
CFH12K Filter Calibration Coefficients from Elixir

The CFH12K photometric calibration coefficients are given below,
assuming the Elixir normalization is used. Note that, for a mosaic
camera, there is a ambiguity of how the different chips in a
flatfield images are to be normalized. For Elixir, normalize a
specific chip (04 in the case of CFH12K) to have a median value of
1.0. We force all chips to have the same number of input photons (by
stacking the same numbers of input images) and normalize the other
chips to match the normalization of the reference chip. The result is
equivalent to treating the mosaic as a single, large collection of
pixels.
filter 
C_{Λ} 
K_{Λ} 
X_{Λ} 
color 
B  26.017  0.15  0.016  BV 
V  26.220  0.12  0.008  BV 
R  26.190  0.09  0.028  VR 
I  26.185  0.04  0.107  RI 
Z  25.830  0.03     
Given m DN per second through the given filter, in an image
taken at airmass z, for a star of the given color (in the
target magnitude system), the magnitude M of a star in
the Landolt (Johnson / KronCousins) system is given by:
M = m + C_{Λ} + K_{Λ}(z  1) +
X_{Λ}color
It is also possible to define alternate color terms from those given
above. Below we list all possible color terms for the four
JohnsonKronCousins bands BVRI and their CFH12K parameters. Since
the colors of stars are highly correlated, these have been determined
by fitting a line to the colors terms of the Landolt reference stars
and adjusting the above parameters based on this fit. This adjustment
does not strongly affect the zero point (C_{Λ}) because
stars of color 0.0 in one filter are nominally assigned to color 0.0
in all other filters. There is an obvious shift in the color slope
(X_{Λ}color) resulting from the different typical
ranges for different colors.
filter 
C_{Λ} 
K_{Λ} 
X_{Λ} 
color 
B  26.017  0.15  0.010  BR 
B  26.017  0.15  0.008  BI 
V  26.220  0.12  0.014  VR 
V  26.220  0.12  0.007  VI 
R  26.189  0.09  0.031  RI 
R  26.190  0.09  0.010  BR 
I  26.187  0.04  0.050  VI 
I  26.187  0.04  0.026  BI 

