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Abstract. Results of photoelectric observations of TT Ari during the 1985-1994 interval are presented. Observations were carried out at the Rozhen and Belogradchik observatories as part of our programme for the study of anti-dwarf novae. The long-term light curve in the standard UBV system is constructed and peculiarities of the long-term behaviour of the star in this time interval are discussed. 21 moments of maxima and 14 moments of minima are added to the list of known maxima and minima of 3.2-hour modulations. The period of 3.2-hour modulations during the 1987/1988, 1989/1990 and 1990/1991 seasons is determined. In our 29 observing runs we searched for 20-min quasi-periodic variations, which were detected in 25 of them. Our results show that in 1989, the 20-min modulation mean period reached a local maximum of 19.45 min and declined afterwards. The mean brightness variability analysis during the aforementioned seasons confirmed the reliability of the 3. d 8 period suspected by Semeniuk et al. (1987).

Aims. We report results of a quantitative colorimetric UBVRI analysis of two flare events on the red dwarf EV Lac. The photometric data were obtained in September 2004, during the multi-site synchronous monitoring from the four observatories in Ukraine, Russia, Greece, and Bulgaria. These observations confirmed the presence of small-scale high-frequency oscillations (HFO) initially detected by Rodonó (1974, A&A, 32, 337) and recently reconfirmed by the authors. Here we discuss the color characteristics of flares and HFO. Methods. Colorimetric analysis had been performed with the help of the time tracks in the UBVRI color-color diagrams from the earliest phase of flare development. Digital filtering technique was used to evaluate the time-dependent color indices. Results. As can be clearly seen in the diagrams, color indices oscillate on a time scale of seconds, far exceeding instrumental errors. Regarding the HFO, we conclude that the bulk of a flare oscillates during a major part of its lifetime between the states of hydrogen plasma opaque and transparent in the Balmer continuum. We find that at the peaks of oscillations the color tracks drift into the regions of color-color diagrams corresponding to a blackbody radiation, which provides an estimate of color temperatures from 17 000 to 22 000 K. We also find that flares cover ∼1% of the stellar disc.

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