First row, left panel: [Mg/Fe] versus [Fe/H] distribution for stars in Nissen & Schuster (2010) sample. Red colours indicate low-α stars, blue colours indicate high-α (thick disc and halo) stars, following the classification given in Nissen & Schuster (2010). First row, middle panel: Toomre diagram of LP First stars (black dots), and of the high-α (thick disc and halo) stars in the Nissen & Schuster (2010) sample (blue squares). First row, right panel: Toomre diagram of LP First stars (black dots), and of the low-α stars in the Nissen & Schuster (2010) sample (red squares). The grey area in this panel and in the previous one separates stars with km s⁻¹ from stars with higher relative velocities with respect to the LSR. The vertical dashed lines separate prograde from retrograde motions. Second row, left panel: [Mg/Fe] versus [Fe/H] distribution for stars in the Gaia DR2-APOGEE sample. The distribution of the whole sample is shown by grey dots and contours, while the distribution of stars selected as in-situ, high-α stars and accreted, low-α stars are shown, respectively, with blue and red dots. Second row, middle panel: Toomre diagram of LP First stars (black dots), and of the high-α stars in the Gaia DR2-APOGEE sample (density map). Second row, right panel: Toomre diagram of LP First stars (black dots), and of the low-α stars in the Gaia DR2-APOGEE sample (density map). The grey dashed curve in this panel and in the previous one separates stars with km s⁻¹ from stars with higher relative velocities with respect to the LSR. The vertical dashed lines separate prograde from retrograde motions.