Abstract
Context. The dissipation of the kinetic energy of wave-like tidal flows within the convective envelope of low-mass stars is one of the key physical mechanisms that shapes the orbital and rotational dynamics of short-period exoplanetary systems. Although low-mass stars are magnetically active objects, the question of how the star’s magnetic field impacts large-scale tidal flows and the excitation, propagation and dissipation of tidal waves still remains open. Aims. Our goal is to investigate the impact of stellar magnetism on the forcing of tidal waves, and their propagation and dissipation in the convective envelope of low-mass stars as they evolve. Methods. We have estimated the amplitude of the magnetic contribution to the forcing and dissipation of tidally induced magneto-inertial waves throughout the structural and rotational evolution 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. Results. We find that the large-scale magnetic field of the star has little influence on the excitation of tidal waves in the case of nearly-circular orbits and coplanar hot-Jupiter planetary systems, but that it has a major impact on the way waves are dissipated. Our results therefore indicate that a full magneto-hydrodynamical treatment of the propagation and dissipation of tidal waves is needed to properly assess the impact of star-planet tidal interactions throughout the evolutionary history of low-mass stars hosting short-period massive planets.
Highlights
Over the last two decades, a large variety of exoplanetary systems has been discovered, primarily through photometric transit and radial velocity observations (e.g. Perryman 2018)
The convective zone (CZ) of a perturbed rotating body is the seat of inertial waves that get dissipated by turbulent friction (e.g. Ogilvie & Lin 2004, 2007), while the radiative zone supports gravito-inertial waves which are dissipated by thermal damping and turbulent friction (e.g. Zahn 1975; Terquem et al 1998; Goodman & Dickson 1998; Barker & Ogilvie 2010)
The influence of magnetism on tidal interaction along the evolution of low-mass stars has been investigated through its impact on tidal excitation and dissipation
Summary
Over the last two decades, a large variety of exoplanetary systems has been discovered, primarily through photometric transit and radial velocity observations (e.g. Perryman 2018). The transition between hydrodynamical and magneto-hydrodynamical (MHD) regimes have been explored in a shearing box model with a uniform magnetic field (Wei 2016) and in spherical geometry with both a uniform field directed along the z-axis and a dipolar magnetic field (Lin & Ogilvie 2018) The authors of these studies both stressed that the Lehnert number Le (Lehnert 1954) determines how important magnetism is to tidal dissipation. In the presence of a magnetic field, the Lorentz force acting on the equilibrium tide is likely to play a role in the excitation of tidal waves This motivates the study of the impact of stellar magnetism on both dissipation and excitation of dynamical tides inside the CZ and along the evolution of low-mass stars. 3 the relative importance of Ohmic over viscous dissipations of tidally induced magneto-inertial waves throughout the evolution of low-mass stars.
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