Presentation Description Information Interrogation Navigation Webda

WEBDA Description


The database level
The cluster level
The star level
The bibliography
Miscellanous topics
The archive level

The Database Level

The database purpose

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 clusters.

It has been developed not only to be an efficient tool to store and retrieve data, but also to provide a versatile environment to analyse the data and study open clusters considered as interesting astrophysical objects worth a systematic study.

The database history

The database for stars in galactic open clusters, known as Base Données Amas (BDA) has been developed since 1987 at the Institute for Astronomy (University of Lausanne, Switzerland) by the author. The extensive collections of observational data cover most significant domains and concerns more than 100000 stars in some 500 NGC, IC and anonymous clusters.

The first database (BDA) used compressed flat ASCII files to store the data. It has been decided in 1996 to migrate to the /rdb database system, which offers a number of interesting facilities, in connection with the development of a public access.

The database contents

The database contents includes measurements in most photometric systems in which cluster stars have been observed, spectroscopic observations, astrometric data, various kinds of useful information, and extensive bibliography. It is possible to perform selection of clusters based on the amount of available data.

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.

The greatest effort has been spent in solving the identification problems raised by the definition of so many different numbering systems and a special interface has been developed to query the cross-reference tables.

Maps for more than 200 clusters have been scanned and included in the database. They are active maps and permit to retrieve basic data (positions, cross-identifications and UBV) simply by clicking on the star images.

The database structure

The database structure uses the directory hierarchy supported by the Unix system. The main directory is the database itself. It contains several sub-directories: description of the database, help information, references, bibliography, programs, perl scripts.

Each cluster defines an independent directory identified by its name and containing the available data in distinct files, one for each data type. This structure allows easy inclusion of any new cluster and any additional data type.

Whenever possible, the records of the various data files have the same structure: star identification, source, data. The files are organised sequentially and, within the files, the entries are sorted by star number and source reference. Due to the small size of many files, there is no need for indexing, but it could be done within /rdb.

The star identification is the main key to access the data, but it is also possible to use filters based on the bibliographic references or astrophysical parameters.

The present database structure is thought of as a first step in the organisation of cluster data and bibliography. When enough data analysis has been performed and only one set of data for each type will be available for each star, it may be perhaps more convenient to adopt another structure and collect all the data in one file for each cluster.

The database engine

WEBDA is a relational database built upon the package /rdb developed by Rod Manis, Evan Schaffer and Robert Jorgensen and described in the book: Unix Relational Database Management (1988, Prentice Hall).

/rdb is a high performance relational database management and application development system designed for Unix and implemented as a suite of 131 shell level commands. It is an extension of the Unix environment.

Database utilities, such as sorttable, jointable, row, column and compute are programs invoked by the shell which read tables from the standard input and write tables to the standard output.

All relational operators are included, as well as several indexing methods, a vi-like forms editor, a powerful report generator and menus.

See the /rdb home page for further information.

With the implementation on the new server in Vienna, several additional commands from Starbase 3.2.3 are also in use.

The Plot-routines are based on Gnuplot 4.2.4. The graphic files are in the .png format. Several plots are based on the GD Graphics Library which is part of the local Perl environment. These packages are all OpenSource available for widely different Operating Systems with a large developing community. I will include stable updates as soon as they are announced and tested.

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The Cluster Level

Catalogues sources

A. Distance, Reddening and Age

The catalogue of cluster parameters prepared by Lyngå (1987, 5th edition, CDS VII/92A) has been used to build the list of known open clusters. However, as the date indicates, this catalogue has not been updated since 1987 and is now, ten years later, partly obsolete, because many new cluster have been observed during the past ten years.

Wilton Dias has compiled a new catalogue of open clusters which contains 1567 objects. New objects will be included in the WEBDA database when astrophysical observations will be published.

Kharchenko, Piskunov, Röser, Schilbach & Scholz have published (2005, Astron. Astrophys. 438, 1163) a catalogue of parameters and properties for 520 open clusters and provide a homogeneous sets of information.

van den Bergh has published (2006, Astron. J. 131, 1559) a catalogue of Diameters of Open Star Clusters including a mixture of new parameters and those from the literature.

Tadross, Werner, Osman & Marie have published (2002, New Astron. 7, 553) a catalogue of parameters and properties for 160 open clusters and provide a homogeneous sets of information.

Loktin, Gerasimenko & Malisheva (2001, Astron. Astrophys. Trans. 20, 607-633) have published a second version of their catalogue reviewing the reddening, distance and age of 423 open clusters on the basis of modern data. These values have been used to update the cluster parameters in the database, because they represent a large and homogeneous set of parameters. The distances are based on a Hyades distance modulus of 3.27 determined by these authors. This value is 0.06 smaller than that found from Hipparcos parallaxes, namely m-M = 3.33 ± 0.01 (Perryman et al. 1998, A&A 331, 81).
The second version supersedes the first catalogue of Loktin & Matkin (1994, Astron. Astrophys. Trans. 4, 153) which contained reddening, distance and age for 330 open clusters.

Dambis (1999, Astronomy Letters, 25, 7) has determined the same parameters for 202 open clusters. There seems to exist a systematic trend between the modulus differences in function of the cluster ages for clusters younger than logt = 8.0.

Finally, the recent literature was searched for further determinations of cluster parameters and found new data for 335 open clusters. The main problem with recent BV, BVI or VI CCD data, is the difficulty of estimating the amount of reddening, because of the frequent absence of any U filter. Therefore, colour excesses are estimated either by comparison with clusters presenting a similar colour-magnitude diagram or by direct adjustement of a theoretical isochrone of a metallicity which seems appropriate. Obviously, these results are first order estimates of the cluster distances and ages and should be used with caution, although they could be rather close to the correct values.

Malysheva (1997, Astron. Letters 23, 585) published a catalogue of parameters for 73 open clusters determined from the uvbyß photometry. These values are in a good agreement with those from Loktin & Matkin.

Dutra & Bica (2000, A&A 359, 347) have compared the colour excesses E(B-V) obtained from far-infrared IRAS and COBE observations with those obtained from visible or JHK observations. They have studied 103 galactic open clusters. The table is ordered in increasing longitude order.

B. Metallicity

Since the last edition of Lyngå's catalogue, new values of the [Fe/H] iron abundances have been determined.
Comprehensive discussions of the available data have been published by:
1) Strobel A. 1991, Astron. Nachr. 312, 177 - 196
Metallicities of open clusters
2) Friel E. 1995, Ann. Rev. Astron. Astrophys. 33, 381
The old open clusters in the Milky Way
She gives a list of [Fe/H] determination mostly based on her own observations, with sources.

3) Twarog B.A., Ashman K.M., Anthony-Twarog B.J. 1997, AJ 114, 2556, (1997AJ....114.2556T)
Some revised observational constraints on the formation and evolution of the galactic disk
Twarog et al. comment on each cluster and have transformed the available data to a common scale.
The values from this paper have been used to replace those existing previously in Lyngå's original catalogue, because it represents so far the largest homogeneous sample of [Fe/H] values.

4) Gratton R. 2000, ASP Conf. Ser. 198, 225
Abundances in open clusters: results and concerns
He independently reduced the various photometric and spectrocopic sources into a homgeneous catalogue of [Fe/H] abundances.

5) Chen L., Hou J.L., Wang J.J. 2003, AJ 125, 1397, (2003AJ....125.1397C)
On the Galactic Disk Metallicity Distribution from Open Clusters. I. New Catalogues and Abundance Gradient
An uncritical compilation of published metallicities from the literature. The values were averaged, no new measurements or independent estimations are listed.

C. Absolute proper motions

W.S. Dias, M. Assafin, V. Flório, B.S. Alessi & V. Líbero (2006, A&A 446, 949) have analysed the UCAC2 catalogue for 430 open clusters and produced a catalogue of absolute proper motions. Futhermore, they have estimated the number of members and membership probabilities.

H. Baumgardt, C. Dettbarn & R. Wielen (2000, A&AS 146, 251) have analysed the Hipparcos observations of 205 open clusters and produced a catalogue of distances and absolute proper motions which is reproduced here. For clusters containing more than one star, the mean cluster parameters have been computed according to the method described by van Leeuwen & Evans (1998, A&AS 130, 157).

E. Glushkova and her group have determined absolute proper motions for a total of 324 open clusters from the Four-Million Star Catalog (4M-catalog) of positions and proper motions. Her description explains how these absolute proper motions were derived. The whole file may be retrieved by http from the Moscow server. However, it is identical to this list.

D. Mean radial velocities

Mermilliod, Mayor, & Udry have published (2008, A&A 485, 303) an updated catalogue of mean radial velocities for 166 open clusters.

Kharchenko, Scholz, Piskunov, Röser, & Schilbach have published (2007, Astron. Nachr. 328, 889) a catalogue of mean radial velocities for 516 open clusters.

A catalogue of mean radial velocities has been built by combining published data. It is primarily based on the work of Rastorguev A.S., Glushkova E.V., Dambis A.K. & Zabolotskikh M.V. (1999, Astron. Letters 25, 689).

Selection on cluster parameters

Samples of clusters can be obtained by performing a selection on the clusters parameters, i.e. coordinates, distances, ages, diameters. The form prepared permits to do the selection on all parameters simultaneously.

To use the form, enter, in the relevant areas, the lower and/or the upper limits. It is possible to fill only the lower limit area, only the upper one or both depending on the selection to be made.

A value in the lower area will perform a selection of clusters with the parameter larger than the limit indicated, while a value in the upper area will perform a selection of clusters with the parameter smaller than the given value. Evidently, if both values are indicated, the parameters of the selected clusters will fall between the two limits.

In the output table, the cluster names are linked to each cluster page, from which an access to the available data is provided.


A. Selection on cluster names

The parameters for all cluster from an author's list (e.g. Trumpler) may be obtained by using the corresponding form. Simply enter the name of the author in the text field.

B. Selection on plots

Clusters may also be selected on active plots, drawing the clusters in right ascension versus declination plane, galactic longitude versus latitude, distance from the Sun or above the galactic plane.

You first need to choose one representation, and will receive a form. Enter the coordinates (both formats are accepted: hour minute or decimal hours or degrees). Do not ask for too large a range, the plots will be too crowded. You can also choose to display the cluster names or not. The default is "not".

Colours are used to indicate roughly the age domain:
Blue: logt < 8.0; Yellow: 8.0 < logt < 9.0, Red: logt > 9.0; Grey: no information.

The resulting maps are active so that you can click on any symbol and get information on the cluster in the right-hand frame, in place of the original menu. Further links to scanned maps, plotted charts or cluster page are provided.

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The star Level

Stellar content

From the catalogue of Lyngå and subsequent information found in the literature, list of clusters containing chemically peculiar stars (Ap and Am), emission-line stars (Be), blue stragglers and red giants have been built. They can be reached from the navigation panel.

Data retrieval for star in an open cluster

To get data from the database for stars in a given clusters, you need to start with the cluster page. It can be reached from the navigation panel, or from any list of clusters.

Data Description

A basic concept in WEBDA is that of data types because in forms you need to choose which kind of data you are interested in. In fact each type of data is stored in a distinct file, whose name corresponds uniquely to a datatype.

A long description of each data type is available. It gives also a description of the field of each record.

Datatype classification

Data types are classifed into five domains:
Coordinates, cross-identifications;
Data in most photometric systems (UBV, uvby, Geneva, DDO and so on.)
Spectral classification, radial velocity, rotational velocity (Vsini);
Membership probability, variability periods, remarks;
Ap and Am stars, Be stars, blue stragglers and red giants.

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Miscellanous Topics

Cross-references tables

The database is founded on a number of cross-refeence tables which collected the various names under which any star has been called in a cluster. An link to the list of tables is provided in the navigation panel. The cluster names are linked to an interface (based on frames) which allows to query the tables. Look at the description and help links provided with table interface.

Scanned maps

A large number of published maps of star clusters have been scanned. They reproduce the original numbering established in the clusters. These maps are active, this means that one can obtain the basic information n the numberbed stars simply by clicking on the stellar images.

References to data sources

For all data collected in the database the data source (reference) is indicated. References are usually listed during data retrieval, but a form is also provided in the navigation panel to directly query the reference files.


Many data for the brighter cluster stars are have been published under HD, DM, LSS, or other designations of astronomical catalogues. These cross-identifications have been collected for a long time during the early development of the database. An interface to the catalogue of cross-identifications with astronomical catalogues is offered to search if a given catalogue number belongs to a cluster field.

The catalogues considered so far are:
The Bright Star catalogue (BS)
The Henry Draper catalogue (HD and HDE)
The various Durchmusterungen (BD, CoD, CpD)
The catalogue of Luminous Stars in the Southern Milky Way (LSS)
The Smithsonian catalogue (SAO)
The catalogue of Variable Stars (GCVS)
The Hipparcos catalogue (HIP)

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Last update: 01 November 2009