Indications for an influence of hot Jupiters on the rotation and activity of their host stars

Context. The magnetic activity of planet-hosting stars is an importantfactor for estimating the atmospheric stability of close-in exoplanetsand the age of their host stars. It has long been speculated thatclose-in exoplanets can influence the stellar activity level. However,testing for tidal or magnetic interaction effects in samples ofplanet-hosting stars is difficult because stellar activity hindersexoplanet detection, so that stellar samples with detected exoplanetsshow a bias toward low activity for small exoplanets. <br/><br/>Aims: Weaim to test whether exoplanets in close orbits influence the stellarrotation and magnetic activity of their host stars. <br/><br/>Methods: Wedeveloped a novel approach to test for systematic activity-enhancementsin planet-hosting stars. We use wide (several 100 AU) binary systems inwhich one of the stellar components is known to have an exoplanet, whilethe second stellar component does not have a detected planet andtherefore acts as a negative control. We use the stellar coronal X-rayemission as an observational proxy for magnetic activity and analyzeobservations performed with Chandra and XMM-Newton. <br/><br/>Results: Wefind that in two systems for which strong tidal interaction can beexpected the planet-hosting primary displays a much higher magneticactivity level than the planet-free secondary. In three systems forwhich weaker tidal interaction can be expected the activity levels ofthe two stellar components agree with each other. <br/><br/>Conclusions:Our observations indicate that the presence of Hot Jupiters may inhibitthe spin-down of host stars with thick outer convective layers. Possiblecauses for this effect include a transfer of angular momentum from theplanetary orbit to the stellar rotation through tidal interaction, ordifferences during the early evolution of the system, where the hoststar may decouple from the protoplanetary disk early because of a gapopened by the forming Hot Jupiter.