Different Fates of Young Star Clusters After Gas Expulsion
  We identify structures of the young star cluster NGC 2232 in the solar
neighborhood (323.0 pc), and a newly discovered star cluster LP 2439 (289.1
pc). Member candidates are identified using the Gaia DR2 sky position, parallax
and proper motion data, by an unsupervised machine learning method,
\textsc{StarGO}. Member contamination from the Galactic disk is further removed
using the color magnitude diagram. The four identified groups (NGC 2232, LP
2439 and two filamentary structures) of stars are coeval with an age of 25 Myr
and were likely formed in the same giant molecular cloud. We correct the
distance asymmetry from the parallax error with a Bayesian method. The 3D
morphology shows the two spherical distributions of clusters NGC 2232 and LP
2439. Two filamentary structures are spatially and kinematically connected to
NGC 2232. Both NGC 2232 and LP 2439 are expanding. The expansion is more
significant in LP 2439, generating a loose spatial distribution with shallow
volume number and mass density profiles. The expansion is suggested to be
mainly driven by gas expulsion. NGC 2232, with 73~percent of the cluster mass
bound, is currently experiencing a process of re-virialization, However, LP
2439, with 52 percent cluster mass being unbound, may fully dissolve in the
near future. The different survivability traces different dynamical states of
NGC 2232 and LP 2439 prior to the onset of gas expulsion. NGC 2232 may have
been substructured and subvirial, while LP 2439 may either have been
virial/supervirial, or it has experienced a much faster rate of gas removal.
