Messina, Sergio

Contact Email: sme@sunct.ct.astro.it
Institute: Catania Astrophysical Observatory, Italy
First Coauthor: Edward F. Guinan
Institute: Villanova University, PA
Research URL:http://www.ct.astro.it/sme/curriculum.html
Subject Area: Single Stars
Waveband: Optical
Technique: Photometry
Presentation: Poster Display
Title: Starspots cycle phase and rotational photometric period variations of young solar-type stars: different patterns of correlation
Abstract: Very accurate values of the starspots cycle length and of the rotational photometric period have been determined for a sample of five among the most extensively observed young solar-type stars: BE Cet, $\kappa^1$ Cet, $\pi^1$ UMa, DX Leo and EK Dra.
Analyses of extended time-series of wide-band photometric observations have shown the existence of periodic or multiperiodic variations of the seasonal mean brightness level (starspots cycles) and periodic variations of the photometric period. The latter resulted to be correlated to the starspots cycle phase. For a few stars (BE Cet, $\pi^1$ UMa, EK Dra) we see that the rotation period tends to decrease steadily during the course of each cycle, jumping back at a higher value at the beginning of a new cycle. This is indeed reminiscent of the sunspot cyclic behaviour, where the latitude of spot formation moves toward the equator, i.e., toward progressively faster rotating latitudes along an activity cycle, thus producing a decrease of the photometric period.
However, the remaining stars of the sample ($\kappa^1$ Cet, DX Leo) show an anti-solar pattern, where the rotation period tends to increase steadily during the course of each cycle, jumping back at a lower value at the beginning of a new cycle. The newly determined cycle length values, the lower limit of the surface differential rotation amplitude ( $\frac{\partial\Omega}{\partial \phi}$) and the clear evidence of the existence of such opposite patterns represent important observational constraints to the current models of generation and evolution of the stellar magnetic activity.