Multiple and changing cycles of active stars II. Results

K. Oláh, Z. Kolláth, T. Granzer, K. G. Strassmeier, A. F. Lanza, S. Järvinen, H. Korhonen, S. L. Baliunas, W. Soon, S. Messina, G. Cutispoto

Published 2009-04-10Version 1

We study the time variations of the cycles of 20 active stars based on decades-long photometric or spectroscopic observations. A method of time-frequency analysis, as discussed in a companion paper, is applied to the data. Fifteen stars definitely show multiple cycles; the records of the rest are too short to verify a timescale for a second cycle. The cycles typically show systematic changes. For three stars, we found two cycles in each of them that are not harmonics, and which vary in parallel, indicating that a common physical mechanism arising from a dynamo construct. The positive relation between the rotational and cycle periods is confirmed for the inhomogeneous set of active stars. Stellar activity cycles are generally multiple and variable.