B fields in OB stars (BOB): Concluding the FORS 2 observing campaign^⋆

¹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
e-mail: mschoell@eso.org
² Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
³ Österreichische Akademie der Wissenschaften, Institut für Weltraumforschung, Schmiedlstraße 6, 8042 Graz, Austria
⁴ Argelander-Institut für Astronomie der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
⁵ Space Sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Quartier Agora, Allée du 6 Août 19c, Bât. B5C, 4000 Liège, Belgium
⁶ Universität Potsdam, Institut für Physik und Astronomie, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany
⁷ Department of Astronomy, University of Michigan, 1085 S. University Avenue, Ann Arbor, MI 48109-1107, USA
⁸ Institut für Astro- und Teilchenphysik, Universität Innsbruck, Technikerstr. 25/8, 6020 Innsbruck, Austria
⁹ St. Petersburg State University, Universitetski pr. 28, 198504 St. Petersburg, Russia
¹⁰ Institute of Astrophysics, KU Leuven, Celestijnlaan 200D, 3001 Leuven, Belgium
¹¹ Instituto de Astrofísica de Canarias, C/vía Láctea s/n, 38205 La Laguna, Spain
¹² Universidad de La Laguna, Departamento de Astrofísica, Avda. Francisco Sanchez 2, 38206 La Laguna, Spain
¹³ Departamento de Física y Astronomía, Universidad de La Serena, Av. Juan Cisternas 1200 Norte, La Serena, Chile
¹⁴ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, PO Box 94249, 1090 GE Amsterdam, The Netherlands

Received: 12 May 2016
Accepted: 11 November 2016

Abstract

Aims. The B fields in OB stars (BOB) Collaboration is based on an ESO Large Programme to study the occurrence rate, properties, and ultimately the origin of magnetic fields in massive stars.

Methods. In the framework of this program, we carried out low-resolution spectropolarimetric observations of a large sample of massive stars using FORS 2 installed at the ESO VLT 8 m telescope.

Results. We determined the magnetic field values with two completely independent reduction and analysis pipelines. Our in-depth study of the magnetic field measurements shows that differences between our two pipelines are usually well within 3σ errors. From the 32 observations of 28 OB stars, we were able to monitor the magnetic fields in CPD −57° 3509 and HD 164492C, confirm the magnetic field in HD 54879, and detect a magnetic field in CPD −62° 2124. We obtain a magnetic field detection rate of 6 ± 3% for the full sample of 69 OB stars observed with FORS 2 within the BOB program. For the preselected objects with a v sin i below 60 km s^-1, we obtain a magnetic field detection rate of 5 ± 5%. We also discuss X-ray properties and multiplicity of the objects in our FORS 2 sample with respect to the magnetic field detections.