Evolution of low-mass stars in the Alpha Persei cluster

The results of a photometric and spectroscopic survey of the Alpha Per cluster are presented in tables, graphs, and diagrams and discussed. From relative-proper-motion determinations on about 4000 stars of V magnitude brighter than about 16 in a 1.2 x 1.2-deg area, 88 probable cluster members are selected for BVRI photometry with the 0.9-m and 1.3-m KPNO telescopes and H-alpha and 519.7-nm observations with echelle spectrographs on the 1.5-m telescope and MMT at Mount Hopkins. An apparent premain sequence is seen, and the positions of the faint cluster members on the V/(V-I) diagram correspond to the 50-Myr isochrone proposed by VandenBerg et al. (1983). The light variations observed in six G and K dwarf members are shown in graphs and attributed to surface spots in rotation. Over 50 percent of the stars of types later than G2 are found to have v sin i = 25-150 km/sec (velocities attributed to spin-up during contraction to the main sequence), and comparison with Hyades K dwarfs suggests spin-down to v sin i less than 10 km/sec over a few times 10 Myr.