4 Results

The new values of amplitude are binned per spectral type and are plotted along with the values presented in Messina et al. (2001) in Figs. 1-3. As expected from the variation of spotted regions area and because of the spatial redistribution on the stellar photosphere, the light curve amplitudes of the stars under analysis were found to be different compared to the previous determinations quoted in the previous section.

Nevertheless, if we consider the data upper envelope, as discussed by Messina et al. (2001), ultra fast rotators with P<1.1 days, despite the high rotation rate, never show amplitudes larger than slower rotators in all the G, K and M mass regimes. The light curve amplitudes of stars with rotation period around 1 day are comparable to the light curve amplitudes of much slower rotators (  days).

In conclusion, the new light curves amplitudes from this monitoring of active members in the Pleiades and Alpha Persei star clusters, selected in the 0.4-1.1 day rotation range, have values as expected based on previous results of Messina et al. (2001).

Acknowledgements

The author is grateful to Dr. R. Ventura for providing him with the periodogram analysis code and to the technical staff of the Catania Astrophysical Observatory for the support provided during the observing run at the "M. G. Fracastoro'' station on Mt. Etna (Italy).

The extensive use of the SIMBAD and ADS databases operated by CDS center, Strasbourg, France, is also gratefully acknowledged.

Active stars research at the Catania Astrophysical Observatory is funded by MURST (Ministero dell'Università e della Ricerca Scientifica e Tecnologica), CNAA (Consorzio Nazionale per l'Astronomia e l'Astrofisica) and the Regione Siciliana, whose financial support is gratefully acknowledged.