Volume 604, August 2017
|Number of page(s)||13|
|Section||Planets and planetary systems|
|Published online||21 August 2017|
Tidal dissipation in rotating low-mass stars and implications for the orbital evolution of close-in massive planets
II. Effect of stellar metallicity
1 Laboratoire AIM Paris-Saclay, CEA/DRF – CNRS – Univ. Paris Diderot – IRFU/SAp, Centre de Saclay, 91191 Gif-sur-Yvette Cedex, France
2 NaXys, Department of Mathematics, University of Namur, 8 Rempart de la Vierge, 5000 Namur, Belgium
3 Department of Astronomy, University of Geneva, Chemin des Maillettes 51, 1290 Versoix, Switzerland
4 IRAP, UMR 5277, CNRS and Université de Toulouse, 14 av. E. Belin, 31400 Toulouse, France
5 LUPM UMR 5299 CNRS/UM, Université de Montpellier, CC 72, 34095 Montpellier Cedex 05, France
6 Physikalisches Institut & Center for Space and Habitability, Universitaet Bern, 3012 Bern, Switzerland
Received: 20 February 2017
Accepted: 24 May 2017
Observations of hot-Jupiter exoplanets suggest that their orbital period distribution depends on the metallicity of the host stars. We investigate here whether the impact of the stellar metallicity on the evolution of the tidal dissipation inside the convective envelope of rotating stars and its resulting effect on the planetary migration might be a possible explanation for this observed statistical trend. We use a frequency-averaged tidal dissipation formalism coupled to an orbital evolution code and to rotating stellar evolution models in order to estimate the effect of a change of stellar metallicity on the evolution of close-in planets. We consider here two different stellar masses: 0.4 M⊙ and 1.0 M⊙ evolving from the early pre-main sequence phase up to the red-giant branch. We show that the metallicity of a star has a strong effect on the stellar parameters, which in turn strongly influence the tidal dissipation in the convective region. While on the pre-main sequence, the dissipation of a metal-poor Sun-like star is higher than the dissipation of a metal-rich Sun-like star; on the main sequence it is the opposite. However, for the 0.4 M⊙ star, the dependence of the dissipation with metallicity is much less visible. Using an orbital evolution model, we show that changing the metallicity leads to different orbital evolutions (e.g., planets migrate farther out from an initially fast-rotating metal-rich star). Using this model, we qualitatively reproduced the observational trends of the population of hot Jupiters with the metallicity of their host stars. However, more steps are needed to improve our model to try to quantitatively fit our results to the observations. Specifically, we need to improve the treatment of the rotation evolution in the orbital evolution model, and ultimately we need to consistently couple the orbital model to the stellar evolution model.
Key words: planet-star interactions / stars: evolution / stars: rotation / stars: abundances / stars: solar-type
© ESO, 2017
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