On the chromospheric activity of low main sequence stars

On the basis of published data on emission fluxes in the cores of H and K CaII lines and on rotation periods of 182 main sequence stars, the dependence of the degree of chromospheric activity on Rossby number reported in the known paper by Noyes et al. from a sample of 41 stars have been reconsidered. An increase of the sample size has changed considerably the shape of the activity-rotation curve. The main difference from previous results implies very weak or even completely absent signs of saturation in stars with small Rossby numbers (predominantly late dwarfs). In the region of large Rossby numbers the shape of the curve depends on the method of calculating Rossby numbers. Deviations of individual stars from a mean curve do not depend on the spectral type, but they are rather large (∼40%) and cannot be ascribed wholly to difference in the age and evolution rate