The ACS Survey of Galactic Globular Clusters. III. The Double Subgiant Branch of NGC 1851
The ACS Survey of Galactic Globular Clusters. III. The Double Subgiant Branch of NGC 1851
Photometry with the Hubble Space Telescope Advanced Camera for Surveys (HST ACS) reveals that the subgiant branch (SGB) of the globular cluster NGC 1851 splits into two well-defined branches. If the split is due only to an age effect, the two SGBs would imply two star formation episodes separated by …