Hertzsprung-Russel diagram of the selected sample of GES stars. Red points correspond to stars with [M/H] > −0.5 dex, green points are intermediate-metallicity stars (−1.0 dex < [M/H] ≤ −0.5 dex), and blue points are metal-poor objects ([M/H] ≤ −1.0 dex). To enhance the best quality data, the points size is inversely proportional to the associated errors in the atmospheric parameters.