Astron. Astrophys. 356, 643-653 (2000)

Multiperiodic light variations of active stars

K. Oláh ¹, Z. Kolláth ¹ and K.G. Strassmeier <sup>2

1</sup> Konkoly Observatory of the Hungarian Academy of Sciences, 1525 Budapest, Hungary (olah@konkoly.hu, kollath@konkoly.hu)
² Institute for Astronomy, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria (strassmeier@astro.univie.ac.at)

Received 2 November 1999 / Accepted 5 January 2000

Abstract

We studied the long-term light behaviour of ten rapidly-rotating active stars (LQ Hya, V833 Tau, EI Eri, V711 Tau, BY Dra, HU Vir, IL Hya, VY Ari, HK Lac, IM Peg) with Fourier analysis. Using photometric databases of up to 30 years in length, we search for periodic or quasi-periodic long-term variations of the overall light levels. Out of the ten stars studied, nine show cyclic variability and six of those seem to vary on two or multiple time-scales. Using additional data from the literature, we found that cycle lengths were generally longer for stars with longer rotation periods. The inverse Rossby numbers of these stars show a correlation with calculated from the shortest cycle length. The cycle lengths of several stars agree well with other types of cycles determined earlier.

Using artificial test data, we found that the cyclic variation of the average light level is determined by the change in the spot/plage coverage alone and that spot migration does not play a significant role in the shape or length of the long-term brightness changes.

Key words: stars: activity stars: binaries: close stars: late-type stars: rotation stars: starspots techniques: photometric

Send offprint requests to: K. Oláh

© European Southern Observatory (ESO) 2000

Online publication: April 10, 2000

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