Two new SB2 binaries with main sequence B-type pulsators in the Kepler field

TL;DR

This study reports two new spectroscopic binary systems with B-type pulsators observed by Kepler, providing detailed orbital and stellar parameters, and analyzing their pulsation modes to enhance understanding of OB star evolution.

Contribution

It introduces two new SB2 binary systems with B-type pulsators, offering orbital solutions, stellar parameters, and pulsation analysis combining spectroscopy and Kepler photometry.

Findings

Detection of tidally excited g modes in one system

Identification of classical g mode pulsations driven by the kappa mechanism

Observation of nonlinear resonant mode excitation in p modes

Abstract

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.