Two Populations of Open Star Clusters in the Galaxy

TL;DR

This study analyzes 593 open star clusters, revealing two distinct populations with different origins, chemical compositions, and orbital characteristics, indicating heterogeneity in the Galactic open cluster system.

Contribution

It identifies and characterizes two populations of open clusters in the Galaxy, highlighting their different origins and physical properties based on a comprehensive catalog analysis.

Findings

Two distinct populations of open clusters identified

One group formed from thin disk interstellar matter

Another group formed through extragalactic interactions

Abstract

Based on our compiled catalogue of fundamental astrophysical parameters for 593 open clusters, we analyze the relations between the chemical composition, spatial positions, Galactic orbital elements, age, and other physical parameters of open star clusters. We show that the population of open clusters is heterogeneous and is divided into two groups differing by their mean parameters, properties, and origin. One group includes the Galactic clusters formed mainly from the interstellar matter of the thin disk with nearly solar metallicities ([Fe/H] > -0.2) and having almost circular orbits a short distance away from the Galactic plane, i.e., typical of the field stars of the Galactic thin disk. The second group includes the peculiar clusters formed through the interaction of extragalactic objects (such as high--velocity clouds, globular clusters, or dwarf galaxies) with the interstellar matter of the thin disk, which, as a result, derived abnormally low (for field thin-disk stars) metallicities and/or Galactic orbits typical of objects of the older Galactic subsystems.