On stellar activity enhancement due to interactions with extrasolar giant planets

We present a first attempt to identify and quantify possible interactions b etween recently discovered extrasolar giant planets (and brown dwarfs) and their host stars, resulting in activity enhancement in the stellar outer at mospheres. Many extrasolar planets have masses comparable to or larger than Jupiter and are within a distance of 0.5 AU, suggesting the possibility of their significant influence on stellar winds, coronae, and even chromosphe res. Beyond the well-known rotational synchronization, the interactions inc lude tidal effects (in which enhanced flows and turbulence in the tidal bul ge lead to increased magnetoacoustic heating and dynamo action) and direct magnetic interaction between the stellar and planetary magnetic fields. We discuss relevant parameters for selected systems and give preliminary estim ates of the relative interaction strengths.