Massive heartbeat stars from TESS. I. TESS sectors 1-16

Abstract

Context. Heartbeat stars are eccentric binaries exhibiting characteristic shape of brightness changes during periastron passage caused primarily by variable tidal distortion of the components. Variable tidal potential can drive tidally excited oscillations (TEOs), which are usually gravity modes. Studies of heartbeat stars and TEOs open a new possibility to probe interiors of massive stars. There are only a few massive (masses of components 2 M ) systems of this type known. Aims. Using TESS data from the first 16 sectors, we searched for new massive heartbeat stars and TEOs using a sample of over 300 eccentric spectroscopic binaries. Methods. We analysed TESS 2-min and 30-min cadence data. Then, we fitted Kumar's analytical model to the light curves of stars showing heartbeats and performed times-series analysis of the residuals searching for TEOs and periodic intrinsic variability. Results. We found 20 massive heartbeat systems, of which seven show TEOs. The TEOs occur at harmonics of orbital frequencies in the range between 3 and 36, with the median value equal to 9, lower than those in known Kepler systems with TEOs. The most massive system in this sample is the quadruple star HD 5980, a member of Small Magellanic Cloud. With the total mass of ∼150 M it is the most massive system showing a heartbeat. Six stars in the sample of the new heartbeat stars are eclipsing. Comparison of the parameters derived from fitting Kumar's model and from light-curve modelling shows that Kumar's model does not provide reliable parameters. In other words, orbital parameters can be reliably derived from fitting heartbeat light curves only if model includes all proximity effects. Finally, intrinsic pulsations of β Cep, SPB, δ Sct, and γ Dor-type were found in nine heartbeat systems. This opens an interesting possibility of studies of pulsation-binarity interaction and the co-existence of forced and self-excited oscillations.

Study of Chemically Peculiar Stars-I : High-resolution Spectroscopy and K2 Photometry of Am Stars in the Region of M44

“…In close binary systems, stellar pulsations may also be tidally induced (Kumar et al 1995;Thompson et al 2012); e.g., KOI-54 (Welsh et al 2011;Fuller & Lai 2012;Burkart et al 2012;O'Leary & Burkart 2014) and KIC 3230227 (Guo et al 2017). Highly eccentric (𝑒 > 0.3) binary systems with orbital periods between a fraction of a day and tens of days showing a sudden increase in brightness at periastron passage, on the order of several parts-per-thousand (ppt), are known as heartbeat (HB) stars (Handler et al 2002;Maceroni et al 2009;Hambleton et al 2013;Beck et al 2014;Hambleton et al 2016Hambleton et al , 2018Kołaczek-Szymański et al 2020). The name stems from the resemblance of the light curve to a heartbeat in an electrocardiogram.…”