Home 

Introduction 

Project 

Results 

Team Members 

Publications 

Data 

Links 

Introduction

Open clusters play an important role in astrophysical studies. Since they consist of stars which have been born and lived together, they provide natural laboratories to prove or rule out theories on the formation and evolution of stars. Each single cluster represents excellent empirical reference sequences which are basic for many contemporary scales and calibrations used in astrophysics, due to the fact that all members have about the same distance from the observers, that they show common space motion, and have uniform chemical composition.

On the other hand, studying the open cluster population provides important information that contributes to a better understanding of the structure and evolution of the Milky Way. In principle, basic parameters like distance, motion, age, and metallicity can be determined for an open cluster more accurately than for a single field star. Actually, they are better tracers of the large scale structure of the Galactic disk population than are field stars. The stellar content of a cluster evolves with time, and internal and external interactions affect the properties of individual cluster members as well as of the whole cluster as a system. Therefore, the spatial structure and mass distribution that we observe today in a given cluster is the result of the original brand marks and the ongoing evolution. As open clusters are found over a broad span of ages, a study of global trends should be possible from a representative sample of clusters with homogeneous data of the main cluster parameters.

Two major problems have to be solved before the population of open clusters in the Galaxy can be studied as a whole in an unbiased way:
  • the cluster sample must be based on homogeneous stellar input data and on common membership and cluster parameter determination techniques, and
  • the sample must be representative for the cluster population. Both requirements can be met in a systematic study of all clusters in the Solar neighbourhood.
According to the latest statistics on Galactic open clusters given by Dias et al. on their web page (http://www.astro.iag.usp.br/~wilton/), there are about 1750 known clusters (and candidates). For this list, Dias and collaborators collected all clusters and their available parameters from the literature (including the results of this project) but also many unpublished data based on private communications and papers in preparation. Since the cluster parameters in the Dias et al. list are based on different data, methods and definitions applied by various authors, and may therefore suffer from different systematic errors, their use in Galactic open cluster population studies should be taken with caution.