Activity-rotation diagram for two intervals of 100 K: 3800-3900 K (left); and 5400-5500 K (right). We use the local minimum (black crosses) to split the sample into fast- and slow-rotating populations. The gray dots show the stars with T_eff within the considered interval. The dotted red line shows the upper edge of the ⟨S_ph⟩ distribution (95^th percentile), while the solid red line shows its smoothed version.