Interpreting the Colour-Magnitude Diagrams of Open Star Clusters through Numerical Simulations

Abstract

We present detailed comparisons between high quality observational colour-magnitude diagrams (CMDs) of open star clusters and synthetic CMDs based on MonteCarlo numerical simulations. The comparisons account for all of the main parameters which determine the shape of the CMD for a stellar population. For the four clusters studied, NGC 6819, NGC 2099 (M37), NGC 2168 (M35) and NGC 2323 (M50), we derive reddening, distance, age, binary fraction, star formation rate and indicative metallicity by comparing the locations and density of points in the observed CMDs to the simulated CMDs. We estimate the uncertainties related to stellar evolution theories by adopting various sets of stellar models for all of the synthetic CMDs and discuss which stellar models provide the theoretical CMDs that best reproduce the observations.