Study of the FU Orionis-type stars

The photoelectric UBVRI-photometry of FU Ori (this prototype of the ''fours'' has increased its brightness by 5sup(m) in 1936/37) was carried out since 1978 to 1985. The results show the persisting slow decrease in brightness of the star in all wavelengths, while the mean colour indexes remain constant. The spectrograms in the blue region show the constancy of the spectral type as well. The patrol photometry of FU Ori in 1984/85 revealed the periodic variations of its brightness and colours with amplitudes of few hundredth of magnitude. The period of these variations P1=18sup(d).35 has changed by a factor of two to P2=9sup(d).19 in November 1984. It is suggested that this pattern of variability was caused by the development of dark spots on the surface of the rapidly rotating star. The comparison of the post flare behavior of FUOri, V1057 Cyg, and V1515 Cyg is present