1997A&A...324..155G

The classical T Tauri star BP Tauri has been simultaneously observed with UBVRI high-speed photometry at a time resolution of 2sec and with the ROSAT PSPC detector during five nights. BP Tauri showed brightness variations on time scales ranging from nights to hours both in the optical and in the X-ray band, however, the night-to-night variations in the optical and X-ray spectral regions were not correlated. On one occasion, a short term optical event with an amplitude in U of ∼0.05mag and a time duration of 1.2-hours occurred, with no corresponding increase in the X-ray count rate during the decay of the event. In conclusion, the observations show that there are no detectable correlations between the optical and X-ray variability of BP Tau on time scales ranging from 1-hour to days. We discuss the possibility that the optical variability of BP Tau is related to accretion of circumstellar material onto the central star, while the X-ray emission presumably comes from magnetically active regions.