Dependence of the modified equivalent width of Ca II K emission on planet mass. Only stars with T_eff ≤ 5500 K and a ≤ 0.15 AU are considered. Modified equivalent width is equivalent width corrected for strong temperature dependence. By definition, the EQW is negative for emission. Consequently, lower values mean higher emission and higher chromospheric activity. Chromospheric activity of stars with more massive planets is higher than in those with less massive planets. Empty triangles denote stars with planets detected by the RV method, full triangles the transit method.