The photometric variability of solar-type stars. II. Stars selected from Wilson's chromospheric activity survey.

The authors have observed eleven solar-type main-sequence stars to search for continuum variability. Stars were selected from Wilson's chromospheric activity survey, and were observed for periods of three to six months with intermediate-band Stroemgren uvby photometry. The authors find evidence that two of these eleven stars are variable and that one other may be. Comparison with contemporaneous Ca II H + K emission flux measurements shows that the amplitude of photometric variability correlates strongly with both the mean emission flux and the amplitude of its variation. Variations in continuum light and emission flux tend to correlate in time, as well, with continuum minima coinciding with emission maxima and vice-versa. The authors infer that the surface activity of these stars tends to be confined to localized activity centers that include both emission plages and dark spots, similar to the active regions observed on the sun.