Stellar wind regimes of close-in extrasolar planets

¹ Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany e-mail: [preusse;kopp;buechner]@mps.mpg.de
² Institut für Theoretische Physik, Technische Universität Braunschweig, Mendelssohnstrasse 3, 38106 Braunschweig, Germany e-mail: u.motschmann@tu-bs.de

Received: 16 July 2004
Accepted: 26 December 2004

Abstract

Close-in extrasolar planets of Sun-like stars are exposed to stellar wind conditions that differ considerably from those for planets in the solar system. Unfortunately, these stellar winds belong to the still unknown parameters of these planetary systems. On the other hand, they play a crucial role in a number of star-planet interaction processes that may lead to observable radiation events. In order to lay a foundation for the investigation of such interaction processes, we estimate stellar wind parameters on the basis of the solar wind model by Weber & Davis and study the implications of the stellar magnetic fields. Our results suggest that in contrast to the solar system planets, some close-in extrasolar planets may be obstacles in a sub-Alfvénic stellar wind flow. In this case, the stellar wind magnetic pressure is comparable to or even larger than the dynamic flow pressure. We discuss possible consequences of these findings for the wind–exoplanet interactions. Further, we derive upper limit estimates for the energies such stellar winds can deposit in the exoplanetary magnetospheres. We finally discuss the implications the sub-Alfvénic environment may have on the star–planet interaction.