Solar and Stellar Activity: Diagnostics and Indices

Abstract

We summarize the fifty-year concerted effort to place the "activity" of the Sun in the context of the stars. As a working definition of solar activity in the context of stars, we adopt those globally-observable variations on time scales below thermal time scales, of ~ 100,000 yr for the convection zone. So defined, activity is dominated by magnetic-field evolution, including the 22-year Hale cycle, the typical time it takes for the quasi-periodic reversal in which the global magnetic-field takes place. This is accompanied by sunspot variations with 11 year periods, known since the time of Schwabe, as well as faster variations due to rotation of active regions and flaring. "Diagnostics and indices" are terms given to the indirect signatures of varying magnetic- fields, including the photometric (broad-band) variations associated with the sunspot cycle, and variations of the accompanying heated plasma in higher layers of stellar atmospheres seen at special optical wavelengths, and UV and X-ray wavelengths. Our attention is also focussed on the theme of the Symposium by examining evidence for deep and extended minima of stars, and placing the 70-year long solar Maunder Minimum into a stellar context.

Invited keynote paper for IAU Symposium No 286, 2012. Comparative Magnetic Minima: Characterizing quiet times in the Sun and stars

References in corpus (6)

• Patterns of photometric and chromospheric variation among Sun-like stars: A 20-year perspective
• Persistent Magnetic Wreaths in a Rapidly Rotating Sun
• Magnetic Cycles in a Convective Dynamo Simulation of a Young Solar-type Star
• Discovery of a 1.6-year Magnetic Activity Cycle in the Exoplanet Host Star iota Horologii
• A Survey of Chromospheric Activity in the Solar-Type Stars in the Open Cluster M67
• Stellar hydrodynamics caught in the act: Asteroseismology with CoRoT and Kepler

Cited by in corpus (2)

• The Solar-Stellar Connection
• Seismology of active stars