The most massive heartbeat: an in-depth analysis of ι Orionis

Abstract

Ori is a well-studied massive binary consisting of an O9 III + B1 III/IV star. Due to its high eccentricity (e = 0.764) and short orbital period (P orb = 29.133 76 d), it has been considered to be a good candidate to show evidence of tidal effects; however, none have previously been identified. Using photometry from the BRIght Target Explorer (BRITE)-Constellation space photometry mission, we have confirmed the existence of tidal distortions through the presence of a heartbeat signal at periastron. We combine spectroscopic and light-curve analyses to measure the masses and radii of the components, revealing Ori to be the most massive heartbeat system known to date. In addition, using a thorough frequency analysis, we also report the unprecedented discovery of multiple tidally induced oscillations in an O star. The amplitudes of the pulsations allow us to empirically estimate the tidal circularization rate, yielding an effective tidal quality factor Q 4 10 4 .