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Multiple and changing cycles of active stars
Astronomy and Astrophysics
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 indoi:10.1051/0004-6361/200811304 fatcat:4xqrl5kuljh3bp26rulm3az7si