Magnetic and tidal migration of close-in planets. Influence of secular evolution on their population

TL;DR

This paper models the combined magnetic and tidal interactions influencing the orbital evolution of close-in exoplanets, explaining observed distributions and their impact on star-planet system detectability and stellar age estimation methods.

Contribution

It introduces a comprehensive numerical model that simultaneously considers magnetic and tidal torques affecting star-planet systems over their evolution.

Findings

Both magnetic and tidal interactions can dominate orbital evolution depending on initial conditions.

Different populations of star-planet systems emerge from combined interactions during various evolutionary phases.

Star-planet interactions significantly influence the distribution of orbital periods during the main sequence.

Abstract

Over the last two decades, a large population of close-in planets has been detected around a wide variety of host stars. Such exoplanets are likely to undergo planetary migration through magnetic and tidal interactions. We aim to follow the orbital evolution of a planet along the structural and rotational evolution of its host star by taking into account simultaneously tidal and magnetic torques, in order to explain some properties of the distribution of observed close-in planets. We rely on a numerical model of a coplanar circular star-planet system taking into account stellar structural changes, wind braking and star-planet interactions, called ESPEM. We browse the parameter space of star-planet systems' configurations and assess the relative influence of magnetic and tidal torques on secular evolution. We then synthesize star-planet populations and confront their distribution in orbital and stellar rotation periods to Kepler satellite data. First, we find that after the dissipation of the protoplanetary disk, both types of interactions can dominate secular evolution depending on the initial configuration of the system and the evolutionary phase considered. Moreover, different populations of star-planet systems emerge from the combined action of both kinds of interactions, according to the evolutionary phase during which the planet migrates significantly. This may affect significantly the detectability of star-planet systems as well as the validity of gyrochonology. All in all, star-planet interactions significantly impact the global distribution in orbital periods during the main sequence, while the global distribution in stellar rotation periods is marginally affected. More precisely, star-planet magnetic interactions significantly affect the distribution of super-Earths around slowly rotating stars, while tidal effects are found to shape the distribution of giant planets.