Comparison of the location of the stars and isochrones on a G magnitude versus (BP−RP) magnitude diagram. The two isochrones on the plot have been computed for an age of 14 Gyr (black line: z = 2 × 10⁻⁵ and blue line: z = 2 × 10⁻⁶). BP−RP (BP and RP are the magnitudes measured respectively by the two low resolution spectrographs, the Blue Photometer (BP) and the Red Photometer (RP) onboard the Gaia satellite) versus the absolute G magnitude, with two different hypotheses for the reddening. The red dots represent the stars assuming E(BP − RP) = 0 whereas the green dots represent our stars’ photometry with an extinction correction E(BP−RP) using the E(B−V) correction of PanSTARRS (Chambers et al. 2016) and the conversion relations E(BP − RP) = E(B − V) + 0.07 and A_G = A_V = 3.1 × E(B − V) (where A_G and A_V are the extinction in the G and the V band) from Andrae et al. (2018).