Space Physics Seminar fall-2018

Close-in planets represent a significant part of the 3000+ know planets as they are most favourable to detect with our current technique. In contrast with the solar-system planets, they generally are expected to orbit in a sub-alfvénic stellar wind, where the perturbations they excite in the corona of their host star are able to travel upwind down to the stellar surface, and potentially induce observable phenomena. The effective connection between the planet and its host takes the form of two Alfvén wings. Depending on the topology of the planetary and stellar magnetic fields, on the rotation profile of the corona, and on the orbital parameters, it is possible that none, one, or the two of the Alfvén wings connect together the star and the planet. I will explore the formation and sustainment of Alfvén wings in global three-dimensional simulations under the magneto-hydrodynamic formalism with the PLUTO code. I model globally the stellar wind of a typical cool star in which a close-in orbiting planet is introduced as a boundary condition. By varying the magnetic topologies of the planetary and stellar magnetic fields, I explore the variety of Alfvén wings that can develop and quantify the Poynting flux flowing through those wings. With an extensive set of simulations, I deduce scaling laws of the amount of magnetic energy such magnetic interactions can channel to the lower stellar corona, as well as the amount of angular momentum that can be exchanged between the two bodies due to magnetic torques. As a result, I parametrize the accessible energy available to modify the apparent magnetic activity of the star. I will also quantify the phase and latitude offsets that can be expected between the planetary subpoint on the stellar surface and the actual location where energy is deposited. I will conclude by showing some preliminary attempts to apply these results to the cases of realistic systems with more complex, non-axisymmetric topologies using of the observed magnetic fields of Kepler-78.