We have conducted VI CCD photometry of the open cluster NGC 6819 in order to understand the effects of dynamical evolution in old open clusters. Our photometry covers 18'× 18' on the sky, centered on the cluster, which seems to cover the whole cluster field. Our photometry reaches down to V ≈ 20.5, which allows us to analyze the luminosity function and spatial distribution of stars brighter than Mv ≈ 8.5. There is a clear evidence for mass segregation in NGC 6819, i.e., the giants and upper main-sequence stars are concentrated in the inner regions, whereas the lower main-sequence stars distribute almost uniformly throughout the cluster. The luminosity function of the main-sequence stars of NGC 6819 is almost flat. The flat luminosity function indicates that a large number of low mass stars has escaped from the cluster unless its initial mass function is much different from the Salpeter type (Φ(m)∝ m-(1+x),x = 1.35).

• YaNG-WOO KANG(Department of Earth Sciences, Pusan National University/Department of Astronomy, Yonsei University)
• HONG BAE ANN(Department of Earth Sciences, Pusan National University)