Astron. Astrophys. Suppl. Ser. 131, 321-344

Long-term monitoring of active stars

VIII. $UBV(RI)_{\rm c}$ photometry collected in February 1992

G. Cutispoto

Osservatorio Astrofisico di Catania, V.le A. Doria 6, I-95125 Catania, Italy
e-mail: gcutispoto@alpha4.ct.astro.it

Received January 28; accepted March 16, 1998

Abstract:

As a part of an extensive program focusing on the global properties and evolution of active stars, high-precision $UBV(RI)_{\rm c}$ photometry of 31 selected stars, collected at the European Southern Observatory over the 14-29 February 1992 interval, is 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 the inferred photometric parallaxes are compared, whenever possible, with the values measured by the Hipparcos satellite. Flare events were detected for the star HD 16157 = CC Eri, EXO 055609-3804.4 = TY Col and HD 119285 = V851 Cen. Optical variability was discovered for the Pop II binary HD 89499. These observations contribute to the establishment of a time-extended photometric database which can give important clues on topics such as the stability of spotted areas, differential rotation, solar-like cycles and the correlation between inhomogeneities at different atmospheric levels.

Key words: stars: activity -- stars: flare -- stars: late-type -- stars: variables -- stars: population II -- stars: pre-main sequence