Rotation period as a function of the effective temperature for Kepler MS single stars. The color-code indicates the density of stars. The dot-dashed line marks the intermediate-P_rot gap. The blue circles highlight the stars belonging to NGC 6811. The symbol size indicates the magnetic activity level inferred through ⟨S​_ph⟩: the larger the symbol, the stronger the magnetic activity. The subpanel zooms into the stars of NGC 6811 within the temperature range in which they cross the gap. The shaded purple region corresponds to the 5200 K < T_eff < 5400 K interval considered in Fig. 1.