The "rotation-activity connection":: Its extension to photospheric activity diagnostics

In this paper rye present the results of a different approach in the study of the so-called rotation-activity connection, which is a well established correlation between rotation and magnetic activity at chromospheric and outer atmospheric levels. The present study concerns the photospheric level and was carried out by using V-band photometric light curve amplitudes as indicators of starspot coverage and of magnetic activity. A high degree of correlation between the envelope of maximum V-band light curve amplitudes and the rotation period is found for the active star members of young open clusters (IC 2602, IC 2391, Alpha Persei, Pleiades and Hyades), as well as for active field stars. This correlation shows a different behaviour in two different rotation period ranges. Moreover, some evidence of a possible activity "saturation" is found among the most rapidly rotating stars of the sample. Additional correlations between photospheric and other magnetic activity indicators in the chromosphere, transition region and corona are also investigated. The results presented here can be considered as: an extension of the well established rotation-activity connection valid from the corona, transition region and chromosphere, down to the photosphere.