High-resolution optical spectra (in black) and best model fits (in red) in the Li I 6708 Å region (left panel) and Rb I 7800 Å region (right panel) for the AGB stars RU Ari, R Cen, SV Cas, and RU Cyg. The derived Li and Rb abundances (in the usual scale log N(X) + 12) are indicated. Synthetic spectra obtained for Li and Rb abundances shifted +0.5 dex (in blue) and −0.5 dex (in green) (these values are ±1.0 for Li in R Cen and SV Cas) from the adopted values are also shown. We note that Li is not detected in the extreme OH/IR AGB star RU Ari, which displays a strong Rb I line that is not detected in the other stars.