DENIS, Deep Near- Infrared Survey of the Southern Sky

Preliminary Release of Point Source Data
from the DENIS project

1  Summary

The DENIS consortium is providing access to a preliminary set of extracted point sources, corresponding to about 120 strips (2% of the southern sky) resulting from observations performed in 1996, in the I, J and Ks bands, using a dedicated 1m-telescope in ESO, La Silla. Data are available through a Web server developed by the CDS (Strasbourg astronomical Data Center).

2  Data reduction.

The observation strips have been reduced in Paris and Leiden Data Analysis Centers, and were selected according to their astrometric and photometric quality, in order to form a representative sample of the current DENIS three-colour (I, J, K short) point source catalogue.
It is to be noted, however, that this is NOT a subset of the final DENIS catalogue of point sources, because some improvements in the pipeline reduction software are still currently being implemented, and will imply a new reduction of already observed data. Planned improvements concern both astrometry (which is based, in the presently released data strips, on the GSC and USNO A1.0 catalogs, while data will eventually be reduced to ICRF by means of the USNO A2.0 and Tycho Reference Catalogs), and photometry (with a better processing of the PSF, not yet implemented in the released data). These improvements are not of such a nature that they will change the statistical interpretation of the currently released data sets.

Overlaps between individual frames (12 arcmin x 12 arcmin) constituting a strip have been processed (with the exception of bad quality flagged sources, which are not matched, and will generally appear duplicated). Eventual overlaps between adjacent strips have NOT been matched in this preliminary release. These elements should be taken carefully into account when working on star counts derived from the released data.

3  Data access through the CDS Web server.

The released data are being made available on-line through the CDS Web server at the following address:

Data are primarily organized by strips of observations (a strip is an elongated rectangular zone of 12 arc minutes width in right ascension, and 30 degrees in declination). A map provides a graphical access to individual strips, while an auxiliary database provides information about night and strip qualities.

In addition a powerful query mechanism provides access to individual data records (including position, I, J, K magnitudes, and a number of additional flags related to the source extraction) for about 22 million of extracted DENIS sources.

Queries can be made for DENIS sources around a given position (center and radius, where the center is to be specified in J2000 coordinates, or by the name of a central object to be resolved by Simbad). Selection of objects in the colour-colour diagrams of specified strips is also possible. Finally, the DENIS database is also available through VizieR and Aladin, where additional query modes and functionalities are available.

The DENIS Website at CDS also includes general information about the DENIS project, including scientific reports, lists of publications, etc.

4  Future evolutions

The DENIS point source data server at CDS will continue to evolve in the future with newly reduced data being gradually incorporated; changes in the data reduction will be posted in the corresponding information pages. It is the policy of the DENIS consortium to release reduced data not later than one year after they have been archived at the Paris Data Analysis Center.

New features for an improved support of the query mechanism and source selections will also be made available as they are being developed.

Suggestions and remarks concerning the service, or questions related to the DENIS data, can be sent to the following e-mail address:

5  Acknowledgements

DENIS is the result of a joint effort involving human and financial contributions of several Institutes mostly located in Europe. It has been supported financially mainly by the French Institut National des Sciences de l'Univers, CNRS, and French Education Ministry, the European Southern Observatory, the State of Baden-Württemberg, and the European Commission under a network of the Human Capital and Mobility program.

Users are free to use the data that they may extract from the databases. Publications based on, or making use of DENIS data should include the following sentence in a footnote to the title :

" (partly) based on DENIS data obtained at the European Southern Observatory"

The DENIS Consortium
21 December 1998