| Passband | Zero-Point | Date | Colour terms | . | . | . |
|---|---|---|---|---|---|---|
| RGO U | 22.37 | Oct 98 | -0.01 U-B | - | - | - |
| - | 22.23 | Dec 98 | -0.08 U-B | - | - | - |
| - | 22.36 | Feb 99 | -0.12 U-B | - | - | - |
| - | 22.30 | Jun 99 | -0.09 U-B | - | - | - |
| KPNO B | 24.70 | Oct 98 | - | -0.09 B-V | - | - |
| - | 24.61 | Dec 98 | - | -0.17 B-V | - | - |
| - | 24.60 | Feb 99 | - | -0.10 B-V | - | - |
| - | 24.51 | Mar 99 | - | -0.13 B-V | - | - |
| - | 24.50 | Apr 99 | - | -0.16 B-V | - | - |
| - | 24.41 | Jun 99 | - | -0.19 B-V | - | - |
| Harris V | 24.51 | Oct 98 | - | - | +0.03 V-R | - |
| - | 24.42 | Dec 98 | - | - | -0.04 V-R | - |
| - | 24.42 | Feb 99 | - | - | -0.01 V-R | - |
| Harris R | 24.46 | Oct 98 | - | - | +0.02 V-R | - |
| - | 24.13 | Dec 98 | - | - | +0.00 V-R | - |
| - | 24.38 | Feb 99 | - | - | -0.01 V-R | - |
| RGO I | 23.77 | Oct 98 | - | - | - | -0.02 R-I |
| - | 23.66 | Dec 98 | - | - | - | -0.07 R-I |
| RGO z' | 22.08 | Oct 98 | - | - | - | -0.52 R-I |
| - | 22.20 | Dec 98 | - | - | - | -0.39 R-I |
| - | 22.24 | Feb 99 | - | - | - | -0.26 R-I |
| - | 22.16 | Apr 99 | - | - | - | -0.55 R-I |
| - | 22.16 | Jun 99 | - | - | - | -0.49 R-I |
| SDSS g' | - | - | - | - | - | - |
| SDSS r' | 24.31 | Mar 99 | - | - | +0.23 V-R | - |
| - | 24.30 | Apr 99 | - | - | +0.18 V-R | - |
| - | 24.24 | Jun 99 | - | - | +0.27 V-R | - |
| SDSS i' | 23.74 | Feb 99 | - | - | - | +0.21 R-I |
| - | 23.56 | Jun 99 | - | - | - | +0.21 R-I |
Notes to table:
An example use of the zero points and colour terms for each passband is
given below:
B'_ccd = 24.51 - 2.5 log10(counts/s) = B - 0.13 B-V
where B'_ccd is the natural CCD + filter system and B, B-V are on
Landolt's 1992 system.
Average extinction coefficients for La Palma of: U = 0.49, B = 0.25, V = 0.15, R = 0.11, I = 0.07, Z = 0.08, have been assumed for the photometric nights used to derive the zero-points and colour terms.
The Z'-band zero-point is in the natural WFC filter + CCD passband and has been approximately normalised to the Vega system using an extrapolated colour correction.
The effective gain (e-/ADU) of the system is 3.12 so to convert the zero-points to photons/s add 1.24 magnitudes.
Some of the zero-point variations are due to the independently derived colour terms for each WFC run. An attempt was made to use only photometric nights in deriving the zero-points but this was not possible for some runs eg. Dec 98 R-band.