The names are of two sorts. The first sort starts with "G" (for "group") followed by a generation number (which is incremented every six months), followed by numbers indicating the RA and Dec of the group centre. For example: G002.003.844+33.133 is and older group centred on RA=33.133 and Dec=3.844. The other sort is based on survey from which the came, either the CFHTLS (with names like D3, W4 etc.) or the NGVS (NGVS+1+1 for example).
The group names are followed by a character(s) indicating the filter UGRIZ. The i.MP9702 filter is denoted "I2".
These are simple FITS files (not multi-extension FITS files) measuring about 20000 pixels by 20000 pixels or about 1 degree by 1 degree, depending on the input dither pattern, and are about 1.7 Gb in size. They have a sky level of 0 counts. They are scaled to have a photometric zero-point of 30.000 in AB magnitudes. That is to say, for each source:
AB_magnitude = -2.5 * log10(ADU) + 30.000
The conversions to Vega and SDSS magnitudes can be found on the filter page.
imcopy G002.003.844+33.133.G.weight.fits.fz G002.003.844+33.133.G.weight.fits
The values of a weight map pixel is proportional to the inverse of the variance of that pixel in the main image.
All magnitudes are on the AB system. The catalogues have a header describing the columns:
# 1 NUMBER Running object number # 2 X_IMAGE Object position along x [pixel] # 3 Y_IMAGE Object position along y [pixel] # 4 ALPHA_J2000 Right ascension of barycenter (J2000) [deg] # 5 DELTA_J2000 Declination of barycenter (J2000) [deg] # 6 MAG_AUTO Kron-like elliptical aperture magnitude [mag] # 7 MAGERR_AUTO RMS error for AUTO magnitude [mag] # 8 MAG_BEST Best of MAG_AUTO and MAG_ISOCOR [mag] # 9 MAGERR_BEST RMS error for MAG_BEST [mag] # 10 MAG_APER Fixed aperture magnitude vector [mag] # 11 MAGERR_APER RMS error vector for fixed aperture mag. [mag] # 12 A_WORLD Profile RMS along major axis (world units) [deg] # 13 ERRA_WORLD World RMS position error along major axis [pixel] # 14 B_WORLD Profile RMS along minor axis (world units) [deg] # 15 ERRB_WORLD World RMS position error along minor axis [pixel] # 16 THETA_J2000 Position angle (east of north) (J2000) [deg] # 17 ERRTHETA_J2000 J2000 error ellipse pos. angle (east of north) [deg] # 18 ISOAREA_IMAGE Isophotal area above Analysis threshold [pixel**2] # 19 MU_MAX Peak surface brightness above background [mag * arcsec**(-2)] # 20 FLUX_RADIUS Fraction-of-light radii [pixel] # 21 FLAGS Extraction flags
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