Exploring the Structure and Evolution of Four Young Open Clusters Near the Galactic Mid-plane via Gaia DR3

TL;DR

The paper analyzes four young open clusters near the Galactic mid-plane using Gaia DR3 to derive membership with UPMASK and infer ages, distances, reddening, and metallicities via Bayesian isochrone fitting. It combines structural, photometric, and kinematic analyses with King-model density profiles, mass–luminosity relations, and galpy-based orbital integrations (MWPotential2014 and spiral-arm potentials) to characterize dynamical states and Galactic orbits. A key finding is the discovery of two distinct substructures within NGC 2384 (NGC 2384a and NGC 2384b) that are at different distances and ages, indicating an optical pair rather than a bound binary; similarly, all clusters lie on low-eccentricity, thin-disk orbits with modest spiral perturbations. The results show mass function slopes near Salpeter, a broad range of total cluster masses, and dynamical states consistent with young clusters retaining natal substructures, with spiral-arm perturbations modestly altering orbital properties. Overall, the study provides refined, Gaia-driven benchmarks for the structure, evolution, and Galactic context of young open clusters in crowded mid-plane environments.

Abstract

We present a comprehensive analysis of four young open clusters, NGC 663, NGC 2301, NGC 2384, and NGC 7510, utilizing high-precision astrometric and photometric data from Gaia DR3. Cluster membership was determined using the UPMASK algorithm, resulting in probable member counts ranging from 337 to 1498 across the clusters. Bayesian MCMC isochrone fitting yielded cluster ages in the range $\log t \sim 7.0$ -$8.15$, with uncertainties of $\sim 0.11$-$0.18$. Reddening values ranged from $E(B-V)=0.093$ mag in NGC 2301 to $1.24$ mag in NGC 7510, consistent with their positions near the Galactic plane. The stellar mass function slopes ($α\approx 2.00$-$2.26$) closely match the Salpeter IMF, with total stellar masses spanning nearly an order of magnitude, from $\sim 486\,M_\odot$ in NGC 2301 to $\sim 3584\,M_\odot$ in NGC 663. Dynamical relaxation times indicate that only NGC 2301 ($τ\approx 10.00$) and NGC 2384b ($τ\approx 2.03$) are dynamically relaxed; the others remain dynamically evolving. Orbital integrations in the MWPotential2014 model reveal nearly circular Galactic orbits with very low eccentricities ($e \approx 0.003$-$0.014$) and small vertical distances ($Z_{\rm max} < 0.142$ kpc), confirming their confinement to the thin disk. SED and kinematic analysis show that NGC 2384a and NGC 2384b are separated by $\sim 0.55$ kpc, indicating an optical pair.

Figures (19)

• Figure 1: Digitized Sky Survey (DSS) images displaying the identification of the open clusters NGC 663, NGC 2301, NGC 2384, and NGC 7510 with the position of each cluster on the Milkyway.
• Figure 2: Histograms of Gaia photometric data for the OCs NGC 663, NGC 2301, NGC 2384, and NGC 7510. The orange dashed line indicates the Gaia completeness limit in each OC.
• Figure 3: The Gaussian fit provides the coordinates of the highest density areas density areas in $\alpha$ and $\delta$, as well as the density contour diagrams illustrating the structural properties of of NGC 663, NGC 2301, NGC 2384, and NGC 7510.
• Figure 4: RDPs of NGC 663, NGC 2301, NGC 2384, and NGC 7510 OCs. The curved solid lines represent the fitting of King's model king1966 and the dashed lines represent the background field density $f_{bg}$.
• Figure 5: Histogram of membership probabilities ($P$) from UPMASK for all stars in the studied clusters. The vertical red dashed line indicates the adopted membership probability threshold of $P \geq 50\%$, which separates likely cluster members from field stars.