3D Morphology of Open Clusters in the Solar Neighborhood with Gaia EDR3:
  its Relation to Cluster Dynamics
  We analyze the 3D morphology and kinematics of 13 open clusters (OCs) located
within 500 pc of the Sun, using Gaia EDR3 and kinematic data from literature.
Members of OCs are identified using the unsupervised machine learning method
StarGO, using 5D parameters (X, Y, Z, $\mu_\alpha \cos\delta, \mu_\delta$). The
OC sample covers an age range of 25Myr--2.65Gyr. We correct the asymmetric
distance distribution due to the parallax error using Bayesian inversion. The
uncertainty in the corrected distance for a cluster at 500~pc is 3.0--6.3~pc,
depending on the intrinsic spatial distribution of its members. We determine
the 3D morphology of the OCs in our sample and fit the spatial distribution of
stars within the tidal radius in each cluster with an ellipsoid model. The
shapes of the OCs are well-described with oblate spheroids (NGC2547, NGC2516,
NGC2451A, NGC2451B, NGC2232), prolate spheroids (IC2602, IC4665, NGC2422,
Blanco1, Coma Berenices), or triaxial ellipsoids (IC2391, NGC6633, NGC6774).
The semi-major axis of the fitted ellipsoid is parallel to the Galactic plane
for most clusters. Elongated filament-like substructures are detected in three
young clusters (NGC2232, NGC2547, NGC2451B), while tidal-tail-like
substructures (tidal tails) are found in older clusters (NGC2516, NGC6633,
NGC6774, Blanco1, Coma Berenices). Most clusters may be super-virial and
expanding. $N$-body models of rapid gas expulsion with an SFE of $\approx 1/3$
are consistent with clusters more massive than $250\rm M_\odot$, while clusters
less massive than 250$\rm M_\odot$ tend to agree with adiabatic gas expulsion
models. Only six OCs (NGC2422, NGC6633, and NGC6774, NGC2232, Blanco1, Coma
Berenices) show clear signs of mass segregation.
