On the kinematic separation of field and cluster stars across the Bulge globular NGC 6528

Abstract

We present deep and precise multi-band photometry of the Galactic Bulge globular cluster NGC6528. The current dataset 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 ten years 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 NGC6528 is coeval with and more metal-rich than 47Tuc. Moreover, it appears older and more metal-poor than the super-metal-rich open cluster NGC6791. 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.

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

References in corpus (3)

• HST Proper Motions and Stellar Dynamics in the Core of the Globular Cluster 47 Tucanae
• Multiple stellar populations in Magellanic Clouds clusters. I. An ordinary feature for intermediate age globulars in the LMC?
• ARGOS II: The Galactic Bulge Survey

Cited by in corpus (24)

• Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST and literature data
• Absolute V-band magnitudes and mass-to-light ratios of Galactic globular clusters
• Chemical analysis of NGC 6528: one of the most metal-rich bulge globular cluster
• The WAGGS project - I. The WiFeS Atlas of Galactic Globular cluster Spectra
• A panchromatic view of the bulge globular cluster NGC 6569
• The Carina Project. VIII. The α-element abundances
• Differential reddening in the direction of 56 Galactic globular clusters
• Digging for relics of the past: the ancient and obscured bulge globular cluster NGC6256
• The Controversial Star-Formation History and Helium Enrichment of the Milky Way Bulge
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XX. Ages of single and multiple stellar populations in seven bulge globular clusters
• Searching for intermediate-mass black holes in globular clusters with gravitational microlensing
• The WAGGS project - II. The reliability of the calcium triplet as a metallicity indicator in integrated stellar light
• First evidence of multi-iron sub-populations in the Bulge Fossil Fragment candidate Liller 1
• The absolute age of the globular cluster M15 using near-infrared adaptive optics images from PISCES/LBT
• Stroemgren - near-infrared photometry of the Baade's Window. I. The bulge globular cluster NGC6528 and the surrounding field
• Impact of distance determinations on Galactic structure. II. Old tracers
• Comparing Observed Stellar Kinematics and Surface Densities in a Low Latitude Bulge Field to Galactic Population Synthesis Models
• Infrared photometry and CaT spectroscopy of globular cluster M 28 (NGC 6626)
• Stellar photometry with Multi Conjugate Adaptive Optics
• Multiple populations within globular clusters in Early-type galaxies Exploring their effect on stellar initial mass function estimates
• One of Everything: The Breakthrough Listen Exotica Catalog
• On the use of asymmetric PSF on NIR images of crowded stellar fields
• Revisited parameters for the twin bulge globular clusters NGC 6528 and NGC 6553
• The globular cluster NGC 6528 the ferrous side of the Galactic Bulge