The large-scale magnetic fields of planet-hosting solar-type stars

Stellar magnetic fields and their associated phenomena influence stellar behaviour and evolution, and potentially have significant impacts on any surrounding planetary system. However, the nature of star-planet interactions is unclear, especially the potential impact on a star of a closely orbiting massive planet with a powerful magnetic field. This thesis presents a spectropolarimetric survey of the large-scale magnetic fields of planet-hosting solar-type stars. While little evidence is found for a systematic difference in the magnetic field characteristics of planet-hosting stars compared with the population of solar-type stars, a small positive correlation is indicated between the magnitude of the tidal effects of the planet on the star and the magnetic field strength. Nevertheless, further spectropolarimetric observations of hot Jupiter hosting systems are required to confirm this tentative relationship. For the particular case of a moderately active star with a thin convective zone and a closely orbiting hot Jupiter (T Boötis) presented here, a remarkably rapid magnetic cycle with a period of - 240 d is discovered. For stars with shallow convective envelopes, this is an unusual occurrence and suggests a possible role for planetary tidal or magnetic interaction with the star’s convective zone and magnetic dynamo. More observations are required to verify this possible star-planet interaction and to extend the work to other similar systems as they come to light from exoplanet surveys