Gauging the Sun: Comparative photometric and magnetic activity measurements of sunlike stars, 1984-2001

Visible light photometric observations of a small sample of sunlike stars with mean chromospheric activity levels similar to or slightly lower than the Sun's suggest that total solar irradiance variations on activity cycle timescales may be comparatively small (Lockwood et al. 1992, Nature 360, 653; Radick et al. 1998, ApJS 118, 239). The Sun's irradiance variation over the past two cycles is 0.04% rms compared with 0.1% rms for the stellar sample measured at Lowell from 1984 to 1995. This assertion can now be tested using new photometric measurements from Fairborn Observatory automated telescopes (1993-2001) that extend the duration of stellar observations to 17 years. Chromospheric activity measurements for these stars come from the Mount Wilson HK program (1966-2001) and the Lowell Observatory Solar Stellar Spectrograph program (1993-2001). In this presentation we will describe efforts to merge the overlapping Lowell and Fairborn photometry and the Mt. Wilson and Lowell HK measurements with the goal of reducing the uncertainties in previous efforts to characterize stellar photometric variations near the limit of detection.