Decadal Variations of Sun-Like Stars

Observations of more than 300 Sun-like field stars carried out at Fair-born Observatory since 1993 now include 168 observed for 10 years or longer. This project, a successor to previous work at Lowell Observatory and Cloudcroft Observatory, beginning in 1955 and continuing for nearly half a century, demonstrates finally that variability at the Sun's low level of total irradiance variation can be detected in stars. By also including Ca II H&K observations from the Mount Wilson and Lowell observatories, we have discovered how the patterns of photometric variability are related to chromospheric activity. We discuss the limitations of detectability imposed by comparison star variability and as an example of a star close to the detection limit we show the evidence for cyclic variability in the solar twin 18 Sco.