Introduction
Project
Results
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Project
Our main motivation for the project is a unbiased study of the open cluster population from a homogeneous set of astrophysical parameters. Since the published cluster data is based on different kind of observations, on different criteria for cluster membership, and on different methods of parameter determination, the homogeneity of the sample cannot be guaranteed. Therefore, we did not make use of cluster parameters compiled in the literature, but we newly determined these parameters from scratch.We started with the compilation of a complete survey of stars and with the reduction (if necessary) of the data to common reference systems. This effort resulted in the All-Sky Compiled Catalogue of 2.5 million stars (ASCC-2.5, Kharchenko 2001, ftp://cdsarc.u-strasbg.fr/pub/cats/I/280A) with absolute proper motions in the Hipparcos system, and with B, V magnitudes in the Johnson photometric system. If available, the catalogue is supplemented with spectral types and radial velocities. The catalogue is complete for stars brighter than V=11.5 mag.
The ASCC-2.5 was used to identify known open clusters and compact associations. We found 520 of about 1750 known clusters (Kharchenko et al. 2004b) and discovered 130 new open clusters (Kharchenko et al. 2005b). An iterative precedure was developed to determine cluster membership based on kinematic and photometric criteria as well as to obtain a uniform set of structural, kinematic and evolutionary parameters (Kharchenko et al. 2004b, 2005a, 2005b) of clusters. For each cluster in our sample, we determined distance and celestial position (i.e. the location in 3D-space), reddening, size (including core and corona radii), kinematics (the mean proper motions in the Hipparcos system), and the cluster age computed from ages of individual members near the Main Sequence turn-off. On the basis of a new cluster membership determination, we derived radial velocities (Kharchenko et al. 2004a) and spatial velocity vectors for 359 clusters of our sample.
The results are presented in three data sets:
The Catalogue of Stars in Open Cluster Areas CSOCA
ftp://cdsarc.u-strasbg.fr/pub/cats/J/other/AN/325/740
The Catalogue of Open Cluster Data COCD
ftp://cdsarc.u-strasbg.fr/pub/cats/J/A+A/438/1163
and the COCD Extension~1
ftp://cdsarc.u-strasbg.fr/pub/cats/J/A+A/440/403
Additionally to the COCD, we prepared the Open Cluster Diagrams Atlas (OCDA) which, for each cluster, presents visual information on the data used for the determination of cluster parameters, on the quality of member selection, and on the accuracy of the derived parameters, see an example.
Alpha Persei (Mel 20), a young open cluster (OCDA page for Mel 20) |
The Pleiades (Mel 22), an open cluster of a moderate age (OCDA page for Mel 22) |
Praesepe (Mel 88), an old open cluster (OCDA page for Mel 88) |
The sample is used to study the population of open clusters in the local Galactic disk by jointly analysing the spatial and kinematic distributions of clusters (Piskunov et al. 2006). Further we use our homogeneous data set on structural parameters of open clusters from the COCD to study general correlations including cluster sizes as well as to analyse the spatial distribution of cluster members from the point of view of mass segregation (Schilbach et al. 2006, submitted).