TY  - JOUR
A1  - Munoz, Melissa
A1  - Moffat, Anthony F. J.
A1  - Hill, Grant M.
A1  - Shenar, Tomer
A1  - Richardson, Noel D.
A1  - Pablo, Herbert
A1  - St-Louis, Nicole
A1  - Ramiaramanantsoa, Tahina
T1  - WR 148: identifying the companion of an extreme runaway massive binary
JF  - Monthly notices of the Royal Astronomical Society
N2  - 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 km s−1 and 79.2 ± 3.1 km s−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 ∼67°, derived from previous polarimetry observations, the system's total mass would be a mere 2–3M⊙⁠, an unprecedented result for a putative massive binary system. However, a system comprising a 37M⊙ secondary (typical mass of an O5V star) and a 33M⊙ primary (given the mass ratio) would infer an inclination of ∼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 km s−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.
KW  - binaries: spectroscopic
KW  - stars: individual: WR 148
KW  - stars: kinematics and dynamics
KW  - stars: mass-loss
KW  - stars: winds, outflows
KW  - stars: Wolf-Rayet
Y1  - 2017
U6  - https://doi.org/10.1093/mnras/stw2283
SN  - 0035-8711
SN  - 1365-2966
VL  - 467
SP  - 3105
EP  - 3121
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
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  - Hainich, Rainer
A1  - Pasemann, Diana
A1  - Todt, Helge Tobias
A1  - Shenar, Tomer
A1  - Sander, Andreas Alexander Christoph
A1  - Hamann, Wolf-Rainer
T1  - Wolf-Rayet stars in the Small Magellanic Cloud I. Analysis of the single WN stars
JF  - Astronomy and astrophysics : an international weekly journal
N2  - 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.
KW  - stars: Wolf-Rayet
KW  - Magellanic Clouds
KW  - stars: early-type
KW  - stars: atmospheres
KW  - stars: winds, outflows
KW  - stars: mass-loss
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201526241
SN  - 1432-0746
VL  - 581
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Shenar, Tomer
A1  - Sablowski, D. P.
A1  - Hainich, Rainer
A1  - Todt, Helge Tobias
A1  - Moffat, Anthony F. J.
A1  - Oskinova, Lida
A1  - Ramachandran, Varsha
A1  - Sana, Hugues
A1  - Sander, Andreas Alexander Christoph
A1  - Schnurr, O.
A1  - St-Louis, N.
A1  - Vanbeveren, D.
A1  - Gotberg, Y.
A1  - Hamann, Wolf-Rainer
T1  - The Wolf-Rayet binaries of the nitrogen sequence in the Large Magellanic Cloud Spectroscopy, orbital analysis, formation, and evolution
JF  - Astronomy and astrophysics : an international weekly journal
N2  - 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.
KW  - stars: massive
KW  - stars: Wolf-Rayet
KW  - Magellanic Clouds
KW  - binaries: close
KW  - binaries: spectroscopic
KW  - stars: evolution
Y1  - 2019
U6  - https://doi.org/10.1051/0004-6361/201935684
SN  - 0004-6361
SN  - 1432-0746
VL  - 627
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
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  - Almeida, Leonardo A.
A1  - Sana, H.
A1  - Taylor, W.
A1  - Barbá, Rodolfo
A1  - Bonanos, Alceste Z.
A1  - Crowther, Paul
A1  - Damineli, Augusto
A1  - de Koter, A.
A1  - de Mink, Selma E.
A1  - Evans, C. J.
A1  - Gieles, Mark
A1  - Grin, Nathan J.
A1  - Hénault-Brunet, V.
A1  - Langer, Norbert
A1  - Lennon, D.
A1  - Lockwood, Sean
A1  - Maíz Apellániz, Jesús
A1  - Moffat, A. F. J.
A1  - Neijssel, C.
A1  - Norman, C.
A1  - Ramírez-Agudelo, O. H.
A1  - Richardson, N. D.
A1  - Schootemeijer, Abel
A1  - Shenar, Tomer
A1  - Soszyński, Igor
A1  - Tramper, Frank
A1  - Vink, J. S.
T1  - The tarantula massive binary monitoring
BT  - I. Observational campaign and OB-type spectroscopic binaries
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context:
Massive binaries play a crucial role in the Universe. Knowing the distributions of their orbital parameters is important for a wide range of topics from stellar feedback to binary evolution channels and from the distribution of supernova types to gravitational wave progenitors, yet no direct measurements exist outside the Milky Way.
Aims:
The Tarantula Massive Binary Monitoring project was designed to help fill this gap by obtaining multi-epoch radial velocity (RV) monitoring of 102 massive binaries in the 30 Doradus region.
Methods: 
In this paper we analyze 32 FLAMES/GIRAFFE observations of 93 O- and 7 B-type binaries. We performed a Fourier analysis and obtained orbital solutions for 82 systems: 51 single-lined (SB1) and 31 double-lined (SB2) spectroscopic binaries.
Results: 
Overall, the binary fraction and orbital properties across the 30 Doradus region are found to be similar to existing Galactic samples. This indicates that within these domains environmental effects are of second order in shaping the properties of massive binary systems. A small difference is found in the distribution of orbital periods, which is slightly flatter (in log space) in 30 Doradus than in the Galaxy, although this may be compatible within error estimates and differences in the fitting methodology. Also, orbital periods in 30 Doradus can be as short as 1.1 d, somewhat shorter than seen in Galactic samples. Equal mass binaries (q> 0.95) in 30 Doradus are all found outside NGC 2070, the central association that surrounds R136a, the very young and massive cluster at 30 Doradus’s core. Most of the differences, albeit small, are compatible with expectations from binary evolution. One outstanding exception, however, is the fact that earlier spectral types (O2–O7) tend to have shorter orbital periods than later spectral types (O9.2–O9.7).
Conclusions: 
Our results point to a relative universality of the incidence rate of massive binaries and their orbital properties in the metallicity range from solar (Z⊙) to about half solar. This provides the first direct constraints on massive binary properties in massive star-forming galaxies at the Universe’s peak of star formation at redshifts z ~ 1 to 2 which are estimated to have Z ~ 0.5 Z⊙.
KW  - stars: early-type
KW  - stars: massive
KW  - binaries: spectroscopic
KW  - binaries: close
Y1  - 2017
U6  - https://doi.org/10.1051/0004-6361/201629844
SN  - 1432-0746
VL  - 598
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Shenar, Tomer
A1  - Richardson, N. D.
A1  - Sablowski, Daniel P.
A1  - Hainich, Rainer
A1  - Sana, H.
A1  - Moffat, A. F. J.
A1  - Todt, Helge Tobias
A1  - Hamann, Wolf-Rainer
A1  - Oskinova, Lida
A1  - Sander, Andreas Alexander Christoph
A1  - Tramper, Frank
A1  - Langer, Norbert
A1  - Bonanos, Alceste Z.
A1  - de Mink, Selma E.
A1  - Gräfener, G.
A1  - Crowther, Paul
A1  - Vink, J. S.
A1  - Almeida, Leonardo A.
A1  - de Koter, A.
A1  - Barbá, Rodolfo
A1  - Herrero, A.
A1  - Ulaczyk, Krzysztof
T1  - The tarantula massive binary monitoring
BT  - II. First SB2 orbital and spectroscopic analysis for the Wolf-Rayet binary R145
JF  - Astronomy and astrophysics : an international weekly journal
N2  - We present the first SB2 orbital solution and disentanglement of the massive Wolf-Rayet binary R145 (P = 159 d) located in the Large Magellanic Cloud. The primary was claimed to have a stellar mass greater than 300 M-circle dot, making it a candidate for being the most massive star known to date. While the primary is a known late-type, H-rich Wolf-Rayet star (WN6h), the secondary has so far not been unambiguously detected. Using moderate-resolution spectra, we are able to derive accurate radial velocities for both components. By performing simultaneous orbital and polarimetric analyses, we derive the complete set of orbital parameters, including the inclination. The spectra are disentangled and spectroscopically analyzed, and an analysis of the wind-wind collision zone is conducted. The disentangled spectra and our models are consistent with a WN6h type for the primary and suggest that the secondary is an O3.5 If*/WN7 type star. We derive a high eccentricity of e = 0 : 78 and minimum masses of M-1 sin(3) i approximate to M-2 sin(3) i = 13 +/- 2 M-circle dot, with q = M-2/M-1 = 1.01 +/- 0.07. An analysis of emission excess stemming from a wind-wind collision yields an inclination similar to that obtained from polarimetry (i = 39 +/- 6 degrees). Our analysis thus implies M-1 = 53(-20)(+40) and M2 = 54(-20)(+40) M-circle dot, excluding M-1 > 300 M-circle dot. A detailed comparison with evolution tracks calculated for single and binary stars together with the high eccentricity suggests that the components of the system underwent quasi-homogeneous evolution and avoided mass-transfer. This scenario would suggest current masses of approximate to 80 M-circle dot and initial masses of M-i,M-1 approximate to 10(5) and M-i,M-2 approximate to 90 M-circle dot, consistent with the upper limits of our derived orbital masses, and would imply an age of approximate to 2.2 Myr.
KW  - binaries: spectroscopic
KW  - stars: Wolf-Rayet
KW  - stars: massive
KW  - Magellanic Clouds
KW  - stars: individual: R 145
KW  - stars: atmospheres
Y1  - 2017
U6  - https://doi.org/10.1051/0004-6361/201629621
SN  - 1432-0746
VL  - 598
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Shenar, Tomer
A1  - Hainich, Rainer
A1  - Todt, Helge Tobias
A1  - Moffat, Anthony F. J.
A1  - Sander, Andreas Alexander Christoph
A1  - Oskinova, Lida
A1  - Ramachandran, Varsha
A1  - Munoz, M.
A1  - Pablo, H.
A1  - Sana, Hugues
A1  - Hamann, Wolf-Rainer
T1  - The shortest-period Wolf-Rayet binary in the small magellanic cloud
BT  - Part of a high-order multiple system Spectral and orbital analysis of SMC AB 6
JF  - Astronomy and astrophysics : an international weekly journal
N2  - 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.
KW  - stars: massive
KW  - binaries: spectroscopic
KW  - stars: Wolf-Rayet
KW  - Magellanic Clouds
KW  - stars: individual: SMC AB 6
KW  - stars: atmospheres
Y1  - 2018
U6  - https://doi.org/10.1051/0004-6361/201833006
SN  - 1432-0746
SN  - 0004-6361
VL  - 616
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Shenar, Tomer
A1  - Hamann, Wolf-Rainer
A1  - Todt, Helge Tobias
T1  - The impact of rotation on the line profiles of Wolf-Rayet stars
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - 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).
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88008
SP  - 193
EP  - 196
ER  - 
TY  - JOUR
A1  - Shenar, Tomer
A1  - Hamann, Wolf-Rainer
A1  - Todt, Helge Tobias
T1  - The impact of rotation on the line profiles of Wolf-Rayet stars
JF  - Astronomy and astrophysics : an international weekly journal
N2  - 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).
KW  - stars: Wolf-Rayet
KW  - Magellanic Clouds
KW  - stars: magnetic field
KW  - stars: massive
KW  - gamma-ray burst: general
KW  - stars: rotation
Y1  - 2014
U6  - https://doi.org/10.1051/0004-6361/201322496
SN  - 0004-6361
SN  - 1432-0746
VL  - 562
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Hamann, Wolf-Rainer
A1  - Gräfener, G.
A1  - Liermann, A.
A1  - Hainich, Rainer
A1  - Sander, Andreas Alexander Christoph
A1  - Shenar, Tomer
A1  - Ramachandran, Varsha
A1  - Todt, Helge Tobias
A1  - Oskinova, Lida
T1  - The Galactic WN stars revisited
BT  - Impact of Gaia distances on fundamental stellar parameters
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Comprehensive spectral analyses of the Galactic Wolf-Rayet stars of the nitrogen sequence (i.e. the WN subclass) have been performed in a previous paper. However, the distances of these objects were poorly known. Distances have a direct impact on the "absolute" parameters, such as luminosities and mass-loss rates. The recent Gaia Data Release (DR2) of trigonometric parallaxes includes nearly all WN stars of our Galactic sample. In the present paper, we apply the new distances to the previously analyzed Galactic WN stars and rescale the results accordingly. On this basis, we present a revised catalog of 55 Galactic WN stars with their stellar and wind parameters. The correlations between mass-loss rate and luminosity show a large scatter, for the hydrogen-free WN stars as well as for those with detectable hydrogen. The slopes of the log L - log M correlations are shallower than found previously. The empirical Hertzsprung-Russell diagram (HRD) still shows the previously established dichotomy between the hydrogen-free early WN subtypes that are located on the hot side of the zero-age main sequence (ZAMS), and the late WN subtypes, which show hydrogen and reside mostly at cooler temperatures than the ZAMS (with few exceptions). However, with the new distances, the distribution of stellar luminosities became more continuous than obtained previously. The hydrogen-showing stars of late WN subtype are still found to be typically more luminous than the hydrogen-free early subtypes, but there is a range of luminosities where both subclasses overlap. The empirical HRD of the Galactic single WN stars is compared with recent evolutionary tracks. Neither these single-star evolutionary models nor binary scenarios can provide a fully satisfactory explanation for the parameters of these objects and their location in the HRD.
KW  - stars: mass-loss
KW  - stars: winds, outflows
KW  - stars: Wolf-Rayet
KW  - stars: atmospheres
KW  - stars: evolution
KW  - stars: distances
Y1  - 2019
U6  - https://doi.org/10.1051/0004-6361/201834850
SN  - 1432-0746
VL  - 625
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Sander, Andreas Alexander Christoph
A1  - Hamann, Wolf-Rainer
A1  - Todt, Helge Tobias
A1  - Hainich, Rainer
A1  - Shenar, Tomer
A1  - Ramachandran, Varsha
A1  - Oskinova, Lida
T1  - The Galactic WC and WO stars
BT  - The impact of revised distances from Gaia DR2 and their role as massive black hole progenitors
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Wolf-Rayet stars of the carbon sequence (WC stars) are an important cornerstone in the late evolution of massive stars before their core collapse. As core-helium burning, hydrogen-free objects with huge mass-loss, they are likely the last observable stage before collapse and thus promising progenitor candidates for type Ib/c supernovae. Their strong mass-loss furthermore provides challenges and constraints to the theory of radiatively driven winds. Thus, the determination of the WC star parameters is of major importance for several astrophysical fields. With Gaia DR2, for the first time parallaxes for a large sample of Galactic WC stars are available, removing major uncertainties inherent to earlier studies. In this work, we re-examine a previously studied sample of WC stars to derive key properties of the Galactic WC population. All quantities depending on the distance are updated, while the underlying spectral analyzes remain untouched. Contrasting earlier assumptions, our study yields that WC stars of the same subtype can significantly vary in absolute magnitude. With Gaia DR2, the picture of the Galactic WC population becomes more complex: We obtain luminosities ranging from log L/L-circle dot = 4.9-6.0 with one outlier (WR 119) having log L/L-circle dot = 4.7. This indicates that the WC stars are likely formed from a broader initial mass range than previously assumed. We obtain mass-loss rates ranging between log(M) over dot = -5.1 and -4.1, with (M) over dot proportional to L-0.68 and a linear scaling of the modified wind momentum with luminosity. We discuss the implications for stellar evolution, including unsolved issues regarding the need of envelope inflation to address the WR radius problem, and the open questions in regard to the connection of WR stars with Gamma-ray bursts. WC and WO stars are progenitors of massive black holes, collapsing either silently or in a supernova that most-likely has to be preceded by a WO stage.
KW  - stars: evolution
KW  - stars: mass-loss
KW  - stars: Wolf-Rayet
KW  - stars: massive
KW  - stars: distances
KW  - Galaxy: stellar content
Y1  - 2019
U6  - https://doi.org/10.1051/0004-6361/201833712
SN  - 1432-0746
VL  - 621
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Gruner, David
A1  - Hainich, Rainer
A1  - Sander, Andreas Alexander Christoph
A1  - Shenar, Tomer
A1  - Todt, Helge Tobias
A1  - Oskinova, Lida
A1  - Ramachandran, Varsha
A1  - Ayres, T.
A1  - Hamann, Wolf-Rainer
T1  - The extreme O-type spectroscopic binary HD 93129A A quantitative, multiwavelength analysis
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. HD 93129A was classified as the earliest O-type star in the Galaxy (O2 If*) and is considered as the prototype of its spectral class. However, interferometry shows that this object is a binary system, while recent observations even suggest a triple configuration. None of the previous spectral analyses of this object accounted for its multiplicity. With new high-resolution UV and optical spectra, we have the possibility to reanalyze this key object, taking its binary nature into account for the first time. Aims. We aim to derive the fundamental parameters and the evolutionary status of HD 93129A, identifying the contributions of both components to the composite spectrum Results. Despite the similar spectral types of the two components, we are able to find signatures from each of the components in the combined spectrum, which allows us to estimate the parameters of both stars. We derive log(L/L-circle dot) = 6.15, T-eff = 52 kK, and log (M)over dot = -4.7[M-circle dot yr(-1)] for the primary Aa, and log(L/L-circle dot) = 5.58, T-eff = 45 kK, and log (M)over dot = -5.8 [M(circle dot)yr(-1)] for the secondary Ab. Conclusions. Even when accounting for the binary nature, the primary of HD 93129A is found to be one of the hottest and most luminous O stars in our Galaxy. Based on the theoretical decomposition of the spectra, we assign spectral types O2 If* and O3 III(f*) to components Aa and Ab, respectively. While we achieve a good fit for a wide spectral range, specific spectral features are not fully reproduced. The data are not sufficient to identify contributions from a hypothetical third component in the system.
KW  - stars: individual: HD 93129A
KW  - stars: atmospheres
KW  - stars: fundamental parameters
KW  - stars: early-typeP
Y1  - 2018
U6  - https://doi.org/10.1051/0004-6361/201833178
SN  - 1432-0746
VL  - 621
PB  - EDP Sciences
CY  - Les Ulis
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  - 
TY  - JOUR
A1  - Ramachandran, Varsha
A1  - Hamann, Wolf-Rainer
A1  - Oskinova, Lida
A1  - Gallagher, J. S.
A1  - Hainich, Rainer
A1  - Shenar, Tomer
A1  - Sander, Andreas Alexander Christoph
A1  - Todt, Helge Tobias
A1  - Fulmer, Leah M.
T1  - Testing massive star evolution, star formation history, and feedback at low metallicity
BT  - Spectroscopic analysis of OB stars in the SMC Wing
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Stars that start their lives with spectral types O and early B are the progenitors of core-collapse supernovae, long gamma-ray bursts, neutron stars, and black holes. These massive stars are the primary sources of stellar feedback in star-forming galaxies. At low metallicities, the properties of massive stars and their evolution are not yet fully explored. Here we report a spectroscopic study of 320 massive stars of spectral types O (23 stars) and B (297 stars) in the Wing of the Small Magellanic Cloud (SMC). The spectra, which we obtained with the ESO Very Large Telescope, were analyzed using state-of-the-art stellar atmosphere models, and the stellar parameters were determined. We find that the stellar winds of our sample stars are generally much weaker than theoretically expected. The stellar rotation rates show broad, tentatively bimodal distributions. The upper Hertzsprung-Russell diagram (HRD) is well populated by the stars of our sample from a specific field in the SMC Wing. A few very luminous O stars are found close to the main sequence, while all other, slightly evolved stars obey a strict luminosity limit. Considering additional massive stars in evolved stages, with published parameters and located all over the SMC, essentially confirms this picture. The comparison with single-star evolutionary tracks suggests a dichotomy in the fate of massive stars in the SMC. Only stars with an initial mass below similar to 30 M-circle dot seem to evolve from the main sequence to the cool side of the HRD to become a red supergiant and to explode as type II-P supernova. In contrast, stars with initially more than similar to 30 M-circle dot appear to stay always hot and might evolve quasi chemically homogeneously, finally collapsing to relatively massive black holes. However, we find no indication that chemical mixing is correlated with rapid rotation. We measured the key parameters of stellar feedback and established the links between the rates of star formation and supernovae. Our study demonstrates that in metal-poor environments stellar feedback is dominated by core-collapse supernovae in combination with winds and ionizing radiation supplied by a few of the most massive stars. We found indications of the stochastic mode of massive star formation, where the resulting stellar population is fully capable of producing large-scale structures such as the supergiant shell SMC-SGS 1 in the Wing. The low level of feedback in metal-poor stellar populations allows star formation episodes to persist over long timescales.
KW  - stars: evolution
KW  - stars: massive
KW  - stars: mass-loss
KW  - Magellanic Clouds
KW  - Hertzsprung-Russell and C-M diagrams
KW  - techniques: spectroscopic
Y1  - 2019
U6  - https://doi.org/10.1051/0004-6361/201935365
SN  - 1432-0746
VL  - 625
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Ramachandran, Varsha
A1  - Hamann, Wolf-Rainer
A1  - Hainich, Rainer
A1  - Oskinova, Lida
A1  - Shenar, Tomer
A1  - Sander, Andreas Alexander Christoph
A1  - Todt, Helge Tobias
A1  - Gallagher, John S.
T1  - Stellar population of the superbubble N206 in the LMC II. Parameters of the OB and WR stars, and the total massive star feedback
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. Clusters or associations of early-type stars are often associated with a "superbubble" of hot gas. The formation of such superbubbles is caused by the feedback from massive stars. The complex N206 in the Large Magellanic Cloud (LMC) exhibits a superbubble and a rich massive star population. Aims. Our goal is to perform quantitative spectral analyses of all massive stars associated with the N206 superbubble in order to determine their stellar and wind parameters. We compare the superbubble energy budget to the stellar energy input and discuss the star formation history of the region. Results. We present the stellar and wind parameters of the OB stars and the two Wolf-Rayet (WR) binaries in the N206 complex. Twelve percent of the sample show Oe/Be type emission lines, although most of them appear to rotate far below critical. We found eight runaway stars based on their radial velocity. The wind-momentum luminosity relation of our OB sample is consistent with the expectations. The Hertzsprung-Russell diagram (HRD) of the OB stars reveals a large age spread (1-30 Myr), suggesting different episodes of star formation in the complex. The youngest stars are concentrated in the inner part of the complex, while the older OB stars are scattered over outer regions. We derived the present day mass function for the entire N206 complex as well as for the cluster NGC2018. The total ionizing photon flux produced by all massive stars in the N206 complex is Q(0) approximate to 5 x 10(50) s(-1), and the mechanical luminosity of their stellar winds amounts to L-mec = 1.7 x 10(38) erg s(-1). Three very massive Of stars are found to dominate the feedback among 164 OB stars in the sample. The two WR winds alone release about as much mechanical luminosity as the whole OB star sample. The cumulative mechanical feedback from all massive stellar winds is comparable to the combined mechanical energy of the supernova explosions that likely occurred in the complex. Accounting also for the WR wind and supernovae, the mechanical input over the last five Myr is approximate to 2.3 x 10(52) erg. Conclusions. The N206 complex in the LMC has undergone star formation episodes since more than 30 Myr ago. From the spectral analyses of its massive star population, we derive a current star formation rate of 2.2 x 10(-3) M-circle dot yr(-1). From the combined input of mechanical energy from all stellar winds, only a minor fraction is emitted in the form of X-rays. The corresponding input accumulated over a long time also exceeds the current energy content of the complex by more than a factor of five. The morphology of the complex suggests a leakage of hot gas from the superbubble.
KW  - stars: massive
KW  - Magellanic Clouds
KW  - stars: winds, outflows
KW  - Hertzsprung-Russell and C-M diagrams
KW  - techniques: spectroscopic
KW  - ISM: bubbles
Y1  - 2018
U6  - https://doi.org/10.1051/0004-6361/201832816
SN  - 1432-0746
VL  - 615
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Huenemoerder, David P.
A1  - Gayley, K. G.
A1  - Hamann, Wolf-Rainer
A1  - Ignace, R.
A1  - Nichols, J. S.
A1  - Oskinova, Lida
A1  - Pollock, A. M. T.
A1  - Schulz, Norbert S.
A1  - Shenar, Tomer
T1  - Probing Wolf-Rayet winds: Chandra/HETG X-ray spectra of WR 6
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - With a deep Chandra/HETGS exposure of WR 6, we have resolved emission lines whose profiles show that the X-rays originate from a uniformly expanding spherical wind of high X-ray-continuum optical depth. The presence of strong helium-like forbidden lines places the source of X-ray emission at tens to hundreds of stellar radii from the photosphere. Variability was present in X-rays and simultaneous optical photometry, but neither were correlated with the known period of the system or with each other. An enhanced abundance of sodium revealed nuclear-processed material, a quantity related to the evolutionary state of the star. The characterization of the extent and nature of the hot plasma in WR 6 will help to pave the way to a more fundamental theoretical understanding of the winds and evolution of massive stars.
KW  - stars: individual (WR 6)
KW  - stars: massive
KW  - stars: Wolf-Rayet
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/815/1/29
SN  - 0004-637X
SN  - 1538-4357
VL  - 815
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Hainich, Rainer
A1  - Ramachandran, Varsha
A1  - Shenar, Tomer
A1  - Sander, Andreas Alexander Christoph
A1  - Todt, Helge Tobias
A1  - Gruner, David
A1  - Oskinova, Lida
A1  - Hamann, Wolf-Rainer
T1  - PoWR grids of non-LTE model atmospheres for OB-type stars of various metallicities
JF  - Astronomy and astrophysics : an international weekly journal
N2  - The study of massive stars in different metallicity environments is a central topic of current stellar research. The spectral analysis of massive stars requires adequate model atmospheres. The computation of such models is difficult and time-consuming. Therefore, spectral analyses are greatly facilitated if they can refer to existing grids of models. Here we provide grids of model atmospheres for OB-type stars at metallicities corresponding to the Small and Large Magellanic Clouds, as well as to solar metallicity. In total, the grids comprise 785 individual models. The models were calculated using the state-of-the-art Potsdam Wolf-Rayet (PoWR) model atmosphere code. The parameter domain of the grids was set up using stellar evolution tracks. For all these models, we provide normalized and flux-calibrated spectra, spectral energy distributions, feedback parameters such as ionizing photons, Zanstra temperatures, and photometric magnitudes. The atmospheric structures (the density and temperature stratification) are available as well. All these data are publicly accessible through the PoWR website.
KW  - stars: massive
KW  - stars: early-type
KW  - stars: atmospheres
KW  - stars: winds
KW  - outflows
KW  - stars: mass-loss
KW  - radiative transfer
Y1  - 2019
U6  - https://doi.org/10.1051/0004-6361/201833787
SN  - 1432-0746
VL  - 621
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Todt, Helge Tobias
A1  - Sander, Angelika
A1  - Hainich, Rainer
A1  - Hamann, Wolf-Rainer
A1  - Quade, Markus
A1  - Shenar, Tomer
T1  - Potsdam Wolf-Rayet model atmosphere grids for WN stars
JF  - Astronomy and astrophysics : an international weekly journal
N2  - We present new grids of Potsdam Wolf-Rayet (PoWR) model atmospheres for Wolf-Rayet stars of the nitrogen sequence (WN stars). The models have been calculated with the latest version of the PoWR stellar atmosphere code for spherical stellar winds. The WN model atmospheres include the non-LTE solutions of the statistical equations for complex model atoms, as well as the radiative transfer equation in the co-moving frame. Iron-line blanketing is treated with the help of the superlevel approach, while wind inhomogeneities are taken into account via optically thin clumps. Three of our model grids are appropriate for Galactic metallicity. The hydrogen mass fraction of these grids is 50%, 20%, and 0%, thus also covering the hydrogen-rich late-type WR stars that have been discovered in recent years. Three grids are adequate for LMC WN stars and have hydrogen fractions of 40%, 20%, and 0%. Recently, additional grids with SMC metallicity and with 60%, 40%, 20%, and 0% hydrogen have been added. We provide contour plots of the equivalent widths of spectral lines that are usually used for classification and diagnostics.
KW  - stars: evolution
KW  - stars: mass-loss
KW  - stars: winds, outflows
KW  - stars: Wolf-Rayet
KW  - stars: atmospheres
KW  - stars: massive
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201526253
SN  - 0004-6361
SN  - 1432-0746
VL  - 579
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Torrejon, Jose M.
A1  - Schulz, Norbert S.
A1  - Nowak, Michael A.
A1  - Oskinova, Lida
A1  - Rodes-Roca, Jose J.
A1  - Shenar, Tomer
A1  - Wilms, Jörn
T1  - On the radial onset of clumping in the wind of the B0I massive star QV  nor
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We present an analysis of a 78 ks Chandra high-energy transmission gratings observation of the B0I star QV Nor, the massive donor of the wind-accreting pulsar 4U1538-52. The neutron star (NS) orbits its companion in a very close orbit (r < 1.4R(*), in units of the stellar radii), thereby allowing probing of the innermost wind regions. The flux of the Fe K alpha line during eclipse reduces to only similar to 30% of the flux measured out of eclipse. This indicates that the majority of Fe fluorescence must be produced in regions close to the NS, at distances smaller than 1R(*) from its surface. The fact that the flux of the continuum decreases to only similar to 3% during eclipse allows for a high contrast of the Fe Ka line fluorescence during eclipse. The line is not resolved and centered at lambda = 1.9368(-0.0018)(+0.0032) angstrom. From the inferred plasma speed limit of v < c Delta lambda/lambda < 800 km s(-1) and range of ionization parameters of log xi =[-1, 2], together with the stellar density profile, we constrain the location of the cold, dense material in the stellar wind of QV Nor using simple geometrical considerations. We then use the Fe K alpha line fluorescence as a tracer of wind clumps and determine that these clumps in the stellar wind of QV Nor (B0I) must already be present at radii r < 1.25R(*), close to the photosphere of the star.
KW  - stars: individual (QV Nor, 4U1538+52)
KW  - stars: winds, outflows
KW  - X-rays: binaries
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/810/2/102
SN  - 0004-637X
SN  - 1538-4357
VL  - 810
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  -