Level of magnetic activity as a function of the surface gravity. Left: chromospheric emission index S_CaII as a function of the surface gravity log g. The color indicates the evolution stage: gray symbols refer to stars with an unknown evolution stage; red symbols refer to RGB stars; and green symbols refer to RC stars. Stars with spot modulation are represented by darker dots than stars with no spot modulation. The symbol changes as a function of evolution stage for stars with no spot modulation. The black line represents the best linear fit given by Eq. (8) computed for the red giants where no spot modulation was detected by Gaulme et al. (2020). Right: corresponding figure for S_ph as measured by Gaulme et al. (2020). The dashed and the dot-dashed black lines represent the best linear fit of S_ph for RGB and RC stars, respectively, given by Eq. (6), computed for the red giants where no spot modulation was measured by Gaulme et al. (2020).