Tidally perturbed pulsations in the pre-main sequence $\delta$ Scuti binary RS Cha

TL;DR

This study investigates tidally perturbed pulsations in the pre-main sequence binary RS Cha, using TESS data to identify pulsation modes influenced by tidal forces, marking a significant step in pre-main sequence asteroseismology.

Contribution

It is the first to analyze tidally perturbed pulsations in a pre-main sequence binary, demonstrating mode identification and testing the theory in this evolutionary stage.

Findings

Evidence for tidally perturbed modes in RS Cha

Identification of mainly dipole modes and one higher-degree mode

Validation of previous spectroscopic results

Abstract

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 $\delta$ Scuti stars and with pulsational characteristics influenced by tidal effects , the first such object observed. We aim to investigate the pulsational properties of the eclipsing binary RS Cha in terms of the theory of tidally perturbed pulsations. 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. 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. 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.