1995A&AS..111..259B

Photographic magnitudes of 29 red dwarf stars have been measured on time scales of 5-90 years using the archival plate collections of the Sternberg State Astronomical Institute (Russia), Astronomical Observatory of Odessa State University (Ukraine) and Sonneberg Observatory (Germany). Long-term changes in yearly mean magnitudes were detected or suspected for 10 objects. Two stars, V833 Tau and PZ Mon, showed remarkable amplitudes of variability up to 0.6mag and 1.0mag respectively. Eight stars have long-term changes in the range from 0.2 to 0.5mag. Variations of other programme stars were less than 0.2mag, which is comparable to the scatter in the mean light of check stars. Typical time scale of the long-term variability is 20-60years.