Presentation Description Information Interrogation Navigation Webda

WEBDA Conception


Site design
Cluster selection
Data query
Data archive
Bibliography query

Site design

This site has been designed to open a public access to a large collection of data for stars in the field of open clusters which covers most aspects of astronomical observations. It has been organised along three channels
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.
Open cluster is the basic unit of the database and the tools of this site have been designed to provide various ways of finding the open star clusters corresponding to your expectations. Once the right clusters have been identified, the data may be reached from the cluster pages.

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.

Finding the existing data

The site offers basically two ways to find the desired information:
by scanning lists of clusters
This first method allows to appreciate the amount of observations presently available for all clusters, by browsing, for example,

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

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 page built dynamically for each cluster, like that for NGC 4755, is the starting point to query the database in more depth and access the stellar data, display images and make data plots.

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.
When a global view of a file content is necesary, it is possible to simply display the file content.

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

Because a long use of the database over the Net may be tedious, the possibility is also offered to download selected, or all, data files for a cluster and copy archive data files. The links to ftp archive data are located at the bottom of the cluster pages.

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

This site offers another possibility to access the astronomical literature on open clusters. This may be useful in the sense that there are no prior selections on journals or books. In addition keywords have been attributed to permit the required versatility in bibliography query.

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

In addition to the cluster names, there is a large list of keywords and it is also possible to use a form to search the keywords relevant to the literature search.

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

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