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.'
author:
- David Yong
- Wako Aoki
- 'David L. Lambert'
- 'Diane B. Paulson'
title: 'Rubidium and lead abundances in giant stars of the globular clusters M 13 and NGC 6752[^1]'
---

Introduction {#sec:intro}
============

Globular clusters are ideal laboratories for testing the predictions of stellar evolution theory (e.g., @renzini88) since the individual stars are believed to be monometallic, coeval, and at the same distance. In a given globular cluster (excluding $\omega$ Cen), spectroscopic observations of individual stars have confirmed that members have uniform compositions, at least for the Fe-peak elements (e.g., see review by @gratton04 and references therein). However, it has been known for many years now that globular clusters exhibit star-to-star abundance variations for the light elements C, N, O, Na, Mg, and Al (e.g., see review by @kraft94). Specifically, the abundances of C and O are low when N is high and anticorrelations are found between O 