# The ACS Survey of Galactic Globular Clusters XIV: Bayesian Single-Population Analysis of 69 Globular Clusters

## TL;DR

This study employs Bayesian methods to analyze HST imaging data, deriving ages, distances, and chemical compositions for 69 globular clusters, providing insights into their formation and evolution.

## Contribution

It introduces a consistent Bayesian framework for single-population analysis of globular clusters, improving parameter estimation accuracy and reproducibility.

## Key findings

- Identified correlations between helium abundance and metallicity.
- Revised age-metallicity relation for globular clusters.
- Found links between helium and cluster properties like binary fraction.

## Abstract

We use Hubble Space Telescope (HST) imaging from the ACS Treasury Survey to determine fits for single population isochrones of 69 Galactic globular clusters. Using robust Bayesian analysis techniques, we simultaneously determine ages, distances, absorptions, and helium values for each cluster under the scenario of a "single" stellar population on model grids with solar ratio heavy element abundances. The set of cluster parameters is determined in a consistent and reproducible manner for all clusters using the Bayesian analysis suite BASE-9. Our results are used to re-visit the age-metallicity relation. We find correlations with helium and several other parameters such as metallicity, binary fraction, and proxies for cluster mass. The helium abundances of the clusters are also considered in the context of CNO abundances and the multiple population scenario.