Colour magnitude diagrams (CMD) of NGC 2243 and NGC 104. Top: CMD showing de-reddened (B − V)₀ vs. M_V, 0 of NGC 2243 (left) and NGC 104 (right). Bottom: CMD showing the adopted T_eff vs. M_V, 0 of NGC 2243 (left) and NGC 104 (right). The lines are isochrone tracks of the clusters taken from BaSTI. The isochrone for NGC 2243 (solid line) is computed assuming Z = 0.008, [α/Fe] = 0.0, Age = 4.0 Gyr (corresponding to [Fe/H] = −0.38). Also shown (dotted line) is the track computed assuming Z = 0.004, [α/Fe] = 0.0, Age = 4.9 Gyr (corresponding to [Fe/H] = −0.69). The isochrone for NGC 104 is computed assuming Z = 0.008, [α/Fe] = +0.4, Age = 12.0 Gyr (corresponding to [Fe/H] = −0.68). There are fewer stars in the (B − V)₀ vs. M_V, 0 diagram of NGC 2243 than its T_eff vs. M_V, 0 because Gaia-ESO does not provide all the B and/or V magnitudes. The dots in the bottom right plot show the stars observed with GIRAFFE, while the crosses show those observed with UVES. The red symbols show our observation programme 104.D-0951(A), while the grey/green symbols show those obtained from the archive.