Activity cycle phase difference Δϕ against the magnetic activity index . Dots show dwarf stars (luminosity class V) and diamonds show (sub-) giants (luminosity class III, IV, IV-V). The colors show different spectral types: F stars (blue), G stars (orange), and K stars (red). The vertical dashed line indicates the approximate location of the Vaughan–Preston gap, with its boundaries indicated by the dotted lines, adopted from Fig. 2 of Noyes et al. (1984). The horizontal dashed lines at Δϕ = 0.5 and Δϕ = 0 mark the region of spot and faculae domination, respectively. The yellow star indicates the position of the Sun, adopting the mean value logR′HK, Sun = −4.94 from Egeland et al. (2017).
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