@article{AlmeidaSanaTayloretal.2017, author = {Almeida, Leonardo A. and Sana, H. and Taylor, W. and Barb{\´a}, Rodolfo and Bonanos, Alceste Z. and Crowther, Paul and Damineli, Augusto and de Koter, A. and de Mink, Selma E. and Evans, C. J. and Gieles, Mark and Grin, Nathan J. and H{\´e}nault-Brunet, V. and Langer, Norbert and Lennon, D. and Lockwood, Sean and Ma{\´i}z Apell{\´a}niz, Jes{\´u}s and Moffat, A. F. J. and Neijssel, C. and Norman, C. and Ram{\´i}rez-Agudelo, O. H. and Richardson, N. D. and Schootemeijer, Abel and Shenar, Tomer and Soszyński, Igor and Tramper, Frank and Vink, J. S.}, title = {The tarantula massive binary monitoring}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {598}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {1432-0746}, doi = {10.1051/0004-6361/201629844}, pages = {36}, year = {2017}, abstract = {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⊙.}, language = {en} } @article{CastroFossatiHubrigetal.2015, author = {Castro, Norberto and Fossati, Luca and Hubrig, Swetlana and Simon D{\´i}az, Sergio and Schoeller, Markus and Ilyin, Ilya and Carrol, Thorsten A. and Langer, Norbert and Morel, Thierry and Schneider, Fabian R. N. and Przybilla, Norbert and Herrero, Artemio and de Koter, Alex and Oskinova, Lida and Reisenegger, Andreas and Sana, Hugues}, title = {B fields in OB stars (BOB) Detection of a strong magnetic field in the O9.7 V star HD 54879}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {581}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, organization = {BOB Collaboration}, issn = {1432-0746}, doi = {10.1051/0004-6361/201425354}, pages = {14}, year = {2015}, abstract = {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.}, language = {en} } @article{ChinHenkelLangeretal.1999, author = {Chin, Y. and Henkel, Carsten and Langer, Norbert and Mauersberger, R.}, title = {The detection of extragalactic 15N : consequences for nitrogeen nucleosynthesis and chemical evolution}, year = {1999}, language = {en} } @article{EvansSmarttLeeetal.2005, author = {Evans, C. J. and Smartt, S. J. and Lee, J. K. and Lennon, D. J. and Kaufer, A. and Dufton, P. L. and Trundle, C. and Herrero, A. and Simon D{\´i}az, Sergio and de Koter, A. and Hamann, Wolf-Rainer and Hendry, M. A. and Hunter, I. and Irwin, M. J. and Korn, A. J. and Kudritzki, R. P. and Langer, Norbert and Mokiem, M. R. and Najarro, F. and Pauldrach, A. W. A. and Przybilla, Norbert and Puls, J. and Ryans, R. S. I. and Urbaneja, M. A. and Venn, K. A. and Villamariz, M. R.}, title = {The VLT-FLAMES survey of massive stars : Observations in the Galactic clusters NGC3293, NGC4755 and NGC6611}, year = {2005}, abstract = {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}, language = {en} } @article{FigerNajarroLanger2000, author = {Figer, Donald F. and Najarro, F. and Langer, Norbert}, title = {The pistol star and massive stars in the galactic center}, year = {2000}, language = {en} } @article{FigerNajarroMorisetal.1998, author = {Figer, Donald F. and Najarro, F. and Moris, Mark and Mclean, Ian S. and Geballe, T. R. and Ghez, A. M. and Langer, Norbert}, title = {The Pistol star}, year = {1998}, language = {en} } @article{FossatiCastroMoreletal.2015, author = {Fossati, Luca and Castro, Norberto and Morel, Thierry and Langer, Norbert and Briquet, Maryline and Carroll, Thorsten Anthony and Hubrig, Swetlana and Nieva, Maria-Fernanda and Oskinova, Lida and Przybilla, Norbert and Schneider, Fabian R. N. and Schoeller, Magnus and Simon D{\´i}az, Sergio and Ilyin, Ilya and de Koter, Alex and Reisenegger, Andreas and Sana, Hugues}, title = {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}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {574}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, organization = {BOB Collaboration}, issn = {0004-6361}, doi = {10.1051/0004-6361/201424986}, pages = {15}, year = {2015}, abstract = {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.}, language = {en} } @article{FryerLangerHegeretal.2002, author = {Fryer, C. L. and Langer, Norbert and Heger, Alexander and Wellstein, Stephan}, title = {The limiting stellar initial mass for black hole formation in close binary}, year = {2002}, abstract = {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.}, language = {en} } @article{GarciaSeguraFrancoLopezetal.2000, author = {Garcia-Segura, Guillermo and Franco, J. and Lopez, J. A. and Langer, Norbert and Rozyczka, M.}, title = {MHD Models for planetary nebulae}, year = {2000}, language = {en} } @article{GarciaSeguraLangerRozyczkaetal.1999, author = {Garcia-Segura, Guillermo and Langer, Norbert and Rozyczka, M. and Franco, J.}, title = {Shaping bipolar and elliptical planetary nebulae : effects of stellar rotation, photoionization heating and magnetic fields}, year = {1999}, language = {en} } @article{GarciaSeguraLangerRozyczkaetal.1999, author = {Garcia-Segura, Guillermo and Langer, Norbert and Rozyczka, M. and Franco, J. and MacLow, Mordecai-Mark}, title = {Hydrodynamics of ring nebulae : magnetic vs. non-magnetic hydro-models}, year = {1999}, language = {en} } @article{GarciaSeguraLangerRozyczkaetal.1998, author = {Garcia-Segura, Guillermo and Langer, Norbert and Rozyczka, M. and MacLow, Mordecai-Mark}, title = {The effects of rotation and stellar magnetic fields on the nebular shapes : LBV nebulae and PNe}, year = {1998}, language = {en} } @article{HainichOskinovaShenaretal.2018, author = {Hainich, Rainer and Oskinova, Lida and Shenar, Tomer and Marchant Campos, Pablo and Eldridge, J. J. and Sander, Andreas Alexander Christoph and Hamann, Wolf-Rainer and Langer, Norbert and Todt, Helge Tobias}, title = {Observational properties of massive black hole binary progenitors}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {609}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {1432-0746}, doi = {10.1051/0004-6361/201731449}, pages = {62}, year = {2018}, abstract = {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.}, language = {en} } @article{HegerJeanninLangeretal.1997, author = {Heger, Alexander and Jeannin, Laurent and Langer, Norbert and Baraffe, Isabelle}, title = {Pulsations in red supergiants with high L/M ratio : implications for the stellar and circumstellar structure of supernova progenitors}, year = {1997}, language = {en} } @article{HegerLanger1998, author = {Heger, Alexander and Langer, Norbert}, title = {The spin-up of contracting red supergiants}, year = {1998}, language = {en} } @article{HegerLangerWoosley1998, author = {Heger, Alexander and Langer, Norbert and Woosley, S. E.}, title = {Nucleosynthesis in rotating massive stars}, year = {1998}, language = {en} } @article{HegerLangerWoosley2000, author = {Heger, Alexander and Langer, Norbert and Woosley, S. E.}, title = {Presupernova evolution of rotating massive stars I : numerical method and evolution of the internal stellar structure}, year = {2000}, language = {en} } @article{HegerWoosleyLanger2000, author = {Heger, Alexander and Woosley, S. E. and Langer, Norbert}, title = {Stellar models including pre-SN/SN phases}, year = {2000}, language = {en} } @article{HenkelChinLangeretal.1999, author = {Henkel, Carsten and Chin, Y. and Langer, Norbert and Mauersberger, R.}, title = {Detection of extragalactic 15N : Nitrogen nucleosynthesis and chemical evolution}, year = {1999}, language = {en} } @article{HerwigBloeckerLangeretal.1999, author = {Herwig, Falk and Bl{\"o}cker, Thomas and Langer, Norbert and Driebe, Thomas}, title = {On the formation of hydrogen-deficient post-AGB stars}, year = {1999}, abstract = {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.}, language = {en} } @article{HubrigSchoellerFossatietal.2015, author = {Hubrig, Swetlana and Schoeller, Markus and Fossati, Luca and Morel, Thierry and Castro, Neves and Oskinova, Lida and Przybilla, Norbert and Eikenberry, Stephen S. and Nieva, Maria Fernanda and Langer, Norbert}, title = {B fields in OB stars (BOB): FORS2 spectropolarimetric follow-up of the two rare rigidly rotating magnetosphere stars HD 23478 and HD 345439}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {578}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, organization = {BOB Collaboration}, issn = {0004-6361}, doi = {10.1051/0004-6361/201526262}, pages = {5}, year = {2015}, abstract = {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.}, language = {en} } @article{HulbertNotaClampinetal.1999, author = {Hulbert, S. and Nota, A. and Clampin, M. and Leitherer, C. and Pasquali, A. and Langer, Norbert and Schulte-Ladbeck, R. E.}, title = {HST WEPCII observation of the inner HR car nebula}, year = {1999}, language = {en} } @article{Langer1998, author = {Langer, Norbert}, title = {Coupled mass and angular momentum loss of massive main sequence stars}, year = {1998}, language = {en} } @article{Langer1997, author = {Langer, Norbert}, title = {The Eddington limit in rotating massive stars}, year = {1997}, language = {en} } @article{Langer1999, author = {Langer, Norbert}, title = {The evolution of non-spherical and non-stationary winds of massive stars}, year = {1999}, language = {en} } @article{LangerBraunWellstein1998, author = {Langer, Norbert and Braun, H. and Wellstein, Stephan}, title = {Massive close binaries as source of galatic 26Al}, year = {1998}, language = {en} } @article{LangerDeutschmannWellsteinetal.2000, author = {Langer, Norbert and Deutschmann, A. and Wellstein, Stephan and H{\"o}flich, P.}, title = {The evolution of main sequence star + white dwarf binary systems towards Type Ia supernovae}, year = {2000}, language = {en} } @article{LangerFliegnerHegeretal.1997, author = {Langer, Norbert and Fliegner, J. and Heger, Alexander and Woosley, S. E.}, title = {Nucleosynthesis in rotating massive stars}, year = {1997}, language = {en} } @article{LangerGarciaSeguraMacLow1999, author = {Langer, Norbert and Garcia-Segura, Guillermo and MacLow, Mordecai-Mark}, title = {Giant outbursts of luminous blue variables and the formation of the homunculus nebula around eta carinae}, year = {1999}, language = {en} } @article{LangerHeerFliegner1997, author = {Langer, Norbert and Heer, A. and Fliegner, Jana Ute}, title = {Rotation : a fundamental parameter of massive stars}, year = {1997}, language = {en} } @article{LangerHeger1998, author = {Langer, Norbert and Heger, Alexander}, title = {B[e] supergiants : what is their evolutionary status?}, year = {1998}, language = {en} } @article{LangerHeger1999, author = {Langer, Norbert and Heger, Alexander}, title = {Massive star evolution}, year = {1999}, language = {en} } @article{LangerHeger1999, author = {Langer, Norbert and Heger, Alexander}, title = {Evolution and explosion of Wolf-Rayet stars}, year = {1999}, language = {en} } @article{LangerHegerBraun1998, author = {Langer, Norbert and Heger, Alexander and Braun, H.}, title = {Nucleosynthesis in massive stars}, year = {1998}, language = {en} } @article{LangerHegerGarciaSegura1998, author = {Langer, Norbert and Heger, Alexander and Garcia-Segura, Guillermo}, title = {Massive stars : the pre-supernova evolution of internal and circumstellar structure}, year = {1998}, language = {en} } @article{LangerHegerWellensteinetal.1999, author = {Langer, Norbert and Heger, Alexander and Wellenstein, Stephan and Herwig, Falk}, title = {Mixing and nucleosynthesis in rotating TP-AGB stars}, year = {1999}, language = {en} } @article{LangerYoonWellsteinetal.2002, author = {Langer, Norbert and Yoon, S.-C and Wellstein, Stephan and Scheithauer, S.}, title = {On the evolution of interacting binaries which contain a white dwarf}, isbn = {1-58381-101-X}, year = {2002}, abstract = {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.}, language = {en} } @article{OsterbartLangerWeigelt1997, author = {Osterbart, R. and Langer, Norbert and Weigelt, G.}, title = {High-resolution imaging of the bipola Red Rectangle}, year = {1997}, language = {en} } @article{PasqualiNotaLangeretal.1999, author = {Pasquali, A. and Nota, A. and Langer, Norbert and Schulte-Ladbeck, R. E. and Clampin, M.}, title = {R4 and its circumstellar nebula : evidence for a binary merger?}, year = {1999}, language = {en} } @article{SchoellerHubrigIlyinetal.2011, author = {Schoeller, M. and Hubrig, Swetlana and Ilyin, Ilya and Kharchenko, N. V. and Briquet, Maryline and Gonzalez, J. F. and Langer, Norbert and Oskinova, Lida}, title = {Magnetic field studies of massive main sequence stars}, series = {Astronomische Nachrichten = Astronomical notes}, volume = {332}, journal = {Astronomische Nachrichten = Astronomical notes}, number = {9-10}, publisher = {Wiley-Blackwell}, address = {Malden}, organization = {MAGORI Collaboration}, issn = {0004-6337}, doi = {10.1002/asna.201111606}, pages = {994 -- 997}, year = {2011}, abstract = {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.}, language = {en} } @article{ShenarRichardsonSablowskietal.2017, author = {Shenar, Tomer and Richardson, N. D. and Sablowski, Daniel P. and Hainich, Rainer and Sana, H. and Moffat, A. F. J. and Todt, Helge Tobias and Hamann, Wolf-Rainer and Oskinova, Lida and Sander, Andreas Alexander Christoph and Tramper, Frank and Langer, Norbert and Bonanos, Alceste Z. and de Mink, Selma E. and Gr{\"a}fener, G. and Crowther, Paul and Vink, J. S. and Almeida, Leonardo A. and de Koter, A. and Barb{\´a}, Rodolfo and Herrero, A. and Ulaczyk, Krzysztof}, title = {The tarantula massive binary monitoring}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {598}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {1432-0746}, doi = {10.1051/0004-6361/201629621}, pages = {16}, year = {2017}, abstract = {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.}, language = {en} } @article{TakahashiFaestermannKienleetal.1998, author = {Takahashi, K. and Faestermann, T. and Kienle, P. and Basch, F. and Langer, Norbert and Wagenhuber, J.}, title = {The 187 Re - 187Os cosmochronometry and chemical evolution in the solar neighborhood}, year = {1998}, language = {en} } @article{WellsteinLanger2001, author = {Wellstein, Stephan and Langer, Norbert}, title = {Constraints on the initial mass limit for black hole information from the massive X-ray binary Wray 977}, isbn = {3-540-41581-5}, year = {2001}, language = {en} } @article{WellsteinLanger1999, author = {Wellstein, Stephan and Langer, Norbert}, title = {Convection and compact stellar remnants in massive close binaries}, year = {1999}, language = {en} } @article{WellsteinLanger1999, author = {Wellstein, Stephan and Langer, Norbert}, title = {Implications of massive close binaries for black hole formation and supernovae}, year = {1999}, language = {en} } @article{WellsteinLangerBraun2001, author = {Wellstein, Stephan and Langer, Norbert and Braun, H.}, title = {Formation of contact in massive close binaries}, year = {2001}, language = {en} } @article{WittkowskiLangerWeigelt1998, author = {Wittkowski, M. and Langer, Norbert and Weigelt, G.}, title = {Diffraction-limited Speckle-Masking interferometry of the red supergiant VY CMa*}, year = {1998}, language = {en} } @article{YoonLangerScheithauer2004, author = {Yoon, S.-C. and Langer, Norbert and Scheithauer, S.}, title = {Effects of rotation on the helium burning shell source in accreting white dwarfs}, issn = {0004-6361}, year = {2004}, abstract = {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}, language = {en} }