Bayesian Analysis of Two Stellar Populations in Galactic Globular Clusters II: NGC 5024, NGC 5272, and NGC 6352

TL;DR

This study employs Bayesian methods to analyze multiple stellar populations in three Galactic globular clusters, determining their ages, compositions, and helium variations with high precision using HST data.

Contribution

It introduces a Bayesian analysis framework that simultaneously fits cluster parameters and multiple stellar populations, including helium variations, in globular clusters.

Findings

Helium abundance differences range from 0.05 to 0.11 among the clusters.

The analysis distinguishes multiple populations with unique helium levels.

Model fits vary with different alpha-element assumptions.

Abstract

We use Cycle 21 Hubble Space Telescope (HST) observations and HST archival ACS Treasury observations of Galactic Globular Clusters to find and characterize two stellar populations in NGC 5024 (M53), NGC 5272 (M3), and NGC 6352. For these three clusters, both single and double-population analyses are used to determine a best fit isochrone(s). We employ a sophisticated Bayesian analysis technique to simultaneously fit the cluster parameters (age, distance, absorption, and metallicity) that characterize each cluster. For the two-population analysis, unique population level helium values are also fit to each distinct population of the cluster and the relative proportions of the populations are determined. We find differences in helium ranging from $\sim$0.05 to 0.11 for these three clusters. Model grids with solar $\alpha$-element abundances ([$\alpha$/Fe] =0.0) and enhanced $\alpha$-elements ([$\alpha$/Fe]=0.4) are adopted.