Colour−magnitude diagram displaying the selection of sources considered stars (selected as explained in Sect. 2.2). The plume on the red side (g − r ≈ 1.2) is composed of the nearby M-dwarfs, whereas the main sequence on the bluer side (0.18 < g − r < 0.6) corresponds to a halo overdensity located at a particular well-defined distance. The cloud of sources at faint magnitudes are faint galaxies that enter the star selection. Left: CMD derived from an image that has not been PSF-corrected. Right: CMD derived from a PSF-corrected image. After homogenizing the PSF, the galaxy contamination decreases markedly below r ≈ 22.