Long-term monitoring of active stars ^*,**

IX. Photometry collected in 1993

¹ Catania Astrophysical Observatory, v. S. Sofia 78, 95125 Catania, Italy e-mail: sme@sunct.ct.astro.it
² Department of Physics and Astronomy, Catania University, v. S. Sofia 78, 95125 Catania, Italy e-mail: mrodono@alpha4.ct.astro.it

Corresponding author: G. Cutispoto, gcutispoto@alpha4.ct.astro.it

Received: 25 October 2000
Accepted: 15 December 2000

Abstract

As a part of an extensive program focused on the global properties and evolution of active stars, high-precision and UBV photometry of 31 selected stars is presented. The observations were collected at the European Southern Observatory over the 31 December 1992-18 January 1993 and the 20 November-3 December 1993 intervals. Additional UBV photometry obtained by the "Phoenix" and by the Catania Astrophysical Observatory Automatic Photoelectric Telescopes from 1990 to 1993 is also presented for some of the program stars. 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. 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 rotation, solar-like cycles and the correlation between inhomogeneities at different atmospheric levels.