similar to those measured in NGC 6752. In general, Rb is not a well studied element and the comparison data are limited.

For NGC 6752, we find a mean abundance \[Rb/Zr\] = $-$0.12 $\pm$ 0.06 ($\sigma$ = 0.13). (This abundance ratio has been shifted to the @smith00 scale.) For the five NGC 6752 giants, the ratio \[Rb/Zr\] appears to show a dispersion. We suspect that this is attributable to measurement uncertainties (primarily for Rb) rather than reflecting a real star-to-star scatter. We do not find a correlation between \[Al/Fe\] and \[Rb/Zr\]. In Figure \[fig:rbzr\], we compare the abundance ratio \[Rb/Zr\] between NGC 6752 and various field and cluster stars. Note that in this Figure we have shifted all abundances onto the @smith00 scale since we will utilize their theoretical predictions from low and intermediate-mass AGBs. At the metallicity of NGC 6752, we find that the two stars in NGC 6752 with the highest values of \[Rb/Fe\] also have the highest values of \[Rb/Zr\]. These two stars have similar \[Rb/Zr\] ratios to the @gratton94 and @tomkin99 samples at the same metallicity. While the $\omega$ Cen giants have abundance ratios \[Rb/Zr\] slightly lower than NGC 6752, this time the NGC 3201 giants 