# Absolute Ages and Distances of 22 GCs using Monte Carlo Main-Sequence Fitting

## TL;DR

This study uses Gaia parallaxes and Monte Carlo modeling to accurately determine the ages and distances of 22 globular clusters, revealing insights into their distribution and evolution within the Milky Way.

## Contribution

It introduces a Monte Carlo method to fit stellar models to Gaia data, improving age and distance estimates for globular clusters with detailed uncertainty analysis.

## Key findings

- Ages range from 10.8 to 13.6 Gyr with ~1.6 Gyr uncertainty.
- Distances have an average uncertainty of 0.15 mag.
- No strong age-distance correlation, but a decreasing age-metallicity relation.

## Abstract

The recent Gaia Data Release 1 of stellar parallaxes provides ample opportunity to find metal-poor main-sequence stars with precise parallaxes. We select 21 such stars with parallax uncertainties better than $\sigma_\pi/\pi\leq0.10$ and accurate abundance determinations suitable for testing metal-poor stellar evolution models and determining the distance to Galactic globular clusters. A Monte Carlo analysis was used, taking into account uncertainties in the model construction parameters, to generate stellar models and isochrones to fit to the calibration stars. The isochrones which fit the calibration stars best were then used to determine the distances and ages of 22 globular clusters with metallicities ranging from -2.4 dex to -0.7 dex. We find distances with an average uncertainty of 0.15 mag and absolute ages ranging from 10.8 - 13.6 Gyr with an average uncertainty of 1.6 Gyr. Using literature proper motion data we calculate orbits for the clusters finding six that reside within the Galactic disk/bulge while the rest are considered halo clusters. We find no strong evidence for a relationship between age and Galactocentric distance, but we do find a decreasing age-[Fe/H] relation.