Calibration of Equilibrium Tide Theory for Extrasolar Planet Systems

TL;DR

This paper develops an empirically calibrated equilibrium tide model for extrasolar planets, explaining their orbital distributions and survival, but not their inflated radii, and highlights differences in dissipation between planets and stars.

Contribution

It introduces a simple, high-order eccentricity model for tidal dissipation in exoplanet systems, calibrated with observational data, and compares it to stellar binary systems.

Findings

Model explains distribution of exoplanet periods, eccentricities, and masses.

Short-period planets around evolved A stars are explained by increased tidal inspiral.

Model does not support tidal dissipation as the cause of inflated planetary radii.

Abstract

We provide an 'effective theory' of tidal dissipation in extrasolar planet systems by empirically calibrating a model for the equilibrium tide. The model is valid to high order in eccentricity and parameterised by two constants of bulk dissipation - one for dissipation in the planet and one for dissipation in the host star. We are able to consistently describe the distribution of extrasolar planetary systems in terms of period, eccentricity and mass (with a lower limit of a Saturn mass) with this simple model. Our model is consistent with the survival of short-period exoplanet systems, but not with the circularisation period of equal mass stellar binaries, suggesting that the latter systems experience a higher level of dissipation than exoplanet host stars. Our model is also not consistent with the explanation of inflated planetary radii as resulting from tidal dissipation. The paucity of short period planets around evolved A stars is explained as the result of enhanced tidal inspiral resulting from the increase in stellar radius with evolution.