II] we identified 1445 variable stars in the field of the cluster, of which 99$\%$ were new discoveries. We found that $\ga 500$ of these variables lie near the cluster main sequence on photometric color-magnitude diagrams (CMDs) and show a correlation between period and magnitude. In this paper we investigate this population of variables arguing that the photometric variations are due to spotted star rotation. We use these variables to study the rotation of F-M main sequence stars at the age of the cluster ($550 \pm 30$ Myr, Paper I; note that for the rest of this paper we adopt this age which was derived by comparison to models with convective overshooting).

Rotation plays an important role in the life of a star. Empirically there is a strong relation between the rotation rate and the activity and age of low-mass stars [@Skumanich.72], with older stars being slower rotators and less active than younger stars. Rotation affects the structure of a star [see @Sills.00] and its evolution may have important consequences for mixing at the base of a star’s convection zone [see the review by @Pinsonneault.97]. Rotation also affects the spectral energy distribution of low-mass stars [@Stauffer.03]. It has even been 