TY  - JOUR
A1  - Evans, C. J.
A1  - Smartt, S. J.
A1  - Lee, J. K.
A1  - Lennon, D. J.
A1  - Kaufer, A.
A1  - Dufton, P. L.
A1  - Trundle, C.
A1  - Herrero, A.
A1  - Simon Díaz, Sergio
A1  - de Koter, A.
A1  - Hamann, Wolf-Rainer
A1  - Hendry, M. A.
A1  - Hunter, I.
A1  - Irwin, M. J.
A1  - Korn, A. J.
A1  - Kudritzki, R. P.
A1  - Langer, Norbert
A1  - Mokiem, M. R.
A1  - Najarro, F.
A1  - Pauldrach, A. W. A.
A1  - Przybilla, Norbert
A1  - Puls, J.
A1  - Ryans, R. S. I.
A1  - Urbaneja, M. A.
A1  - Venn, K. A.
A1  - Villamariz, M. R.
T1  - The VLT-FLAMES survey of massive stars : Observations in the Galactic clusters NGC3293, NGC4755 and NGC6611
N2  - We introduce a new survey of massive stars in the Galaxy and the Magellanic Clouds using the Fibre Large Array Multi- Element Spectrograph ( FLAMES) instrument at the Very Large Telescope ( VLT). Here we present observations of 269 Galactic stars with the FLAMES- Giraffe Spectrograph ( R similar or equal to 25 000), in fields centered on the open clusters NGC3293, NGC4755 and NGC6611. These data are supplemented by a further 50 targets observed with the Fibre- Fed Extended Range Optical Spectrograph ( FEROS, R = 48 000). Following a description of our scientific motivations and target selection criteria, the data reduction methods are described; of critical importance the FLAMES reduction pipeline is found to yield spectra that are in excellent agreement with less automated methods. Spectral classifications and radial velocity measurements are presented for each star, with particular attention paid to morphological peculiarities and evidence of binarity. These observations represent a significant increase in the known spectral content of NGC3293 and NGC4755, and will serve as standards against which our subsequent FLAMES observations in the Magellanic Clouds will be compared
Y1  - 2005
ER  - 
TY  - JOUR
A1  - Yoon, S.-C.
A1  - Langer, Norbert
A1  - Scheithauer, S.
T1  - Effects of rotation on the helium burning shell source in accreting white dwarfs
N2  - We investigate the effects of rotation on the behavior of the helium-burning shell source in accreting carbon- oxygen white dwarfs, in the context of the single degenerate Chandrasekhar mass progenitor scenario for type la supernovae (SNe Ia). We model the evolution of helium-accreting white dwarfs of initially 1 M-circle dot, assuming four different constant accretion rates (2, 3, 5 and 10 x 10(-7) M-circle dot/yr). In a one-dimensional approximation, we compute the mass accretion and subsequent nuclear fusion of helium into carbon and oxygen, as well as angular momentum accretion, angular momentum transport inside the white dwarf, and rotationally induced chemical mixing. Our models show two major effects of rotation: a) The helium-burning nuclear shell source in the rotating models is much more stable than in corresponding non-rotating models - which increases the likelihood that accreting white dwarfs reach the stage of central carbon ignition. This effect is mainly due to rotationally induced mixing at the CO/He interface which widens the shell source, and due to the centrifugal force lowering the density and degeneracy at the shell source location. b) The C/O-ratio in the layers which experience helium shell burning - which may affect the energy of an SN Ia explosion - is strongly decreased by the rotationally induced mixing of a-particles into the carbon-rich layers. We discuss implications of our results for the evolution of SNe la progenitors
Y1  - 2004
SN  - 0004-6361
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  - Langer, Norbert
A1  - Heger, Alexander
A1  - Garcia-Segura, Guillermo
T1  - Massive stars : the pre-supernova evolution of internal and circumstellar structure
Y1  - 1998
ER  - 
TY  - JOUR
A1  - Langer, Norbert
A1  - Braun, H.
A1  - Wellstein, Stephan
T1  - Massive close binaries as source of galatic 26Al
Y1  - 1998
ER  - 
TY  - JOUR
A1  - Figer, Donald F.
A1  - Najarro, F.
A1  - Moris, Mark
A1  - Mclean, Ian S.
A1  - Geballe, T. R.
A1  - Ghez, A. M.
A1  - Langer, Norbert
T1  - The Pistol star
Y1  - 1998
ER  - 
TY  - JOUR
A1  - Garcia-Segura, Guillermo
A1  - Langer, Norbert
A1  - Rozyczka, M.
A1  - MacLow, Mordecai-Mark
T1  - The effects of rotation and stellar magnetic fields on the nebular shapes : LBV nebulae and PNe
Y1  - 1998
ER  - 
TY  - JOUR
A1  - Heger, Alexander
A1  - Langer, Norbert
A1  - Woosley, S. E.
T1  - Nucleosynthesis in rotating massive stars
Y1  - 1998
ER  - 
TY  - JOUR
A1  - Takahashi, K.
A1  - Faestermann, T.
A1  - Kienle, P.
A1  - Basch, F.
A1  - Langer, Norbert
A1  - Wagenhuber, J.
T1  - The 187 Re - 187Os cosmochronometry and chemical evolution in the solar neighborhood
Y1  - 1998
ER  - 
TY  - JOUR
A1  - Langer, Norbert
A1  - Heger, Alexander
A1  - Braun, H.
T1  - Nucleosynthesis in massive stars
Y1  - 1998
ER  - 
TY  - JOUR
A1  - Langer, Norbert
A1  - Heger, Alexander
T1  - B[e] supergiants : what is their evolutionary status?
Y1  - 1998
ER  - 
TY  - JOUR
A1  - Heger, Alexander
A1  - Langer, Norbert
T1  - The spin-up of contracting red supergiants
Y1  - 1998
ER  - 
TY  - JOUR
A1  - Langer, Norbert
T1  - Coupled mass and angular momentum loss of massive main sequence stars
Y1  - 1998
ER  - 
TY  - JOUR
A1  - Wittkowski, M.
A1  - Langer, Norbert
A1  - Weigelt, G.
T1  - Diffraction-limited Speckle-Masking interferometry of the red supergiant VY CMa*
Y1  - 1998
ER  - 
TY  - JOUR
A1  - Langer, Norbert
A1  - Fliegner, J.
A1  - Heger, Alexander
A1  - Woosley, S. E.
T1  - Nucleosynthesis in rotating massive stars
Y1  - 1997
ER  - 
TY  - JOUR
A1  - Langer, Norbert
A1  - Heer, A.
A1  - Fliegner, Jana Ute
T1  - Rotation : a fundamental parameter of massive stars
Y1  - 1997
ER  - 
TY  - JOUR
A1  - Langer, Norbert
T1  - The Eddington limit in rotating massive stars
Y1  - 1997
ER  - 
TY  - JOUR
A1  - Heger, Alexander
A1  - Jeannin, Laurent
A1  - Langer, Norbert
A1  - Baraffe, Isabelle
T1  - Pulsations in red supergiants with high L/M ratio : implications for the stellar and circumstellar structure of supernova progenitors
Y1  - 1997
ER  - 
TY  - JOUR
A1  - Osterbart, R.
A1  - Langer, Norbert
A1  - Weigelt, G.
T1  - High-resolution imaging of the bipola Red Rectangle
Y1  - 1997
ER  - 
TY  - JOUR
A1  - Fryer, C. L.
A1  - Langer, Norbert
A1  - Heger, Alexander
A1  - Wellstein, Stephan
T1  - The limiting stellar initial mass for black hole formation in close binary
N2  - We present models for the complete life and death of a 60 Msolar star evolving in a close binary system, from the main-sequence phase to the formation of a compact remnant and fallback of supernova debris. After core hydrogen exhaustion, the star expands, loses most of its envelope by Roche lobe overflow, and becomes a Wolf-Rayet star. We study its post-mass transfer evolution as a function of the Wolf-Rayet wind mass-loss rate (which is currently not well constrained and will probably vary with the initial metallicity of the star). Varying this mass-loss rate by a factor of 6 leads to stellar masses at collapse that range from 3.1 up to 10.7 Msolar. Because of different carbon abundances left by core helium burning and nonmonotonic effects of the late shell-burning stages as function of the stellar mass, we find that, although the iron core masses at collapse are generally larger for stars with larger final masses, they do not depend monotonically on the final stellar mass or even the C/O core mass. We then compute the evolution of all models through collapse and bounce. The results range from strong supernova explosions (Ekin>1051ergs) for the lower final masses to the direct collapse of the star into a black hole for the largest final mass. Correspondingly, the final remnant masses, which were computed by following the supernova evolution and fallback of material for a timescale of about one year, are between 1.2 and 10 Msolar. We discuss the remaining uncertainties of this result and outline the consequences of our results for the understanding of the progenitor evolution of X-ray binaries and gamma-ray burst models.
Y1  - 2002
ER  - 
TY  - JOUR
A1  - Langer, Norbert
A1  - Yoon, S.-C
A1  - Wellstein, Stephan
A1  - Scheithauer, S.
T1  - On the evolution of interacting binaries which contain a white dwarf
N2  - We discuss the evolution of white dwarf containing binaries, in particular such systems consisting of a white dwarf and a main sequence star which have the potential to produce a Type Ia supernova. After investigating current problems in connecting observations of supersoft X-ray sources with such systems, we consider two major problems which theoretical models encounter to produce Chandrasekhar-mass white dwarfs: the helium shell burning instability and the white dwarf spin-up. We conclude by suggesting that the formation of Chandrasekhar-mass white dwarfs may be easier when these two problem are considered simultaneously.
Y1  - 2002
SN  - 1-58381-101-X
ER  - 
TY  - JOUR
A1  - Wellstein, Stephan
A1  - Langer, Norbert
T1  - Constraints on the initial mass limit for black hole information from the massive X-ray binary Wray 977
Y1  - 2001
SN  - 3-540-41581-5
ER  - 
TY  - JOUR
A1  - Wellstein, Stephan
A1  - Langer, Norbert
A1  - Braun, H.
T1  - Formation of contact in massive close binaries
Y1  - 2001
ER  - 
TY  - JOUR
A1  - Heger, Alexander
A1  - Woosley, S. E.
A1  - Langer, Norbert
T1  - Stellar models including pre-SN/SN phases
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Langer, Norbert
A1  - Deutschmann, A.
A1  - Wellstein, Stephan
A1  - Höflich, P.
T1  - The evolution of main sequence star + white dwarf binary systems towards Type Ia supernovae
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Figer, Donald F.
A1  - Najarro, F.
A1  - Langer, Norbert
T1  - The pistol star and massive stars in the galactic center
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Garcia-Segura, Guillermo
A1  - Franco, J.
A1  - Lopez, J. A.
A1  - Langer, Norbert
A1  - Rozyczka, M.
T1  - MHD Models for planetary nebulae
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Heger, Alexander
A1  - Langer, Norbert
A1  - Woosley, S. E.
T1  - Presupernova evolution of rotating massive stars I : numerical method and evolution of the internal stellar structure
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Wellstein, Stephan
A1  - Langer, Norbert
T1  - Convection and compact stellar remnants in massive close binaries
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Langer, Norbert
A1  - Heger, Alexander
T1  - Massive star evolution
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Pasquali, A.
A1  - Nota, A.
A1  - Langer, Norbert
A1  - Schulte-Ladbeck, R. E.
A1  - Clampin, M.
T1  - R4 and its circumstellar nebula : evidence for a binary merger?
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Hulbert, S.
A1  - Nota, A.
A1  - Clampin, M.
A1  - Leitherer, C.
A1  - Pasquali, A.
A1  - Langer, Norbert
A1  - Schulte-Ladbeck, R. E.
T1  - HST WEPCII observation of the inner HR car nebula
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Langer, Norbert
T1  - The evolution of non-spherical and non-stationary winds of massive stars
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Langer, Norbert
A1  - Heger, Alexander
A1  - Wellenstein, Stephan
A1  - Herwig, Falk
T1  - Mixing and nucleosynthesis in rotating TP-AGB stars
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Wellstein, Stephan
A1  - Langer, Norbert
T1  - Implications of massive close binaries for black hole formation and supernovae
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Langer, Norbert
A1  - Garcia-Segura, Guillermo
A1  - MacLow, Mordecai-Mark
T1  - Giant outbursts of luminous blue variables and the formation of the homunculus nebula around eta carinae
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Garcia-Segura, Guillermo
A1  - Langer, Norbert
A1  - Rozyczka, M.
A1  - Franco, J.
A1  - MacLow, Mordecai-Mark
T1  - Hydrodynamics of ring nebulae : magnetic vs. non-magnetic hydro-models
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Langer, Norbert
A1  - Heger, Alexander
T1  - Evolution and explosion of Wolf-Rayet stars
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Garcia-Segura, Guillermo
A1  - Langer, Norbert
A1  - Rozyczka, M.
A1  - Franco, J.
T1  - Shaping bipolar and elliptical planetary nebulae : effects of stellar rotation, photoionization heating and magnetic fields
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Herwig, Falk
A1  - Blöcker, Thomas
A1  - Langer, Norbert
A1  - Driebe, Thomas
T1  - On the formation of hydrogen-deficient post-AGB stars
N2  - We present an evolutionary sequence of a low mass star from the Asymtotic Giant Branch (AGB) through its post- AGB stage, during which its surface chemical composition changes from hydrogen-rich to strongly hydrogen-deficient as consequence of a very late thermal pulse, following the so-called born-again scenario. The internal structure and abundance changes during this pulse are computed with a %newly developed numerical method which allows the physically consistent calculation of stellar layers where thermonuclear and mixing time scale are comparable --- a situation which occurs when the helium flash driven convection zone extends to the hydrogen-rich surface layers during the pulse peak. The final surface mass fractions are [He/C/O]=[0.38/0.36/0.22], where the high oxygen abundance is due to diffusive overshoot employed during the AGB evolution. These models are the first to achieve general agreement with the surface abundance pattern observed in hydrogen-deficient post-AGB stars --- e.g. the PG 1159 stars or the WR-type central stars of planetary nebulae ---, confirming the born-again scenario with a physically consistent calculation and supporting the occurrence of convective overshooting in thermally pulsing AGB stars.
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Henkel, Carsten
A1  - Chin, Y.
A1  - Langer, Norbert
A1  - Mauersberger, R.
T1  - Detection of extragalactic 15N : Nitrogen nucleosynthesis and chemical evolution
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Chin, Y.
A1  - Henkel, Carsten
A1  - Langer, Norbert
A1  - Mauersberger, R.
T1  - The detection of extragalactic 15N : consequences for nitrogeen nucleosynthesis and chemical evolution
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Castro, Norberto
A1  - Fossati, Luca
A1  - Hubrig, Swetlana
A1  - Simon Díaz, Sergio
A1  - Schoeller, Markus
A1  - Ilyin, Ilya
A1  - Carrol, Thorsten A.
A1  - Langer, Norbert
A1  - Morel, Thierry
A1  - Schneider, Fabian R. N.
A1  - Przybilla, Norbert
A1  - Herrero, Artemio
A1  - de Koter, Alex
A1  - Oskinova, Lida
A1  - Reisenegger, Andreas
A1  - Sana, Hugues
T1  - B fields in OB stars (BOB) Detection of a strong magnetic field in the O9.7 V star HD 54879
JF  - Astronomy and astrophysics : an international weekly journal
N2  - The number of magnetic stars detected among massive stars is small; nevertheless, the role played by the magnetic field in stellar evolution cannot be disregarded. Links between line profile variability, enhancements/depletions of surface chemical abundances, and magnetic fields have been identified for low-mass B-stars, but for the O-type domain this is almost unexplored. Based on FORS 2 and HARPS spectropolarimetric data, we present the first detection of a magnetic field in HD54879, a single slowly rotating O9.7 V star. Using two independent and different techniques we obtained the firm detection of a surface average longitudinal magnetic field with a maximum amplitude of about 600 G, in modulus. A quantitative spectroscopic analysis of the star with the stellar atmosphere code FASTWIND results in an effective temperature and a surface gravity of 33 000 +/- 1000K and 4.0 +/- 0.1 dex. The abundances of carbon, nitrogen, oxygen, silicon, and magnesium are found to be slightly lower than solar, but compatible within the errors. We investigate line-profile variability in HD54879 by complementing our spectra with spectroscopic data from other recent OB-star surveys. The photospheric lines remain constant in shape between 2009 and 2014, although H alpha shows a variable emission. The H alpha emission is too strong for a standard O9.7 V and is probably linked to the magnetic field and the presence of circumstellar material. Its normal chemical composition and the absence of photospheric line profile variations make HD54879 the most strongly magnetic, non-variable single O-star detected to date.
KW  - stars: atmospheres
KW  - stars: evolution
KW  - stars: magnetic field
KW  - stars: massive
KW  - stars: individual: HD 54879
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201425354
SN  - 1432-0746
VL  - 581
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Schoeller, M.
A1  - Hubrig, Swetlana
A1  - Ilyin, Ilya
A1  - Kharchenko, N. V.
A1  - Briquet, Maryline
A1  - Gonzalez, J. F.
A1  - Langer, Norbert
A1  - Oskinova, Lida
T1  - Magnetic field studies of massive main sequence stars
JF  - Astronomische Nachrichten = Astronomical notes
N2  - We report on the status of our spectropolarimetric observations of massive stars. During the last years, we have discovered magnetic fields in many objects of the upper main sequence, including Be stars, beta Cephei and Slowly Pulsating B stars, and a dozen O stars. Since the effects of those magnetic fields have been found to be substantial by recent models, we are looking into their impact on stellar rotation, pulsation, stellar winds, and chemical abundances. Accurate studies of the age, environment, and kinematic characteristics of the magnetic stars are also promising to give us new insight into the origin of the magnetic fields. Furthermore, longer time series of magnetic field measurements allow us to observe the temporal variability of the magnetic field and to deduce the stellar rotation period and the magnetic field geometry. Studies of the magnetic field in massive stars are indispensable to understand the conditions controlling the presence of those fields and their implications on the stellar physical parameters and evolution.
KW  - stars: early-type
KW  - stars: magnetic fields
KW  - stars: kinematics
KW  - techniques: polarimetric
Y1  - 2011
U6  - https://doi.org/10.1002/asna.201111606
SN  - 0004-6337
VL  - 332
IS  - 9-10
SP  - 994
EP  - 997
PB  - Wiley-Blackwell
CY  - Malden
ER  - 
TY  - JOUR
A1  - Fossati, Luca
A1  - Castro, Norberto
A1  - Morel, Thierry
A1  - Langer, Norbert
A1  - Briquet, Maryline
A1  - Carroll, Thorsten Anthony
A1  - Hubrig, Swetlana
A1  - Nieva, Maria-Fernanda
A1  - Oskinova, Lida
A1  - Przybilla, Norbert
A1  - Schneider, Fabian R. N.
A1  - Schoeller, Magnus
A1  - Simon Díaz, Sergio
A1  - Ilyin, Ilya
A1  - de Koter, Alex
A1  - Reisenegger, Andreas
A1  - Sana, Hugues
T1  - B fields in OB stars (BOB): on the detection of weak magnetic fields in the two early B-type stars beta CMa and epsilon CMa Possible lack of a "magnetic desert" in massive stars
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Only a small fraction of massive stars seem to host a measurable structured magnetic field, whose origin is still unknown and whose implications for stellar evolution still need to be assessed. Within the context of the "B fields in OB stars (BOB)" collaboration, we used the HARPSpol spectropolarimeter to observe the early B-type stars beta CMa (HD 44743; B1 II/III) and epsilon CMa (HD 52089; B1.5II) in December 2013 and April 2014. For both stars, we consistently detected the signature of a weak (<30 G in absolute value) longitudinal magnetic field, approximately constant with time. We determined the physical parameters of both stars and characterise their X-ray spectrum. For the beta Cep star beta CMa, our mode identification analysis led to determining a rotation period of 13.6 +/- 1.2 days and of an inclination angle of the rotation axis of 57.6 +/- 1.7 degrees, with respect to the line of sight. On the basis of these measurements and assuming a dipolar field geometry, we derived a best fitting obliquity of about 22 degrees and a dipolar magnetic field strength (B-d) of about 100 G (60 < B-d < 230 G within the 1 sigma level), below what is typically found for other magnetic massive stars. This conclusion is strengthened further by considerations of the star's X-ray spectrum. For epsilon CMa we could only determine a lower limit on the dipolar magnetic field strength of 13 G. For this star, we determine that the rotation period ranges between 1.3 and 24 days. Our results imply that both stars are expected to have a dynamical magnetosphere, so the magnetic field is not able to support a circumstellar disk. We also conclude that both stars are most likely core hydrogen burning and that they have spent more than 2/3 of their main sequence lifetime. A histogram of the distribution of the dipolar magnetic field strength for the magnetic massive stars known to date does not show the magnetic field "desert" observed instead for intermediate-mass stars. The biases involved in the detection of (weak) magnetic fields in massive stars with the currently available instrumentation and techniques imply that weak fields might be more common than currently observed. Our results show that, if present, even relatively weak magnetic fields are detectable in massive stars and that more observational effort is probably still needed to properly access the magnetic field incidence.
KW  - stars: atmospheres
KW  - stars: evolution
KW  - stars: magnetic field
KW  - stars: individual: epsilon CMa
KW  - stars: individual: beta CMa
KW  - stars: massive
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201424986
SN  - 0004-6361
SN  - 1432-0746
VL  - 574
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Hubrig, Swetlana
A1  - Schoeller, Markus
A1  - Fossati, Luca
A1  - Morel, Thierry
A1  - Castro, Neves
A1  - Oskinova, Lida
A1  - Przybilla, Norbert
A1  - Eikenberry, Stephen S.
A1  - Nieva, Maria Fernanda
A1  - Langer, Norbert
T1  - B fields in OB stars (BOB): FORS2 spectropolarimetric follow-up of the two rare rigidly rotating magnetosphere stars HD 23478 and HD 345439
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Aims. Massive B-type stars with strong magnetic fields and fast rotation are very rare and pose a mystery for theories of star formation and magnetic field evolution. Only two such stars, called sigma Ori E analogues, were known until recently. A team involved in APOGEE, one of the Sloan Digital Sky Survey III programs, announced the discovery of two additional rigidly rotating magnetosphere stars, HD 23478 and HD 345439. The magnetic fields in these newly discovered sOri E analogues have not been investigated so far.
 Methods. In the framework of our ESO Large Programme and one normal ESO programme, we carried out low-resolution FORS 2 spectropolarimetric observations of HD 23478 and HD 345439.
 Results. In the measurements of hydrogen lines, we discover a rather strong longitudinal magnetic field of up to 1.5 kG in HD 23478 and up to 1.3 kG using the entire spectrum. The analysis of HD 345439 using four subsequent spectropolarimetric subexposures does not reveal a magnetic field at a significance level of 3 sigma. On the other hand, individual subexposures indicate that HD 345439 may host a strong magnetic field that rapidly varies over 88 min. The fast rotation of HD 345439 is also indicated by the behaviour of several metallic and He I lines in the low-resolution FORS 2 spectra that show profile variations already on this short time-scale.
KW  - stars: early-type
KW  - stars: fundamental parameters
KW  - stars: variables: general
KW  - stars: magnetic field
KW  - stars: individual: HD 23478
KW  - stars: individual: HD 345439
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201526262
SN  - 0004-6361
SN  - 1432-0746
VL  - 578
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  - Hainich, Rainer
A1  - Oskinova, Lida
A1  - Shenar, Tomer
A1  - Marchant Campos, Pablo
A1  - Eldridge, J. J.
A1  - Sander, Andreas Alexander Christoph
A1  - Hamann, Wolf-Rainer
A1  - Langer, Norbert
A1  - Todt, Helge Tobias
T1  - Observational properties of massive black hole binary progenitors
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context:
The first directly detected gravitational waves (GW 150914) were emitted by two coalescing black holes (BHs) with masses of ≈ 36 M⊙ and ≈ 29 M⊙. Several scenarios have been proposed to put this detection into an astrophysical context. The evolution of an isolated massive binary system is among commonly considered models.
Aims:
Various groups have performed detailed binary-evolution calculations that lead to BH merger events. However, the question remains open as to whether binary systems with the predicted properties really exist. The aim of this paper is to help observers to close this gap by providing spectral characteristics of massive binary BH progenitors during a phase where at least one of the companions is still non-degenerate.
Methods:
Stellar evolution models predict fundamental stellar parameters. Using these as input for our stellar atmosphere code (Potsdam Wolf-Rayet), we compute a set of models for selected evolutionary stages of massive merging BH progenitors at different metallicities.
Results:
The synthetic spectra obtained from our atmosphere calculations reveal that progenitors of massive BH merger events start their lives as O2-3V stars that evolve to early-type blue supergiants before they undergo core-collapse during the Wolf-Rayet phase. When the primary has collapsed, the remaining system will appear as a wind-fed high-mass X-ray binary. Based on our atmosphere models, we provide feedback parameters, broad band magnitudes, and spectral templates that should help to identify such binaries in the future.
Conclusions:
While the predicted parameter space for massive BH binary progenitors is partly realized in nature, none of the known massive binaries match our synthetic spectra of massive BH binary progenitors exactly. Comparisons of empirically determined mass-loss rates with those assumed by evolution calculations reveal significant differences. The consideration of the empirical mass-loss rates in evolution calculations will possibly entail a shift of the maximum in the predicted binary-BH merger rate to higher metallicities, that is, more candidates should be expected in our cosmic neighborhood than previously assumed.
KW  - gravitational waves
KW  - binaries: close
KW  - stars: early-type
KW  - stars: atmospheres
KW  - stars: winds
KW  - outflows
KW  - stars: mass-loss
Y1  - 2018
U6  - https://doi.org/10.1051/0004-6361/201731449
SN  - 1432-0746
VL  - 609
PB  - EDP Sciences
CY  - Les Ulis
ER  -