A robust statistical estimation of the basic parameters of single stellar populations. I. Method

TL;DR

This paper introduces a new statistical method that accurately determines key properties of single stellar populations by analyzing star counts along isochrones, reducing degeneracies and systematic uncertainties.

Contribution

The paper presents a robust, objective statistical technique that significantly improves the accuracy of inferring stellar population parameters from color-magnitude diagrams.

Findings

Can infer age, metallicity, distance, and reddening with confidence intervals.

Systematic uncertainties from field contamination and binaries are negligible or controlled.

Provides an easy-to-implement algorithm for stellar population analysis.

Abstract

The colour-magnitude diagrams of resolved single stellar populations, such as open and globular clusters, have provided the best natural laboratories to test stellar evolution theory. Whilst a variety of techniques have been used to infer the basic properties of these simple populations, systematic uncertainties arise from the purely geometrical degeneracy produced by the similar shape of isochrones of different ages and metallicities. Here we present an objective and robust statistical technique which lifts this degeneracy to a great extent through the use of a key observable: the number of stars along the isochrone. Through extensive Monte Carlo simulations we show that, for instance, we can infer the four main parameters (age, metallicity, distance and reddening) in an objective way, along with robust confidence intervals and their full covariance matrix. We show that systematic uncertainties due to field contamination, unresolved binaries, initial or present-day stellar mass function are either negligible or well under control. This technique provides, for the first time, a proper way to infer with unprecedented accuracy the fundamental properties of simple stellar populations, in an easy-to-implement algorithm.