Open clusters and galactic structure.

A total of 610 references to 434 clusters are employed in the compilation of a catalog of open clusters with color-magnitude diagrams on the UBV or RGU systems. Estimates of reddening, distance modulus, age and number of cluster members are included. Although the sample is considered representative of the discoverable clusters in the galaxy, the observed distribution is nonuniform because of interstellar obscuration. Cluster distribution in the galactic plane is found to be dominated by the locations of dust clouds rather than by spiral structure. The distributions of clusters as a function of age and richness class show that the lifetimes of poor clusters are much shorter than rich ones, and that clusters in the outer disk survive longer than those in the inner disk. An outer disk age which is only about 50% the age of the globular clusters is indicated by cluster statistics. The thickening of the galactic disk with increasing galactocentric distance may be due to either a younger dynamical age or a lower gravitational potential in the outer regions.