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  -