Star-planet interactions VI. Tides, stellar activity and planet evaporation

TL;DR

This study models the evolution of close-in star-planet systems, considering stellar rotation, tides, and planet evaporation, and finds good agreement with observed exoplanet distributions, especially regarding the Neptunian desert and radius valley features.

Contribution

It provides a comprehensive, self-consistent model of star-planet interactions including tides and evaporation, improving understanding of observed exoplanet distributions without fine-tuning.

Findings

Agreement with observed exoplanet distributions

Upper limit for orbital period of bare-core planets

Insights into the Neptunian desert and radius valley

Abstract

Tidal interactions and planet evaporation processes impact the evolution of close-in star-planet systems. We study the impact of stellar rotation on these processes. We compute the time evolution of star-planet systems consisting of a planet with initial mass between 0.02 and 2.5 M$_{ Jup}$ (6 and 800 M$_{ Earth}$), in a quasi-circular orbit with an initial orbital distance between 0.01 and 0.10 au, around a solar-type star evolving from the Pre-Main-Sequence (PMS) until the end of the Main-Sequence (MS) phase. We account for the evolution of: the stellar structure, the stellar angular momentum due to tides and magnetic braking, the tidal interactions (equilibrium and dynamical tides in stellar convective zones), the mass-evaporation of the planet, and the secular evolution of the planetary orbit. We consider that at the beginning of the evolution, the proto-planetary disk has fully dissipated and planet formation is complete. Both a rapid initial stellar rotation, and a more efficient angular momentum transport inside the star, in general, contribute toward the enlargement of the domain which is devoid of planets after the PMS phase, in the plane of planet mass vs. orbital distance. Comparisons with the observed distribution of exoplanets orbiting solar mass stars, in the plane of planet mass vs. orbital distance (addressing the "Neptunian desert" feature), show an encouraging agreement with the present simulations, especially since no attempts have been made to fine-tune initial parameters of the models to fit the observations. We also obtain an upper limit for the orbital period of bare-core planets, that agrees with observations of the "radius valley" feature in the plane of planet radius vs. orbital period. The two effects, tides and planet evaporation, should be accounted for simultaneously and in a consistent way, with a detailed model for the evolution of the star.