A Bayesian Analysis of the Ages of Four Open Clusters

Abstract

In this paper we apply a Bayesian technique to determine the best fit of stellar evolution models to find the main sequence turn off age and other cluster parameters of four intermediate-age open clusters: NGC 2360, NGC 2477, NGC 2660, and NGC 3960. Our algorithm utilizes a Markov chain Monte Carlo technique to fit these various parameters, objectively finding the best-fit isochrone for each cluster. The result is a high-precision isochrone fit. We compare these results with the those of traditional "by-eye" isochrone fitting methods. By applying this Bayesian technique to NGC 2360, NGC 2477, NGC 2660, and NGC 3960, we determine the ages of these clusters to be 1.35 ± 0.05, 1.02 ± 0.02, 1.64 ± 0.04, and 0.860 ± 0.04 Gyr, respectively. The results of this paper continue our effort to determine cluster ages to higher precision than that offered by these traditional methods of isochrone fitting.

Characterising open clusters in the solar neighbourhood with the Tycho-Gaia Astrometric Solution

“…Given a set of stellar isochrones, BASE-9 compares the theoretical photometry with the observed one, taking into account the presence of unre-solved binary stars as well as the probability that each individual star is a cluster member or a field star. More insight on the capabilities of BASE-9 can be found in Jeffery et al (2016). We set BASE-9 to provide a posterior distribution for four parameters: age (log t), metallicity ([Fe/H]), distance modulus ((m − M) V ), and V-band extinction (A V = 3.1 × E(B − V)).…”

“…Article number, page 8 of 15 Following the approach of Jeffery et al (2016), for every OC we performed five runs of BASE-9 sampling 3000 points each, using slightly different starting points. The first run started from the literature value for age, extinction, and metallicity, and the distance modulus used was the one determined in Sect.…”

“…For simplicity we only report here the mean and standard deviation of those posterior distributions. As pointed out by Jeffery et al (2016), the uncertainties on the cluster parameters reflect the internal precision of the procedure (the certainty with which a certain PARSEC isochrone represents the data better than a different PARSEC isochrone), rather than an absolute accuracy. An example of CMD, along with isochrones sampled from the posterior distribution, is shown in Fig.…”

Bayesian analysis of two stellar populations in Galactic globular clusters– III. Analysis of 30 clusters

“…In the past, isochrones have primarily been fit to observations of star clusters by eye, trying different parameters and nudging isochrones in color-magnitude space until a solution looks good (Jeffery et al 2016, in press). However, with our approach we are able to numerically determine the set of parameters for clusters using an in-depth grid of theoretical models (von Hippel et al 2006, De Gennaro et al 2009, Jeffery et al 2016). We apply this method to 30 Galactic globular clusters, each fit with two dominant populations of stars, in order to better understand the relationships and origins of multiple populations.…”

A catalog of 159,238 white dwarf ages

“…We have developed a Bayesian statistical method for fitting stellar evolution models to photometry, which is further aided by priors on distance, metallicity, or other parameters. Our method has been successfully applied to single stellar populations in open clusters (DeGennaro et al 2009;Jeffery et al 2011;Hills et al 2015;Jeffery et al 2016;Bossini et al 2019), multiple populations in globular clusters (Wagner-Kaiser et al 2016a,b), binary field stars (Fouesneau et al 2019), and single WD field stars (O'Malley, von Hippel & van Dyk 2013). We refer to our code suite as BASE-9, for Bayesian Analysis of Stellar Evolution with nine parameters.…”