%0 Thesis
%A Arunima, Arunima
%T Young Star Clusters:characterising their history using unbound members
%I University Cologna
%V Masterarbeit
%M FZJ-2022-04223
%P 111 p
%D 2022
%Z Masterarbeit, University Cologna, 2022
%X Most stars do not form in isolation, but in groups referred to as star clusters. The characterization of star clusters using the astrometry of their members has been revolutionized by Gaia as it provides an unprecedented precision which makes the membership determination more accurate and complete than ever. The data show that most young clusters expand, supporting the hypothesis that the gas expulsion process at the end of the star formation leads to cluster expansion. This makes young clusters highly dynamic entities where the observations only provide snapshots of the cluster’s evolution. The central aim of this study is to investigate how a cluster’s past can be recovered from the present astrometry of its members. We take into account the dynamic nature of the cluster and the observational limitations.To this end, we perform simulations, using NBODY6++, of clusters modelled using observationally motivated initial conditions and mass-radius relations to recreate the star clusters in the solar neighbourhood. The simulations start after the star formation in the cluster has been completed and provide the complete 3D positions and velocities of the members until 10 Myr. In the past studies of star clusters, the focus was mainly on the stars that remain bound to the cluster. However, this work shows that the unbound stars retain more information about the past of the cluster than the bound stars due to numerous close encounters amongst the latter. Backtracking the unbound members can provide theoriginal size and age of the cluster at the time of gas expulsion - two parameters that are still poorly constrained. However, observational challenges such as uncertainty in velocities and masses of the members and incomplete membership limit the accuracy of the derived parameters. Uncertainties affect the derived pre-expansion cluster size more significantly than the value of the time of gas expulsion. The distinction of bound and unbound members in the observational scenario also presents a difficulty due to the dynamic nature of young clusters. Velocity vector direction relative to the cluster centre often fails as a distinction criterion. Immediately after gas expulsion, bound and unbound members occupy the same space in distance and velocity distributions up to 5 Myr. This leads to highly inaccurate classification if the much-used ad hoc distance and velocity cut-offs are applied during the early evolution of the cluster. However, this work provides cut-off suggestions for clusters along with their performance measures that can be applied to the observations of (at least) 5 Myr old clusters. Finally, the application of the backtracking analysis using the members of the Upper Scorpius association provides kinematic age estimates in the range of 2 - 4.3 Myr, which does not agree with the isochronal estimates of its age. However, it is in agreement with other kinematic studies of the area. In summary, considering unbound members for the kinematic analysis of a cluster can provide better constraints on the past parameters of the cluster.
%F PUB:(DE-HGF)19
%9 Master Thesis
%U https://juser.fz-juelich.de/record/910873