期刊
ASTRONOMY & ASTROPHYSICS
卷 501, 期 2, 页码 703-713出版社
EDP SCIENCES S A
DOI: 10.1051/0004-6361/200811304
关键词
stars: activity; stars: atmospheres; stars: late-type; starspots
资金
- Hungarian Research Grants OTKA [T-048961, T-068626]
- JPL [12700064]
- Smithsonian Institution Restricted Endowment funds
- NASA [NNX07AI356]
- Vienna-AIP APTs in southern Arizona
- State of Brandenburg MWFK
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.
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