Fractional chromospheric Hα flux, , as a function of fractional chromospheric Ca II H and K flux, flux, both on a logarithmic scale. Filled symbols indicate stars without known planetary systems, and open symbols indicate stars with known planetary systems. In this plot, only stars with Hα in emission (>0) are shown. A linear fit is shown with a dashed red line, and a 1:1 relation is plotted as a dotted gray line.