Deep HST Photometry of NGC 6388: Age and Horizontal Branch Luminosity

Abstract

Using the Hubble Space Telescope, we have obtained the first color-magnitude diagram (CMD) to reach the main-sequence turnoff of the Galactic globular cluster NGC 6388. From a comparison between the cluster CMD and 47 Tucanae's, we find that the bulk of the stars in these two clusters have nearly the same age and chemical composition. On the other hand, our results indicate that the blue horizontal branch and RR Lyrae components in NGC 6388 are intrinsically overluminous, which must be due to one or more, still undetermined, non-canonical second parameter(s) affecting a relatively minor fraction of the stars in NGC 6388.

4 pages, 3 colored figures. LOW-RESOLUTION VERSION. The interested reader is strongly encouraged to download the full-resolution preprint from http://www.astro.puc.cl/~mcatelan/N6388-HST.pdf

References in corpus (3)

• An empirical calibration of the mixing-length parameter alpha
• Image-Subtraction Photometry of Variable Stars in the Globular Clusters NGC 6388 and NGC 6441
• Observations of the Hot Horizontal-Branch Stars in the Metal-Rich Bulge Globular Cluster NGC 6388 - Indications of Helium Enrichment and a Lesson in Crowded Field Spectroscopy

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• The presence of intermediate-mass black holes in globular clusters and their connection with extreme horizontal branch stars
• MCAO near-IR photometry of the Globular Cluster NGC 6388: MAD observations in crowded fields
• Constraints on Helium Enhancement in the Globular Cluster M3 (NGC 5272): The Horizontal Branch Test
• Fake star formation bursts: blue horizontal branch stars masquerade as young stars in optical integrated light spectroscopy
• On the Origin of Bimodal Horizontal-Branches in Massive Globular Clusters: The Case of NGC 6388 and NGC 6441
• The Blue Hook Populations of Massive Globular Clusters
• Quantifying mass segregation and new core radii for 54 milky way globular clusters
• X-ray Binaries in the Ultrahigh Encounter Rate Globular Cluster NGC 6388
• Mid-UV Narrow-Band Indices of Evolved Simple Stellar Populations
• Overluminous Blue Horizontal Branch Stars Formed by Low Mass Companions
• Near-infrared observations of RR Lyrae and Type II Cepheid variables in the metal-rich bulge globular cluster NGC 6441
• The XMM-Newton Slew view of IGRJ17361-4441: a transient in the globular cluster NGC 6388
• The Ages of Stars: The Horizontal Branch