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Abstract: Evidence of magnetic interaction between late-type stars and close-in giantplanets is provided by the observations of stellar hot spots rotatingsynchronously with the planets and showing an enhancement of chromospheric andX-ray fluxes. We investigate star-planet interaction in the framework of amagnetic field model of a stellar corona, considering the interaction betweenthe coronal field and that of a planetary magnetosphere moving through thecorona. The energy budget of the star-planet interaction is discussed assumingthat the planet may trigger a release of the energy of the coronal field bydecreasing its relative helicity. The observed intermittent character of thestar-planet interaction is explained by a topological change of the stellarcoronal field, induced by a variation of its relative helicity. The modelpredicts the formation of many prominence-like structures in the case of highlyactive stars owing to the accumulation of matter evaporated from the planetinside an azimuthal flux rope in the outer corona. Moreover, the model canexplain why stars accompanied by close-in planets have a higher X-rayluminosity than those with distant planets. It predicts that the bestconditions to detect radio emission from the exoplanets and their host starsare achieved when the field topology is characterized by field lines connectedto the surface of the star, leading to a chromospheric hot spot rotatingsynchronously with the planet. The main predictions of the model can beverified with present observational techniques, by a simultaneous monitoring ofthe chromospheric flux and X-ray or radio emission, and spectropolarimetricobservations of the photospheric magnetic fields.

Author: A. F. Lanza


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