Stellar Activity Enhancement by Planets: Theory and Observations

Abstract

Many of the newly discovered exoplanets are gas giants in close proximity to their parent stars. Therefore, they raise tides on their host stars, and (if similar to Jupiter) will likely have substantial magnetospheres which can interact with stellar magnetic field. Both tidal and magnetospheric interactions can enhance stellar activity levels. An initial search for such planet-induced activity using the Ca ii IR triplet found no clear signal, but recently a more sensitive study using the Ca ii H and K lines has uncovered evidence for planet-enhanced emission on HD 179949, and hints of it in other systems. The phase dependence of the enhanced emission for HD 179949 suggests a magnetospheric interaction. We discuss a simple model of this interaction, the implications of this possible detection for diagnosing exoplanetary magnetospheres, and future observations.