Free access article

A&A 440, 735-741 (2005)
DOI: 10.1051/0004-6361:20053297

Spots on EK Draconis

Active longitudes and cycles from long-term photometry

S. P. Järvinen^{1, 2}, S. V. Berdyugina^{2, 3} and K. G. Strassmeier<sup>1

1</sup>  Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
    e-mail: [sjarvinen;kstrassmeier]@aip.de
²  Astronomy Division, PO Box 3000, 90014 University of Oulu, Finland
³  Institute of Astronomy, ETH Zentrum, 8092 Zürich, Switzerland
    e-mail: sveta@astro.phys.ethz.ch

(Received 25 April 2005 / Accepted 30 May 2005)

Abstract
We analyse photometric observations of the young active star EK Dra, altogether about 21 years. Similar to the ZAMS stars LQ Hya and AB Dor, EK Dra shows long-lived, non-axisymmetric spot distribution with active longitudes on opposite hemispheres. At least two activity cycle can be found from the data. The first cycle originates from repeated switches of the activity between two active longitudes in about (2-2.25)-year intervals, resulting in a cycle of about (4-4.5) years. The second cycle is of the order of 10.5 years and comes from migration of the active longitudes. Our data cover two consecutive cycles. The periodicity is also present in the maximum, the mean and the minimum stellar brightness. Additionally, there is a long-term trend. If we combine our data with the Sonneberg plate measurements, we can conclude that the overall brightness of EK Dra has been continuously decreasing at least for the last 45 years. A comparison with current sunspot activity reveals many similarities between the Sun and EK Dra.

Key words: stars: activity -- stars: starspots

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