2003A&A...400..659C

As part of an extensive program focused on the global properties and evolution of active stars, high-precision UBV(RI)_c and UBV photometry of 18 selected stars is presented. UBV(RI)_c observations were collected at the European Southern Observatory over the intervals 21-28 September 1994 and 25 November-05 December 1994. Additional UBV photometry obtained late in 1994 by Catania Astrophysical Observatory Automatic Photoelectric Telescope is also presented. Significant evolution of the light curves, period variations and evidence for long-term variability of the global degree of spottedness are found. Some spectral classifications are revised and photometric parallaxes are compared, whenever possible, with the values measured by the Hipparcos satellite. These observations are finalized to the construction of an extended photometric database, which can give important clues on topics such as the stability of spotted areas, differential stellar rotation, solar-like activity cycles and the correlation between inhomogeneities at different atmospheric levels.