Context: OB stars are important in the chemistry and evolution of the Universe, but the sample of targets well understood from an asteroseismological point of view is still too limited to provide feedback on the current evolutionary models. Our study
extends this sample with two spectroscopic binary systems. AIMS. 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 beta Cep and SPB 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 use 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 use 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 kappa mechanism in the B type primary, and explain the unexpected power in the p mode region as a result of nonlinear resonant mode excitation.
Context. OB stars are important building blocks of the Universe, but we have only a limited sample of them well understood enough from an asteroseismological point of view to provide feedback on the current evolutionary models. Our study adds one spe
cial case to this sample, with more observational constraints than for most of these stars. Aims. Our goal is to analyse and interpret the pulsational behaviour of the B3 IV star HD 43317 using the CoRoT light curve along with the ground-based spectroscopy gathered by the Harps instrument. This way we continue our efforts to map the Beta Cep and SPB instability strips. Methods. We used different techniques to reveal the abundances and fundamental stellar parameters from the newly-obtained high-resolution spectra. We used various time-series analysis tools to explore the nature of variations present in the light curve. We calculated the moments and used the pixel-by-pixel method to look for line profile variations in the high-resolution spectra. Results. We find that HD 43317 is a single fast rotator (v_rot ~ 50% v_crit) and hybrid SPB/Beta Cep-type pulsator with Solar metal abundances. We interpret the variations in photometry and spectroscopy as a result of rotational modulation connected to surface inhomogeneities, combined with the presence of both g and p mode pulsations. We detect a series of ten consecutive frequencies with an almost constant period spacing of 6339 s as well as a second shorter sequence consisting of seven frequencies with a spacing of 6380 s. The dominant frequencies fall in the regime of gravito-inertial modes.
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. Our goal is to analyse and interpret t
he 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 Beta Cep instability strip. We compare 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 match the results with evolutionary tracks to estimate stellar parameters. We use various time series analysis tools to explore the nature of the variations present in the light curve. Additional calculations are carried out based on distance and historical position measurements of the components to impose constraints on the binary orbit. We find that HD 51756 is a wide binary with both a slow (v sin i approx 28 km s^-1) and a fast (v sin i approx 170 km s^-1) early-B rotator whose atmospheric parameters are similar (T_eff approx 30000 K and log g approx 3.75). We are unable to detect pulsation in any of the components, and we interpret the harmonic structure in the frequency spectrum as sign of rotational modulation, which is compatible with the observed and deduced stellar parameters of both components. 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.
