the Binary Population and Spectral Synthesis evolution code. Results. AB6 contains at least four stars. The 6.5 d period WR binary comprises the WR primary (WN3:h, star A) and a rather rapidly rotating (v(eq) = 265 km s(-1)) early O-type companion (O5.5 V, star B). Static N III and N IV emission lines and absorption signatures in He lines suggest the presence of an early-type emission line star (O5.5 I(f), star C). Finally, narrow absorption lines portraying a long-term radial velocity variation show the existence of a fourth star (O7.5 V, star D). Star D appears to form a second 140 d period binary together with a fifth stellar member, which is a B-type dwarf or a black hole. It is not clear that these additional components are bound to the WR binary. We derive a mass ratio of M-O/M-WR = 2.2 +/- 0.1. The WR star is found to be less luminous than previously thought (log L = 5.9 [L-circle dot]) and, adopting M-O = 41 M-circle dot for star B, more massive (M-WR = 18 M-circle dot). Correspondingly, the WR star does not exceed the Eddington limit. We derive the initial masses of M-i,M-WR = 60 M-circle dot and M-i,M-O = 40 M-circle dot and an age of 3.9 Myr for the system. The WR binary likely experienced nonconservative mass transfer in the past supported by the relatively rapid rotation of star B. Conclusions. Our study shows that AB6 is a multiple - probably quintuple - system. This finding resolves the previously reported puzzle of the WR primary exceeding the Eddington limit and suggests that the WR star exchanged mass with its companion in the past.},
  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{RichardsonRussellStJeanetal.2017,
  author    = {Richardson, Noel D. and Russell, Christopher M. P. and St-Jean, Lucas and Moffat, Anthony F. J. and St-Louis, Nicole and Shenar, Tomer and Pablo, Herbert and Hill, Grant M. and Ramiaramanantsoa, Tahina and Corcoran, Michael and Hamuguchi, Kenji and Eversberg, Thomas and Miszalski, Brent and Chene, Andre-Nicolas and Waldron, Wayne and Kotze, Enrico J. and Kotze, Marissa M. and Luckas, Paul and Cacella, Paulo and Heathcote, Bernard and Powles, Jonathan and Bohlsen, Terry and Locke, Malcolm and Handler, Gerald and Kuschnig, Rainer and Pigulski, Andrzej and Popowicz, Adam and Wade, Gregg A. and Weiss, Werner W.},
  title     = {The variability of the BRITE-est Wolf-Rayet binary, gamma(2) Velorum-I. Photometric and spectroscopic evidence for colliding winds},
  series = {Monthly notices of the Royal Astronomical Society},
  volume    = {471},
  journal   = {Monthly notices of the Royal Astronomical Society},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0035-8711},
  doi       = {10.1093/mnras/stx1731},
  pages     = {2715 -- 2729},
  year      = {2017},
  abstract  = {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.},
  language  = {en}
}
@article{AldorettaStLouisRichardsonetal.2016,
  author    = {Aldoretta, E. J. and St-Louis, N. and Richardson, N. D. and Moffat, Anthony F. J. and Eversberg, T. and Hill, G. M. and Shenar, Tomer and Artigau, E. and Gauza, B. and Knapen, J. H. and Kubat, Jiř{\´i} and Kubatova, Brankica and Maltais-Tariant, R. and Munoz, M. and Pablo, H. and Ramiaramanantsoa, T. and Richard-Laferriere, A. and Sablowski, D. P. and Simon-Diaz, S. and St-Jean, L. and Bolduan, F. and Dias, F. M. and Dubreuil, P. and Fuchs, D. and Garrel, T. and Grutzeck, G. and Hunger, T. and Kuesters, D. and Langenbrink, M. and Leadbeater, R. and Li, D. and Lopez, A. and Mauclaire, B. and Moldenhawer, T. and Potter, M. and dos Santos, E. M. and Schanne, L. and Schmidt, J. and Sieske, H. and Strachan, J. and Stinner, E. and Stinner, P. and Stober, B. and Strandbaek, K. and Syder, T. and Verilhac, D. and Waldschlaeger, U. and Weiss, D. and Wendt, A.},
  title     = {An extensive spectroscopic time series of three Wolf-Rayet stars - I. The lifetime of large-scale structures in the wind of WR 134},
  series = {Monthly notices of the Royal Astronomical Society},
  volume    = {460},
  journal   = {Monthly notices of the Royal Astronomical Society},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0035-8711},
  doi       = {10.1093/mnras/stw1188},
  pages     = {3407 -- 3417},
  year      = {2016},
  abstract  = {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.},
  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{ShenarHainichTodtetal.2016,
  author    = {Shenar, Tomer and Hainich, Rainer and Todt, Helge Tobias and Sander, Andreas Alexander Christoph and Hamann, Wolf-Rainer and Moffat, Anthony F. J. and Eldridge, J. J. and Pablo, H. and Oskinova, Lida and Richardson, N. D.},
  title     = {Wolf-Rayet stars in the Small Magellanic Cloud II. Analysis of the binaries},
  series = {American mineralogist : an international journal of earth and planetary materials},
  volume    = {591},
  journal   = {American mineralogist : an international journal of earth and planetary materials},
  publisher = {EDP Sciences},
  address   = {Les Ulis},
  issn      = {1432-0746},
  doi       = {10.1051/0004-6361/201527916},
  pages     = {25},
  year      = {2016},
  abstract  = {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.},
  language  = {en}
}
@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{EversbergAldorettaKnapenetal.2015,
  author    = {Eversberg, T. and Aldoretta, E. J. and Knapen, J. H. and Moffat, Anthony F. J. and Morel, T. and Ramiaramanantsoa, T. and Rauw, G. and Richardson, N. D. and St-Louis, N. and Teodoro, M.},
  title     = {World-wide amateur observations},
  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-opus4-87705},
  pages     = {71 -- 74},
  year      = {2015},
  abstract  = {For some years now, spectroscopic measurements of massive stars in the amateur domain have been fulfilling professional requirements. Various groups in the northern and southern hemispheres have been established, running successful professional-amateur (ProAm) collaborative campaigns, e.g., on WR, O and B type stars. Today high quality data (echelle and long-slit) are regularly delivered and corresponding results published. Night-to-night long-term observations over months to years open a new opportunity for massive-star research. We introduce recent and ongoing sample campaigns (e.g. ∊ Aur, WR 134, ζ Pup), show respective results and highlight the vast amount of data collected in various data bases. Ultimately it is in the time-dependent domain where amateurs can shine most.},
  language  = {en}
}
@article{MunozMoffatHilletal.2015,
  author    = {Munoz, M. and Moffat, Anthony F. J. and Hill, G. M. and Richardson, N. D. and Pablo, H.},
  title     = {The missing Wolf-Rayet X-ray binary systems},
  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-opus4-88082},
  pages     = {225 -- 228},
  year      = {2015},
  abstract  = {We investigate the rarity of the Wolf-Rayet X-ray binaries (WRXRBs) in contrast to their predecessors, the high mass X-ray binaries (HMXRBs). Recent studies suggest that common envelope (CE) mergers during the evolution of a HMXRBs may be responsible (Linden et al. 2012). We conduct a binary population synthesis to generate a population of HMXRBs mimicking the Galactic sample and vary the efficiency parameter during the CE phase to match the current WRXRB to HMXRB ratio. We find that ∼50\% of systems must merge to match observational constraints.},
  language  = {en}
}
@article{KanarekSharaFahertyetal.2015,
  author    = {Kanarek, G. and Shara, M. and Faherty, J. and Zurek, D. and Moffat, Anthony F. J.},
  title     = {New Galactic 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-opus4-88448},
  pages     = {359},
  year      = {2015},
  abstract  = {Over the course of 6 months in 2013, we observed nearly 400 Wolf-Rayet candidates in the Galactic plane. Preliminary results from this dataset are presented.},
  language  = {en}
}
@article{BibbySharaZureketal.2015,
  author    = {Bibby, J. and Shara, M. and Zurek, D. and Crowther, P. A. and Moffat, Anthony F. J. and Drissen, L. and Wilde, M.},
  title     = {The Distribution of Massive Stars in M101},
  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-opus4-88402},
  pages     = {355},
  year      = {2015},
  abstract  = {75 WR stars and 164 RSGs are identified in a single WFC3 pointing of our M101 survey. We find that within it's large star-forming complex NGC 5462 WR stars are preferentially located in the core whilst RSGs are found in the halo, suggesting two bursts of star-formation. A review of our WR candidates reveals that only ∼30\% are detected in the archival broad-band ACS imaging whilst only ∼50\% are associated with HII regions.},
  language  = {en}
}
@article{Moffat2015,
  author    = {Moffat, Anthony F. J.},
  title     = {General overview 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-opus4-87552},
  pages     = {13 -- 18},
  year      = {2015},
  abstract  = {Although we all use the name Wolf-Rayet to refer to specific groups of stars, "Wolf-Rayet" per se is really an astrophysical phenomenon of fast-moving, hot plasma, normally expanding around a hot star. However, expediency demands that we follow established traditions by referring to three specific kinds of WR stars: (1) cWR, "classical" He-burning descendants of massive, O-type stars, presumably all of which pass through a WR stage; (2) WNh, the most massive and luminous hydrogen-rich main-sequence stars with strong winds; and (3) [WR], the central stars of some 15 \% of Planetary Nebulae. Wolf-Rayet stars are the epitome of relatively stable stars with the highest mass-loss rates for their kind. It behooves us to understand the what, how and why of this circumstance, along with its manyfold and fascinating consequences.},
  language  = {en}
}
@article{AldorettaStLouisRichardsonetal.2015,
  author    = {Aldoretta, E. J. and St-Louis, N. and Richardson, N. D. and Moffat, Anthony F. J. and Eversberg, T. and Hill, G. M.},
  title     = {The Results of the 2013 Pro-Am Wolf-Rayet Campaign},
  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-opus4-87713},
  pages     = {75 -- 78},
  year      = {2015},
  abstract  = {Professional and amateur astronomers around the world contributed to a 4-month long campaign in 2013, mainly in spectroscopy but also in photometry, interferometry and polarimetry, to observe the first 3 Wolf-Rayet stars discovered: WR 134 (WN6b), WR 135 (WC8) and WR 137 (WC7pd+O9). Each of these stars are interesting in their own way, showing a variety of stellar wind structures. The spectroscopic data from this campaign were reduced and analyzed for WR 134 in order to better understand its behavior and long-term periodicity in the context of CIRs in the wind. We will be presenting the results of these spectroscopic data, which include the confirmation of the CIR variability and a time-coherency of ∼ 40 days (half-life of ∼ 20 days).},
  language  = {en}
}
@article{PabloMoffat2015,
  author    = {Pablo, H. and Moffat, Anthony F. J.},
  title     = {WR Time Series Photometry},
  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-opus4-88031},
  pages     = {205 -- 208},
  year      = {2015},
  abstract  = {We take a comprehensive look at Wolf Rayet photometric variability using the MOST satellite. This sample, consisting of 6 WR stars and 6 WC stars defies all typical photometric analysis. We do, however, confirm the presence of unusual periodic signals resembling sawtooth waves which are present in 11 out of 12 stars in this sample.},
  language  = {en}
}
@article{PabloRichardsonMoffatetal.2015,
  author    = {Pablo, Herbert and Richardson, Noel D. and Moffat, Anthony F. J. and Corcoran, Michael and Shenar, Tomer and Benvenuto, Omar and Fuller, Jim and Naze, Yael and Hoffman, Jennifer L. and Miroshnichenko, Anatoly and Apellaniz, Jesus Maiz and Evans, Nancy and Eversberg, Thomas and Gayley, Ken and Gull, Ted and Hamaguchi, Kenji and Hamann, Wolf-Rainer and Henrichs, Huib and Hole, Tabetha and Ignace, Richard and Iping, Rosina and Lauer, Jennifer and Leutenegger, Maurice and Lomax, Jamie and Nichols, Joy and Oskinova, Lida and Owocki, Stan and Pollock, Andy and Russell, Christopher M. P. and Waldron, Wayne and Buil, Christian and Garrel, Thierry and Graham, Keith and Heathcote, Bernard and Lemoult, Thierry and Li, Dong and Mauclaire, Benjamin and Potter, Mike and Ribeiro, Jose and Matthews, Jaymie and Cameron, Chris and Guenther, David and Kuschnig, Rainer and Rowe, Jason and Rucinski, Slavek and Sasselov, Dimitar and Weiss, Werner},
  title     = {A coordinated X-Ray and optical campaign of the nearest massive eclipsing binary, delta ORIONIS Aa. III. Analysis of optical photometric (most) and spectroscopic (ground based) variations},
  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/809/2/134},
  pages     = {11},
  year      = {2015},
  abstract  = {We report on both high-precision photometry from the Microvariability and Oscillations of Stars (MOST) space telescope and ground-based spectroscopy of the triple system delta Ori A, consisting of a binary O9.5II+early-B (Aa1 and Aa2) with P = 5.7 days, and a more distant tertiary (O9 IV P > 400 years). This data was collected in concert with X-ray spectroscopy from the Chandra X-ray Observatory. Thanks to continuous coverage for three weeks, the MOST light curve reveals clear eclipses between Aa1 and Aa2 for the first time in non-phased data. From the spectroscopy, we have a well-constrained radial velocity (RV) curve of Aa1. While we are unable to recover RV variations of the secondary star, we are able to constrain several fundamental parameters of this system and determine an approximate mass of the primary using apsidal motion. We also detected second order modulations at 12 separate frequencies with spacings indicative of tidally influenced oscillations. These spacings have never been seen in a massive binary, making this system one of only a handful of such binaries that show evidence for tidally induced pulsations.},
  language  = {en}
}
@article{ShenarOskinovaHamannetal.2015,
  author    = {Shenar, Tomer and Oskinova, Lida and Hamann, Wolf-Rainer and Corcoran, Michael F. and Moffat, Anthony F. J. and Pablo, Herbert and Richardson, Noel D. and Waldron, Wayne L. and Huenemoerder, David P. and Maiz Apellaniz, Jesus and Nichols, Joy S. and Todt, Helge Tobias and Naze, Yael and Hoffman, Jennifer L. and Pollock, Andy M. T. and Negueruela, Ignacio},
  title     = {A coordinated X-Ray and optical campaign of the nearest massive eclipsing binary, delta ORIONIS Aa. IV. A multiwavelength, non-lte spectroscopic analysis},
  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/809/2/135},
  pages     = {20},
  year      = {2015},
  abstract  = {Eclipsing systems of massive stars allow one to explore the properties of their components in great detail. We perform a multi-wavelength, non-LTE analysis of the three components of the massive multiple system delta Ori A, focusing on the fundamental stellar properties, stellar winds, and X-ray characteristics of the system. The primary's distance-independent parameters turn out to be characteristic for its spectral type (O9.5 II), but usage of the Hipparcos parallax yields surprisingly low values for the mass, radius, and luminosity. Consistent values follow only if delta Ori lies at about twice the Hipparcos distance, in the vicinity of the sigma-Orionis cluster. The primary and tertiary dominate the spectrum and leave the secondary only marginally detectable. We estimate the V-band magnitude difference between primary and secondary to be Delta V approximate to 2.(m)8. The inferred parameters suggest that the secondary is an early B-type dwarf (approximate to B1 V), while the tertiary is an early B-type subgiant (approximate to B0 IV). We find evidence for rapid turbulent velocities (similar to 200 km s(-1)) and wind inhomogeneities, partially optically thick, in the primary's wind. The bulk of the X-ray emission likely emerges from the primary's stellar wind (logL(X)/L-Bol approximate to -6.85), initiating close to the stellar surface at R-0 similar to 1.1 R-*. Accounting for clumping, the mass-loss rate of the primary is found to be log (M) over dot approximate to -6.4 (M-circle dot yr(-1))., which agrees with hydrodynamic predictions, and provides a consistent picture along the X-ray, UV, optical, and radio spectral domains.},
  language  = {en}
}
@article{NicholsHuenemoerderCorcoranetal.2015,
  author    = {Nichols, Joy and Huenemoerder, David P. and Corcoran, Michael F. and Waldron, Wayne and Naze, Yael and Pollock, Andy M. T. and Moffat, Anthony F. J. and Lauer, Jennifer and Shenar, Tomer and Russell, Christopher M. P. and Richardson, Noel D. and Pablo, Herbert and Evans, Nancy Remage and Hamaguchi, Kenji and Gull, Theodore and Hamann, Wolf-Rainer and Oskinova, Lida and Ignace, Rosina and Hoffman, Jennifer L. and Hole, Karen Tabetha and Lomax, Jamie R.},
  title     = {A COORDINATED X-RAY AND OPTICAL CAMPAIGN OF THE NEAREST MASSIVE ECLIPSING BINARY, delta ORIONIS Aa. II. X-RAY VARIABILITY},
  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/809/2/133},
  pages     = {21},
  year      = {2015},
  abstract  = {We present time-resolved and phase-resolved variability studies of an extensive X-ray high-resolution spectral data set of the delta Ori Aa binary system. The four observations, obtained with Chandra ACIS HETGS, have a total exposure time of approximate to 479 ks and provide nearly complete binary phase coverage. Variability of the total X-ray flux in the range of 5-25 is is confirmed, with a maximum amplitude of about +/- 15\% within a single approximate to 125 ks observation. Periods of 4.76 and 2.04 days are found in the total X-ray flux, as well as an apparent overall increase in the flux level throughout the nine-day observational campaign. Using 40 ks contiguous spectra derived from the original observations, we investigate the variability of emission line parameters and ratios. Several emission lines are shown to be variable, including S XV, Si XIII, and Ne IX. For the first time, variations of the X-ray emission line widths as a function of the binary phase are found in a binary system, with the smallest widths at phi = 0.0 when the secondary delta Ori Aa2 is at the inferior conjunction. Using 3D hydrodynamic modeling of the interacting winds, we relate the emission line width variability to the presence of a wind cavity created by a wind-wind collision, which is effectively void of embedded wind shocks and is carved out of the X-ray-producing primary wind, thus producing phase-locked X-ray variability.},
  language  = {en}
}