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We study the time variations of the cycles of 20 active stars based ondecades-long photometric or spectroscopic observations. A method oftime-frequency analysis, as discussed in a companion paper, is applied to thedata. Fifteen stars definitely show multiple cycles; the records of the restare too short to verify a timescale for a second cycle. The cycles typicallyshow systematic changes. For three stars, we found two cycles in each of themthat are not harmonics, and which vary in parallel, indicating that a commonphysical mechanism arising from a dynamo construct. The positive relationbetween the rotational and cycle periods is confirmed for the inhomogeneous setof active stars. Stellar activity cycles are generally multiple and variable.

Multiple and changing cycles of active stars II. Results