Structural properties of subgroups of stars associated with open clusters

TL;DR

This study investigates the structural properties and subgroups of stars in open clusters using Gaia DR3 data, Bayesian analysis, and comparisons with N-body simulations to understand cluster morphology and evolution.

Contribution

It introduces a Bayesian multi-dimensional approach to identify subgroups and characterizes their structure, providing new insights into cluster morphology and evolution.

Findings

Double components found in Markarian 38 and NGC 2659.

Five clusters confirmed as single, no substructure.

Structural parameters compared with N-body simulations.

Abstract

Recent studies have identified star clusters with multiple components based on accurate spatial distributions and/or proper motions from Gaia DR3, utilising diverse diagnostics to improve our understanding of subgroup evolution. These findings motivated us to search for subgroups among the objects examined in our previous work, which employed fractal statistics. The present study considers seven open clusters that exhibit significant dispersion in age and/or proper motion distributions, suggesting that they would not be single clusters. For characterizing the stellar groups, we calculate the membership probability using Bayesian multi-dimensional analysis by fitting the observed proper motion distribution of the candidates. A probability distribution is also used to determine the distance of the cluster, which is obtained from the mean value of the distance modes. The photometry from Gaia DR3 is compared with evolutionary models to estimate the cluster age and total mass. In our sample, double components are found only for Markarian 38 and NGC 2659. The other five clusters are confirmed as being single. The structural parameters, such as Q, Lambda_MSR and Sigma_LDR are compared with results from N-body simulations to investigate how the morphology of the stellar clustering evolves. The new results, for a more complete sample of cluster members, provide a better definition of the distribution type (central concentration or substructured region) inferred from the m-s plot.