Time Evolution of the Magnetic Activity Cycle Period

Details Time Evolution of the Magnetic Activity Cycle Period Time Evolution of the Magnetic Activity Cycle Period

May 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...498l..51b&link_type=abstract

Astrophysical Journal Letters v.498, p.L51

Astronomy and Astrophysics

Astronomy

53

Stars: Magnetic Fields, Stars: Activity, Stars: Evolution, Stars: Late-Type

Scientific paper

We propose a new interpretation of the relationships between the dynamo cycle period ( P_{{cyc}} ) as observed in Ca II H and K, the rotational period ( P_{{rot}} ), the activity level, and other stellar properties. Viewed within this framework, the data suggest that the dynamo alpha -parameter increases with magnetic field strength, contrary to the conventional idea of alpha -quenching. The data also suggest a possibly discontinuous dependence of the ratio of cycle to rotation frequency, omega _{{cyc}}/ Omega , as a function of Rossby number, Ro (or equivalently, activity or age). Stars evolve with omega _{{cyc}}/ Omega ~t^{-0.35} (or Ro-0.7), until age t~2-3 Gyr (roughly at the Vaughan-Preston gap), where a sharp transition occurs, in which omega _{{cyc}}/ Omega increases by a factor of ~6. Thereafter, evolution with omega _{{cyc}}/ Omega ~t^{-0.35} continues. The age at which transition occurs may be mass dependent, with K stars making the transition first.

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