2001A&A...372..119O

We analysed all the existing photometric observations of V833 Tau and found long-term variability on time scales of ≃70 years, 6.5 years and 2.4 years. Using V and I_C-band data from 1990-2000, we obtained starspot surface distributions from 20 suitable light curves. We found that the spot-area changes generally follow the long-term light variations. Spot temperatures are determined for each of the datasets and an average value of 1230K±270K relative to the photosphere is found. This value agrees with previous results from TiO modeling (1330K±110K). Small scale spot temperature and area changes are recovered during 1997-1999, that we explain with a variable spot/faculae ratio. A powerful flare in UBV(RI)_C was observed in 1993 November. A 10000K fit yielded a total emitted flare energy of more than 10³⁴ ergs from an area of about 1.3% of the stellar surface, 60% of it in the V(RI)_C bands. The flare characteristics are compared to another, 100-times smaller flare observed earlier in 1983.