Theoretical investigation of the occurrence of tidally excited oscillations in massive eccentric binary systems

TL;DR

This study uses theoretical models and machine learning to analyze how tidal forces induce oscillations in massive eccentric binary stars, revealing diverse resonance behaviors and their dependence on stellar evolution.

Contribution

It provides a comprehensive theoretical framework and statistical analysis of resonance occurrences in massive binary systems, highlighting the role of TEOs in stellar angular momentum transport.

Findings

Resonance occurrence varies widely across evolutionary stages.

TEOs are more frequent near the terminal age main sequence.

Resonance behaviors are diverse, including long and absent resonances.

Abstract

Massive and intermediate-mass stars reside in binary systems much more frequently than low-mass stars. Binaries containing massive main-sequence (MS) component(s) are often characterised by eccentric orbits, and can be observed as eccentric ellipsoidal variables (EEVs). The orbital phase-dependent tidal potential acting on the components of EEV can induce tidally excited oscillations (TEOs). We investigate how the history of resonances between the eigenmode spectra of the EEV components and the tidal forcing frequencies depends on the initial parameters of the system. We synthesised 20,000 evolutionary models of the EEVs across the MS. Later, we calculated the eigenfrequencies for each model. We focused only on the $l=2$, $m=0,+2$ modes. Knowing the temporal changes in the orbital parameters of simulated EEVs and the changes of the eigenfrequency spectra for both components, we were able to determine so-called `resonance curves', which describe the overall chance of a resonance occurring. We analysed the resonance curves by constructing basic statistics for them and analysing their morphology using machine learning methods, including the Uniform Manifold Approximation and Projection tool. The EEV resonance curves from our sample are characterised by striking diversity, including the occurrence of exceptionally long resonances or the absence of resonances for long evolutionary times. Both components may be subject to increased resonance rates as they approach the TAMS. On average, we should observe TEOs more frequently in EEVs containing massive components than intermediate-mass ones. TEOs will be particularly well-pronounced for EEVs with the component(s) close to the TAMS. Given the total number of resonances and their rates, TEOs may play an important role in the transport of angular momentum within massive and intermediate-mass stars (mainly near TAMS).