2013/12/31 by E. P. Lagioia, A. P. Milone, P. B. Stetson +15 · 1 citation
Physics and Astronomy · #Advanced Camera for Surveys #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Astrophysics and Star Formation Studies #Bulge #Globular cluster #Horizontal branch #Hubble space telescope #Open cluster #Photometry (optics) #Physics #Proper motion #Red-giant branch #Star cluster #Stars #Stellar, planetary, and galactic studies #astro-ph.SR
paper · pdf · doi:10.1088/0004-637x/782/1/50
published as E.P. Lagioia et al. 2014, ApJ, 782, 50 · 14 pages, 12 figures (2 at low resolution); added references; corrected figure 3, 4, 5, 8 and 9; results unchanged. Erratum to be published in ApJ
openalex publication_date 2014/01/27 · arxiv created 2014/03/05 · arxiv updated 2014/03/06 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We present deep and precise multi-band photometry of the Galactic bulge globular cluster NGC 6528. The current data set includes optical and near-infrared images collected with ACS/WFC, WFC3/UVIS, and WFC3/IR on board the Hubble Space Telescope . The images cover a time interval of almost 10 yr, and we have been able to carry out a proper-motion separation between cluster and field stars. We performed a detailed comparison in the m F814W , m F606W − m F814W color–magnitude diagram with two empirical calibrators observed in the same bands. We found that NGC 6528 is coeval with and more metal-rich than 47 Tuc. Moreover, it appears older and more metal-poor than the super-metal-rich open cluster NGC 6791. The current evidence is supported by several diagnostics (red horizontal branch, red giant branch bump, shape of the sub-giant branch, slope of the main sequence) that are minimally affected by uncertainties in reddening and distance. We fit the optical observations with theoretical isochrones based on a scaled-solar chemical mixture and found an age of 11 ± 1 Gyr and an iron abundance slightly above solar ([Fe/H] = +0.20). The iron abundance and the old cluster age further support the recent spectroscopic findings suggesting a rapid chemical enrichment of the Galactic bulge.