2021MNRAS.500.4338A

In this work, we investigate the dynamical properties of 38 Galactic open clusters: 34 of them are located at low Galactic latitudes (|b| < 10°) and are projected against dense stellar fields; the other four comparison objects present clearer contrasts with the field population. We determine structural and time-related parameters that are associated with the clusters' dynamical evolution: core (r_c), tidal (r_t), and half-mass (r_hm) radii, ages (t), and crossing times (t_cr). We have also incorporated results for 27 previously studied clusters, creating a sample of 65, spanning the age and Galactocentric distance (R_G) ranges 7.0 < log t < 9.7 and 6 < R_G (kpc) < 13. We employ a uniform analysis method which incorporates photometric and astrometric data from the Gaia DR2 catalogue. Member stars are identified by employing a decontamination algorithm which operates on the 3D astrometric space of parallax and proper motion and attributes membership likelihoods for stars in the cluster region. Our results show that internal relaxation causes r_c to correlate negatively with the dynamical ratio τ_dyn = t/t_cr. This implies that dynamically older systems tend to be more centrally concentrated. The more concentrated ones tend to present smaller r_hm/r_t ratios, which means that they are less subject to tidal disruption. The analysis of coeval groups at compatible R_G suggests that the inner structure of clusters is reasonably insensitive to variations in the external tidal field. Additionally, our results confirm, on average, an increase in r_t for regions with less-intense Galactic gravitational fields.