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 - Hubrig, Swetlana A1 - Fossati, Luca A1 - Carroll, Thorsten Anthony A1 - Castro, Norberto A1 - Gonzalez, J. F. A1 - Ilyin, Ilya A1 - Przybilla, Norbert A1 - Schoeller, M. A1 - Oskinova, Lida A1 - Morel, T. A1 - Langer, N. A1 - Scholz, Ralf-Dieter A1 - Kharchenko, N. V. A1 - Nieva, M. -F. T1 - B fields in OB stars (BOB): The discovery of a magnetic field in a multiple system in the Trifid nebula, one of the youngest star forming regions JF - Astronomy and astrophysics : an international weekly journal N2 - Aims. Recent magnetic field surveys in O- and B-type stars revealed that about 10% of the core-hydrogen-burning massive stars host large-scale magnetic fields. The physical origin of these fields is highly debated. To identify and model the physical processes responsible for the generation of magnetic fields in massive stars, it is important to establish whether magnetic massive stars are found in very young star-forming regions or whether they are formed in close interacting binary systems. Methods. In the framework of our ESO Large Program, we carried out low-resolution spectropolarimetric observations with FORS 2 in 2013 April of the three most massive central stars in the Trifid nebula, HD 164492A, HD 164492C, and HD 164492D. These observations indicated a strong longitudinal magnetic field of about 500-600 G in the poorly studied component HD 164492C. To confirm this detection, we used HARPS in spectropolarimetric mode on two consecutive nights in 2013 June. Results. Our HARPS observations confirmed the longitudinal magnetic field in HD 164492C. Furthermore, the HARPS observations revealed that HD 164492C cannot be considered as a single star as it possesses one or two companions. The spectral appearance indicates that the primary is most likely of spectral type B1-B1.5 V. Since in both observing nights most spectral lines appear blended, it is currently unclear which components are magnetic. Long-term monitoring using high-resolution spectropolarimetry is necessary to separate the contribution of each component to the magnetic signal. Given the location of the system HD 164492C in one of the youngest star formation regions, this system can be considered as a Rosetta Stone for our understanding of the origin of magnetic fields in massive stars. KW - binaries: close KW - stars: early-type KW - stars: fundamental parameters KW - stars: magnetic field KW - stars: variables: general KW - stars: individual: HD 164492C Y1 - 2014 U6 - https://doi.org/10.1051/0004-6361/201423490 SN - 0004-6361 SN - 1432-0746 VL - 564 PB - EDP Sciences CY - Les Ulis ER -