Main Scientific Results

• A newly developed iterative pipeline was used to determine cluster membership based on combined spatial/kinematic/photometric criteria. For 520 known clusters a uniform set of structural (location, size), kinematic (proper motions and radial velocities), and evolutionary (age) parameters was derived. For the first time, we derived:
• distances for 200 clusters,
• radial velocities for 94 clusters,
• ages for 196 clusters (see an example).



• For a systematic search of new open clusters a multi-parameter search pipeline was implemented, which is based on the analysis of the properties of known clusters already identified in the ASCC-2.5. As a result 130 clusters were discovered. Membership and astrophysical parameters were derived for them in the same way as for the 520 previously known clusters.



• Our sample of 650 clusters is complete within a distance of 0.85 kpc from the Sun, with about 260 clusters being located within that limit (see a diagram).



• Fluctuations in the spatial and velocity distributions reveal the existence of open cluster complexes (OCCs) with the youngest of these OCCs being apparently a signature of Gould's Belt, whereas the oldest and sparsest group includes the Hyades and Praesepe (see a diagram).



• The total surface density of open clusters is Σ≈ 114 kpc^-2 which, by a factor of 5, exceeds the value known from previous studies. The respective number of open clusters in the Galactic disk can be estimated as ≈ 10⁵ at present, and the formation rate and lifetime of open clusters are 0.23 ± 0.03 kpc^-2 Myr^-1 and 322 ± 31 Myr, respectively.



• The latter implies a total number of cluster generations in the history of the Galaxy between 30 and 40, which allows only 10% of the total Galactic stellar disk population having ever passed an open cluster membership.



• The angular sizes of open clusters are systematically underestimated in the literature.



• Older clusters inside the solar orbit are significantly smaller than outside, and larger old clusters live more frequently further away from the plane and at larger Galactocentric distances (see a diagram).



• For clusters with (V - M_V) < 10.5, the apparent cluster radii decrease by a factor of about 2 from an age of 10 Myr to an age of 1 Gyr. This effect can be explained by mass segregation.



• We found evidence for mass segregation for the majority of clusters older than 30 Myr. In the group of the youngest clusters (between 5 and 30 Myr), about one half shows no segregation at all, whereas the other half is segregated. In both groups mass segregation gets stronger until an age between 50 and 100 Myr. In older clusters the evolution of the massive stars is the most prominent effect, since the limiting magnitude of the ASCC-2.5 prevents us to observe fainter stars.