The Space Distribution Of Open Clusters

There are thousands of stellar systems in the Galaxy, which is of great value for us to study the formation, the structure and even the evolution of the Milky Way. Different stellar systems have not only different properties but also different spatial distributions. Open clusters, which belong to PopI, constitute plane sub-system.Open clusters mainly distributed in the Galactic disk and young open clusters are on the spiral arms especially. So we can investigate the scale height of the disk and even the structure of the spiral arms. On the other hand, because of the wide range of open clusters in ages, from dozens of Myr to 10 Gyr, it can help us investigate the stellar properties of different ages and constrain the star formation theory. In this thesis, we focus on the distributions and properties of open clusters and hope to find several characteristics of Galactic disk.This paper has based on the database of 2008 published by Dias, which is the supplement on'New Catalog of Optically Visible Open Clusters and Candidates'by Dias in 2002 combined with other recently research results. The database includes the data in Lynga (1987) catalogue, Mermilliod's (1995) and another 476 objects which are not included in Lynga (1987) catalogue. Besides that, data of kinematics (proper motions and radial velocities) which were not presented in the old catalogues, is included. Based on the statistical analysis of global properties of open clusters, we aim at deriving disk properties, such as scale height above the Galactic plane of the Sun. We hope the results can provide clues on the evolution of the Galaxy.The distance of clusters should be available to obtain the statistical properties of open clusters and scale height of the Galactic disk. The number of sample clusters is 1622 in all but only 1008 have distances. In order to make full use of sample clusters and heighten the reliability of the statistical results, we suppose those unknown distance clusters follow the same diameter (DA) distribution of 1008 known distance clusters. The simulated distances for clusters with unknown distances are obtained by Monte Carlo simulations. From the statistical properties of open clusters, such as Galactic longitude, Galactic latitude, distance to the Sun, Galactocentric distance, distance from Galactic plane, it turns out that the mean scale height of open clusters is～150pc which is between the result of Pang's (～50.5pc) and Janes & Phelips'(～394.5pc). Since Pang derived the scale height perpendicular to the galactic plane by young open cluster fitting and Janes & Phelips by old open cluster fitting, it turns out that old open clusters are preferentially located far from the galactic plane and in the outer part of the galactic disk. On the other hand, the distribution of clusters along the Galactic plane can not be described exponentially because the dust extinction is serious in the disk, especially the direction to the Galactic Center. This result is the same with Pang's.