A small spectral region close to the Li I 607.8 nm line for our 15 MS sample stars (first and second panels), and the spectral region close to the Na I 568.8 nm line for the 6 giant stars observed with HARPS-N (third panel). The vertical lines indicate all the Y/U lines we used in the analysis. We also show examples of synthetic spectrum fits for the 21 stars analysed (see text), while the 6 stars close to the MSTO excluded from analysis are shown separately (fourth panel).