Age distribution (left), Kiel diagram (centre), and age-metallicity coverage (right) for each step of the selection process, before visual inspection. In the centre panel, PARSEC isochrones at different ages and metallicities are shown in grey; at the bottom left, the average error in log g and T_eff for the full sample is shown. The peak at 19 Gyr visible in the histogram is due to contaminants (see Sect. 3.1 and Appendix A.1).