Chemical abundances (left) and metallicities (right) of stars included in the RPM sample as derived from cross-matching to APOGEE DR16 and to LAMOST DR4. In both panels, we denote the distribution of the full samples provided by each of these surveys, after quality cuts, in black, while in blue we denote the subset that overlaps with the RPM sample. The vast majority of these stars are clearly all metal-poor, as expected for halo stars.