We present measurements of the neutron-capture elements Rb and Pb in five giant stars of the globular cluster NGC 6752 and Pb measurements in four giants of the globular cluster M 13 .
The abundances were derived by comparing synthetic spectra with high resolution , high signal-to-noise ratio spectra obtained 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 \pm 0.06 ( \sigma = 0.14 ) , [ Rb/Zr ] = - 0.12 \pm 0.06 ( \sigma = 0.13 ) , and [ Pb/Fe ] = - 0.17 \pm 0.04 ( \sigma = 0.08 ) .
In M 13 the mean abundance is [ Pb/Fe ] = - 0.28 \pm 0.03 ( \sigma = 0.06 ) .
Within the measurement uncertainties , we find no evidence for a star-to-star variation for either 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 have slightly lower abundances of [ Rb/Fe ] and [ Rb/Zr ] compared to the small sample of field stars at the same metallicity .
For M 13 and NGC 6752 the Pb abundances are in accord with predictions from a Galactic chemical evolution model .
If metal-poor intermediate-mass asymptotic giant branch stars did produce the globular cluster abundance anomalies , then such stars do not synthesize significant quantities of Rb or Pb .
Alternatively , if such stars do synthesize large amounts of Rb or Pb , then they are not responsible for the abundance anomalies seen in globular clusters .