Magnetic Activity Cycles across the HR-Diagram

Berdyugina Svetlana, sveta@kis.uni-freiburg.de; KIS, Freiburg - NAI UH, Hawaii; Germany

Abstract
Magnetic cycles are probably the least understood phenomenon in stellar variability. For instance, with more than 400 years of sunspot measurements we still have only a vague idea about the origin and operation of the solar 11- and 22-year cycle, while data on activity cycles in other stars are limited at best to several decades. Here I will review the current standing in observations of cyclic magnetic activity in various types of stars. I will attempt to construct a coherent picture of this enigmatic phenomenon and will identify the key measurements that are needed for constraining models of stellar dynamos.