Upper panel: distribution on log I_Hα activity for the full sample (black), stars with positive correlation coefficient higher than 0.5 (hatched grey), and stars with negative correlation coefficient lower than −0.5 (filled grey). Vertical lines are the medians of the distributions with a black line for the full sample, a dashed line for the positively correlated stars, and a dotted line for the negatively correlated stars. Lower panel: same as the upper panel but using a relative distribution on log I_Hα.