Inertial waves in differentially rotating low-mass stars and tides

TL;DR

This paper investigates how differential rotation in low-mass stars affects inertial wave propagation and tidal dissipation, revealing broadened frequency ranges and complex wave behaviors that influence star-planet interactions.

Contribution

It introduces a model of inertial modes in differentially rotating stars, showing how differential rotation alters wave propagation and dissipation compared to solid-body rotation assumptions.

Findings

Differential rotation broadens inertial wave frequency range.

Inertial waves can be confined to parts of the stellar envelope.

Shear layers and attractor cycles influence wave behavior.

Abstract

Star-planet tidal interactions may result in the excitation of inertial waves in the convective region of stars. Their dissipation plays a prominent role in the long-term orbital evolution of short-period planets. If the star is assumed to be rotating as a solid-body, the waves' Doppler-shifted frequency is restricted to $[-2 \Omega, 2 \Omega]$ ($\Omega$ being the angular velocity of the star) and they can propagate in the entire convective region. However, turbulent convection can sustain differential rotation with an equatorial acceleration (as in the Sun) or deceleration that may modify waves propagation. We thus explore the properties of inertial modes of oscillation in a conically differentially rotating background flow whose angular velocity depends on the latitudinal coordinate only, close to what is expected in the external convective envelope of low-mass stars. We find that their frequency range is broadened by differential rotation, and that they may propagate only in a restricted part of the envelope. In some cases, inertial waves form shear layers around short-period attractor cycles. In others, they exhibit a remarkable behavior when a turning surface or a corotation layer exists in the star. We discuss how all these cases can impact tidal dissipation in stars.