Structure and Evolution of Multi-Cluster within Galactic Disc: Gaia DR3 Insights into Eight Open Clusters

TL;DR

This study demonstrates how Gaia DR3 enables a homogeneous, multi-parameter analysis of eight open clusters (NGC 559, NGC 1817, NGC 2141, NGC 7245, Ruprecht 15, Ruprecht 137, Ruprecht 142, Ruprecht 169) to quantify their structure, stellar content, and dynamics within the Galactic disc. Structural parameters are derived from King-profile fits to radial density profiles, while ages, metallicities, distances, and reddening are obtained via PARSEC isochrone fitting to cleaned CMDs. The authors compute luminosity and mass functions, total cluster masses, and mass-segregation signatures, and assess dynamical states through relaxation times and KS tests, finding most clusters dynamically relaxed with MF slopes near Salpeter and mass segregation evident in several clusters. Kinematic analyses using convergent-point methods and galpy orbit integrations show near-circular, thin-disc orbits with low $Z_{ m max}$, confirming disc membership and providing insight into the clusters’ dynamical evolution and Galactic context. A notable result is NGC 7245, identified as a binary cluster candidate due to its bimodal radial-density structure and dual kinematic components, illustrating Gaia DR3’s power for uncovering complex cluster architectures and their evolutionary histories.

Abstract

In this study, we present a comprehensive analysis of the structural, astrophysical, and dynamical properties of eight open clusters: NGC 559, NGC 1817, NGC 2141, NGC 7245, Ruprecht 15, Ruprecht 137, Ruprecht 142, and Ruprecht 169, using precise astrometric and photometric data from Gaia Data Release 3. By fitting the King model to the radial density profiles, we determined the structural parameters of the clusters, including core and limiting radii, which were found to range from 3.07 to 16.21 arcmin and from 9.97 to 25.97 arcmin, respectively. Fundamental astrophysical parameters were derived by fitting PARSEC isochrones to the colour-magnitude diagrams. The results show that the clusters have logarithmic ages between 7.95 and 9.34, metallicities in the range 0.007 to 0.015, and heliocentric distances between 1640 and 5203 pc. The total stellar masses of the clusters were estimated to lie between 257 and 1916 solar masses. For most of the clusters, the mass function slopes are consistent with the Salpeter initial mass function. Our dynamical analysis indicates that all clusters, except Ruprecht 15, are dynamically relaxed. In addition, the spatial distribution and the bimodal structure observed in the radial density profile of NGC 7245 provide strong evidence that this object is a binary cluster candidate. Finally, kinematic analysis and orbit integrations demonstrate that all clusters exhibit dynamical properties fully consistent with membership in the Galactic thin disc.

Figures (16)

• Figure 1: The spatial distribution of the eight target OCs (red dots) projected onto the Galactic plane. The positions of the Sun (yellow dot) and the Galactic Centre (blue dot) are marked for reference against a schematic representation of the MW's spiral arms and bar.
• Figure 2: Finding charts of the investigated OCs in the equatorial coordinate system. The coordinate frame is oriented such that north increases upward, while east increases to the left.
• Figure 3: The distribution of $G$-apparent magnitudes for stars located in the fields of the eight OCs. Vertical red dashed lines denote the photometric completeness limits.
• Figure 4: Determination of the cluster centres for the eight target OCs. The peaks of the Gaussian fits (dashed red lines) are adopted as the new cluster centres, with the mean values and standard deviations noted in each panel.
• Figure 5: The RDPs of the NGC 559 & NGC 1817 clusters represented by the black dots. The dashed red line represents the King1962 fitting while the blue dashed line marks the background density $f_{\rm bg}$.