Multisite continuous spectroscopy. III. Photometric analysis and SPOT modelling of the light curves of HR 1099 before and after the 1989 optical flares.

We present the UBV and UBV(RI) c photometry of HR 1099 (= V711 Tau) carried out at the Beijing Astronomical Observatory and the European Southern Observatory (La Silla, Chile) during the second MUSICOS campaign in 1989. Except for the zeropoint, the light curves at both observatories coincide with each other and are combined to form unified light curves. A photometric analysis is carried out by using the spot approximation based on the Roche model. The light curves are obviously asymmetric and show an unusual phase shift of light minimum which is different in different wave bands. It is found that two cool and one hot spots can reconstruct simultaneously the main characteristics of all 5 UBV(RI) c light curves and that two adjacent spots, one cool and the other hot, created a large temperature gradient distribution along the longitude which is responsible for the phase shift in different wave bands