Theoretical EW ratios for log  g = 4.2 of the suitable Si II and Si III lines in the spectrum with proper atomic data. Theoretical values are plotted for two values of the microturbulence, ξ = 1   km s^-1 (full lines) and ξ = 5   km s^-1 (dashed lines), and four values of the Si abundance, log  ϵ(Si) = 7.54, 7.34, 7.14, 6.94 dex. The two horizontal lines represent the observed values with their error bar.