Estimated flicker index associated to granulation (α_g) as a function of stellar parameters. From left to right: stellar mass, radius, effective temperature, surface gravity, apparent magnitude, and normalized ν_max resulting from (4). Top: values obtained from the MCMC analyses. The color code indicates the apparent magnitude of the target: m_v < 10 (black) and m_v > 10 (gray). The star symbol represents the index derived for the Sun based on VIRGO green channel observations: α_g = 1.26 with σ_W = 5 ppm. The square symbol represents the index obtained after adding a HF noise level (corresponding to that seen in Kepler observations of the Sun-like star KIC 3427720) to the VIRGO subseries. Bottom: values obtained after interpolation that corresponds to a HF level of σ_W = 30 ppm (see Sect. 4.3). The color code indicates here the data with R² > 0.8 (i.e., the best fits, black) and R² > 0.5 (blue). The triangle symbol represents the value of the flicker index derived by adding a WGN of σ_W = 30 ppm in solar VIRGO observations, for which we find: α_g = 0.9464. This is the raw level of HF noise we expect for Sun-like stars observed with CHEOPS. Pearson (ρ_P) and Spearman’s (ρ_S) coefficients associated with these plots for the best targets (R² > 0.9) are indicated on each panel.