WEBDA Conception

Contents

Site design

Cluster selection

Data query

Data archive

Bibliography query

the description channel

presents most aspects of the underlying database and data organisation, explains how to use the forms and describes the arrangement of the lists and various output formats;

the information channel

initially presents the database contents in the form of lists and permit any one to find his or her way to the data;

the interrogation channel

offers forms to query the database and perform selections on its content.

The links to WEBDA tools and facilities are grouped in the navigation panel which is the heart of the site.

In each channel, four levels have been distinguished:

The database level

is concerned with the database contents, i.e. the number and lists of clusters for which a given type of data is available, and the number of stars observed in each cluster;

The cluster level

refers to the cluster parameters (distances, ages, and so on) and properties;

The stellar level

is formed by the data themselves, their references, as well as the definition of the datatypes and the stellar content of star clusters (peculiar stars, blue stragglers, red giants). It also offers information on stellar identifications and numbering systems, and charts of the clusters;

The archive level

is formed by all archive data files which can be retrieved by ftp.

by scanning lists of clusters

This first method allows to appreciate the amount of observations presently available for all clusters, by browsing, for example,

• the global database contents,
• the lists of clusters ordered by increasing right ascension
• the list of archive data files.

by performing selections

This second method allows to locate the potentially interesting open clusters by performing selections on

• the amount of existing data
• the parameters of clusters.

Both methods finally present lists of open clusters and provide links to each cluster page, which is the starting point for further queries. The clusters are ordered by alphabetical order.

The query of stellar data

The cluster page is the place collecting most available knowledge on the clusters, starting with the usual cluster parameters (coordinates, distance, age) and a photography, when one is available. The data retrieval is conceived as

a query by star number

to get the data on one or more stars,

a selection on observational data

to build sample of stars, redder than a given value, with rotation larger than another value, and so on.

a query of the data sources

to get the bibliographic reference and go back to the original articles,

a query the bibliography

to get the bibliography of the last 2, 3 or 5 years on each cluster.

If a chart has been scanned and is displayed on the screen, it is tempting to click on a star numbered on the chart to know what it is. This facility has been developed for 200 clusters for which have an convenient chart has been published. A click on any numbered star will display the basic data, like the coordinates, the BS, HD or DM numbers, the UBV magnitudes and colours and spectral type.

The colour-magnitude diagram is the most meaningful summary of the cluster properties and one is proposed for many clusters based on the UBV photometric data. Other planes are of course interesting and these can be plotted on-line on the user demand. If more specfic work is required, it is always possible to copy data from the database to the user's computer and plot any diagram with the favourite graphic package. This is why links areprovided to the existing archive data files, if any.

The retrieval of archive data

All the information on the archive data file has been gathered in the list of archive files in the information channel. Each item presents the cluster name, the kind of data each file contains and the reference to the published paper.

The access to the literature

The bibliography on open clusters covering the period from 1969 to present days can be accessed:

• by keywords
• by authors' names.

The "SIMBAD / NED" bibcodes have been added to the bibliographic files to provide a link to ADS Abstract Service and get the article abstracts.