Relation between σ(S_ph) and ⟨S_ph⟩ for the two populations of stars, above and below the intermediate-P_rot gap. Left: same as in Fig. 2 but for main-sequence GKM stars. The color code indicates whether they belong to the fast- (red) or slow-rotating (black) populations. For F stars (T_eff ≥ 6000 K), the rotation-period distribution is unimodal, and, thus, F stars are not considered here. Right: distribution of the log σ(S_ph) residuals computed after accounting for the dependences on the different parameters. The distributions for the fast- (red) or slow-rotating (gray) populations are illustrated by the KDE.