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B fields in OB stars (BOB): FORS2 spectropolarimetric follow-up of the two rare rigidly rotating magnetosphere stars HD 23478 and HD 345439

  • 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,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.show moreshow less

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Metadaten
Author:Swetlana Hubrig, Markus Schoeller, Luca Fossati, Thierry Morel, Neves Castro, Lida M. Oskinova, Norbert Przybilla, Stephen S. Eikenberry, Maria Fernanda Nieva, Norbert Langer
DOI:https://doi.org/10.1051/0004-6361/201526262
ISSN:0004-6361 (print)
ISSN:1432-0746 (online)
Parent Title (English):Astronomy and astrophysics : an international weekly journal
Publisher:EDP Sciences
Place of publication:Les Ulis
Document Type:Article
Language:English
Year of first Publication:2015
Year of Completion:2015
Creating Corporation:BOB Collaboration
Release Date:2017/03/27
Tag:stars: early-type; stars: fundamental parameters; stars: individual: HD 23478; stars: individual: HD 345439; stars: magnetic field; stars: variables: general
Volume:578
Pagenumber:5
Funder:Belspo; Alexander von Humboldt Foundation; DLR [50OR 1302]
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Physik und Astronomie
Peer Review:Referiert