Relations between log $\mathcal{F}$_RV and B − V (or T_eff) adopted in different works. For the works using C_cf and K instead of $\mathcal{F}$_RV, the values of $\mathcal{F}$_RV are estimated by Eq. (11). The dashed-dotted, dashed, and dotted lines represent the results using K = 0.76 × 10⁶, 1.07 × 10⁶ and 1.29 × 10⁶ erg cm² s⁻¹, respectively. The gray circles represent the $\mathcal{F}$_RV values estimated from the PHOENIX model used for deriving Eq. (15). The solid black line is derived from Eq. (15), with log g = 4.44 dex and [Fe/H] = 0.0 dex.