Radial migration in open clusters

The first sample is composed of ~40 open clusters and the second one of ~66000 main sequence turn off 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 [7.5-9kpc], 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.

A qualitative comparison of kinematic and orbital properties revealed that clusters younger than 2-3Gyr are more resistant to perturbations than field stars, and they move along quasi-circular orbits. Conversely, clusters older than approximately 3Gyr 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 differences 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_phi_ and L_Z_) do not reach a sufficient statistical significance. 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 differences between clusters and isolated stars. To validate the results, new studies that increase the sample of open clusters, especially at older ages, are needed.