Rotation of solar-like main sequence stars

The results of the photometric survey of 16 solar-type, active, field stars are presented. During our observations 9 stars showed appreciable light variability with amplitudes of a few hundredths of a magnitude but for three of them periods could not be determined. Most of the observed variable stars have periods shorter than about 10 days. It is suggested that, similarly as is observed in the Hyades cluster, small amplitude light variations are quite common among active field solar-type dwarfs with rotation periods around one week or less. A strong modulation of amplitude of some variable stars over the time scale of years is demonstrated. The amplitude may sometimes decrease even below the detectability threshold. A special case is HD 17576 – a visual binary consisting of a G0 dwarf and a much fainter hot subdwarf. It has the largest amplitude of all the stars observed, which suggests an intense spot activity, a very strong H and K line core emission and a very high X-ray emission flux, close to the saturation limit. Yet its variability period is equal to 18.74 days – almost an order of magnitude longer than expected for such an active dwarf