Expanding associations in the Vela-Puppis region: 3D structure and
  kinematics of the young population
  The Vela-Puppis region is known to host the Vela OB2 association as well as
several young clusters featuring OB and pre-main sequence stars. Several
spatial and kinematic subgroups have been identified in the recent years. By
grouping stars based on their positions and velocity we can address the quetion
of the dynamical history of the region and the mechanisms that drove stellar
formation. The Gaia DR2 astrometry and photometry enables us to characterise
the 3D spatial and 3D kinematic distribution of young stars and to estimate the
ages of the identified components. We use an unsupervised classification method
to group stars based on their proper motions and parallax. We perform a study
of the expansion rates of the different identified groups from 3D velocities,
and from corrected tangential velocities. We make use of theoretical isochrones
to estimate ages. The young stars can be separated into seven main groups of
different ages and kinematical distribution. All groups are found to be
expanding, although the expansion is mostly not isotropic. The size of the
region, the age substructure, and the anistropic expansion rates are compatible
with a prolonged period of star formation in a turbulent molecular cloud, and
that the dispersion of the stars cannot be explained by gas expulsion alone.
