Scheme of the location of the star NGC 4590-3584 in the T_eff– log g plane (main panel) according to different chemical analyses: the red circle indicates the photometric parameters, the green circle the position of the star when the constraint of null σ_χ is fulfilled, and the blue circle the position of the star according to the spectroscopic determination of the parameters. For each of these (T_eff, log g) pairs, the run of [Fe/H] as a function of χ is shown (both neutral and single ionised lines shown as black and red circles, respectively).