An important aspect in the evolutionary scenario of cool stars is their rotation. We will observe cool stars in different open clusters with known ages between 50 Myr and 2.0 Gyr and precisely identify their rotational periods for comparisons with evolutionary models. Starspots modulate the stellar flux within a few percent and may be used to provide true stellar rotation rates (without sini ambiguity). Our goal is to provide a large sample (more than 1,000) of rotational periods to define a conclusive empirical law between the rotational period, the mass, and the age of F-M dwarf stars. Detecting longer periods in intermediate-age cluster stars will constrain the internal differential rotation, hoping to lift differential-rotation models to a new generation. Using image-stacking, we boost the S/N to >1,000:1 even for the fainter cool stars in the fields. The time-series observations will cover each cluster for 100-150 consecutive nights, depending on declination, and will be made in the Sloan r bandpass. For calculations of astrophysical properties, i.e. metallicity, effective temperature, and gravity, we will employ the Strömgren bandpasses. One-time narrow-band Ha photometry is employed for the detection of chromospheric activity.
