Evolved Stars in the Core of the Massive Globular Cluster NGC 2419

Abstract

We present an analysis of optical and ultraviolet Hubble Space Telescope photometry for evolved stars in the core of the distant massive globular cluster NGC 2419. We characterize the horizontal branch (HB) population in detail including corrections for incompleteness on the long blue tail. We present a method for removing (to first order) lifetime effects from the distribution of HB stars to facilitate more accurate measurements of helium abundance for clusters with blue HBs and to clarify the distribution of stars reaching the zero-age HB. The population ratio R = N_HB / N_RGB implies there may be slight helium enrichment among the EHB stars in the cluster, but that it is likely to be small (dY < 0.05). An examination of the upper main sequence does not reveal any sign of multiple populations. Through comparisons of optical CMDs, we present evidence that the EHB clump in NGC 2419 contains the end of the canonical horizontal branch, and that the boundary between the normal HB stars and blue hook stars shows up as a change in the density of stars in the CMD. This corresponds to a spectroscopically-verified gap in NGC 2808 and an "edge" in omega Cen. The more clearly visible HB gap at V = 23.5 appears to be too bright.(Abridged)

27 pages, 25 figures (some bitmapped), uses emulateapj, accepted to Astronomical Journal

References in corpus (14)

• The ACS Survey of Galactic Globular Clusters. I. Overview and Clusters Without Previous HST Photometry
• The ACS Survey of Galactic Globular Clusters. III. The Double Subgiant Branch of NGC 1851
• The ACS Survey of Galactic Globular Clusters: M54 and Young Populations in the Sagittarius Dwarf Spheroidal Galaxy
• NGC 6441: another indication for a very high helium content in Globular Cluster stars
• The Peculiar Horizontal Branch Morphology of the Galactic Globular Clusters NGC 6388 and NGC 6441: new insights from UV observations
• The First Empirical Mass Loss Law for Population II Giants
• Another Non-segregated Blue Straggler Population in a Globular Cluster: the Case of NGC 2419
• Blue Straggler Stars in the Unusual Globular Cluster NGC 6388
• Fe and Al Abundances for 180 Red Giants in the Globular Cluster Omega Centauri (NGC 5139)
• The Dearth of UV-Bright Stars in M32: Implications for Stellar Evolution Theory
• A Spitzer Space Telescope Atlas of omega Centauri: The Stellar Population, Mass Loss, and the Intracluster Medium
• Na-O Anticorrelation and HB. IV. Detection of He-rich and He-poor stellar populations in the globular cluster NGC 6218
• On the remote Galactic globular cluster NGC 2419
• Observational consequences of the hypothesized helium rich stellar population in Omega Centauri

Cited by in corpus (5)

• The Swift UVOT Stars Survey: I. Methods and Test Clusters
• On the radial distribution of horizontal branch stars in ngc2808
• Blue Hook Stars in Globular Clusters
• UV-Bright Stellar Populations and Their Evolutionary Implications in the Collapsed-Core Cluster M15
• Hubble Space Telescope photometry of multiple stellar populations in the inner parts of NGC 2419