WEBDA Information
Contents
- 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:
- The database global content,
- The cluster lists,
- 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 description | Clusters | Mesures | Stars |
|---|
| UBV CCD | 317 | 477191 |
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:
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 data source (reference) sequential number,
- The list of authors,
- The journal volume and page and year,
- The full title of the paper,
- The "SIMBAD / NED" bibliographical code.
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:
- The cluster names,
- The right ascension and declination for the epoch 1950,
- The galactic longitude and latitude l and b
- The distance d and distance-modulus m-M
- The colour-excess E(B-V)
- The logarithm of the age log t
- The earliest spectral type at turnoff ST
- The vertical distance from the galactic plane Z
- The cluster diameter D
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.
Cross-references
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 number of the star on the chart.
- The number of the star in the database, if different.
The link under this number will display the form to query the database by star number.
- The Right Ascension and Declination for 1950.
- Common astronomical catalogue numbers when relevant: BS (HR), HD, DM, LSS, GCVS.
The link under the HD numbers allows to query the SIMBAD with the HD number.
- The UBV magnitude and colours, (Source priority: pe, CCD, pg data), RI when available.
If not, uvby, RGU.
- The spectral type (MKK or Harvard)
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:
- The cluster name,
- The file name,
- The kind of data,
- The size of the file,
- The authors' names,
- The article reference.
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.
Last modification: 19 October 2005