Abstract
view Abstract Citations (441) References (151) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Horizontal-Branch Stars in Globular Clusters. II. The Second Parameter Phenomenon Lee, Young-Wook ; Demarque, Pierre ; Zinn, Robert Abstract Using synthetic horizontal-branch models, we have investigated the origin of the systematic variation in horizontal-branch (HB) morphology with galactocentric distance (RG) among globular clusters. The variations in He abundance, CNO abundance, and core mass required separately to explain this effect are inconsistent with either the observed properties of the RR Lyrae variables or the observed main-sequence turnoffs in the clusters. There is also no clear evidence that the trend with RG is related to the central concentrations, central densities, or absolute magnitudes of the clusters. The variations in cluster age required to explain this effect are not in conflict with any observations. A detailed comparison of our synthetic HB calculations with pairs of clusters of very different HB morphology but similar (Fe/H) reveals reasonably good agreement between the age differences inferred from HB morphology and the main-sequence turnoff. The major source of uncertainty is the need for ad hoc hypotheses in the modeling of the HB morphologies of a few peculiar clusters (e.g., NGC 6752). Nonetheless, there is firm evidence for age variations of several gigayears (as much as approximately 5 Gyr) among the halo globular clusters. Our results support the hypothesis of Searle & Zinn that the inner halo is more uniform in age and is older in the mean than the outer halo, and we estimate this difference to be approximately 2 Gyr. Publication: The Astrophysical Journal Pub Date: March 1994 DOI: 10.1086/173803 Bibcode: 1994ApJ...423..248L Keywords: Globular Clusters; Horizontal Branch Stars; Star Formation; Stellar Models; Abundance; Stellar Composition; Stellar Luminosity; Astrophysics; GALAXY: FORMATION; GALAXY: GLOBULAR CLUSTERS: GENERAL; STARS: EVOLUTION; STARS: HORIZONTAL-BRANCH full text sources ADS | data products SIMBAD (83) Related Materials (1) Part 1: 1990ApJ...350..155L
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