A new look at Sco OB1 association with Gaia DR2
  We present and discuss photometric optical data in the area of the OB
association Sco OB1 covering about 1 squared degree. UBVI photometry is
employed in tandem with Gaia DR2 data to investigate the 3 dimensional
structure and the star formation history of the region. By combining parallaxes
and proper motions we identify 7 physical groups located between the young open
cluster NGC 6231 and the bright nebula IC4628. The most prominent group
coincides with the sparse open cluster Trumpler 24. We confirm the presence of
the intermediate age star cluster VdB-Hagen 202, which is unexpected in this
environment, and provide for the first time estimates of its fundamental
parameters. After assessing individual groups membership, we derive mean proper
motion components, distances, and ages. The seven groups belong to two
different families. To the younger family (family I) belong several pre-Main
Sequence stars as well. These are evenly spread across the field, and also in
front of VdB-Hagen 202. VdB-Hagen 202 and two smaller, slightly detached,
groups of similar properties form family II, which do not belong to the
association, but are caught in the act of passing through it. As for the
younger population, this forms an arc-like structure from the bright nebula IC
4628 down to NGC 6231, as previously found. Moreover, the pre-Main Sequence
stars density seems to increase from NGC 6231 northward to Trumpler 24.
