Abstract
The long term changes of the quiet-state luminosity and the flare activity of the flare stars EV Lac and BY Dra during the decade 1971–80 have been studied using the photoelectric observations in the International UBV System carried out with the 30-inch Cassegrain reflector of the Department of Geodetic Astronomy, University of Thessaloniki installed at the Stephanion Observatory, as well as all other relevant data available. The quiet-state luminosity of the star EV Lac shows long-term fluctuations with an amplitude of 0 . m 3 and a period of about 5 years. The flare activity of this star shows similar variations, which in most of the cases run parallel to the fluctuations of the quiet-state luminosity. The quiet-state luminosity of the star BY Dra shows also longterm fluctuations. The current cycle has a duration of at least 14 years and an amplitude of more than 0 . m 3. Long-term changes are also indicated for the flare activity of this star, although the observational data available are rather limited.
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