Interplay of tidal evolution and stellar wind braking in the rotation of stars hosting massive close-in planets

TL;DR

This paper applies creep tide theory to study the rotation evolution of stars with massive close-in planets, considering stellar wind braking, and finds that active stars tend to rotate slower than their orbital periods, affecting age estimation methods.

Contribution

It introduces a model combining tidal evolution and stellar wind braking to analyze the rotation of stars hosting massive close-in planets, highlighting limitations of gyrochronology.

Findings

Active stars with close-in planets rotate slower than orbital periods.

Tidal evolution can invalidate gyrochronology for systems within 0.03-0.04 AU.

Rotation evolution depends on stellar activity and planetary mass.

Abstract

This paper deals with the application of the creep tide theory (Ferraz-Mello, Cel. Mech. Dyn. Astron. vol. 116, 109, 2013) to the study of the rotation of stars hosting massive close-in planets. The stars have nearly the same tidal relaxation factors as gaseous planets and the evolution of their rotation is similar to that of close-in hot Jupiters: they tidally evolve towards a stationary solution. However, stellar rotation may also be affected by stellar wind braking. Thus, while the rotation of a quiet host star evolves towards a stationary attractor with a frequency ($1+6e^2$) times the orbital mean-motion of the companion, the continuous loss of angular momentum in an active star displaces the stationary solution towards slower values: Active host stars with big close-in companions tend to have rotational periods larger than the orbital periods of their companions. The study of some hypothetical examples shows that because of tidal evolution, the rules of gyrochronology cannot be used to estimate the age of one system with a large close-in companion, no matter if the star is quiet or active, if the current semi-major axis of the companion is smaller than 0.03--0.04 AU. Details on the evolution of the systems: CoRoT LRc06E21637, CoRoT-27, Kepler-75, CoRoT-2, CoRoT-18, CoRoT-14 and on hypothetical systems with planets of mass 1--4 M_Jup in orbit around a star similar to the Sun are given.