Examples of how [Fe/H] is determined from each absorption line as a function of v_micro : here for the case for Betelgeuse. Top and bottom panels show the results with VALD3 and MB99, respectively. Left panels show the measurements for all the Fe I lines preselected in Sect. 3.3, and middle panels do for the lines satisfying conditions (i)–(v) in the main text (Sect. 3.5.2) and eventually used. Right panels show the measurements after the correction term Δ[Fe/H]_i defined in Eq. (8) subtracted. Each curve in the figures corresponds to each absorption line color-coded according to log τ_Ross of the line-forming layer of the line; a lighter color corresponds to a larger log τ_Ross and thus a smaller EW. The dot on each curve indicates the [Fe/H] value determined with the corresponding v_micro . No dots are plotted where the fitting for a line with a value of v_micro failed.