Data content

The database tries to collect all published data for stars in open clusters that may be useful either to determine the star membership, or to study the stellar content and properties of the cluster. The data are usually recorded in their original form, with an indication of the source, but also as averaged values or selected data when relevant. The mean values for UBV (photoelectric, photographic or CCD) are not kept in the database, but can readily be computed. It presently contains:

• astrometric data: coordinates, rectangular positions, and some proper motions;
• photometric data in most systems in which cluster stars have been observed;
• spectroscopic data: spectral classification, radial- and rotational velocities;
• bibliographic information;
• specific information: (a) membership probabilities, (b) orbital elements of spectroscopic binaries, (c) remarks on peculiarity, variability, duplicity, (d) identifications of double star components, (e) cross-identifications with astronomical catalogues, (f) list of red giants in the cluster field and of non-member stars.

Table 2.1 gives an insight into the present content of the database; it lists for each kind of data the number of clusters involved, the number of measurements, and the number of stars concerned, except for the references and bibliography where the number of entries is indicated. The completeness of the data base should be rather high for many types of data, and is still improving.

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Apart from the published data found in the literature, the database contains also information that was accumulated in the past or prepared especially for it to enhance its capabilities:

• Cross-reference tables contain the basic cross-identifications between the various numbering systems in a cluster. A large part of the work has been done by the author.
• Rectangular (x, y) positions (usually in arbitrary units) have been collected from the literature or measured on published photographs with a digitizing tablet. A file collects the information relevant to the scale of the (x, y) positions and the sources of the data.
• Published photographs defining cluster numbering systems have been scanned and included in the database. About 180 maps have already been processed.