gyre_tides: Modeling binary tides within the gyre stellar oscillation code

TL;DR

The paper introduces gyre_tides, a new tool within the GYRE code that models binary star tides using a multipolar and Fourier-series approach, providing accurate solutions and revealing differences from traditional modal methods.

Contribution

We developed gyre_tides, a novel executable in GYRE that directly solves linear tidal response equations, enhancing modeling capabilities for binary star tides with improved accuracy.

Findings

General agreement with existing literature results

Identified differences between direct solutions and modal decomposition methods

Applicable to modeling equilibrium and dynamical tides in aligned binaries

Abstract

We describe new functionality in the GYRE stellar oscillation code for modeling tides in binary systems. Using a multipolar expansion in space and a Fourier-series expansion in time, we decompose the tidal potential into a superposition of partial tidal potentials. The equations governing the small-amplitude response of a spherical star to an individual partial potential are the linear, non-radial, non-adiabatic oscillation equations with an extra inhomogeneous forcing term. We introduce a new executable, gyre_tides, that directly solves these equations within the GYRE numerical framework. Applying this to selected problems, we find general agreement with results in the published literature but also uncover some differences between our direct solution methodology and the modal decomposition approach adopted by many authors. In its present form gyre_tides can model equilibrium and dynamical tides of aligned binaries in which radiative diffusion dominates the tidal dissipation (typically, intermediate and high-mass stars on the main sequence). Milestones for future development include incorporation of other dissipation processes, spin-orbit misalignment, and the Coriolis force arising from rotation.