COORDINATED OBSERVATIONS OF THE RED DWARF FLARE STAR EV-LACERTAE IN 1991

Results of cooperative optical observations of EV Lac in September 199 1 are presented. During 50 hours of photoelectric monitoring more than 40 flares were detected, including several events of moderate power a nd one very strong flare with amplitude DELTAU = 3.7 mag and duration of about half hour. Detailed colour analysis of this strong flare indi cates that, near the brightness maximum, the flare emission was close to black body radiation with a contribution of radiation from hydrogen plasma, optically thick in the Balmer continuum. The spottedness of t he star during this campaign was very even: the detected amplitude of slow brightness variations with the rotational period was DELTAV = 0.0 17 mag, corresponding to a differential spottedness between the darkes t and the brightest stellar hemispheres of only about 3%. The polariza tion of stellar radiation during the most powerful flare did not excee d 1%.