A kinematic and structural study of young open clusters in the Milky Way Galaxy using Gaia DR3 catalogue

TL;DR

This study probes 14 young open clusters within $1$ kpc using Gaia DR3 to map membership, derive fundamental parameters, and investigate internal dynamics as a function of stellar mass. Membership is determined with a Gaussian Mixture Model and cluster properties are inferred by fitting PARSEC isochrones through a two-step process (least-squares pre-fit and MCMC refinement), yielding ages in $[6,8]$ in log$_{10}$ years and distances in the $[334,910]$ pc range, with masses spanning $0.13$–$13.77\,M_\odot$. A key finding is mass-dependent transverse velocity dispersion in several clusters, indicating dynamical relaxation, along with the identification of walkaway candidates among BA-type stars and evidence of sub-structuring and elongation in some clusters. These results provide quantitative benchmarks for simulations of cluster dynamical evolution, mass segregation, and massive-star ejection processes in young stellar systems, and demonstrate the utility of Gaia DR3 data for precise cluster kinematics.

Abstract

We aim to identify the cluster members, estimate cluster properties, study the dynamical state of the clusters as a function of mass, trace the existence of dynamical effects in massive stars, and check for spatial patterns of members in young clusters. We studied 14 young open clusters located within 1 kpc using the data from Gaia DR3 with the membership estimated using the GMM method. The cluster parameters such as age, distance, metallicity, and extinction were estimated by fitting PARSEC isochrones to the CMDs. These clusters are found to have ages between 6-90 Myr, located between 334-910 pc, covering a mass range, of 0.13 to 13.77 solar mass. In five of these clusters, stars from F to M spectral type show increasing velocity dispersion, a signature for dynamical relaxation. We detect high proper motion for B and A-type stars, possible walkaway stars in the other five clusters, Alessi Teutsch 5, ASCC 16, ASCC 21, IC 2395, and NGC 6405. We demonstrate the existence of mass-dependent velocity dispersion in young clusters suggestive of dynamical relaxation. The typical range of transverse velocity dispersion is found to be 0.40 - 0.70 km/s for young clusters.

Figures (10)

• Figure 1: Spatial plot for all the OCs. Black and gray dots represent the cluster members and field stars, respectively. The red line represents the isodensity contours.
• Figure 2: Vector Point Diagram (VPD) for all the OCs. Red and green dots represent the cluster members and field stars, respectively.
• Figure 3: Isochrone-fitting using least-square minimization for all the OCs. Here, brown dots represent the cluster members; the blue line represents the isochrone for pre-main sequence (PMS) stars, and the red line represents the isochrone for main sequence (MS) stars. Also, $log_{10} (Age)$, Metallicity (M/H), Distance (D) in PC, and Extinction in Gmag ($A_G$) estimated from isochrone fitting are mentioned in the plots. The black lines represent isochrone with $log_{10} (Age) \pm$0.1.
• Figure 4: Isochrone-fitting using MCMC for all the OCs. Here, brown dots represent the cluster members; the blue line represents the isochrone, and the black cross represents the possible walkaway stars.
• Figure 5: Mass vs Transverse velocity dispersion. (a) Statistically significant ones (b) May have statistical insignificance.