Observed α-to-iron element abundance ratios as a function of [Fe/H]. The value of [α/Fe I] is computed as an average of the following elements: Mg I, Si I, Ca I, and Ti I. The meaning of symbols: the square is for the thick disc star, the circles are for the red giant branch stars, the plus sign marks a subgiant star, and the triangle is for the red clump star. The blue symbols mean that a star is at the evolutionary stage below the red giant luminosity bump, and the red is for stars at the evolutionary stage above the RGB luminosity bump.