Terapix Star Formation Region IC 1396, © 2002 CFHT
WIRDS-WIRCAM explanatory table
by HJMCC HJMCC - Updated October 13th, 2009

ProductDescription
Stacked Images All stacks are produced by a weighted median of all input images and combined using SWarp using a lancos 2 interpolation kernel. Equatorial Coordinate is system, J2000 (ICRS) and a TAN projection has been used. All images are 19354x19354 pixels and have a pixel scale 0.186 arc-second/pixel. The center positions of each stack corresponds to the corresponding CFHTLS images. 2MASS is used as the astrometric reference catalogue.

FILENAME for stacks:

WIRDS_[filter]_[RA][DEC]_T0001.fits

where filter can be J,H, or Ks and RA, DEC corresponds to the tangent point of the field centre.

Weight map images FITS weight map image. There is one weight map image for each FITS image. Output weight maps are produced during the image stacking using Weightwatcher in SWarp. The pixel weight is defined as the local sky background flux variance.

FILENAME:

WIRDS_[filter]_[RA][DEC]_T0001.weight.fits

Seeing The "Terapix seeing" is defined as twice the median FLUX_RADIUS of a selection of point sources on each CCD. FLUX_RADIUS, as measured by SExtractor, is the radius of the disk that contains 50% of the total flux (it is sometimes called rh in the literature).

For a Gaussian profile, the "Terapix" seeing is equal to the Full Width at Half Maximum (FWHM). For a typical wircam /megacam Point Spread Function (PSF), the Terapix seeing is slightly larger ( 10%) than the true PSF FWHM.

Completeness A completeness estimate is computed by adding point sources to the final stack and measuring what fraction of objects are recovered as a function of magnitude using SExtractor.
Effective area Effective area is derived by subtracting from the fields all the masked POLYGON areas defined using the WIRDS_JHK_[RA][DEC]_T0001.reg mask files.

chi2 catalogues These catalogues were produced using SExtractor in dual-image mode, using the CFHTLS-gri chisquared and weight map as a detection image. Each catalogue id for each filter for a given field refers to the same object. Columns of catalogs with '.cat' extentions are defined in the '.param' files. They are listed in the CFHTLS catalogue parameter list. Note that these catalogues have not been corrected for galactic extinction, although the merged catalogue contains the E(B-V) values.

FILENAME:

WIRDS_[D1-95]_[filter]_grichi2_[RA][DEC]_T0001.cat

single-band catalogues These catalogues were produced using SExtractor. Columns are defined in the '.param' files. They are listed in the CFHTLS catalogue parameter list. Note that these catalogues have not been corrected for galactic extinction, although the merged catalogue contains the E(B-V) values.

FILENAME:

WIRDS_[D1-95]-Ks_[filter]_[RA][DEC]_T0001.cat

Three colour images Produced by combining the stacked FITS images in JHK using STIFF. These are 2 x 2 binned colour images. The R,G,B color balance and cuts are primarily optimised for visual inspection as a quality assessment tool. It is primarily used to check filter-to-filter astrometric calibration and whether colour gradients are visible in objects, resulting from poor overlaps between each filter, in particular far from the centre of the field.


Site Map  -  Administration  -  Contact
© Terapix 2003-2011