Tidal evolution of the rotation of stars hosting massive planets

• Grant number: 15/18043-3
• Support type: Scholarships in Brazil - Scientific Initiation
• Effective date (Start): October 01, 2015
• Effective date (End): September 30, 2016
• Field of knowledge: Physical Sciences and Mathematics - Astronomy
• Principal Investigator: Sylvio Ferraz de Mello
• Grantee: Lucas Ferreira da Rosa Moda
• Home Institution: Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

Recently, bright stars with transiting planets discovered by Kepler and CoRoT missions have been used on the determination of diverse orbital parameters of the system, as well as the dissipation and the rotation of its components. It is possible, through a technique known as "gyrochronology", that takes into account the angular momentum loss due to stellar wind, to estimate the star's age; however, in case there is a close-in massive companion (a hot Jupiter), the tidal effect is relevant to the evolution of the star's rotation, and the actual models of gyrochronology lose their validity in this scenario. In this case, the star's rotation period initially increases, due to the strong loss of angular momentum, when the star still spins in high velocity. Notwithstanding, at some point, the break lessens and begins to be overcome by the transfer of angular momentum from the planet's orbit to the star, whose rotation then starts to decelerate until the inevitable fall of the companion in the star, when a rapid decrease in its rotation is observed. In this project, we explore the interaction between the star and its companion, utilizing variants of the gamma-break.f program, whose code adopts the creep tide theory, developed in IAG (Ferraz-Mello, 2013). Actual simulations, made with a sun-like star that hosts a planet with the mass of Jupiter, indicate that this effect is relevant only for the cases in which the planet is within a distance of 0.05 AU (for farther planets, the orbital period variation is too small, and the star's rotation is controlled mainly by the brake due to the solar wind), although more tests need to be done. Thereat, we will vary several parameters (orbital period, semi major axis, eccentricity, mass and radius from planet and star, break, initial rotation period, relaxation factor) in an attempt to find a universal limit for which the angular momentum injection due to the tide is still significant. Thereby, we will be able to determine with a higher precision the age of stars hosting a hot Jupiter.