Tidal dissipation in rotating solar-type stars

Abstract

We calculate the excitation and dissipation of low-frequency tidal oscillations in uniformly rotating solar-type stars. For tidal frequencies smaller than twice the spin frequency, inertial waves are excited in the convective envelope and are dissipated by turbulent viscosity. Enhanced dissipation occurs over the entire frequency range rather than in a series of very narrow resonant peaks, and is relatively insensitive to the effective viscosity. Hough waves are excited at the base of the convective zone and propagate into the radiative interior. We calculate the associated dissipation rate under the assumption that they do not reflect coherently from the center of the star. Tidal dissipation in a model based on the present Sun is significantly enhanced through the inclusion of the Coriolis force but may still fall short of that required to explain the circularization of close binary stars. However, the dependence of the results on the spin frequency, tidal frequency, and stellar model indicate that a more detailed evolutionary study including inertial and Hough waves is required. We also discuss the case of higher tidal frequencies appropriate to stars with very close planetary companions. The survival of even the closest hot Jupiters can be plausibly explained provided that the Hough waves they generate are not damped at the center of the star. We argue that this is the case because the tide excited by a hot Jupiter in the present Sun would marginally fail to achieve nonlinearity. As conditions at the center of the star evolve, nonlinearity may set in at a critical age, resulting in a relatively rapid inspiral of the hot Jupiter.