Dynamical Tides in Compact White Dwarf Binaries: Influence of Rotation

TL;DR

This paper investigates how rotation influences tidal interactions in compact white dwarf binaries, revealing that rotation significantly affects retrograde and inertial waves, which impacts the systems' evolution and spin dynamics.

Contribution

It introduces a detailed analysis of rotational effects on tidal waves in white dwarfs using the traditional approximation, highlighting new dynamical forcing terms and their implications.

Findings

Rotation alters retrograde gravity and inertial waves significantly.

Previous models of tidal spin-up are not substantially changed by rotation.

New dynamical tidal forcing terms are identified near synchronous rotation.

Abstract

Tidal interactions play an important role in the evolution and ultimate fate of compact white dwarf (WD) binaries. Not only do tides affect the pre-merger state (such as temperature and rotation rate) of the WDs, but they may also determine which systems merge and which undergo stable mass transfer. In this paper, we attempt to quantify the effects of rotation on tidal angular momentum transport in binary stars, with specific calculations applied to WD stellar models. We incorporate the effect of rotation using the traditional approximation, in which the dynamically excited gravity waves within the WDs are transformed into gravito-inertial Hough waves. The Coriolis force has only a minor effect on prograde gravity waves, and previous results predicting the tidal spin-up and heating of inspiraling WDs are not significantly modified. However, rotation strongly alters retrograde gravity waves and inertial waves, with important consequences for the tidal spin-down of accreting WDs. We identify new dynamical tidal forcing terms that arise from a proper separation of the equilibrium and dynamical tide components; these new forcing terms are very important for systems near synchronous rotation. Additionally, we discuss the impact of Stokes drift currents on the wave angular momentum flux. Finally, we speculate on how tidal interactions will affect super-synchronously rotating WDs in accreting systems.