1995A&AS..114..509A

Result. of coordinated observations of the flare star EV Lac in September 1992 are presented. Among 25 flares detected during 28 hours on patrol in Crimea four had large enough amplitudes to permit the quantitative analysis of their radiation by colour-colour diagrams. Calculation of V-I colour index for different radiation sources enable us to analyze the whole UBVRI wavelength range. The detected amplitude of the slow brightness variations with the rotational period of the star was 0.058mag; this corresponds to a differential spottedness between the darkest and the brightest stellar hemispheres of about 12%. Strong variations of the equivalent width of the H_β emission line, its broadening and the veiling of the intensity jumps at the TiO molecular band heads were measured during powerful events. Broadened emission H_β line profiles were fitted by either two gaussians with very different widths or by sets of gaussians with the instrumental resolution width. Several non-hydrogen emissions were found in the flare spectra. Sporadic decametric emission of the star is suggestively discovered. Apparently, it correlates with the general level of the stellar activity, and a brightness temperature of these radio bursts was about 10¹⁸K. Centimetre wavelength radiation was found to be weak at the times of the flares. On the basis of these facts some ideas on the nature of decametric radio bursts are shortly discussed.