The eccentric massive binary V380 Cyg: revised orbital elements and interpretation of the intrinsic variability of the primary component*

Abstract

We present a detailed analysis and interpretation of the high-mass binary\nV380 Cyg, based on high-precision space photometry gathered with the Kepler\nspace mission as well as high-resolution ground-based spectroscopy obtained\nwith the HERMES spectrograph attached to the 1.2m Mercator telescope. We derive\na precise orbital solution and the full physical properties of the system,\nincluding dynamical component mass estimates of 11.43+/-0.19 and 7.00+/-0.14\nsolar masses for the primary and secondary, respectively. Our frequency\nanalysis reveals the rotation frequency of the primary in both the photometric\nand spectroscopic data and additional low-amplitude stochastic variability at\nlow frequency in the space photometry with characteristics that are compatible\nwith recent theoretical predictions for gravity-mode oscillations excited\neither by the convective core or by sub-surface convective layers. Doppler\nImaging analysis of the silicon lines of the primary suggests the presence of\ntwo high-contrast stellar surface abundance spots which are located either at\nthe same latitude or longitude. Comparison of the observed properties of the\nbinary with present-day single-star evolutionary models shows that the latter\nare inadequate and lack a serious amount of near-core mixing.\n