[α/Fe] versus [Fe/H] for the whole sample (middle) and for stars with T_eff = T_⊙  ±  300 K (top). Magenta squares refer to halo stars. Blue filled circles are the separation points between low- and high-α stars, which are minimas of the [α/Fe] histograms for five metallicity bins (from [Fe/H] = −0.7 to 0.25) and the blue dashed curve is the corresponding separation curve passing on that points. The bottom panel is the [α/Fe] versus [Fe/H] plot for the whole sample in several bins of metallicity. The blue triangles refer to the thick disk stars, black filled circles to the metal-rich high-α stars (hαmr), and the red crosses to the thin disk stars. Error bars in the lower panel correspond to the standard deviations, and the error bar in the upper and middle panels are the average errors in the [α/Fe] and [Fe/H].