Selection of NGC 6304 membership. Top left: spatial distribution of observed stars within the APOGEE-2 survey area. The dashed black circumference indicates the tidal radius of the cluster (t_r=15.25′). NGC 6316 can be seen to the NE. Top right: PM distribution of the stars within the tidal radius obtained from Gaia DR3. The dashed circumference has a radius of 0.5 [mas/yr]. Bottom left: selection in the RV vs. [Fe/H] plane from ASPCAP for the candidate members. The point with error bars shows the mean RV and its standard deviation from the Baumgardt et al. (2023) database. Bottom right: G vs. (G_bp − G_rp) CMD. Final selected members are shown in all plots as points color-coded according to their S/N, while the field stars are represented as gray dots. The plotted isochrone of 12 Gyr represents the best PARSEC fit. Black squares in the plots are those stars with S/N > 70.