Table of contents:
Zero Points Measurements Using Standards - Introduction
Standard stars are observed every photometric night with WIRCam, on
average 2 times per night for each filter. Our standards are no longer picked
from the UKIRT (FS) list, but from HST CALSPEC spectrophotometric standards,
for which spectra have been measured both in visible and NIR, and magnitudes
in all filters are computed from total throughput at CFHT, including
atmosphere, optics, filters, detectors.
Measurements are made automatically based on the WCS in the
headers of the processed images and the known star position. Note that wide
band standards are generally observed with the telescope defocused by 0.5mm to
prevent saturation. FLUXBEST of SExtractor is used to obtain each measurement
in ADU on individual (not stacked) images.
The Zero Point vs. Date plots show the ZP measured for each run since
2011, with additional measurements from 2007. It can be seen that the
instrument has been stable for 10 years. Chip-to-chip offsets are no longer
measured as ZP are calibrated on chip #4 and chip-to-chip offsets now
correspond to the ratios of the medians of the flat-fields in each chip with
respect to chip #4.
last update: December 11, 2017
Plots of WIRCam Zero Points
FILTER |
Zero Point vs. Modified Julian Date |
Y J LowOH1 LowOH2 |
 |
H CH4On CH4Off W |
 |
Ks H2 BrG KCont CO |
 |
H |
 |
|
Old Table of WIRCam Zero Points and Chip to Chip Offsets
# April 3 2007 - Loic Albert
# Created.
# July 27 2007 - Loic Albert
# Added one column, ZP_WONLC (Zero point without non-linearity correction) which gives the
# offset to apply to the zero point for data that has not been linearized.
# Added a VERSION column to tell which sets are used in different IIWI versions.
# August 16 2007 - Loic Albert
# Added entries for use with iiwi version 1.0 with non-linearity correction, but only valid for semesters 06B/07A. Will
# need to analyze 05B/06A standards to add their values to use with iiwi 1.0.
# February 26 2008 - Loic Albert
# Added the 08Aw01 data.
# April 3 2008 - Loic Albert
# Make ready for version 1.5 of `I`iwi.
# May 29 2008 - Loic Albert
# Modified to provide temporary ZP for the 08AW02 and 08AW03 runs.
# June 2 2008 - Loic Albert
# Updated for 08Aw01 to 08Aw03 runs.
# June 27 2008 - Loic Albert
# Updated temporarily to process standards of 08Aw04.
# September 11 2008 - Loic Albert
# Updated temporarily to include 08Bw02.
# October 15 2008 - Loic Albert
# Updated to include 08Bw03.
#
# This file tabulates the filter zero points and chip to chip zero point offsets. Here, the zero point is the Vega magnitude at which a flux of 1 ADU/sec is detected. The
# values are based on measurements of standard stars analyzed in the wircam_analyzestandard procedure. For chip to chip offset, the reference detector is chip #60 (extension 4).
# A jump in zero point occured when the WIRCam gain was changed from ~2.5e-/ADU to ~3.7e-/ADU (an exact factor of 1.5) in August 2006 but the reality is that, if expressed as
# the magnitude at which 1 e-/sec is detected, the "real" sensitivity of WIRCam has not changed. Note that the chip to chip offsets adopted for most narrow-band filters is that
# of its corresponding wide-band filter (e.g. H2, BRG and KCONT are that of KS), simply because not enough measurements exist for narrow-band filters. No noticeable trend of
# zero point with time has been observed so far with WIRCam. Flux measurements are made on fully processed single images using FLUXBEST of SExtractor.
#
#VERSIO STARTDATE ENDDATE FILTER ZP ZP_ERR ZP_WONLC ZP_EXT1 ZP_EXT1_ERR ZP_EXT2 ZP_EXT2_ERR ZP_EXT3 ZP_EXT3_ERR ZP_EXT4 ZP_EXT4_ERR COLTERM GAIN
0.9.4 2005-11-01T00:00:01 2006-08-15T23:59:59 Y 24.289 0.099 -0.000 +0.021 0.011 -0.144 0.009 -0.004 0.007 +0.000 0.011 0.0 2.5
0.9.4 2005-11-01T00:00:01 2006-08-15T23:59:59 J 24.120 0.040 -0.000 +0.027 0.021 -0.114 0.019 -0.013 0.015 -0.003 0.013 0.0 2.5
0.9.4 2005-11-01T00:00:01 2006-08-15T23:59:59 H 24.280 0.063 -0.000 -0.001 0.053 -0.078 0.041 -0.039 0.052 -0.005 0.032 0.0 2.5
0.9.4 2005-11-01T00:00:01 2006-08-15T23:59:59 KS 23.552 0.049 -0.000 +0.019 0.025 -0.060 0.023 -0.029 0.023 -0.001 0.017 0.0 2.5
0.9.4 2005-11-01T00:00:01 2006-08-15T23:59:59 LOWOH1 21.477 0.072 -0.000 +0.054 0.050 -0.109 0.053 -0.017 0.056 +0.000 0.033 0.0 2.5
0.9.4 2005-11-01T00:00:01 2006-08-15T23:59:59 LOWOH2 25.0 9.999 -0.000 +0.027 0.021 -0.114 0.019 -0.013 0.015 -0.003 0.013 0.0 2.5
0.9.4 2005-11-01T00:00:01 2006-08-15T23:59:59 CH4ON 23.167 0.053 -0.000 -0.001 0.053 -0.078 0.041 -0.039 0.052 -0.005 0.032 0.0 2.5
0.9.4 2005-11-01T00:00:01 2006-08-15T23:59:59 CH4OFF 23.156 0.044 -0.000 -0.001 0.053 -0.078 0.041 -0.039 0.052 -0.005 0.032 0.0 2.5
0.9.4 2005-11-01T00:00:01 2006-08-15T23:59:59 H2 20.999 0.078 -0.000 +0.019 0.025 -0.060 0.023 -0.029 0.023 -0.001 0.017 0.0 2.5
0.9.4 2005-11-01T00:00:01 2006-08-15T23:59:59 KCONT 25.0 9.999 -0.000 +0.019 0.025 -0.060 0.023 -0.029 0.023 -0.001 0.017 0.0 2.5
0.9.4 2005-11-01T00:00:01 2006-08-15T23:59:59 BRG 20.848 0.079 -0.000 +0.019 0.025 -0.060 0.023 -0.029 0.023 -0.001 0.017 0.0 2.5
# Starting with semester 06B, the gain was changed x1.5 to 3.7 e-/adu
0.9.4 2006-08-16T00:00:01 2007-08-31T23:59:59 Y 23.820 0.099 -0.000 +0.021 0.011 -0.144 0.009 -0.004 0.007 +0.000 0.011 0.0 3.7
0.9.4 2006-08-16T00:00:01 2007-08-31T23:59:59 J 23.651 0.040 -0.000 +0.027 0.021 -0.114 0.019 -0.013 0.015 -0.003 0.013 0.0 3.7
0.9.4 2006-08-16T00:00:01 2007-08-31T23:59:59 H 23.811 0.063 -0.000 -0.001 0.053 -0.078 0.041 -0.039 0.052 -0.005 0.032 0.0 3.7
0.9.4 2006-08-16T00:00:01 2007-08-31T23:59:59 KS 23.083 0.049 -0.000 +0.019 0.025 -0.060 0.023 -0.029 0.023 -0.001 0.017 0.0 3.7
0.9.4 2006-08-16T00:00:01 2007-08-31T23:59:59 LOWOH1 21.008 0.072 -0.000 +0.054 0.050 -0.109 0.053 -0.017 0.056 +0.000 0.033 0.0 3.7
0.9.4 2006-08-16T00:00:01 2007-08-31T23:59:59 LOWOH2 25.0 9.999 -0.000 +0.027 0.021 -0.114 0.019 -0.013 0.015 -0.003 0.013 0.0 3.7
0.9.4 2006-08-16T00:00:01 2007-08-31T23:59:59 CH4ON 22.698 0.053 -0.000 -0.001 0.053 -0.078 0.041 -0.039 0.052 -0.005 0.032 0.0 3.7
0.9.4 2006-08-16T00:00:01 2007-08-31T23:59:59 CH4OFF 22.687 0.044 -0.000 -0.001 0.053 -0.078 0.041 -0.039 0.052 -0.005 0.032 0.0 3.7
0.9.4 2006-08-16T00:00:01 2007-08-31T23:59:59 H2 20.530 0.078 -0.000 +0.019 0.025 -0.060 0.023 -0.029 0.023 -0.001 0.017 0.0 3.7
0.9.4 2006-08-16T00:00:01 2007-08-31T23:59:59 KCONT 25.0 9.999 -0.000 +0.019 0.025 -0.060 0.023 -0.029 0.023 -0.001 0.017 0.0 3.7
0.9.4 2006-08-16T00:00:01 2007-08-31T23:59:59 BRG 20.379 0.079 -0.000 +0.019 0.025 -0.060 0.023 -0.029 0.023 -0.001 0.017 0.0 3.7
#VERSIO STARTDATE ENDDATE FILTER ZP ZP_ERR ZP_WONLC ZP_EXT1 ZP_EXT1_ERR ZP_EXT2 ZP_EXT2_ERR ZP_EXT3 ZP_EXT3_ERR ZP_EXT4 ZP_EXT4_ERR COLTERM GAIN
0.9.5 2005-11-01T00:00:01 2006-08-15T23:59:59 Y 24.289 0.099 -0.000 +0.021 0.011 -0.144 0.009 -0.004 0.007 +0.000 0.011 0.0 2.5
0.9.5 2005-11-01T00:00:01 2006-08-15T23:59:59 J 24.120 0.040 -0.000 +0.027 0.021 -0.114 0.019 -0.013 0.015 -0.003 0.013 0.0 2.5
0.9.5 2005-11-01T00:00:01 2006-08-15T23:59:59 H 24.280 0.063 -0.000 -0.001 0.053 -0.078 0.041 -0.039 0.052 -0.005 0.032 0.0 2.5
0.9.5 2005-11-01T00:00:01 2006-08-15T23:59:59 KS 23.552 0.049 -0.000 +0.019 0.025 -0.060 0.023 -0.029 0.023 -0.001 0.017 0.0 2.5
0.9.5 2005-11-01T00:00:01 2006-08-15T23:59:59 LOWOH1 21.477 0.072 -0.000 +0.054 0.050 -0.109 0.053 -0.017 0.056 +0.000 0.033 0.0 2.5
0.9.5 2005-11-01T00:00:01 2006-08-15T23:59:59 LOWOH2 25.0 9.999 -0.000 +0.027 0.021 -0.114 0.019 -0.013 0.015 -0.003 0.013 0.0 2.5
0.9.5 2005-11-01T00:00:01 2006-08-15T23:59:59 CH4ON 23.167 0.053 -0.000 -0.001 0.053 -0.078 0.041 -0.039 0.052 -0.005 0.032 0.0 2.5
0.9.5 2005-11-01T00:00:01 2006-08-15T23:59:59 CH4OFF 23.156 0.044 -0.000 -0.001 0.053 -0.078 0.041 -0.039 0.052 -0.005 0.032 0.0 2.5
0.9.5 2005-11-01T00:00:01 2006-08-15T23:59:59 H2 20.999 0.078 -0.000 +0.019 0.025 -0.060 0.023 -0.029 0.023 -0.001 0.017 0.0 2.5
0.9.5 2005-11-01T00:00:01 2006-08-15T23:59:59 KCONT 25.0 9.999 -0.000 +0.019 0.025 -0.060 0.023 -0.029 0.023 -0.001 0.017 0.0 2.5
0.9.5 2005-11-01T00:00:01 2006-08-15T23:59:59 BRG 20.848 0.079 -0.000 +0.019 0.025 -0.060 0.023 -0.029 0.023 -0.001 0.017 0.0 2.5
# Starting with semester 06B, the gain was changed x1.5 to 3.7 e-/adu
0.9.5 2006-08-16T00:00:01 2007-08-31T23:59:59 Y 23.820 0.099 -0.000 +0.021 0.011 -0.144 0.009 -0.004 0.007 +0.000 0.011 0.0 3.7
0.9.5 2006-08-16T00:00:01 2007-08-31T23:59:59 J 23.651 0.040 -0.010 +0.027 0.021 -0.114 0.019 -0.013 0.015 -0.003 0.013 0.0 3.7
0.9.5 2006-08-16T00:00:01 2007-08-31T23:59:59 H 23.811 0.063 -0.020 -0.001 0.053 -0.078 0.041 -0.039 0.052 -0.005 0.032 0.0 3.7
0.9.5 2006-08-16T00:00:01 2007-08-31T23:59:59 KS 23.083 0.049 -0.010 +0.019 0.025 -0.060 0.023 -0.029 0.023 -0.001 0.017 0.0 3.7
0.9.5 2006-08-16T00:00:01 2007-08-31T23:59:59 LOWOH1 21.008 0.072 -0.000 +0.054 0.050 -0.109 0.053 -0.017 0.056 +0.000 0.033 0.0 3.7
0.9.5 2006-08-16T00:00:01 2007-08-31T23:59:59 LOWOH2 25.0 9.999 -0.000 +0.027 0.021 -0.114 0.019 -0.013 0.015 -0.003 0.013 0.0 3.7
0.9.5 2006-08-16T00:00:01 2007-08-31T23:59:59 CH4ON 22.698 0.053 -0.000 -0.001 0.053 -0.078 0.041 -0.039 0.052 -0.005 0.032 0.0 3.7
0.9.5 2006-08-16T00:00:01 2007-08-31T23:59:59 CH4OFF 22.687 0.044 -0.000 -0.001 0.053 -0.078 0.041 -0.039 0.052 -0.005 0.032 0.0 3.7
0.9.5 2006-08-16T00:00:01 2007-08-31T23:59:59 H2 20.530 0.078 -0.000 +0.019 0.025 -0.060 0.023 -0.029 0.023 -0.001 0.017 0.0 3.7
0.9.5 2006-08-16T00:00:01 2007-08-31T23:59:59 KCONT 25.0 9.999 -0.000 +0.019 0.025 -0.060 0.023 -0.029 0.023 -0.001 0.017 0.0 3.7
0.9.5 2006-08-16T00:00:01 2007-08-31T23:59:59 BRG 20.379 0.079 -0.000 +0.019 0.025 -0.060 0.023 -0.029 0.023 -0.001 0.017 0.0 3.7
#VERSIO STARTDATE ENDDATE FILTER ZP ZP_ERR ZP_WONLC ZP_EXT1 ZP_EXT1_ERR ZP_EXT2 ZP_EXT2_ERR ZP_EXT3 ZP_EXT3_ERR ZP_EXT4 ZP_EXT4_ERR COLTERM GAIN
# Starting with semester 06B, the gain was changed x1.5 to 3.7 e-/adu
1.0 2006-08-16T00:00:01 2007-12-31T23:59:59 Y 23.700 0.055 -0.000 +0.007 0.028 -0.142 0.022 -0.022 0.030 -0.007 0.019 0.0 3.7
1.0 2006-08-16T00:00:01 2007-12-31T23:59:59 J 23.668 0.050 -0.010 +0.016 0.031 -0.114 0.026 -0.032 0.042 -0.005 0.021 0.0 3.7
1.0 2006-08-16T00:00:01 2007-12-31T23:59:59 H 23.866 0.066 -0.020 -0.02 0.04 -0.084 0.049 -0.05 0.04 -0.005 0.041 0.0 3.7
1.0 2006-08-16T00:00:01 2007-12-31T23:59:59 KS 23.097 0.052 -0.010 +0.004 0.036 -0.061 0.027 -0.032 0.036 -0.001 0.022 0.0 3.7
1.0 2006-08-16T00:00:01 2007-12-31T23:59:59 LOWOH1 21.012 0.162 -0.000 +0.016 0.031 -0.114 0.026 -0.032 0.042 -0.005 0.021 0.0 3.7
1.0 2006-08-16T00:00:01 2007-12-31T23:59:59 LOWOH2 25.0 9.999 -0.000 +0.016 0.031 -0.114 0.026 -0.032 0.042 -0.005 0.021 0.0 3.7
1.0 2006-08-16T00:00:01 2007-12-31T23:59:59 CH4ON 22.713 0.042 -0.000 -0.02 0.04 -0.084 0.049 -0.05 0.04 -0.005 0.041 0.0 3.7
1.0 2006-08-16T00:00:01 2007-12-31T23:59:59 CH4OFF 22.680 0.042 -0.000 -0.02 0.04 -0.084 0.049 -0.05 0.04 -0.005 0.041 0.0 3.7
1.0 2006-08-16T00:00:01 2007-12-31T23:59:59 H2 20.520 0.069 -0.000 +0.004 0.036 -0.061 0.027 -0.032 0.036 -0.001 0.022 0.0 3.7
1.0 2006-08-16T00:00:01 2007-12-31T23:59:59 KCONT 20.200 0.265 -0.000 +0.004 0.036 -0.061 0.027 -0.032 0.036 -0.001 0.022 0.0 3.7
1.0 2006-08-16T00:00:01 2007-12-31T23:59:59 BRG 20.355 0.100 -0.000 +0.004 0.036 -0.061 0.027 -0.032 0.036 -0.001 0.022 0.0 3.7
#VERSIO STARTDATE ENDDATE FILTER ZP ZP_ERR ZP_WONLC ZP_EXT1 ZP_EXT1_ERR ZP_EXT2 ZP_EXT2_ERR ZP_EXT3 ZP_EXT3_ERR ZP_EXT4 ZP_EXT4_ERR COLTERM GAIN
1.0 2008-02-16T00:00:01 2008-02-26T23:59:59 Y 23.864 0.028 -0.000 +0.007 0.028 -0.142 0.022 -0.022 0.030 -0.007 0.019 0.0 3.7 #measured on ext4 only
1.0 2008-02-16T00:00:01 2008-02-26T23:59:59 J 23.668 0.050 -0.010 +0.016 0.031 -0.114 0.026 -0.032 0.042 -0.005 0.021 0.0 3.7 #no measurement
1.0 2008-02-16T00:00:01 2008-02-26T23:59:59 H 23.866 0.066 -0.020 -0.02 0.04 -0.084 0.049 -0.05 0.04 -0.005 0.041 0.0 3.7 #no measurement
1.0 2008-02-16T00:00:01 2008-02-26T23:59:59 KS 23.097 0.052 -0.010 +0.004 0.036 -0.061 0.027 -0.032 0.036 -0.001 0.022 0.0 3.7 #no measurement
1.0 2008-02-16T00:00:01 2008-02-26T23:59:59 LOWOH1 21.012 0.162 -0.000 +0.016 0.031 -0.114 0.026 -0.032 0.042 -0.005 0.021 0.0 3.7 #not in
1.0 2008-02-16T00:00:01 2008-02-26T23:59:59 LOWOH2 25.0 9.999 -0.000 +0.016 0.031 -0.114 0.026 -0.032 0.042 -0.005 0.021 0.0 3.7 #not in
1.0 2008-02-16T00:00:01 2008-02-26T23:59:59 CH4ON 22.743 0.035 -0.000 -0.02 0.04 -0.084 0.049 -0.05 0.04 -0.005 0.041 0.0 3.7 #measured on ext4 only
1.0 2008-02-16T00:00:01 2008-02-26T23:59:59 CH4OFF 22.719 0.048 -0.000 -0.02 0.04 -0.084 0.049 -0.05 0.04 -0.005 0.041 0.0 3.7 #measured on ext4 only
1.0 2008-02-16T00:00:01 2008-02-26T23:59:59 H2 20.568 0.023 -0.000 +0.004 0.036 -0.061 0.027 -0.032 0.036 -0.001 0.022 0.0 3.7 #measured on ext4 only
1.0 2008-02-16T00:00:01 2008-02-26T23:59:59 KCONT 20.200 0.265 -0.000 +0.004 0.036 -0.061 0.027 -0.032 0.036 -0.001 0.022 0.0 3.7 #not in
1.0 2008-02-16T00:00:01 2008-02-26T23:59:59 BRG 20.403 0.015 -0.000 +0.004 0.036 -0.061 0.027 -0.032 0.036 -0.001 0.022 0.0 3.7 #measured on ext4 only
#VERSIO STARTDATE ENDDATE FILTER ZP ZP_ERR ZP_WONLC ZP_EXT1 ZP_EXT1_ERR ZP_EXT2 ZP_EXT2_ERR ZP_EXT3 ZP_EXT3_ERR ZP_EXT4 ZP_EXT4_ERR COLTERM GAIN
1.5 2008-02-16T00:00:01 2008-10-27T23:59:59 Y 23.819 0.059 -0.000 +0.007 0.028 -0.142 0.022 -0.022 0.030 -0.007 0.019 0.0 3.7
1.5 2008-02-16T00:00:01 2008-10-27T23:59:59 J 23.726 0.040 -0.010 +0.016 0.031 -0.114 0.026 -0.032 0.042 -0.005 0.021 0.0 3.7
1.5 2008-02-16T00:00:01 2008-10-27T23:59:59 H 23.896 0.047 -0.020 -0.02 0.04 -0.084 0.049 -0.05 0.04 -0.005 0.041 0.0 3.7
1.5 2008-02-16T00:00:01 2008-10-27T23:59:59 KS 23.134 0.042 -0.010 +0.004 0.036 -0.061 0.027 -0.032 0.036 -0.001 0.022 0.0 3.7
1.5 2008-02-16T00:00:01 2008-10-27T23:59:59 LOWOH1 21.012 0.162 -0.000 +0.016 0.031 -0.114 0.026 -0.032 0.042 -0.005 0.021 0.0 3.7
1.5 2008-02-16T00:00:01 2008-10-27T23:59:59 LOWOH2 25.0 9.999 -0.000 +0.016 0.031 -0.114 0.026 -0.032 0.042 -0.005 0.021 0.0 3.7
1.5 2008-02-16T00:00:01 2008-10-27T23:59:59 CH4ON 22.775 0.041 -0.000 -0.02 0.04 -0.084 0.049 -0.05 0.04 -0.005 0.041 0.0 3.7
1.5 2008-02-16T00:00:01 2008-10-27T23:59:59 CH4OFF 22.750 0.052 -0.000 -0.02 0.04 -0.084 0.049 -0.05 0.04 -0.005 0.041 0.0 3.7
1.5 2008-02-16T00:00:01 2008-10-27T23:59:59 H2 20.600 0.047 -0.000 +0.004 0.036 -0.061 0.027 -0.032 0.036 -0.001 0.022 0.0 3.7
1.5 2008-02-16T00:00:01 2008-10-27T23:59:59 KCONT 20.200 0.265 -0.000 +0.004 0.036 -0.061 0.027 -0.032 0.036 -0.001 0.022 0.0 3.7
1.5 2008-02-16T00:00:01 2008-10-27T23:59:59 BRG 20.441 0.050 -0.000 +0.004 0.036 -0.061 0.027 -0.032 0.036 -0.001 0.022 0.0 3.7
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