Two new SB2 binaries with main sequence B-type pulsators in the Kepler field ^{⋆,⋆⋆,⋆⋆⋆,⋆⋆⋆⋆}

¹ Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
e-mail: Peter.Papics@ster.kuleuven.be
² Department of Astrophysics, IMAPP, University of Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
³ Institut d’Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, Bât B5c, 4000 Liège, Belgium
⁴ Instituto de Astrofisica de Canarias, 38205 La Laguna, Tenerife, Spain
⁵ Dept. Astrofísica, Universidad de La Laguna (ULL), 38206 Lagona, Tenerife, Spain
⁶ Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK
⁷ Department of Astronomy, University of California, Berkeley, CA 94720-3411, USA
⁸ Department of Astronomy, New Mexico State University, Las Cruces, NM 88001, USA
⁹ Instytut Astronomiczny, Uniwersytet Wrocławski, Kopernika 11, 51-622 Wrocław, Poland
¹⁰ Centro de Astrofísica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
¹¹ Departamento Física e Astronomia, Faculdade de Ciências da Universidade do Porto, Portugal

Received: 11 January 2013
Accepted: 4 April 2013

Abstract

Context. OB stars are important in the chemistry and evolution of the Universe, but the sample of targets that is well understood from an asteroseismological point of view is still too limited to provide feedback on the current evolutionary models.

Aims. We extend this sample with two spectroscopic binary systems. Our goal is to provide orbital solutions, fundamental parameters, and abundances from disentangled high-resolution high signal-to-noise spectra, as well as to analyse and interpret the variations in the Kepler light curve of these carefully selected targets. This way we continue our efforts to map the instability strips of β Cep and slowly pulsating B stars using the combination of high-resolution ground-based spectroscopy and uninterrupted space-based photometry.

Methods. We fit Keplerian orbits to radial velocities measured from selected absorption lines of high-resolution spectroscopy using synthetic composite spectra to obtain orbital solutions. We used revised masks to obtain optimal light curves from the original pixel-data from the Kepler satellite, which provided better long-term stability compared to the pipeline-processed light curves. We used various time-series analysis tools to explore and describe the nature of variations present in the light curve.

Results. We find two eccentric double-lined spectroscopic binary systems containing a total of three main sequence B-type stars (and one F-type component), of which at least one in each system exhibits light variations. The light curve analysis (combined with spectroscopy) of the system of two B stars points towards the presence of tidally excited g modes in the primary component. We interpret the variations seen in the second system as classical g mode pulsations driven by the κ mechanism in the B type primary, and explain the unexpected power in the p mode region as the result of nonlinear resonant mode excitation.