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G. W. Lockwood (Lowell Observatory), R. R. Radick (Air Force Research Laboratory), G. W. Henry (Tennessee State University), S. L. Baliunas (Center for Astrophysics)
By merging Stromgren b and y photometry of a sample of 34 Sun-like stars measured at the Lowell Observatory and Fairborn Observatory we can now compare 18 years of photometric data with parallel measurements of chromospheric activity from the Mount Wilson HK program. Nearly doubling the length of the 7-11 year time series discussed previously (Radick et al. 1998, ApJS 118, 239; Lockwood et al. 1992 Nature 360, 653) firms up the statistical significance of previously noted patterns of variation. The full range of variability has probably now been observed for most stars in our sample.
Stellar brightness and chromospheric variations follow fairly tight power law relations with respect to mean chromospheric activity. Both diminish with decreasing mean chromospheric activity (or increasing stellar age). The Sun's chromospheric variability lies slightly above the mean stellar power law, but its brightness variations (less than 0.1% over the 11-year solar cycle) appear somewhat low compared with stars of similar activity levels.
Stellar brightness variations are negatively or positively correlated with chromospheric variations depending on mean chromospheric activity, The Sun lies close to the dividing line. A few stars appear to violate the general pattern.
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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.