Highly dynamically evolved intermediate-age open clusters

TL;DR

This study analyzes seven intermediate-age open clusters using multi-band photometry and Gaia data, revealing their dynamical evolution, sizes, and mass properties, with some not being true clusters.

Contribution

It provides detailed structural and astrophysical properties of seven open clusters, highlighting their evolved dynamical states and differences from similar nearby clusters.

Findings

Ruprecht 3 and ESO 436-2 are likely not physical clusters.

Remaining clusters are intermediate-age, small, and dynamically evolved.

Cluster masses are 10-15% of similar nearby clusters.

Abstract

We present a comprehensive UBVRI and Washington CT1T2 photometric analysis of seven catalogued open clusters, namely: Ruprecht 3, 9, 37, 74, 150, ESO 324-15 and 436-2. The multi-band photometric data sets in combination with 2MASS photometry and Gaia astrometry for the brighter stars were used to estimate their structural parameters and fundamental astrophysical properties. We found that Ruprecht 3 and ESO 436-2 do not show self-consistent evidence of being physical systems. The remained studied objects are open clusters of intermediate-age (9.0 < log(t yr-1) < 9.6), of relatively small size (r_cls ~ 0.4 - 1.3 pc) and placed between 0.6 and 2.9 kpc from the Sun. We analized the relationships between core, half-mass, tidal and Jacoby radii as well as half-mass relaxation times to conclude that the studied clusters are in an evolved dynamical stage. The cluster masses obtained by summing those of the observed cluster stars resulted to be ~ 10-15 per cent of the masses of open clusters of similar age located closer than 2 kpc from the Sun. We found that cluster stars occupy volumes as large as those for tidally filled clusters.