Gravito-inertial modes in a differentially rotating spherical shell

TL;DR

This study investigates axisymmetric gravito-inertial modes in a differentially rotating star's radiative zone, revealing how these modes propagate, concentrate energy, and may influence stellar tidal interactions.

Contribution

It provides the first detailed analysis of gravito-inertial modes in a differentially rotating spherical shell using spectral simulations and characteristic theory.

Findings

Modes can propagate throughout or be restricted within the shell.

Some modes concentrate energy around short-period shear layers called attractors.

Attractors' Lyapunov exponents depend on background stratification and oscillation frequency.

Abstract

Oscillations have been detected in a variety of stars, including intermediate- and high-mass main sequence stars. While many of these stars are rapidly and differentially rotating, the effects of rotation on oscillation modes are poorly known. In this communication we present a first study on axisymmetric gravito-inertial modes in the radiative zone of a differentially rotating star. These modes probe the deep layers of the star around its convective core. We consider a simplified model where the radiative zone of a star is a linearly stratified rotating fluid within a spherical shell, with differential rotation due to baroclinic effects. We solve the eigenvalue problem with high-resolution spectral simulations and determine the propagation domain of the waves through the theory of characteristics. We explore the propagation properties of two kinds of modes: those that can propagate in the entire shell and those that are restricted to a subdomain. Some of the modes that we find concentrate kinetic energy around short-period shear layers known as attractors. We characterise these attractors by the dependence of their Lyapunov exponent with the \BV frequency of the background and the oscillation frequency of the mode. Finally, we note that, as modes associated with short-period attractors form dissipative structures, they could play an important role for tidal interactions but should be dismissed in the interpretation of observed oscillation frequencies.