COORDINATED OBSERVATIONS OF THE RED DWARF FLARE STAR EV LACERTAE IN 1992

Results of coordinated observations of the hare star EV Lac in Septemb er 1992 are presented. Among 25 hares detected during 28 hours on patr ol in Crimea four had large enough amplitudes to permit the quantitati ve analysis of their radiation by colour-colour diagrams. Calculation of V - I colour index for different radiation sources enable us to ana lyze the whole UBVRI wavelength range. The detected amplitude of the s low brightness variations with the rotational period of the star was 0 .058 mag; this corresponds to a differential spottedness between the d arkest and the brightest stellar hemispheres of about 12%. Strong vari ations of the equivalent width of the H-beta emission Line, its broade ning and the veiling of the intensity jumps at the TiO molecular band heads were measured during powerful events. Broadened emission H-beta 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 hare spectra. Sporad ic decametric emission of the star is suggestively discovered. Apparen tly, it correlates with the general level of the stellar activity, and a brightness temperature of these radio bursts was about 10(18) K. Ce ntimetre 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 decam etric radio bursts are shortly discussed.