Although they are relatively frequent as free-floating objects, brown dwarfs are scarcely found as companions to solar-type stars. The paucity of brown dwarfs in close-orbits first noticed by radial velocity surveys has led to the concept of the "brown dwarf desert".
Dr. Guillot will show that this desert concerns in fact close companions with masses larger than about 3 Jupiter masses orbiting G-type stars. On the other hand, photometric surveys have shown that in fact F-type stars do possess close-in, massive companions. Dr. Guillot will show that this is explained by the loss of an initial population of close-in massive giant planets and brown dwarfs due to tidal interactions: Because stars orbit less rapidly than their close-in companions, the tide raised on the star causes the companion to loose angular momentum and spiral in. The effect is much more pronounced around G-type stars because of a larger magnetic braking and because of increased dissipation, probably by internal gravity waves.
Dr. Guillot will use statistical methods to compare observations and model results and derive constraints on the tidal dissipation in stars as a function of their interior properties. This provides a powerful way to analyze the population of exoplanets and tie present observations with initial conditions at the time of the formation of these systems.