Based on our compiled catalogue of fundamental astrophysical parameters for 593 open clusters , we analyze the relations between the chemical composition , spatial positions , Galactic orbital elements , age , and other physical parameters of open star clusters .
We show that the population of open clusters is heterogeneous and is divided into two groups differing by their mean parameters , properties , and origin .
One group includes the Galactic clusters formed mainly from the interstellar matter of the thin disk with nearly solar metallicities ( [ Fe / H ] > -0.2 ) and having almost circular orbits a short distance away from the Galactic plane , i. e. , typical of the field stars of the Galactic thin disk .
The second group includes the peculiar clusters formed through the interaction of extragalactic objects ( such as high–velocity clouds , globular clusters , or dwarf galaxies ) with the interstellar matter of the thin disk , which , as a result , derived abnormally low ( for field thin-disk stars ) metallicities and/or Galactic orbits typical of objects of the older Galactic subsystems .
About 70 % of the clusters older than 1Â Gyr have been found to be peculiar , suggesting a slower disruption of clusters with noncircular high orbits .
Analysis of orbital elements has shown that the bulk of the clusters from both groups were formed within a Galactocentric radius of \approx 10.5 kpc and closer than \approx 180 pc from the Galactic plane , but owing to their high initial velocities , the peculiar clusters gradually took up the volumes occupied by the objects of the thick disk , the halo , and even the accreted halo of the Galaxy .
Analysis of the relative abundances of magnesium ( a representative of the \alpha -elements ) in clusters that , according to their kinematical parameters , belong to different Galactic subsystems has shown that all clusters are composed of matter incorporating the interstellar matter of a single protogalactic cloud in different proportions , i. e. , reprocessed in genetically related stars of the Galaxy .
The [ Mg/Fe ] ratios for the clusters with thick-disk kinematics are , on average , overestimated , just as for the field stars of the so-called ” metal–rich wing ” of the thick disk .
For the clusters with halo kinematics , these ratios exhibit a very large spread , suggesting that they were formed mainly from matter that experienced a history of chemical evolution different from the Galactic one .
We point out that a large fraction of the open clusters with thin-disk kinematics have also been formed from matter of an extragalactic nature within the last \approx 30 Myr .