The final \[Fe/H\] was taken to be the mean of all Fe lines. Our stellar parameters for the M 13 giants compare very well with those derived by @shetrone96a [@shetrone96b], @sneden04a, and @cohen05.

Rubidium abundances
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For the M 13 giants, the HDS spectra did not incorporate the Rb line so we were only able to measure Rb in the NGC 6752 giants. The abundances were determined via spectrum synthesis of the Rb[i]{} line near 7800 Å (see Figures \[fig:b702\_rb\] and \[fig:mg1\_rb\]). Spectrum synthesis was essential for determining accurate abundances due to hyperfine splitting and isotopic shifts as well as blending from a stronger Si[i]{} line. While the 7800 Å Rb[i]{} line is only 3-4% deep relative to the continuum, the high quality spectra allow us to measure an abundance from this line. Following @tomkin99, the wavelengths and relative strengths for the isotopic and hyperfine structure components were taken from @lambert76 and we assumed a solar isotope ratio of $^{85}$Rb/$^{87}$Rb = 3. The macroturbulent broadening was assumed to have a Gaussian form and was estimated by fitting the profile of the nearby Ni[i]{} line at 7798 Å. We then generated synthetic spectra and varied the Si and Rb abundances to 