Kiel diagram of the selected samples A and C of bright giant stars. Upper panel: selection of sample A targets (blue dots) in the Kiel diagram using the selection criteria of the calcium query (cf. Appendix A). The box with solid lines shows the initial sample A before we applied the cut-off in T_eff. As a visual reference, the grey points represent the MW population from the initial selection (including all stellar types from the GSP-Spec catalogue). We overplot isochrones based on BaSTI stellar evolution models and density contours of the stellar distribution with contour lines enclosing fractions of 90, 75, 60, 45, 30 and 20% of the total number of stars. Lower panel: same, but showing the sample C selection (red dots). The box with dashed lines shows the initial sample C before we applied the cut in T_eff.