ИСТИНА

The results of photoelectric UBV-observations of DF Tau are given, which were carried out with 60-cm reflector of the Crimean Station of the Sternberg Astronomical Institute in 1967-77. It is shown that the observed radiation of DF Tau can be represented as consisting of photospheric radiation (color indices of which correspond to the spectral type dM0, non-variable UV-excess and additional emission appearing only during flares. It is proposed that the variability of DF Tau is due to flares with an energy release of 10 to the 33rd ergs. The mean duration of flares is about 1.5-5 days. Shorter flares were also observed with duration of 1-2 hours and amplitudes not greater than 0.5m. Probably, the nature of all flares is the same. The fast variability of DF Tau and T Tau is displayed with characteristic time in tens of seconds.