P vs. (K_s − [22])₀ diagram of 1091 MACHO Galactic bulge Miras from Bernhard & Hümmerich (2013). The solid line is the relation that was found to best separate Tc-poor from Tc-rich stars (Eq. (1)). MACHO Miras falling above this line, i.e. putative Tc-poor stars, are plotted as grey symbols, whereas Miras below the line, i.e. putative Tc-rich stars, as black symbols. Large symbols represent the Plaut stars analysed for their Tc content in Uttenthaler et al. (2007; blue: Tc-poor, red: Tc-rich). The dashed lines are the linear fits to the Tc-poor and Tc-rich Miras from the upper panel of Fig. 3.