Rotational Periods and Starspot Activity of Young Solar-Type Dwarfs in the Open Cluster IC 4665

We present the results of a V-band photometric monitoring survey of 15 late-type dwarfs in the young open cluster IC 4665. Low-amplitude periodic light variations are found for 8 stars and ascribed to the modulation by starspots that cover typically a few percent of the stellar disk. Periods range from 0.6 to 3.7 d, translating to equatorial velocities between 13 and 93 km/s. That no period longer than 4 d was detected suggests a relative paucity of extremely slow rotators (V(sub eq) much less than 10 km/s) among late-type dwarfs in IC 4665. The fractional number of slow rotators in IC 4665 is similar to that of Alpha Per cluster, suggesting that IC 4665 is close in age to Alpha Per (approx. 50 Myr).