Exploring the dynamical state of Galactic open clusters using Gaia DR3 and observational parameters

• Published in: Monthly notices of the Royal Astronomical Society Vol. 539; no. 3; pp. 2513 - 2536
• Main Authors: Angelo, M S, Santos, J F C, Corradi, W J B, Maia, F F S
• Format: Journal Article
• Language: English
• Published: 01.05.2025
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/staf584

Galactic open clusters (OCs) are subject to internal and external destructive effects that gradually deplete their stellar content, leaving imprints on their structure. To investigate their dynamical state from an observational perspective, we employed Gaia DR3 data to perform a comprehensive analysis of 174 OCs ($\sim$10 per cent of Dias et al.’s catalogue). We employed radial density profiles and astrometrically decontaminated colour–magnitude diagrams to derive structural parameters, distance, mass, and time-related quantities. We explored the parameters space and searched for connections relating the clusters’ structure with the internal evolutionary state and the external Galactic tidal field. Correlations were verified after segregating the sample according to the Galactocentric distance and half-light to Jacobi radius ratio ($r_h/R_J$). This tidal filling ratio decreases with both the cluster mass and dynamical age. At a given evolutionary stage, OCs with larger $r_h/R_J$ tend to present larger fractions of mass loss due to dynamical effects. Regarding the impact of the external conditions, we identified different evaporation regimes: for ambient densities ($\rho _{\textrm {amb}}$) larger than $\sim$0.1 ${\rm M}_{\odot }$ pc$^{-3}$, clusters tend to be more tidally filled as they are subject to weaker tidal stresses. For $\rho _{\textrm {amb}}\lesssim 0.1\, {\rm M}_{\odot }$ pc$^{-3}$, the opposite occurs: $R_J$ increases for smaller $\rho _{\textrm {amb}}$, causing $r_h/R_J$ to decrease. In turn, two-body relaxation tends to compact the cluster core, which is less sensitive to variations of the external potential. The higher the degree of central concentration, the larger the number of relaxation times a cluster takes until its dissolution.