Multiple and changing cycles of active stars
Konkoly Observatory of the Hungarian Academy of Sciences, 1525 Budapest, Hungary e-mail: email@example.com
2 Astrophysical Institute Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
3 INAF - Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
4 Tuorla Observatory, University of Turku, 21500 Piikkiö, Finland
5 Astronomy Division, PO Box 3000, 90014 University of Oulu, Finland
6 ESO, Karl-Schwarzschild Strasse 2, 85748 Garching bei Munchen, Germany
7 Harvard - Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
Accepted: 27 March 2009
Aims. We study the time variations in the cycles of 20 active stars based on decade-long photometric or spectroscopic observations.
Methods. A method of time-frequency analysis, as discussed in a companion paper, is applied to the data.
Results. Fifteen stars definitely show multiple cycles, but 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 vary in parallel, indicating 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.
Conclusions. Stellar activity cycles are generally multiple and variable.
Key words: stars: activity / stars: atmospheres / stars: late-type / starspots
© ESO, 2009