Studies of the open cluster M 11. I. Proper motion measurement and membership determination

From PDS microdensitometer measurements of 10 plate pairs of the open cluster M 11 with epoch differences of 16–70 years taken with our 40 cm double astrograph, the relative proper motions of 872 stars in the cluster region are determined. 85% of these have accuracies better than 0.1 arcsec per century. The distribution parameters of stars with different magnitudes are found from a new mathematical model. The membership probabilities of the stars are calculated. 541 stars have membership probabilities higher than 0.7. The new approach of membership determination is shown to be not only theoretically rigorous, but also practically feasible, and more reasonable results can be obtained from its use. Some evidence is found for mass segregation in space and lesser evidence for mass segregation in velocity space.