Left:radial velocity semi-amplitude of the stellar activity signal as a function of the line depth d for the correlated symmetric-unblended lines (grey dots). The data are binned into nine bins of size 0.1 (black dots), and the best fit for a second-order polynomial in 1∕d is shown by the black line. Right: radial velocity of the subselections of lines falling in the area of the left plot panel. The RV amplitude grows from strong (blue) to shallow (red) lines.