R mode oscillations ubiquitous in stars

TL;DR

This paper reviews the properties and detection of r-mode oscillations in various rotating stars, highlighting their ubiquity and potential for measuring stellar rotation frequencies.

Contribution

It provides a comprehensive overview of r-mode oscillations in different star types and discusses their observational signatures and implications for stellar rotation analysis.

Findings

R modes are nearly toroidal and weakly affected by buoyancy.

R modes are excited mechanically and are ubiquitous in rotating stars.

Detection of r modes allows determination of stellar rotation frequencies.

Abstract

We discuss properties and examples of r-mode (large scale Rossby wave) oscillations in rotating stars. Motions are nearly toroidal but affected weakly by buoyancy. R modes seem to be excited mechanically in most cases, and ubiquitous in various types of rotating stars;e.g., fast rotating $\gamma$ Dor stars, spotted stars, eclipsing binary stars, Be stars, and accreting white dwarfs. In the Fourier spectrum of a star, even (i.e., symmetric to the equator) r modes of azimuthal order $m$ appear as a group of frequencies just below $m$ times the rotation frequency. From this property, a rotation frequency can be determined if r modes are detected. We discuss r modes in KIC8462852 (Boyajian's star), KIC9117875 (Am star), KIC6128830 (HgMn star), and the accreting white dwarf in the dwarf nova GW Lib.