The low mass population of the Vela OB2 association from Gaia
  The first Gaia Data Release presents an opportunity to characterise the
low-mass population of OB associations, providing larger statistical samples
and better constraints on the formation and evolution of clusters and
associations. Using previously known low mass members in a small region of Vela
OB2 we have designed selection criteria that combine Gaia and 2MASS photometry,
independently of any astrometric information, to identify low-mass
pre-main-sequence (PMS) stars over the wider association area. Our method picks
out the known clusters of young stars around $\gamma^2$ Velorum and NGC-2547,
but also identifies other over-densities that may represent previously unknown
clusters. There are clear differences in the spatial distributions of the
low-mass and the high-mass OB populations, suggesting either that the structure
and dynamics of these populations has evolved separately or that the initial
mass function can vary considerably on small scales within a single
association.
