Presentation Description Information Interrogation Navigation Webda

WEBDA Information


This channel
Database level
Cluster level
Star level
Archive level

The information channel

The information channel has been set up to provide an alternative way to form-based query for locating data.

The links proposed in the column labelled Information in the navigation panel will display lists of clusters in which interesting clusters can be directly selected.

In these lists, the cluster names are usually linked to the cluster pages, from where the data can be accessed.

The Database Level

The information at the database level consists of three successive steps:
  1. The database global content,
  2. The cluster lists,
  3. The detailed content lists.

Global contents

The global information on the database contents presents a list of the data types considered in the database and the number of clusters having such data, together with the total number of stars and measurements it represents.

A line like:

Data descriptionClustersMesuresStars
UBV CCD317477191 379342

means that 317 open clusters have been observed in the UBV (or BV) photometric system with a CCD camera. The total number of stars is equal to 379342, and, when taking into account the fact that some clusters have been observed by more than one group, the total number of measurements it represents is 477191.

The link associated with the number of clusters will produce a list of the 146 clusters, ordered by cluster names in alphabetical order.

Cluster list

The cluster list presents the names of the clusters concerned with the kind of data selected, the number of stars observed and the total number of measurements it represents. If these numbers are not equal, it means that there are several sources of data.

The line like:

Cluster nameMesuresStars
NGC 4755 8971 8314

indicates that, for the open cluster NGC 4755, the database contains CCD data in the UBV photometric system for 8971 stars, with a total of 8314 measurements.

The link under the cluster name will lead you to the cluster page, from where one can access not only the desired data, but also all the information available on this cluster.

The link under the number of stars will produce a detailed list of the datafile contents, containing the number of stars observed in each data source and a list the corresponding bibliographic references.

When data for a cluster have been published but have not yet been included in the database, the number of measurements is indicated, but the number of stars is kept to 0. In this way, the existence of data is recognized.

The reference to the published papers may be obtained via the bibliography form, by using the cluster name as a keyword and/or the kind of data, like, for example: Tr14 UBV CCD
The data file may be retrieved with the link on data archives at the bottom of each cluster page.

Detailed list

The detailed list presents a summary of the number of stars observed in each data source and displays the corresponding bibliographic references. This allows to quickly determine which are the most interesting sources of data.

In most cases, the reference to published articles gives

The link below the journal name will display the whole set of data from that paper.

The link below the BibCode is connected with the ADS Abstract Service and will display the abstract of the article.

The Cluster Level

Cluster catalogue

The information at the cluster level consists of different versions of the catalogue of open clusters arranged according to different criteria. The links under the cluster names lead directly to the cluster pages. The catalogue of open cluster parameters of Lyngå (5th edition, Strasbourg 1987) has been used to establish the present list of open clusters. Unfortunately, this catalogue has not been maintained since that time, although distance and age determinations have been published for a growing number of new clusters, resulting mainly from observations made with CCD cameras.

The catalogue of open star clusters may be browsed in several versions differing only by the parameter on which the sort has been done:

Equatorial coordinates
They are four files containing the list of clusters by interval of 6 hours to keep them is a reasonnable size. These four^ files are ordered by increasing right ascension
Galactic longitudes
Similar files, ordered by increasing galactic latitude, have been formed.
Cluster distances
A subset of the catalogue of open clusters presents the clusters closer to the Sun than 1000 pc (1kpc) and has also been sorted by increasing distance. Only those clusters for which a distance has been determined photometrically are included in the list.
The information contained in these lists is: Lists by cluster metallicities will be prepared, as well as lists of absolute proper motion and mean radial velocities.

Cluster parameters

To palliate to this lack of a up-to-date homogeneous compilation of cluster parameters, two solutions have been considered.
1) Loktin & Matkin catalogue
These two russian authors have reanalysed the UBV photometric data of 330 open clusters and determined their distances and reddenings. Their parameters have been introduced in the tables to replace the previous information.
2) Literature results
For clusters recently observed, the published parameters were included in the database files. Evidently, this introduces a great inhomogeneity in the tabulated data. However, it will allow to form much more complete lists of observed clusters and better samples in the database queries.
The determination of clusters parameters on a uniform basis represents a very large amount of work. One first needs to compare the available data source and correct for existing drifts or systematic errors and define a sample representative of the cluster population. Indeed, when only B and V, or V and I, colours have been observed, the selection of cluster members may be uncertain at faint magnitudes. This kind of problems was a main motivation to build a database and design tools to find a solution.

Due to the large number of cluster observed to date, the completion of a modern catalogue of cluster parameters would require a collaboration between several goups.

The star level

The information at the star level consists mainly of list of clusters containing various kinds of interesting stars, like chemically peculiar stars (Ap and Am), emission-line stars (Be), blue stragglers and red giants. The links provided in these tables will lead to the cluster pages from where the desired information and data can be found.

The access to these lists are grouped in the Navigation Panel.

Lists of interesting stars

The interest of open clusters also results from their stellar content which offers several types of peculiar stars. The database contains files with mostly star numbers of the discovered abnormal stars and red giants. These list can be used to retrieve the available data for these specific stars in one query.

Chemically peculiar stars (Ap and Am)
The lists of clusters containing chemically peculiar stars have been established from the published spectral classifications. The census of these stars in open clusters is far from being complete and or even satisfactory. The number of clusters searched for peculiar stars is by no means large enough so that we are be able to understand the developement of chemical peculiarity with age.
Emission-line stars (Be)
The list of Be and shell stars has also been established from the published spectral classification and the various surveys of the Milky Way.
Blue stragglers
The list of blue stragglers has been taken from the Catalogue of blue stragglers in open clusters. Although I do not agree with some of the stars retained in the lists, the whole catalogue provides a useful material for further studies of the blue straggler phenomenon in open clusters of all ages.
Red giants
Red giant are not peculiar stars but they are interesting objects, mainly as concerns the determination of the chemical composition by mean of photometric or spectroscopic observations. List of confirmed or candidate red giants in the field of open clusters may be useful for many observing projects.
The lists of red giants has been developed as a side product from the radal-velocity observing program conducted by the author. The compilation of red giants (members and possible members) has been extended to most clusters, even if their stars were too faint for being observed with the CORAVEL radial-velocity scanner.


The second part of the star level is formed by the cross-reference lists. The corresponding lists or forms are reached from the Navigation Panel.

Cross-identifications with astronomical catalogues
The brightest stars in many open clusters have an identification in common astronomical catalogues, like the Bright Star Catalogue, the Henry Draper catalogue, the north and south Durchmusterungen. Because many data for cluster stars have been published in the literature under these types of star designations, it has been necessary to develop a catalogue of cross-identifications with common astronomical catalogues to find the relevant data.
Cross-reference tables
A most serious problem when working with star clusters is that concerning the numbering system inside the clusters. Because many numbering systems have been developed by various persons, it is sometimes quite difficult and time consuming to collect data from various sources when each one is using its own numbering system.
To solve this problem, I have undertaken to establish systematically the cross-references between the existing numbering systems in most clusters, in addition to the information I could find in the literature.
These tables contains in the first column the adopted numbering system for a cluster, often based on the most convenient star list, extended to include further stars not included in the adopted numbering system. The following columns contains the numbers attributed by each author to the same star.
The navigation panel offers links either to lists or to forms to access the corresponding information.

Scanned maps

A large number of published maps, defining cluster numbering systems, have been scanned. The list of scanned maps indicate the cluster names, the sizes of the GIF images, the sources of the maps (Authors' names and journal).

Click on the authors's names to get the corresponding maps (there may two or three different maps for some clusters).
Click on the cluster name to display the cluster page.

The maps are active, this means that is is possible to get basic data on the stars simply by clicking on the numbered stellar images. The information is displayed in the right-hand frame and contains:

The Archive Level

The archive level provides a list of most original files received from a large number of colleagues who were so kind as to send me a copy of their data in electronic format. I am very grateful to them, because it helped me very much to develop the database.

Many files are now available on the Strasbourg CDS Service for Published Tables and a copy of those collected there has been kept.

The WEBDA list of archive data collects these files for NGC, IC and anon clusters separately.
The columns of the table give successively:

To transfer a file, press SHIFT on the keyboard and click simultaneously on the name of the file to transfer.

The existing archive files for a given cluster may also be reached from the links located at the bottom of each cluster page.

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Last modification: 19 October 2005