Search for star-planet interaction
  We analyse the chromospherical activity of stars with extrasolar planets and search for a possible correlation between the equivalent width of the core of Ca II K line and orbital parameters of the planet. We found a statistically significant evidence that the equivalent width of the Ca II K line reversal, which originates in the stellar chromosphere depends on the orbital period P_orb of the exoplanet. Planets orbiting stars with T_eff < 5500 K and with P_orb < 20 days generally have much stronger emission than planets at similar temperatures but at longer orbital periods. P_orb=20 days marks a sudden change in behaviour, which might be associated with a qualitative change in the star-planet interaction. 
Tereza Krejcova, Jan Budaj and Julius Koza
astro-ph.EP