Chromospheric flux ratio, log , as a function of the rotation period, P_rot (in days). The black dots correspond to the Kepler seismic solar analogs, and the red squares to the solar-analog stars found in the MWO sample of FGK stars. Each represented Kepler star is referred by the same number as given in Tables 2 and 3. The position of the Sun is also indicated with its astronomical symbol for a log  (Hall et al. 2009) and a rotation of 25 days.