Photometric index S_ph (percent) as a function of rotation period P_rot (days) for the RGs with rotational modulation. The photometric index S_ph is plotted in log scale, P_rot in linear scale. Blue squares indicate the nonoscillating RGs, red disks the RGBs, darker green upward-pointing triangles the low-mass RCs, and lighter downward-pointing triangles high-mass RCs. The markers that display black edges are confirmed spectroscopic binaries. Black dots indicate RV stable RGs. The gray background reflects the distribution of S_ph of the inactive stars (the darker, the higher).