A comprehensive analysis of NGC 2158 in Gaia era: photometric parameters, apex and orbit

TL;DR

This study analyzes NGC 2158 using Gaia-DR2 data, determining its physical parameters, kinematics, and orbit, revealing it as a dynamically relaxed, old open cluster with specific motion characteristics and oscillations.

Contribution

It provides a comprehensive analysis of NGC 2158's photometric, kinematic, and orbital properties using Gaia data, including new measurements of its orbit and dynamical state.

Findings

NGC 2158 is a 9.38 Gyr old, dynamically relaxed open cluster.

The cluster's mean proper motion is (−0.203, −1.99) mas/yr.

The orbit indicates movement towards the Solar antapex with significant Z oscillations.

Abstract

We present an investigation of NGC 2158 using Gaia-DR2 data. We identified 800 most likely cluster members with membership probability higher than 90%. The mean proper motions of this object are determined as (mu_{x}=-0.203 \pm 0.003, mu_{y}=-1.99 \pm 0.004) mas yr^{-1}. The limiting radius, log(age), and distance of the cluster are obtained as 23.5 arcmin, 9.38 \pm 0.04 Gyr and 4.69 \pm 0.22 kpc, respectively. The overall mass function slope (0.93 \pm 0.14) is flatter than the Salpeter value (1.35) within the mass range 1.17-1.44 M_\odot. This cluster also shows the mass-segregation effect and our study demonstrates that NGC 2158 is a dynamically relaxed open cluster. Using the AD-diagram, the apex coordinates of the cluster are obtained in different ways and examined using (\mu_{U},\mu_{T}) diagram. The best value of apex coordinates is determined as A=87.24^\circ \pm 1.60^\circ, D=-36.61^\circ \pm 5.30 ^\circ. We also determined the orbit of the cluster and found that NGC 2158 moves almost in the Solar antapex direction. The resulting spatial velocity of NGC 2158 is 51 km s^{-1}. A significant oscillations along the Z-coordinate up to 529~pc is detected. Various scenarios regarding the origin of this cluster are also discussed.