The most massive globular cluster in the Milky Way, Centauri, is thought to be the remaining core of a disrupted dwarf galaxy, as expected within the model of hierarchical merging. It contains several stellar populations having different heavy elemental abundances supplied by supernovaea process known as metal enrichment. Although M 22 appears to be similar to Cen, other peculiar globular clusters do not. Therefore Cen and M 22 are viewed as exceptional, and the presence of chemical inhomogeneities in other clusters is seen as pollution from the intermediate-mass asymptotic-giant-branch stars expected in normal globular clusters. Here we report Ca abundances for seven globular clusters and compare them to Cen. Calcium and other heavy elements can only be supplied through numerous supernovae explosions of massive stars in these stellar systems, but the gravitational potentials of the present-day clusters cannot preserve most of the ejecta from such explosions. We conclude that these globular clusters, like Cen, are most probably the relics of more massive primeval dwarf galaxies that merged and disrupted to form the proto-Galaxy
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Acknowledgements J.-W.L. thanks A. Walker for providing the CTIO Ca filter transmission curve, D. Yong for NGC 1851 spectroscopic data before publication, and A. Yushchenko for discussions on spectrum synthesis. Support for this work was provided by the National Research Foundation of Korea to the Astrophysical Research Center for the Structure and Evolution of the Cosmos (ARCSEC). This work was based on observations made with the CTIO 1.0-m telescope, which is operated by the SMARTS consortium.
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