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J/A+A/506/999       Photometric Calibration of SNLS            (Regnault+, 2009)

Photometric Calibration of the SuperNova Legacy Survey Fields. Regnault N., Conley A., Guy J., Sullivan M., Cuillandre J.-C., Astier P., Balland C., Basa S., Carlberg R.G., Fouchez D., Hardin D., Hook I.M., Howell D.A., Pain R., Perrett K., Pritchet C.J. <Astron. Astrophys. 506, 999 (2009)> =2009A&A...506..999R
ADC_Keywords: Photometry, sensitivity functions ; Photometry, SDSS Keywords: cosmology: observations - techniques: photometric - methods: observational Description: 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 non-uniformities of the MegaCam imager photometric response have been mapped as a function of the position on the focal plane. The fluxes, measured on the survey images processed with the CFHT Elixir pipeline, have been corrected for these non-uniformities in order to obtain measurements that are uniform at the ∼1% level. The MegaCam passband transmissions were found to be non-uniform, the filters being 3 to 6 nanometers bluer on the edges of the camera than on the center. This result agrees with the filter scans provided by the filter manufacturer (Sagem/REOSC). This has important consequences on the definition of the MegaCam magnitudes: the natural magnitude system depends on the focal plane location where the observations were made. In order not to break the connection between calibrated magnitudes and their physical flux counterparts, we chose to report the *natural magnitudes* of each object, measured in the MegaCam passbands, at the focal plane location where the object was observed. We call this system, "Local Natural Magnitudes". The non-uniformities of the MegaCam effective passbands are small and, for main sequence stellar objects, they may be accounted for using linear color corrections. The relation between the Local Natural Magnitudes of a given star, observed at two locations x_0 and x of the focal plane are: g|x = g|x_0 + dkggr(x) * ( (g-r)|x_0 - (g-r)BD+17|x_0 ) ... z|x = z|x_0 + dkziz(x) * ( (i-z)|x_0 - (i-z)BD+17|x_0 ) where the dk(x) are (position dependant) color terms. We provide dk(x) maps for each MegaCam band (see below). The SNLS 3 year calibration relies on the (Landolt, 1992AJ....104..340) standard star catalog. Landolt fields are observed during each photometric night along with the SNLS fields. Zero-points 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 (this paper, table 7). The tertiary star Local Natural Magnitudes are defined so that the associated physical broadband flux f|x is given by: f|x = 10{-0.4*(m|x-mref)}*∫[Sref(l)*T(l;x)]dl where m|x is the tertiary star magnitudes at location x on the focal plane, mref is the MegaCam magnitude of BD+17 4708 (at the center of the focal plane, see table 7 of this paper), Sref(l) is the SED of BD+17 4708 measured in 2004AJ....128.3053B, and T(l;x) is the effective passband of MegaCam at location x. Attached is all the necessary information to tie MegaCam observations to this system. We provide (a) the griz magnitudes of the SNLS tertiary standards for all four SNLS fields (b) the MegaCam open transmission and the ugriz MegaCam filter scans at various position along a diagonal (c) the final uncertainty budget in the form of 3 covariance matrices. The u-band observations of the SNLS DEEP fields are not formally part of the SNLS. Nevetheless we give u-band magnitudes for a subset of the SNLS tertiary stars. Objects: ------------------------------------------------- RA (2000) DE Designation(s) ------------------------------------------------- 22 11 31.4 +18 05 34 BD+17 4708 = HIP 109558 ------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table19.dat 153 2546 Tertiary rgiz catalog for the SNLS field D1 table20.dat 153 3878 Tertiary rgiz catalog for the SNLS field D2 table21.dat 153 2827 Tertiary rgiz catalog for the SNLS field D3 table22.dat 153 5294 Tertiary rgiz catalog for the SNLS field D4 d1u.dat 54 1394 D1 tertiary stars u-band magnitudes d2u.dat 54 2349 D2 tertiary stars u-band magnitudes d3u.dat 54 714 D3 tertiary stars u-band magnitudes d4u.dat 54 3051 D4 tertiary stars u-band magnitudes tabled1.dat 123 9 Full covariance matrix of the BD+17 4708 MegaCam and Landolt magnitude uncertainties tabled2.dat 123 9 Covariance matrix of the uncertainties affecting (1) the differences between the tertiary MegaCam magnitudes and the MegaCam magnitudes of BD+17 4708 and (2) the Landolt magnitudes of BD+17 4708 tabled3.dat 123 9 Covariance matrix of the uncertainties affecting the synthetic instrumental magnitudes of BD+17 4708 table13.dat 15 7190 Open transmission of the MegaCam imager (no filters) table14.dat 95 1545 u_M filter scan (Sagem/REOSC) table15.dat 95 371 g_M filter scan (Sagem/REOSC) table16.dat 95 357 r_M filter scan (Sagem/REOSC) table17.dat 95 446 i_M filter scan (Sagem/REOSC) table18.dat 95 632 z_M filter scan (Sagem/REOSC) dkuug.fit 2880 78 dk(x) map (u band) dkggr.fit 2880 78 dk(x) map (g band) dkrri.fit 2880 78 dk(x) map (r band) dkiri.fit 2880 78 dk(x) map (i band) dkziz.fit 2880 78 dk(x) map (z band)
Byte-by-byte Description of file: table19.dat table2?.dat
Bytes Format Units Label Explanations
1- 9 F9.5 deg RAdeg Right ascension, in decimal degrees (J2000) 13- 21 F9.5 deg DEdeg Declination, in decimal degrees (J2000) 25- 30 F6.3 mag gmag ?=-1 g-band magnitude (Vega-like system) 34- 39 F6.3 mag e_gmag ?=-1 Uncertainty on the g-band magnitude 43- 45 I3 --- o_gmag [1,40]?=-1 Number of observations 49- 54 F6.3 --- dkg ?=-1 Grid g-band dk color term for this object 58- 63 F6.3 mag rmag ?=-1 r-band magnitude(Vega-like system) 67- 72 F6.3 mag e_rmag ?=-1 Uncertainty on the r-band magnitude 76- 78 I3 --- o_rmag [1,40]?=-1 Number of observations 82- 87 F6.3 --- dkr ?=-1 Grid r-band dk color term for this object 91- 96 F6.3 mag imag ?=-1 i-band magnitude(Vega-like system) 100-105 F6.3 mag e_imag ?=-1 Uncertainty on the i-band magnitude 109-111 I3 --- o_imag [1,40]?=-1 Number of observations 115-120 F6.3 --- dki ?=-1 Grid i-band dk color term for this object 124-129 F6.3 mag zmag ?=-1 z-band magnitude(Vega-like system) 133-138 F6.3 mag e_zmag ?=-1 Uncertainty on the z-band magnitude 142-144 I3 --- o_zmag [1,40]?=-1 Number of observations 148-153 F6.3 --- dkz ?=-1 Grid z-band dk color term for this object
Byte-by-byte Description of file: d1u.dat d2u.dat d3u.dat d4u.dat
Bytes Format Units Label Explanations
1- 9 F9.5 deg RAdeg Right ascension, in decimal degrees (J2000) 13- 21 F9.5 deg DEdeg Declination, in decimal degrees (J2000) 25- 30 F6.3 mag umag u-band magnitude 34- 39 F6.3 mag e_umag uncertainty on the u-band magnitude 43- 45 I3 --- o_umag number of observations 49- 54 F6.3 --- dku grid u-band dk color term for this object
Byte-by-byte Description of file: tabled1.dat tabled2.dat tabled3.dat
Bytes Format Units Label Explanations
1- 11 E11.5 --- C1 Covariance matrix coefficient (Δg) 15- 25 E11.5 --- C2 Covariance matrix coefficient (Δr) 29- 39 E11.5 --- C3 Covariance matrix coefficient (Δi) 43- 53 E11.5 --- C4 Covariance matrix coefficient (Δz) 57- 67 E11.5 --- C5 Covariance matrix coefficient (U_ref_) 71- 81 E11.5 --- C6 Covariance matrix coefficient (B_ref_) 85- 95 E11.5 --- C7 Covariance matrix coefficient (V_ref_) 99-109 E11.5 --- C8 Covariance matrix coefficient (R_ref_) 113-123 E11.5 --- C9 Covariance matrix coefficient (I_ref_)
Byte-by-byte Description of file: table13.dat
Bytes Format Units Label Explanations
1- 7 F7.1 0.1nm WL Wavelength 9- 15 F7.4 --- OT [0,1] Open Transmission (no filters) (1)
Note (1): product of (a) the transmission of the optical system, including the camera window, (b) the mirror reflectivity (c) the average transmission of the atmosphere above Mauna Kea and (c) the average quantum efficiency of the MegaCam CCDs.
Byte-by-byte Description of file: table1[45678].dat
Bytes Format Units Label Explanations
1- 5 I5 0.1nm WL Wavelength 9- 14 F6.4 --- T000 [0,1] Transmission at the center of the filter 18- 23 F6.4 --- T023 [0,1] Transmission at 23mm from the center 27- 32 F6.4 --- T047 [0,1] Transmission at 47mm from the center 36- 41 F6.4 --- T070 [0,1] Transmission at 70mm from the center 45- 50 F6.4 --- T093 [0,1] Transmission at 93mm from the center 54- 59 F6.4 --- T117 [0,1] Transmission at 117mm from the center 63- 68 F6.4 --- T140 [0,1] Transmission at 140mm from the center 72- 77 F6.4 --- T163 [0,1] Transmission at 163mm from the center 81- 86 F6.4 --- T186 [0,1] Transmission at 186mm from the center 90- 95 F6.4 --- T210 [0,1] Transmission at 210mm from the center
Acknowledgements: Nicolas Regnault, nicolas.regnault(at)lpnhe.in2p3.fr References: Guy et al, 2009, in prep. "The Supernova Legacy Survey 3rd Year Sample: Photometric Properties of 245 high redshift Type Ia Supernovae."
(End) Nicolas Regnault [CNRS/IN2P3/LPNHE], Patricia Vannier [CDS] 27-Aug-2009
(End) Nicolas Regnault [CNRS/IN2P3/LPNHE], Patricia Vannier [CDS] 27-Aug-2009
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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