Star-Planet Interaction: The Curious Case of the Planet Spoon-feeding Its Host Star (and Other Amenities)

We report two cases of Star-Planet Interaction (SPI) in two systems with hot Jupiters: HD 189733 and HD 17156. We used HST-COS to study the FUV variability of HD 189733 after the planetary eclipse. With the support of MHD simulations, we evince that material is likely evaporating from the planet and accreting onto the parent star. This produces a hot spot on the stellar surface, co-moving with the planetary motion and responsible of the X-ray and FUV variability at peculiar planetary phases. In HD 17156, which hosts a hot Jupiter in an eccentric orbit, we observed an enhancement of the X-ray activity at the passage of its planet at the periastron. The origin can be due to magnetic reconnection between the planetary and stellar magnetic fields, or due to material tidally stripped from the planet and accreting onto the star.