Rubidium and Lead Abundances in Giant Stars of the Globular Clusters M13 and NGC 6752

We present measurements of the neutron-capture elements Rb and Pb in fivegiant stars of the globular cluster NGC 6752 and Pb measurements in four giantsof the globular cluster M 13. The abundances were derived by comparingsynthetic spectra with high resolution, high signal-to-noise ratio spectraobtained using HDS on the Subaru telescope and MIKE on the Magellan telescope.The program stars span the range of the O-Al abundance variation. In NGC 6752,the mean abundances are [Rb/Fe] = -0.17 +/- 0.06 (sigma = 0.14), [Rb/Zr] =-0.12 +/- 0.06 (sigma = 0.13), and [Pb/Fe] = -0.17 +/- 0.04 (sigma = 0.08). InM 13 the mean abundance is [Pb/Fe] = -0.28 +/- 0.03 (sigma = 0.06). Within themeasurement uncertainties, we find no evidence for a star-to-star variation foreither Rb or Pb within these clusters. None of the abundance ratios [Rb/Fe],[Rb/Zr], or [Pb/Fe] are correlated with the Al abundance. NGC 6752 may haveslightly lower abundances of [Rb/Fe] and [Rb/Zr] compared to the small sampleof field stars at the same metallicity. For M 13 and NGC 6752 the Pb abundancesare in accord with predictions from a Galactic chemical evolution model. Ifmetal-poor intermediate-mass asymptotic giant branch stars did produce theglobular cluster abundance anomalies, then such stars do not synthesizesignificant quantities of Rb or Pb. Alternatively, if such stars do synthesizelarge amounts of Rb or Pb, then they are not responsible for the abundanceanomalies seen in globular clusters.Comment: Accepted for publication in Ap