Selection of the APOGEE RC samples. Top: low-α (green) and high-α (orange) RC sequences. The separation border corresponding to Eq. (19) is shown with dashed black line. Bottom: selected low-α and high-α RC populations in the R-z plane. Dashed lines mark the adopted limits for the galactocentric distance and height. The radial binning of the low-α population corresponds to run0 (see text). The adopted position of the Sun is marked with a yellow dot.