2006A&A...460..317P

The observations of enhanced chromospheric activity on HD 179949 as well as on υ And with the same periods as their close-in planets seem to indicate some kind of magnetic interaction between star and planet. A constraint to any possible model are the large phase angles of 60° and 169°, respectively. We present a simple model, which is based on the propagation of Alfven waves within the stellar wind flow relative to the planet and which can meet this restriction. In the solar system such a model is successfully used to explain the current system between Io and Jupiter.