Hierarchical Star Formation: Stars and Stellar Clusters in the Gould
  Belt
  We perform a study of the spatial and kinematical distribution of young open
clusters in the solar neighborhood, discerning between bound clusters and
transient stellar condensations within our sample. Then, we discriminate
between Gould Belt (GB) and local Galactic disk (LGD) members, using a previous
estimate of the structural parameters of both systems obtained from a sample of
O-B6 Hipparcos stars. Using this classified sample we analyze the spatial
structure and the kinematic behavior of the cluster system in the GB. The two
star formation regions that dominate and give the GB its characteristic
inclined shape show a striking difference in their content of star clusters:
while Ori OB1 is richly populated by open clusters, not a single one can be
found within the boundaries of Sco OB2. This is mirrored in the velocity space,
translating again into an abundance of clusters in the region of the kinematic
space populated by the members of Ori OB1, and a marginal number of them
associated to Sco OB2. In the light of these results we study the nature of the
GB with respect to the optical segment of the Orion Arm, and we propose that
the different content of star clusters, the different heights over the Galactic
plane and the different residual velocities of Ori OB1 and Sco OB2 can be
explained in terms of their relative position to the density maximum of the
Local Arm in the solar neighborhood. Although morphologically intriguing, the
GB appears to be the result of our local and biased view of a larger star
cluster complex in the Local Arm, that could be explained by the internal
dynamics of the Galactic disk.
