Statistics of BY Draconis variables

A statistical survey of 113 spotted red dwarf stars that are known or suspected BY Draconis variables is presented. Typical indicators of stellar photometric activity-the amplitudes of the rotational modulation and seasonal mean brightness variations Delta V and Delta(V)-are compared to the global parameters of the stars. First, photometric variability shows a weak dependence on spectral type; second, Delta V and Delta(V) grow with increasing stellar rotational velocity and decreasing Rossby number, with the dependences saturating at the critical values V-crit similar to 15-20 km/s and Ro(crit) similar to 0.2-0.3; and third, the Sun as a star fits well into the derived relations. Thus, the spottedness of stars, like other indicators of stellar activity, depends on their global parameters. (C) 2000 MAIK "Naukal/Interperiodica".