A Dynamical Evolution Study of 40 2MASS Open Clusters

TL;DR

This study examines the dynamical evolution of 40 open clusters using 2MASS data, revealing bifurcated growth patterns, mass segregation, and the impact of stellar black holes on cluster expansion.

Contribution

It provides new insights into the dynamical processes of open clusters, including bifurcation in size evolution and the role of mass segregation, based on a large sample with detailed photometric analysis.

Findings

Bifurcation in cluster size evolution with age.

Detection of mass segregation in some clusters.

Most clusters' mass functions align with Kroupa's initial mass function.

Abstract

We investigate the dynamical evolution of 40 open clusters (OCs) by means of their astrophysical parameters derived from field-decontaminated 2MASS photometry. We find a bifurcation in the planes core radius vs. age and cluster radius vs. age, in which part of the clusters appear to expand with time probably due to the presence of stellar black holes while others seem to shrink due to dynamical relaxation. Mass functions (MFs) are built for 3$/$4 of the sample (31 OCs), which are used to search for indications of mass segregation and external dynamical processes by means of relations among astrophysical, structural and evolutionary parameters. We detect a flattening of MF slopes ocurring at the evolutionary parameters $\tau_{core}\leq 32$ and $\tau_{overall}\leq 30$, respectively. Within the uncertainties involved, the overall MF slopes of 14 out of 31 OCs with $m_{overall} > 500~M_{\odot}$ are consistent with Kroupa's initial mass function, implying little or no dynamical evolution for these clusters. The remaining 17 OCs with MF slopes departing from that of Kroupa show mild/large scale mass segregation due to dynamical evolution.