| Authors |
Viscasillas Vazquez, Carlos ; Magrini, L ; Spina, L ; Tautvaišienė, Gražina ; Van der Swaelmen, M ; Randich, S ; Sacco, G. G |
| Abstract [eng] |
Context. The survival time of a star cluster depends on its total mass, density, and thus size, as well as on the environment in which it was born and in which lies. Its dynamical evolution is influenced by various factors such as gravitational e ects of the Galactic bar, spiral structures, and molecular clouds. Overall, the factors that determine the longevity of a cluster are complex and not fully understood. Aims. This study aims to investigate whether open clusters and field stars respond di erently to the perturbations that cause radial migration. In particular, we aim to understand the nature of the oldest surviving clusters. Methods. We compared the time evolution of the kinematic properties of two Gaia DR3 samples. The first sample is composed of 40 open clusters and the second one of 66 000 main sequence turn o field stars. Both of the samples are composed of stars selected with the same quality criterion, and they belong to the thin disc, are in a similar metallicity range, are located in the same Galactocentric region [7.5–9 kpc], and have ages greater than 1 Gyr. We performed a statistical analysis comparing the properties of the samples of the field stars and of the open clusters. Results. A qualitative comparison of kinematic and orbital properties revealed that clusters younger than 2–3 Gyr are more resistant to perturbations than field stars, and they move along quasi-circular orbits. Conversely, clusters older than approximately 3 Gyr have more eccentric and inclined orbits than isolated stars in the same age range. Such orbits lead the older clusters to reach higher elevations on the Galactic plane, maximising their probability to survive several more gigayears. A formal statistical analysis revealed that there are di erences among the time evolution of most of the kinematic and orbital properties of the field stars and open clusters. However, the comparison between some properties (e.g., V and LZ) do not reach a sucient statistical significance. Conclusions. Our results suggest that the oldest surviving clusters are usually more massive and move on orbits with a higher eccentricity. Although they are still reliable tracers of the Galaxy’s past composition, they do not reflect the composition of the place where they are currently found. Therefore, we cannot avoid considering kinematic properties when comparing data and models of chemical evolution and also taking into account the intrinsic di erences between clusters and isolated stars. To validate the results, new studies that increase the sample of open clusters, especially at older ages, are needed. |
