The age distribution and total lifetimes of open clusters

The age distribution of galactic clusters is obtained from well-observed star clusters, and it is concluded that the observed age distribution of clusters within 1000 pc is not seriously affected by the selection effects. If we assume that the rate of formation of clusters is constant, the observed age distributions of clusters for Trumpler's different richness classes have been obtained; and it is found that the rich clusters have longer lifetimes than the poor clusters.The lifetimes of clusters log(_1/2) for different richness classes obtained in the present study differ significantly from the lifetimes obtained by Janes and Adler (1982), because the lifetimes obtained by Janes and Adler may have been affected by the age-dependent selection effects which grow with increasing distance. From the observed age distribution of all clusters within 1000 pc the results obtained in the present study are in close agreement with the lifetimes obtained by Wielen (1971a).