Patterns of Variation among Sun‐like Stars

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Abstract
We examine the patterns of variation among a sample of 35 stars that includes the Sun, particularly on the timescale of the 11 yr solar activity cycle. Our investigation uses contemporaneous photometric and chromospheric HK emission time series measurements from the Lowell and Mount Wilson Observatories, and comparable solar data. We find that the photometric and HK variability of the stars in our sample can be related to their average level of chromospheric activity by power laws. The photometric variability of the Sun may be somewhat subdued for its average activity level. We find that the younger, more active stars in our sample tend to become fainter as their HK emission increases, whereas the older, less active stars tend to become brighter as their HK emission increases, as the Sun does during its activity cycle.