Cycles on the Solar-type Stars and Cooler Dwarfs

Features of the development of activity cycles in the solar-type stars and fast-rotating cool dwarfs have been considered for 65 stars observed in some decades. Cycles with duration of 7–18 years compared to the solar cycle were found for about 50% of the studied stars. In cooler dwarfs with rotation periods of less than 5 days, cyclic changes in brightness occur on longer scales, up to 80 years. Activity of the highest level is produced on K dwarfs; their main cycles are long and have the highest amplitudes. Both old and young solar-type stars show a similar tendency in increasing the cycle length with a slower rotation. No evidence for a relation between the rotation period and duration of cycles was found for cool dwarfs with P rot < 5 days.