DENIS first release documentation
This page describes the content of the DENIS first data release.
Note that these data are now obsolete. You should
use the new released data instead.
What kind of data are released?
Where can I find information on the content of the catalogue?
What is the meaning of the different flags?
The first release of DENIS data at CDS is a database of point sources
providing astrometric and photometric data, as well as a set of flags,
for the sources extracted from the images.
This is not yet a part of the final DENIS catalogue.
The basic unit for data released at CDS is the DENIS strip.
This means that point sources are stored into separated
tables, each table corresponding to a single strip.
Those strips have been selected for having good astrometric
and photometric quality.
Be aware that:
Inside a single strip, association has been done,
between bands (I, J, K_s), and overlapping images.
Objects from filtered, characterized catalogs are associated
based on their positional coincidence and their flags.
The positional coincidence is determined by examining the
elliptical shape parametrization of each entry.
When two extractions are in overlap with each other,
they are associated only if their
IMA_Flags equal zero.
When there is one entry with a non-zero IMA_Flag,
it will not be associated
and thus ends up as a separate
entry in the general catalog. This is to avoid merging
of good and bad detections.
When a source is present several times in a given band and
associated, according to the previous criteria, the
resulting entry in the general catalogue
will carry the simple flux average for the magnitudes
and the weighted average for the coordinates.
No pairing is done between adjacent strips.
If the same star is detected in the overlap of two
adjacent strips (consecutive slots), it will appear
twice, with one record for each strip.
Content of point sources catalogues
This section gives additionnal information on the content of
the catalogue output, described in the
- DENIS identifier: The recommended way to
designate the DENIS sources is JHHMMSS.s-DDMMSS
- SeqNr: Numbering of the source in the original catalogue
- MAG_APER 7'': Magnitude derived from the flux collected
in a fixed 7'' aperture centered on the source.
- MAG_APER 15'': Same as above with 15'' aperture.
- MAG_AUTO: Automatic (Kron type) scaling elliptical
- Stellarity of object: a value of 1 identifies
the object as a star, and a value of 0 indicates an extended
Caution: actually, this value
is not fully reliable, because PSF fitting is not done in
the version of SExtractor used. See the
SExtractor documentation for details.
- Extraction flag: defined by SExtractor during
Only objects with EXTR_flag<8 were
kept in the catalogue.
- 1: the object has neighbours, bright and close enough to
significantly bias the MAG_AUTO photometry, or bad pixels;
- 2: the object was originally blended with another one;
- 4: at least one pixel of the object is saturated (or very close to);
- 8: the object is truncated (too close to an image boundary);
- 16: object's aperture data are incomplete or corrupted;
- 32: object's isophotal data are incomplete or corrupted;
- 64: a memory overflow occurred during deblending;
- 128: a memory overflow occurred during extraction.
- Image flag: derived during image processing:
Only objects with IMA_flag=0 were
kept in the catalogue.
- 1: regression failed for this pixel;
- 2: flat derived is less than 0.01;
- 3: abnormaly high flat;
- 4: abnormaly high residual after adjustment;
- 5: bias away from mean by more than 5 sigmas;
- 9: insufficient pixels left after iterative clipping.
- Artifact flag: identifies detector/instrument specific
- 1: Glitch;
- 2: Optical Ghost;
- 4: Saturation in I.
- Merged objects:
- 0: no detection;
- 1: good detection;
- 2 +: object merge.
- Field position: refers back to the frame sequence
number (in the range [0..179]) of the image from which the
was extracted. In case of a merge, one of the frame numbers in
the merge is given.