E. Gullbring et al., SIMULTANEOUS OPTICAL AND ROSAT X-RAY OBSERVATIONS OF THE CLASSICAL T-TAURI STAR BP-TAURI, Astronomy and astrophysics, 324(1), 1997, pp. 155-160
The classical T Tauri star BP Tauri has been simultaneously observed w
ith UBVRI high-speed photometry at a time resolution of 2 sec and with
the ROSAT PSPC detector during five nights. BP Tauri showed brightnes
s variations on time scales ranging from nights to hours both in the o
ptical and in the X-ray band, however, the night-to-night variations i
n the optical and X-ray spectral regions were not correlated. On one o
ccasion, a short term optical event with an amplitude in U of similar
to 0.05(m) and a time duration of 1.2 hours occurred, with no correspo
nding increase in the X-ray count rate during the decay of the event.
In conclusion, the observations show that there are no detectable corr
elations between the optical and X-ray variability of BP Tau on time s
cales ranging from 1 hour to days. We discuss the possibility that the
optical variability of BP Tau is related to accretion of circumstella
r material onto the central star, while the X-ray emission presumably
comes from magnetically active regions.