Photometric data processing. Left panel: all stars within the FOV obtained from the HST Project (GO-11628, PI: Noyola). Middle panel: final differential-reddening-corrected CMD with selected stars (black) and discarded stars (grey). The Gaia EDR3 member stars from the Vasiliev & Baumgardt (2021) catalogue matched with 2MASS to obtain the HST are shown in red. The green triangles represent the observed stars with HST magnitudes obtained from the isochrone calibration, and the sizes are from the S/N. The HB region is plotted in blue. Right panel: differential reddening map for stars within a half-light radius. The resolution of the map is 0.024 arcminutes (1.44 arcsec).