A dynamical evolution study of 40 2MASS open clusters

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 versus age and cluster radius versus 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 three-fourth of the sample (31 OCs), which are used to search for indications of mass segregation and external dynamical processes by means of relations between astrophysical, structural, and evolutionary parameters. We detect a flattening of MF slopes occurring at the evolutionary parameters (core) <= 32 and (overall) <= 30, respectively. Within the uncertainties involved, the overall MF slopes of 14 out of 31 OCs with m(overall) > 500 M-circle dot 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.