CoRoT high-precision photometry of the B0.5 IV star HD 51756^{⋆,⋆⋆,⋆⋆⋆}

¹ Instituut voor Sterrenkunde, K.U. Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
e-mail: peter.papics@ster.kuleuven.be
² LESIA, UMR8109, Université Pierre et Marie Curie, Université Denis Diderot, Observatoire de Paris, 92195 Meudon Cedex, France
³ Department of Astrophysics, IMAPP, University of Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
⁴ Instytut Astronomiczny, Uniwersytet Wroclawski, Kopernika 11, 51-622 Wroclaw, Poland
⁵ European Southern Observatory (ESO), Alonso de Córdova 3107, Vitacura, Cassilla 19001, Santiago, Chile
⁶ INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate (LC), Italy
⁷ Institut für Astronomie, Universität Wien, Türkenschanzstrasse 17, 1180 Vienna, Austria
⁸ Laboratoire AIM, CEA/DSM-CNRS-Université Paris Diderot, CEA, IRFU, SAp, Centre de Saclay, 91191 Gif-sur-Yvette, France
⁹ Institut d’Astrophysique Spatiale, CNRS/Univ. Paris-Sud, Bât. 121, 91405 Orsay Cedex, France

Received: 11 November 2010
Accepted: 14 January 2011

Abstract

Context. OB stars are important constituents for the ecology of the Universe, and there are only a few studies on their pulsational properties detailed enough to provide important feedback on current evolutionary models.

Aims. Our goal is to analyse and interpret the behaviour present in the CoRoT light curve of the B0.5 IV star HD 51756 observed during the second long run of the space mission and to determine the fundamental stellar parameters from ground-based spectroscopy gathered with the Coralie and Harps instruments after checking for signs of variability and binarity, thus making a step further in mapping the top of the β Cep instability strip.

Methods. We compared the newly obtained high-resolution spectra with synthetic spectra of late O-type and early B-type stars computed on a grid of stellar parameters. We matched the results with evolutionary tracks to estimate stellar parameters. We used various time series analysis tools to explore the nature of the variations present in the light curve. Additional calculations were carried out based on distance and historical position measurements of the components to impose constraints on the binary orbit.

Results. We find that HD 51756 is a wide binary with both a slow (vsini ≈ 28   km   s^-1) and a fast (vsini ≈ 170   km   s^-1) early-B rotator whose atmospheric parameters are similar (T_eff ≈ 30   000   K and log g ≈ 3.75). We are unable to detect pulsation in any of the components, and we interpret the harmonic structure in the frequency spectrum as a sign of rotational modulation, which is compatible with the observed and deduced stellar parameters of both components.

Conclusions. The non-detection of pulsation modes provides a feedback on the theoretical treatment, given that non-adiabatic computations applied to appropriate stellar models predict the excitation of both pressure and gravity modes for the fundamental parameters of this star.