Tidally Excited Oscillations in Heartbeat Binary Stars: Pulsation Phases and Mode Identification

TL;DR

This study analyzes pulsation phases in heartbeat binary stars to understand tidal interactions, finding that simple models explain many cases but deviations reveal complex physics like non-adiabatic effects and resonances.

Contribution

It provides the first detailed analysis of pulsation phases in tidally excited oscillations, highlighting the role of mode geometry and axis alignment in explaining observations.

Findings

More than half of systems match adiabatic mode predictions

Significant deviations observed in some systems suggest non-adiabatic effects

Deviations can probe resonances and mode physics in tidal oscillations

Abstract

Tidal forces in eccentric binary stars known as heartbeat stars excite detectable oscillations that shed light on the processes of tidal synchronization and circularization. We examine the pulsation phases of tidally excited oscillations (TEOs) in heartbeat binary systems. The target list includes four published heartbeat binaries and four additional systems observed by {\it Kepler}. To the first order, the pulsation phases of TEOs can be explained by the geometric effect of the dominant $l=2$, $m=0$, or $\pm 2$ modes assuming pulsations are adiabatic. We found that this simple theoretical interpretation can account for more than half of the systems on the list, assuming their spin and orbit axes are aligned. We do find significant deviations from the adiabatic predictions for some other systems, especially for the misaligned binary KIC 8164262. The deviations can potentially help to probe the non-adiabaticity of pulsation modes as well as resonances in the tidal forcing.