TY  - GEN
A1  - Morel, T.
A1  - Castro, Norberto
A1  - Fossati, Luca
A1  - Hubrig, Swetlana
A1  - Langer, N.
A1  - Przybilla, Norbert
A1  - Schöller, Markus
A1  - Carroll, Thorsten Anthony
A1  - Ilyin, Ilya
A1  - Irrgang, Andreas
A1  - Oskinova, Lida
A1  - Schneider, Fabian R. N.
A1  - Simon Díaz, Sergio
A1  - Briquet, Maryline
A1  - González, Jean-Francois
A1  - Kharchenko, Nina
A1  - Nieva, M.-F.
A1  - Scholz, Ralf-Dieter
A1  - de Koter, Alexander
A1  - Hamann, Wolf-Rainer
A1  - Herrero, Artemio
A1  - Maíz Apellániz, Jesus
A1  - Sana, Hugues
A1  - Arlt, Rainer
A1  - Barbá, Rodolfo H.
A1  - Dufton, Polly
A1  - Kholtygin, Alexander
A1  - Mathys, Gautier
A1  - Piskunov, Anatoly E.
A1  - Reisenegger, Andreas
A1  - Spruit, H.
A1  - Yoon, S.-C.
T1  - The B fields in OB stars (BOB) survey
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - The B fields in OB stars (BOB) survey is an ESO large programme collecting spectropolarimetric observations for a large number of early-type stars in order to study the occurrence rate, properties, and ultimately the origin of magnetic fields in massive stars. As of July 2014, a total of 98 objects were observed over 20 nights with FORS2 and HARPSpol. Our preliminary results indicate that the fraction of magnetic OB stars with an organised, detectable field is low. This conclusion, now independently reached by two different surveys, has profound implications for any theoretical model attempting to explain the field formation in these objects. We discuss in this contribution some important issues addressed by our observations (e.g., the lower bound of the field strength) and the discovery of some remarkable objects.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 821 
KW  - magnetic fields
KW  - stars: early-type
KW  - stars: magnetic fields
KW  - stars: individual (HD 164492C, CPD –57 ◦ 3509, HD 54879, β CMa, ε CMa)
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-415238
SN  - 1866-8372
IS  - 821
ER  - 
TY  - JOUR
A1  - Tramper, F.
A1  - Straal, S. M.
A1  - Sanyal, D.
A1  - Sana, Hugues
A1  - de Koter, A.
A1  - Gräfener, G.
A1  - Langer, N.
A1  - Vink, J. S.
A1  - de Mink, S. E.
A1  - Kaper, L.
T1  - Massive Wolf-Rayet stars on the verge to explode
BT  - the properties of the WO stars
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - The enigmatic oxygen-sequence Wolf-Rayet stars represent a rare stage in the evolution of massive stars. Their properties can provide unique constraints on the pre-supernova evolution of massive stars. This work presents the results of a quantitative spectroscopic analysis of the known single WO stars, with the aim to obtain the key stellar parameters and deduce their evolutionary state.X-Shooter spectra of the WO stars are modeled using the line-blanketed non-local thermal equilibrium atmosphere code cmfgen. The obtained stellar parameters show that the WO stars are very hot, with temperatures ranging from 150 kK to 210 kK. Their chemical composition is dominated by carbon (>50%), while the helium mass fraction is very low (down to 14%). Oxygen mass fractions reach as high as 25%. These properties can be reproduced with dedicated evolutionary models for helium stars, which show that the stars are post core-helium burning and very close to their eventual supernova explosion. The helium-star masses indicate initial masses or approximately 40 - 60M⊙.Thus, WO stars represent the final evolutionary stage of stars with estimated initial masses of 40 - 60M⊙. They are post core-helium burning and may explode as type Ic supernovae within a few thousand years.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-87786
SP  - 109
EP  - 112
ER  -