CFHTLS Users - Paris Supernova & Cosmology Group - IN2P3

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsPhotometric CalibrationNicolas Regnaultnicolas.regnault@lpnhe.in2p3.frLPNHE - IN2P3 - CNRS - University Paris 6 and Paris 7SNLS Collaboration MeetingNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

OutlineInternal CalibrationThe Landolt System Flux ScaleMegacam Zero Points1 Internal Calibration2 The Landolt System Flux Scale3 Megacam Zero PointsNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

OutlineInternal CalibrationThe Landolt System Flux ScaleMegacam Zero Points1 Internal Calibration2 The Landolt System Flux Scale3 Megacam Zero PointsNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsInternal CalibrationUniformityLinearityRepeatabilityNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsThe Photometric GridDEC (deg)11.51110.5Modeling the non-uniformities of thephotometric responsePlate scale variationsscattered lightDense stellar fields (RA=20:00:00, DEC=10:00:00)1013 dithered exposures variable steps:∼ 100 pixels → half a camera9.5299.5 300 300.5 301 301.5RA (deg)Reobserved after each significantmodification of the opticsNo control observationsgrid corrections applied to the pixels by the Elixir pipeline(scatter flats or photometric flats)Nicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsAnalysis of the Photometric GridEach CCD is divided into 4 × 9 cells (δzp) / 2 × 3 cells (δk)∼ 50, 000 − 100, 000, isolated, well measured stars,each observed on ∼6 (3 – 12) cellsWe use the star flux measurements to measure:Modelan intercalibration coefficient w.r.t. the reference cell, δzp cella possible color term drift w.r.t the reference cell, δk cellm(star, cell) = m(star) + δzp(cell) [+δk(cell) × col(star)]Large fit !1295 (δzp) + 215 (δk) = 1510 (δzp + δk) calibrationparameters∼ 100, 000 star fluxes (known only on the reference cell)Nicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

SimulationInternal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsPhotometric DistorsionFITccd430.010-0.01-0.02ccd430-0.020.0080.0060.0040.002-0.032-0.042-0.040-0.051-0.061-0.06-0.07-0.0800 1 2 3 4 5 6 7 8 9ccd-0.0800 1 2 3 4 5 6 7 8 9ccd0 200 400 600 800 1000 1200 1400Cell numberColor termsFITccd40.04ccd40.010.0350.0430.0330.0050.030.02520.0220.0200.01510.0110.010.00500 1 2 3 4 5 6 7 8 9ccd000 1 2 3 4 5 6 7 8 9ccd0-0.010 200 400 600 800 1000 1200 1400Cell NumberNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

SimulationInternal CalibrationThe Landolt System Flux ScaleMegacam Zero Pointsdzp_allConstant 0.9848dk_allConstant 0.97351Mean -0.0005861Mean 0.0005631Sigma 0.004048Sigma 0.0045550.80.80.60.60.40.40.20.20-0.02 -0.015 -0.01 -0.005 0 0.005 0.01 0.015 0.02dzp - dzpfit MC0-0.02 -0.015 -0.01 -0.005 0 0.005 0.01 0.015 0.02dzp - dzpfit MCMC- dzpfitdzp0.0050- dk MCdk fit0.0250.02-0.0050.015-0.01-0.015-0.020 200 400 600 800 1000 1200 1400cell numberNicolas Regnault nicolas.regnault@lpnhe.in2p3.fr0.010.0050-0.0051200 1400 1600 1800 2000 2200 2400 2600cell numberPhotometric Calibration

δzp, u-bandInternal CalibrationThe Landolt System Flux ScaleMegacam Zero Points$dZP$ MAP 2003.5 u(ug)$dZP$ MAP 2005.5 u(ug)3-0.12-0.103-0.14-0.12-0.12-0.04-0.042-0.022-0.02CCD-0.10-0.08CCD-0.1011-0.080-0.12-0.06-0.10-0.120-0.14-0.12-0.06-0.120 1 2 3 4 5 6 7 8CCD0 1 2 3 4 5 6 7 8CCDNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

δzp, g-bandInternal CalibrationThe Landolt System Flux ScaleMegacam Zero Points$dZP$ MAP 2003.5 g(gr)$dZP$ MAP 2005.5 g(gr)3-0.08-0.06-0.083-0.10-0.10-0.0222-0.02-0.04CCDCCD-0.0811-0.06-0.040-0.080-0.10-0.080 1 2 3 4 5 6 7 8CCD0 1 2 3 4 5 6 7 8CCDNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

δzp, r-bandInternal CalibrationThe Landolt System Flux ScaleMegacam Zero Points$dZP$ MAP 2003.5 r(ri)$dZP$ MAP 2005.5 r(ri)3-0.10-0.08-0.08-0.103-0.12-0.10-0.12-0.04-0.042-0.022-0.02CCDCCD110-0.10-0.08-0.06-0.100-0.12-0.10-0.08-0.06-0.080 1 2 3 4 5 6 7 8CCD0 1 2 3 4 5 6 7 8CCDNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

δzp, i-bandInternal CalibrationThe Landolt System Flux ScaleMegacam Zero Points$dZP$ MAP 2003.5 i(ri)$dZP$ MAP 2005.5 i(ri)3-0.06-0.063-0.08-0.08-0.02-0.0222CCDCCD-0.0611-0.040-0.06-0.060-0.08-0.04-0.060 1 2 3 4 5 6 7 8CCD0 1 2 3 4 5 6 7 8CCDNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

δzp, z-bandInternal CalibrationThe Landolt System Flux ScaleMegacam Zero Points$dZP$ MAP 2003.5 z(iz)$dZP$ MAP 2005.5 z(iz)3-0.06-0.063-0.08-0.06-0.02-0.0222CCDCCD-0.06-0.0411-0.040-0.06-0.060-0.10-0.08-0.060 1 2 3 4 5 6 7 8CCD0 1 2 3 4 5 6 7 8CCDNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsElixir ResidualsFITccd40.060.0530.040.0320.0210.01000 1 2 3 4 5 6 7 8 9ccdNicolas Regnault nicolas.regnault@lpnhe.in2p3.fr Photometric Calibration-0.01

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsHow do we convert δk ′ s → δλ ′ s ?More complicated than just: δk = δλ/(λ 1 − λ 2 )We use the (Pickles, 1992) library, a model of the SNLSpassbands, and we simulate the δk(δλ) function.We find (δλ in nanometers):δλ uδλ gδλ rδλ iδλ z= 91.1 × δk(u, ug)= 97.8 × δk(g, gr)= 100.7 × δk(r, ri)= 170.7 × δk(i, ri)= 157.7 × δk(z, iz)Nicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

δλ, u-bandInternal CalibrationThe Landolt System Flux ScaleMegacam Zero Points$dl$ MAP 2003.5 u(ug)3-1.00+0.002CCD10+0.00+0.000 1 2 3 4 5 6 7 8CCDNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

-1.00δλ, u-bandInternal CalibrationThe Landolt System Flux ScaleMegacam Zero Points$dl$ MAP 2003.5 u(ug)$dl$ MAP 2005.5 u(ug)33+0.00-1.00+0.0022CCDCCD10+0.00+0.0010+0.00+0.000 1 2 3 4 5 6 7 8CCD0 1 2 3 4 5 6 7 8CCDNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

δλ, g-bandInternal CalibrationThe Landolt System Flux ScaleMegacam Zero Points$dl$ MAP 2005.5 g(gr)32-2.00CCD100 1 2 3 4 5 6 7 8CCDNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

δλ, g-bandInternal CalibrationThe Landolt System Flux ScaleMegacam Zero Points$dl$ MAP 2003.5 g(gr)$dl$ MAP 2005.5 g(gr)33-2.0022-2.00CCDCCD11-1.00000 1 2 3 4 5 6 7 8CCD0 1 2 3 4 5 6 7 8CCDNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

δλ, r-bandInternal CalibrationThe Landolt System Flux ScaleMegacam Zero Points$dl$ MAP 2005.5 r(ri)3-3.00-3.002-1.00CCD-2.001-3.0000 1 2 3 4 5 6 7 8CCDNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

δλ, r-bandInternal CalibrationThe Landolt System Flux ScaleMegacam Zero Points$dl$ MAP 2003.5 r(ri)$dl$ MAP 2005.5 r(ri)33-3.00-3.00-3.00-2.0022-1.00CCD-3.00CCD-2.0011-3.000-4.000-3.000 1 2 3 4 5 6 7 8CCD0 1 2 3 4 5 6 7 8CCDNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

-3.00δλ, i-bandInternal CalibrationThe Landolt System Flux ScaleMegacam Zero Points$dl$ MAP 2005.5 i(ri)3-5.00-4.00-2.00-4.00-5.002-1.00-3.00CCD10-5.00-4.00-4.000 1 2 3 4 5 6 7 8CCDNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

-3.00δλ, i-bandInternal CalibrationThe Landolt System Flux ScaleMegacam Zero Points$dl$ MAP 2003.5 i(ri)$dl$ MAP 2005.5 i(ri)3-5.00-3.00-2.00-4.00-5.003-5.00-4.00-2.00-4.00-5.0022-1.00-3.00CCD-4.00CCD11-5.00-4.00-5.00-5.00-4.00-4.00000 1 2 3 4 5 6 7 8CCD0 1 2 3 4 5 6 7 8CCDNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

δλ, z-bandInternal CalibrationThe Landolt System Flux ScaleMegacam Zero Points$dl$ MAP 2005.5 z(iz)3-4.00-6.00-5.00-3.002-2.00CCD-5.001-5.00-6.0000 1 2 3 4 5 6 7 8CCDNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

-6.00δλ, z-bandInternal CalibrationThe Landolt System Flux ScaleMegacam Zero Points$dl$ MAP 2003.5 z(iz)$dl$ MAP 2005.5 z(iz)33-4.00-6.00-3.00-5.00-3.00-2.00CCD2-4.00-4.00-5.00CCD2-2.00-5.0011-5.00-5.00000 1 2 3 4 5 6 7 8CCD0 1 2 3 4 5 6 7 8CCDNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsConsistency Checks-3.00-4.00-3.00$dl$ MAP 2005.5 i(ri)$dl$ MAP 2005.5 i(iz)3-5.00-4.00-2.00-4.00-5.003-5.00-2.00-4.00-5.00-6.002-1.002-1.00-3.00-3.00CCDCCD11-5.00-4.00-4.00-6.00-5.00-4.00-5.00000 1 2 3 4 5 6 7 8CCD0 1 2 3 4 5 6 7 8CCDNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsConsistency Checks$dl$ MAP 2005.5 r(gr)$dl$ MAP 2005.5 r(ri)3-3.00-2.003-3.00-3.002-1.002-1.00-3.00CCDCCD-2.0011-3.00-3.00000 1 2 3 4 5 6 7 8CCD0 1 2 3 4 5 6 7 8CCDNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsSDSS Southern StripNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsWhy Does Uniformity Matter ?Number of Landolt Stars(Focal Plane Position)90038007002600CCD500400130020001000 1 2 3 4 5 6 7 8CCD0Nicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsREOSC (2003) Scans versus GridCentral Wl(Ang)Central Wl(Ang)4840483548304825482048154810480548004795479076407620760075807560GridReoscg0 50 100 150Radius(mm)GridReosc75400 50 100 150Radius(mm)Nicolas Regnault nicolas.regnault@lpnhe.in2p3.friCentral Wl(Ang)Central Wl(Ang)62506240623062206210620061906180617088608850884088308820881088008790878087708760GridReoscr0 50 100 150Radius(mm)GridReoscz0 50 100 150Radius(mm)Photometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsWhat’s next ?We (SNLS) correct for the residual non-uniformities at theflux (/color) levelWe have implemented a model of the radially variablepassbands (from the REOSC filter scans)It would be great to have the new δzp grids applied directly tothe pixels ⇒ flat photometry for objects of a reference color(which color should we choose ?)How do we go about it ?independant analysis of the grid dataset by another group ?checks on a smaller dataset (one DEEP field, a few wide fields,MAPC dithers) ?Nicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

OutlineInternal CalibrationThe Landolt System Flux ScaleMegacam Zero Points1 Internal Calibration2 The Landolt System Flux Scale3 Megacam Zero PointsNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsMagnitude SystemNatural Magnitudes( ∫ )φ(λ)T (λ; x) dλm(x) = −2.5 log 10∫φref (λ) T (λ; x) dλCalibration Model˜m(x 3 , t) = m 3 (x 3 ) + δk(x 3 ) × (col ref − col g ) + ZP(t)˜m(x 2 , t) = m 2 + C(col 2 ) + δk(x 2 ) × (col 2 − col g ) + ZP(t)Nicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsThe Landolt Flux ScaleHow do we convert Landolt magnitudes to flux ?(Landolt colors to flux ratio)∫Φ L = 10 −0.4m L× 10 +0.4m ref× S ref (λ)B(λ)dλ (1)We need a model of the Landolt passbands.We need to know the magnitudes of the fundamental fluxstandard in the Landolt system.Nicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsLandolt System PassbandsNot known with precisionUBV close to (Johnson, 1953)Johnson UBV not well defined eitherRI close to Cousins R c I cBut there are differences.⇒ We start with the (Bessel, 1990) recommendantions. Weallow each filter to shift by an unknown quantity δλ filterB(λ) −→ B(λ − δλ)Nicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsLandolt (Johnson-Cousins) Fundamental SEDVega usually chosen as the fundamental flux standardBut we could choose any other star or set of stars with knownspectra and known Landolt magnitudes.The CALSPEC library provides one with spectra taken withHST (STIS/NICMOS) (supplemented with ground basedspectroscopy).We start with the latest HST Vega SED determination(Bohlin, 2006) from CALSPEC as a fundamental standardNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsMagnitudes of Vega in the Landolt SystemThe Traditional wayHistorical color indexes (Johnson et al, 195X;196X)Color transformations (Landolt, 1973;1983;1992;2007)V B − V U − B V − R R − Ihist 0.030 0.000 -0.010 0.000 0.006L83 0.024 -0.002 -0.007 -0.0002 0.0049Determination of the V − R color problematic (connectionbetween the Johnson and Cousins systems). Nomeasurements of V − R availableSeveral measurements of R do not agree. (Ask Alex fordetails)Long transformation chain. Drifts ?Nicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsMagnitudes of Vega in the Landolt SystemThe CALSPEC way(Landolt & Uomoto, 2007) report magnitudes of 31 HSTspectrophotometric standards. Among them, 5 standards withHST-only SEDs. (+1 (Landolt, 1992) standard with an HSTSED).Same spectroscopy source as the one we took the Vega SEDfrom.Determination of δλ and m ref by minimizing:χ 2 =N∑starss=1N∑bandsb=1w sb (m obs (s, b) − m synth (s, b; δλ, m ref )) 2Nicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsThe CALSPEC analysisNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsCALSPEC Internal DispersionDispersion of ∼ 1% within the CALSPEC / (Landolt &Uomoto, 2007) dataNot described by the uncertainties reported by (Landolt &Uomoto, 2007) and CALSPEC/Bohlin.Set the scales of the uncertaintiesHow do we account for it ?→ in release 2008-06-06, we attributed all this uncertainty to theLandolt measurements (without correlations)Nicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsCALSPEC Internal dispersionU − V B − V V − R V − I B − RCAN 0.0124 0.0069 0.0069 0.0069 –CALSPEC +ZP 0.0263 0.0072 0.0051 0.0081 0.0070CALSPEC +ZP (new) 0.0132 0.0057 0.0041 0.0043 0.0056Nicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsConclusion on the CALSPEC analysisThe CALSPEC analysis is now stableMagnitudes of Vega compatible w/ historical magnitudes(except in R)Nicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

OutlineInternal CalibrationThe Landolt System Flux ScaleMegacam Zero Points1 Internal Calibration2 The Landolt System Flux Scale3 Megacam Zero PointsNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsThe Megacam Zero-Points – Tertiary StandardsNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibrationmodel the colortransformations usingpiecewise-linear functionsuse synthetic photometry tomodel these transformationsphysical modelδλ and m V fitted alongwith the ZP (w/CALPSEC constraints)full covariance matrix ofcalibration parametersg − Bi − I0.80.70.60.50.40.30.20.10.0−0.1−0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6B − V0.250.200.150.100.050.00−0.05−0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8R − Ir − Rz − I0.300.250.200.150.100.050.00−0.05−0.2 0.0 0.2 0.4 0.6 0.8 1.0V − R0.150.100.050.00−0.05−0.10−0.15−0.20−0.25−0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8R − I

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsCalibration FitWe want to propagate the uncertainties (including thecorrelations) of the (Landolt & Uomoto, 2007) baseddeterminations of δλ, m V .Incorporate them into the fit as a prior.χ 2 =∑ i w (i CTip + D T ) 2z + m 2i + δk(x i ) δcol 2i − ˜m i +(p − p 0 ) T W p (p − p 0 )with p = (δλ, m V )Multiband fit. Fit all zero points at once.Nicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsMegacam Zero Points0.050.050.040.04mV ega(B)0.030.02mV ega(V )0.030.020.010.010.00−4 −2 0 2 4δλB (nm)0.00−4 −2 0 2 4δλV (nm)0.050.050.040.04mV ega(R)0.030.02mV ega(I)0.030.020.010.010.00−4 −2 0 2 4δλR (nm)Nicolas Regnault nicolas.regnault@lpnhe.in2p3.fr0.00−10 −5 0 5 10δλI (nm)Photometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsThe Megacam Zero-Points – Tertiary StandardsAs of todayU B V R Iδλ +10.57 −12.89 +12.48 +33.85 +67.01U − V B − V — R − V I − V∆m V +0.0242 −0.0050 — +0.0054 +0.00021% differences in the riz zero points (Fr calibration may stillchange on this aspect).Nicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsCalibration Fit26.6526.6026.5525.9525.9025.85ZP (B)26.50ZP (V )25.8026.4525.7526.4025.7026.350 200 400 600 800 1000 1200 1400date (days since 2003/01/01)25.650 200 400 600 800 1000 1200 1400date (days since 2003/01/01)25.5524.5525.5024.5025.4524.45ZP (R)25.40ZP (I)24.4025.3524.3525.3024.3025.250 200 400 600 800 1000 1200 1400date (days since 2003/01/01)24.250 200 400 600 800 1000 1200 1400date (days since 2003/01/01)Nicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsCalibration Fit0.80.30g − B0.70.60.50.40.30.20.10.0−0.1−0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6B − Vr − R0.250.200.150.100.050.00−0.05−0.2 0.0 0.2 0.4 0.6 0.8 1.0V − R0.250.150.200.150.100.050.00i − I0.10z − I−0.050.050.00−0.10−0.15−0.20−0.05−0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8R − I−0.25−0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8R − INicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration

Internal CalibrationThe Landolt System Flux ScaleMegacam Zero PointsFull uncertainty matrixNicolas Regnault nicolas.regnault@lpnhe.in2p3.frPhotometric Calibration