Philip G. Judge, Michael J. Thompson
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 \sim 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.
View original:
http://arxiv.org/abs/1201.4625
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