The orbits of open clusters in the Galaxy

TL;DR

This study analyzes the kinematics and orbits of 488 open clusters in the Galaxy, revealing their velocity dispersions, orbital characteristics, and metallicity gradients, contributing to understanding Galactic structure and evolution.

Contribution

It provides a comprehensive analysis of open cluster orbits using multiple Galactic potential models and assesses the impact of observational uncertainties on orbital parameters.

Findings

Velocity ellipsoid indicates a young thin disc population.

Velocity dispersions increase with cluster age.

Radial metallicity gradient is approximately -0.07 dex/kpc.

Abstract

We present and analyze kinematics and orbits for a sample of 488 open clusters in the Galaxy. The velocity ellipsoid for our present sample is derived as ($\sigma_{U}$, $\sigma_{V}$, $\sigma_{W})$=$(28.7$, 15.8, 11.0) km s$^{-1}$ which represents a young thin disc population. We also confirm that the velocity dispersions increase with the age of cluster subsample. The orbits of open clusters are calculated with three Galactic gravitational potential models. The errors of orbital parameters are also calculated considering the intrinsic variation of the orbital parameters and the effects of observational uncertainties. The observational uncertainties dominate the errors of derived orbital parameters. The vertical motions of clusters calculated using different Galactic disc models are rather different. The observed radial metallicity gradient of clusters is derived with a slope of $b=-0.070\pm0.011$ dex kpc$^{-1}$. The radial metallicity gradient of clusters based on their apogalactic distances is also derived with a slope of $b=-0.082\pm0.014$ dex kpc$^{-1}$. The distribution of derived orbital eccentricities for open clusters is very similar to the one derived for the field population of dwarfs and giants in the thin disc.