Extracting parameters from Colour-Magnitude Diagrams

TL;DR

This paper introduces a straightforward method to derive astrophysical parameters from star cluster colour-magnitude diagrams by matching observed Hess diagrams with a grid of isochrones, effectively recovering cluster properties.

Contribution

The paper presents a novel, efficient approach for extracting multiple cluster parameters simultaneously from CMDs using a solution map based on isochrone fitting.

Findings

Method accurately recovers input parameters in simulated tests.

Applied to real clusters, it successfully determines age, metallicity, reddening, and distance.

Approach is robust across different cluster types.

Abstract

We present a simple approach for obtaining robust values of astrophysical parameters from the observed colour-magnitude diagrams (CMDs) of star clusters. The basic inputs are the Hess diagram built with the photometric measurements of a star cluster and a set of isochrones covering wide ranges of age and metallicity. In short, each isochrone is shifted in apparent distance modulus and colour excess until it crosses over the maximum possible Hess density. Repeating this step for all available isochrones leads to the construction of the solution map, in which the optimum values of age and metallicity - as well as foreground/background reddening and distance from the Sun - can be searched for. Controlled tests with simulated CMDs show that the approach is efficient in recovering the input values. We apply the approach to the open clusters M\,67, NGC\,6791, and NGC\,2635, which are characterised by different ages, metallicities and distances from the Sun.