We have carried out high-precision photometry on a large number of archival HST images of the Galactic globular cluster NGC 6752, to search for signs of multiple stellar populations. We find a broadened main sequence, and demonstrate that this broadening cannot be attributed either to binaries or to photometric errors. There is also some indication of a main-sequence split. No significant spread could be found along the subgiant branch, however. Ground-based photometry reveals that in the U vs. (U-B) color-magnitude diagram the red-giant branch exhibits a clear color spread, which we have been able to correlate with variations in Na and O abundances. In particular the Na-rich, O-poor stars identified by Carretta et al. (2007) define a sequence on the red side of the red-giant branch, while Na-poor, O-rich stars populate a bluer, more dispersed portion of the red-giant branch.
@article{arxiv.0912.2055,
title = {Multiple stellar populations in the Galactic globular cluster NGC 6752},
author = {A. P. Milone and G. Piotto and I. R. King and L. R. Bedin and J. Anderson and A. F. Marino and Y. Momany and L. Malavolta and S. Villanova},
journal= {arXiv preprint arXiv:0912.2055},
year = {2014}
}
Comments
31 pages, 12 figures; Accepted for Publication in the Astrophysical Journal