A small survey of the magnetic fields of planet-host stars

Using spectropolarimetry, we investigate the large-scale magnetic topologies of stars hosting close-in exoplanets. A small survey of 10 stars has been done with the twin instruments Télescope Bernard Lyot /NARVAL and Canada-France-Hawaii Telescope/ESPaDOnS between 2006 and 2011. Each target consists of circular polarization observations covering 7-22 d. For each of the seven targets in which a magnetic field was detected, we reconstructed the magnetic field topology using Zeeman-Doppler imaging. Otherwise, a detection limit has been estimated. Three new epochs of observations of t Boo are presented, which confirm magnetic polarity reversal. We estimate that the cycle period is 2 yr, but recall that a shorter period of 240 d cannot still be ruled out. The result of our survey is compared to the global picture of stellar magnetic field properties in the mass-rotation diagram. The comparison shows that these giant planet-host stars tend to have similar magnetic field topologies to stars without detected hot Jupiters. This needs to be confirmed with a larger sample of stars.