[Na/Fe] versus [Fe/H] for 50 M giants in our sample. The arrangement of the figures and markers is similar to Fig. 1. We exclude [Na/Fe] abundances from the three K-band lines to estimate the mean [Na/Fe] abundance since the abundances from these lines are sub-solar for the sub-solar metallicity stars. This is inconsistent with the abundances from H-band lines, as well as in APOGEE and other optical studies (see also Figs. 25–27).