Abstract
Abstract The results of photometric, spectral and radio studies of the flare star EV Lac we obtained during the course of cooperative observations in 1994 and 1995 are presented. A quantitative analysis of the radiation emitted by two powerful flares using the colour-colour diagram confirms the previous conclusion on the essential heterogeneity of matter radiating in optical flares. From simultaneous observations of the star in UBVRI, K and H bands no significant brightness variations in IR were found in coincidence with observed small-amplitude optical flares, except a gradual decrease in the K-band following a 1.0 mag flare in the U-band. A differential spottedness of bright and dark hemispheres of EV Lac is estimated using observations in separate seasons and the total stellar spottedness is determined within the framework of the zonal spottedness model. Spectra of quiet and active states of the star in the blue-green region in 1994 and in the red region in 1995 are described: the characteristics of the quiet chromosphere in the Hα, Hβ, HΔ lines, their widening during flares, the strengthening of neutral helium lines and the appearance of emission lines of He II and metals are presented. The monitoring of EV Lac in decametric wavelengths with the largest radio telescope UTR-2 led to the detection of 18 radio bursts, one of which satisfies the majority of criteria of signals of non-terrestrial origin and coincides in time with an optical flare.
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