Location of our sample of sub-giant and giant field stars in the HR diagram in the four metallicity bins. The stars (filled circles) are colour-coded by their masses: in pink we show stars with M ≤ 1.2 M_⊙, in yellow we plot stars with 1.2 M_⊙ < M ≤ 2.2 M_⊙, and in red we show stars with M > 2.2 M_⊙. The Li-rich giant stars with a mass determination are marked with green stars. The theoretical evolutionary tracks are plotted for masses between 1 and 3 M_⊙. In the top left panel, corresponding to the metallicity bin with [Fe/H]  ≤ −0.5, we adopt the tracks computed for [Fe/H]  = −0.56, while in the other bins we plot the tracks at the solar metallicity.