Impact of Stellar Magnetism on Star-planet Tidal Interactions

Over the last two decades, about 4000 exoplanets have been discovered around low-mass stars. For the shortest period exoplanets, star-planet tidal interactions are likely to have played a major role in the ultimate orbital evolution and on the spin axis evolution of the host stars. Although low-mass stars are magnetically active objects, the question of how the star's magnetic field impacts the excitation, propagation and dissipation of tidal waves remains open. In this work, we have derived the magnetic contribution to the tidal force and estimated its amplitude all along the structural and rotational evolutions of low-mass stars (from M to F-type). For this purpose, we have used detailed grids of rotating stellar models computed with the stellar evolution code STAREVOL. The amplitude of dynamo-generated magnetic fields is estimated via physical scaling laws at the base and the top of the convective envelope. We find that the star's magnetic field has little influence on the excitation of tidal waves in near circular and coplanar Hot-Jupiter systems, but that it has a major impact on the waves dissipation. Our results therefore indicate that a full MHD treatment of the propagation and dissipation of tidal waves is needed to assess the impact of star-planet tidal interactions for all low-mass stars along their evolution.