Extracting parameters from colour–magnitude diagrams

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.

Ensemble Properties of the White Dwarf Population of the Old, Solar Metallicity Open Star Cluster Messier 67*

“…For this work we adopt the second-ranked cluster photometric parameters from Bonatto et al (2015), which are consistent with those of Chen et al (2014): d = 880 ± 20 pc, E(B −V ) = 0.02 ± 0.02, Z = 0.019 ± 0.003, and age = 3.54 ± 0.15 Gyr. This choice was guided in large part by the desire to use a consistent set of isochrones (the PARSEC 1.2S isochrones, Chen et al 2015) for the different open cluster WD populations analyzed in Paper II.…”

The White Dwarfs of the Old, Solar Metallicity Open Star Cluster Messier 67: Properties and Progenitors

“…Even more compelling, the distance is fully consistent with the Gaia DR2 parallax derived for the cluster by Gaia Collaboration et al (2018). The Bonatto et al (2015) model-derived M67 distance corresponds to a parallax of = 1.136±0.025 mas, while the Gaia DR2 cluster parallax is = 1.1325±0.0011 mas.…”

“…We take the following steps in order to ensure we compare consistently derived values: (1) our M67 WD Note-Sharp-eyed readers may notice that these initial masses are systematically higher by a ≈ 0.03M than in Figure 9 of Paper I. This is due to the masses in that figure having been calculated for Z = 0.0152, inconsistent with our adopted metallicity of Z = 0.019 from Bonatto et al (2015). This error does not affect any of our conclusions from Paper I.…”

“…To simplify our comparisons with their IFMR and WD data, we focus on color-magnitude diagram derived parameters based on the PARSEC 1.2S isochrones (Bressan et al 2012;Chen et al 2015). Bonatto et al (2015) use the PARSEC evolutionary models and an iterative fit to the Hess diagram for M67 to derive optimum values of the cluster parameters. Their best-fitting model has significantly subsolar metallicity, which is at odds with M67's spectroscopically determined near-solar metallicity (e.g., Pasquini et al 2008).…”

Membership and age determination of M67 open cluster using GAIA EDR3 data

“…Converting the value of metallicity obtained from ASteCA in z to the more commonly used [F e/H] according to [8] gives us a value of -0.008 ± 0.0538 [F e/H]. Earlier works on M67 obtain a metallicity [F e/H] of 0.00 ± 0.06 [20] and -0.001 ± 0.003 [21]. Some values of reddening obtained from previous works on M67 include E B−V =0.03 [24] and E B−V =0.041 ± 0.004 [22].…”