Tidally perturbed pulsations in the pre-main sequence δ Scuti binary RS Cha

Abstract

Context. Stellar components in binaries are subject to tidal forces which influence asteroseismic properties. Tidally pertubed pulsations have been reported for different objects but none of these are in their pre-main sequence phase of evolution. This makes RS Cha, consisting of two δ Scuti stars and with pulsational characteristics influenced by tidal effects, the first such object observed. Aims. We aim to investigate the pulsational properties of the eclipsing binary RS Cha in terms of the theory of tidally perturbed pulsations. Methods. Based on photometric time series obtained from the TESS satellite, we performed binary modelling using PHOEBE to interpret the binary light curve and to allow the investigation of the pulsations of both components in RS Cha. We modelled the detrended light curve with the superposition of linear modes. The frequencies were then interpreted as self excited modes perturbed by tidal forces. Results. We find evidence for tidally perturbed modes, which enables the identification of pulsation modes. RS Cha mainly exhibits dipole modes, while one prominent l = 2 or l = 3 mode is also inferred. The latter verifies previous results from spectroscopic time series. Conclusion. This work shows that RS Cha is an ideal candidate to test the theory of tidally perturbed pulsations within the framework of asteroseismic modelling. The identification of multiple pulsation modes using this theory is unprecedented and will be a keystone in the future of pre-main sequence asteroseismology. However, amplitude modulation caused by the changing light ratio during the orbital phase in an eclipsing binary also plays a significant role, which can complicate mode identification.

Gravity darkening and tidally perturbed stellar pulsation in the misaligned exoplanet system WASP-33

“…Indeed, the pulsational frequencies are close to the orbital harmonics, and while there is no exact coincidence, the pulsational frequencies are observed to be shifted a little bit rightwards (towards higher frequencies). The rightward shifted pulsational frequencies are known as perturbed frequencies and they are similarly interpreted in the case of V453 Cyg (Southworth et al 2020), V1031 Ori (Lee 2021) and RS Cha (Steindl et al 2021). In these systems, the perturbations have been identified in p modes alone.…”

Asteroseismology of Close Binary Stars: Tides and Mass Transfer

“…Observational work includes Balona (2018), in which he applied the above perturbative theory to KIC 4142768 6 . Tidally perturbed oscillations have been found in U Gru (Bowman et al, 2019b), V453 Cyg (Southworth et al, 2020), VV Ori (Southworth et al, 2021), and RS Cha (Steindl et al, 2021).…”

TESS Eclipsing Binary Stars. I. Short cadence observations of 4584 eclipsing binaries in Sectors 1-26

“…The advent of the TESS mission has also revealed a new class of pulsating stars in binaries, wherein the pulsation axis is "tidally tilted", producing a characteristic amplitude and phase modulation (Handler et al 2020;Kurtz et al 2020;Fuller et al 2020;Rappaport et al 2021). Additionally, a few studies have reported the detection of so-called "tidally perturbed" pulsations, where a series of pulsations that are nearly equidistantly spaced by the orbital frequency were detected (Bowman et al 2019;Steindl et al 2021;Southworth et al 2020). Such systems cannot currently be explained by the same model as the "tidally tilted" pulsators, and seem to have a separate connection to the interplay between tides and pulsations.…”