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Filter u g r i z
- ApCorr - ApCorr - ApCorr - ApCorr - ApCorr
D1 0.003 0.002 0.007 0.005 0.006 0.002 0.001 0.001 0.005 0.001
D2 0.002 0.001 0.002 0.002 0.004 0.002 0.001 0.002 0.004 0.002
D3 0.006 0.008 0.014 0.001 0.004 0.001 0.001 0.002 0.000 0.001
D4 0.014 0.007 0.033 0.003 0.015 0.007 0.002 0.000 0.008 0.001
Table 1: Zero-point difference for Deep field exposures before and after L99 observations, with and without the
application of an aperture correction (left and right columns for each filter, respectively). In all cases except D3-u ∗
the application of the aperture correction reduces the difference.
obstacle.
3.7.5 SNLS standard star catalogue
The complete CFHTLS-T0007 release (both Deep and Wide) are photometrically calibrated using the
SuperNova Legacy Survey (SNLS) tertiary standards catalogs. These catalogs have been produced and
release as products of the SuperNova Legacy Survey. They have been made available at CDS in the
catalog interface Vizier 18 . The detailled description of the production of the catalogs is described in
(Regnault et al., 2009).
A summary of the description is reproduced here.
This is the photometric calibration of the SuperNova Legacy Survey (SNLS) three year
dataset. The SNLS corresponds to the DEEP component of the larger Canada-France-
Hawaii Telescope Legacy Survey (CFHTLS). The SNLS repeatedly monitors four one square
degree fields (labeled D[1-4]) with the MegaCam wide-field imager, in the g, r, i and z bands.
u-band observations of the same fields are also available, although not formally part of the
SNLS dataset.
(...)
The SNLS 3 year calibration relies on the ((Landolt, 1992)) standard star catalog. Landolt
fields are observed during each photometric night along with the SNLS fields. Zeropoints
are derived from these observations. Stable and isolated stars are detected on the
SNLS fields and selected as "tertiary standards". The calibrated magnitudes of each tertiary
standard obtained under photometric conditions are combined to produce a calibration
catalog for each SNLS field.
(...)
To interpret the tertiary standard magnitudes as physical fluxes, we need a primary standard,
i.e. a star with known MegaCam magnitudes and whose spectral energy distribution
has been measured absolutely. The SNLS uses BD+17 4708 whose SED has been measured
in Bohlin & Gilliland, 2004, Cat. J/AJ/128/3053 using the HST STIS and NICMOS spectrographs.
BD+17 4708 has not been directly observed by SNLS, however, its MegaCam
magnitudes were inferred from its known Landolt magnitudes ((Regnault et al., 2009), table
7).
(...)
18 http://cdsarc.u-strasbg.fr/viz-bin/Cat?J/A%2bA/506/999
18