% IMPORTANT: The following is UTF-8 encoded.  This means that in the presence
% of non-ASCII characters, it will not work with BibTeX 0.99 or older.
% Instead, you should use an up-to-date BibTeX implementation like “bibtex8” or
% “biber”.

@MASTERSTHESIS{Arunima:910873,
      author       = {Arunima, Arunima},
      title        = {{Y}oung {S}tar {C}lusters:characterising their history
                      using unbound members},
      school       = {University Cologna},
      type         = {Masterarbeit},
      reportid     = {FZJ-2022-04223},
      pages        = {111 p},
      year         = {2022},
      note         = {Masterarbeit, University Cologna, 2022},
      abstract     = {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.},
      cin          = {JSC},
      cid          = {I:(DE-Juel1)JSC-20090406},
      pnm          = {899 - ohne Topic (POF4-899)},
      pid          = {G:(DE-HGF)POF4-899},
      typ          = {PUB:(DE-HGF)19},
      url          = {https://juser.fz-juelich.de/record/910873},
}