Tidal dissipation by inertial waves in differentially rotating convective envelopes of low-mass stars

TL;DR

This study investigates how differential rotation in low-mass stars' convective envelopes affects inertial wave dissipation, revealing the importance of corotation resonances in the orbital and rotational evolution of close star-planet systems.

Contribution

It introduces numerical simulations of tidally excited inertial waves in differentially rotating stellar envelopes, highlighting the impact of differential rotation on wave propagation and dissipation.

Findings

Differential rotation modifies inertial wave frequency range and propagation.

Corotation resonances significantly influence wave dissipation.

Dissipation depends on stellar mass, rotation profile, and viscosity.

Abstract

Tidal interactions in close star-planet or binary star systems may excite inertial waves (their restoring force is the Coriolis force) in the convective region of the stars. The dissipation of these waves plays a prominent role in the long-term orbital and rotational evolution of the bodies involved. If the primary star rotates as a solid body, inertial waves have a Doppler-shifted frequency restricted to the range $[-2\Omega, 2\Omega]$ ($\Omega$ 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 modifies the frequency range and propagation domain of inertial waves and allows corotation resonances for non-axisymmetric oscillations. In this work, we perform numerical simulations of tidally excited inertial waves in a differentially rotating convective envelope with a conical (or latitudinal) rotation profile. The tidal forcing that we adopt contains spherical harmonics that correspond to the case of a circular and coplanar orbit. We study the viscous dissipation of the waves as a function of tidal frequency for various stellar masses and differential rotation parameters, as well as its dependence on the turbulent viscosity coefficient. We compare our results with previous studies assuming solid-body rotation and point out the potential key role of corotation resonances in the dynamical evolution of close-in star-planet or binary systems.