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  - 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  - Wellstein, Stephan
A1  - Langer, Norbert
A1  - Braun, H.
T1  - Formation of contact in massive close binaries
Y1  - 2001
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
T1  - Convection and compact stellar remnants in massive close binaries
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  - 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  - 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  - 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  - 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  - Osterbart, R.
A1  - Langer, Norbert
A1  - Weigelt, G.
T1  - High-resolution imaging of the bipola Red Rectangle
Y1  - 1997
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  - 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  - 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  - 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  - Langer, Norbert
A1  - Heger, Alexander
T1  - Massive star evolution
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  - 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
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  -