Solar Physics Division Meeting 2000, June 19-22
Session 10. Living with a Star 4: Solar-stellar Connection
Oral, Chair: M. S. Giampapa, Tuesday, June 20, 2000, 4:00-5:00pm, Forum

## [10.01] Making Sense of Stellar Activity Cycle Periods

S.H. Saar (SAO)

I explore relationships between the magnetic activity cycle frequency \omega\rm cyc, the rotational frequency \Omega, and other stellar properties in a large sample of dwarfs, evolved stars, active binaries, and the secondaries of CV systems. The cycles are derived from various sources, including periodicities in Ca {\sc ii}, photometry, and orbital period changes. Dimensional (\omega\rm cyc vs. \Omega) and non-dimensional (\omega\rm cyc/\Omega vs. Ro-1; where Ro is the Rossby number) parameterizations give similar results. Stars are concentrated on three main branches" with different relationships between \omega\rm cyc and \Omega; the branches may converge at very short \Omega. The oldest, lowest activity stars tend to occupy the branch with the highest \omega\rm cyc. Some stars have additional secondary \omega\rm cyc (perhaps analogous to the Sun's Gleissberg" cycle) lying on other branches; the preferred branch of the primary \omega\rm cyc may be mass and \Omega dependent. The density of stars along each branch also depends on \Omega and hence age, indicating \omega\rm cyc evolves in time, but in a complex, sometimes multi-valued fashion. I discuss some possible implications for dynamo theory and evolution.

This work is supported by NSF grant AST-9528563.