Activity-rotation diagram for the NGC 6811 members (circles) in four T_eff ranges around the transition associated with the intermediate-P_rot gap. To better identify the gradual S​_ph shift, the crosses represent NGC 6811 members, but of any T_eff. The reference Kepler single MS sample is shown by the dots and density contours in gray. The color-code for the circles and dots is related to the distance to the intermediate-P_rot gap, which corresponds to the difference between the logarithm of a given star’s P_rot minus the logarithm of the gap location (truncated at δlog ± 0.4 for illustration purposes). The lightest colors correspond to the stars closest to the gap.