SIMULTANEOUS OPTICAL AND IR PHOTOMETRY OF THE T-TAURI STAR RU LUPI

Two simultaneous optical and IR photometric observation runs of RU Lupi were carried out at the European Southern Observatory (ESO) in February 1983 and in June 1986 within the framework of a large multifrequency coordinated campaign of observations. RU Lupi was found in two different states. In the first case the star was in "quiescence", in the second it was brighter and showed larger variations due to a flare like event (FLE). A positive correlation between luminosity and its variations has been found. A Fourier analysis of the light curve available in literature was performed to point out the rotational period. The analysis of these data excludes any periodicity. Our colour-colour diagnostic diagram clearly shows that RU Lupi variability is mainly due to a strong photospheric an chromospheric activity.