# The Pseudosynchronization of Binary Stars Undergoing Strong Tidal Interactions

## TL;DR

This study investigates the rotation periods of heartbeat binary stars experiencing strong tidal interactions, revealing that most are not pseudosynchronized and often rotate slightly slower than theoretical predictions, indicating additional physical influences.

## Contribution

It provides observational measurements of stellar rotation in heartbeat binaries and compares them to tidal synchronization theory, highlighting discrepancies and potential new physical mechanisms.

## Key findings

- Most heartbeat stars are not pseudosynchronized with their orbits.
- Many stars rotate at about 3/2 times the predicted pseudosynchronization period.
- Stars tend to reach a spin equilibrium slightly longer than theoretical predictions.

## Abstract

Eccentric binaries known as heartbeat stars experience strong dynamical tides as the stars pass through periastron, providing a laboratory to study tidal interactions. We measure the rotation periods of 24 heartbeat systems, using the Kepler light curves to identify rotation peaks in the Fourier transform. Where possible, we compare the rotation period to the pseudosynchronization period derived by Hut 1981. Few of our heartbeat stars are pseudosynchronized with the orbital period. For four systems, we were able to identify two sets of rotation peaks, which we interpret as the rotation from both stars in the binary. The majority of the systems have a rotation period that is approximately 3/2 times the pseudosynchronization period predicted by Hut 1981, suggesting that other physical mechanisms influence the stars' rotation, or that stars typically reach tidal spin equilibrium at a rotation period slightly longer than predicted.