Globular Clusters in the Outer Galactic Halo: AM-1 and Palomar 14

Abstract

AM-1, at ~120 kpc, and Pal 14, at ~70 kpc, are two of the most distant Galactic globular clusters known. We present Hubble Space Telescope WFPC2 photometry of AM-1 and Pal 14 that reveals unprecedented depth and detail in the color-magnitude diagrams of these two clusters. Absolute and relative age measurements confirm that both are younger than the inner halo globular cluster M 3 by 1.5-2 Gyr, assuming all three clusters have similar compositions. Thus AM-1 and Pal 14 join Pal 3, Pal 4, and Eridanus (studied by Stetson et al.) as distant Galactic globular clusters with red horizontal branches and young ages relative to the inner halo. Within the context of the entire body of research on the ages of second parameter globular clusters, the observed correlation between age and horizontal branch morphology suggests that age is the best candidate for the second parameter. However, this conclusion is tempered by the lack of precise chemical abundance determinations for a significant fraction of second parameter globular clusters.

22 pages, 8 figures, accepted by AJ

References in corpus (15)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• The Photometric Performance and Calibration of the HST Advanced Camera For Surveys
• WFPC2 Stellar Photometry with HSTphot
• Homogeneous Photometry for Star Clusters and Resolved Galaxies. II. Photometric Standard Stars
• The ACS Survey of Galactic Globular Clusters. I. Overview and Clusters Without Previous HST Photometry
• The YY Isochrones for alpha-element Enhanced Mixtures
• The ACS Survey of Galactic Globular Clusters. II. Stellar Evolution Tracks, Isochrones, Luminosity Functions, and Synthetic Horizontal-Branch Models
• The properties of Galactic globular cluster sub-systems
• A Comparison of Elemental Abundance Ratios in Globular Clusters, Field Stars, and Dwarf Spheroidal Galaxies
• The Line-of-Sight Depth of Populous Clusters in the Small Magellanic Cloud
• Heavy Element Diffusion in Metal Poor Stars
• NGC 2419, M92, and the Age Gradient in the Galactic Halo
• Ages for Globular Clusters in the Outer Galactic Halo: The Second Parameter Clusters Palomar~3, Palomar~4 and Eridanus
• CCD Photometry of the Classic Second Parameter Globular Clusters M3 and M13
• Probable member stars of the gravitational theory-testing globular clusters AM 1, Pal 3 and Pal 14

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