Calibrations
PQ objects were matched to primary objects from SDSSDR6 which were classified
as stellar in all 5 SDSS bands.
At least 15 matched stellar objects were required on each frame that was
retained.
Zero-point offsets and aperture corrections were
obtained and applied to these object on a chip/frame basis. Median offset from
SDSS was then determined:
ZPshift = median(SDSS-PQ)
The following second order calibration terms were determined as a function of
chip:
- Nonlinearity terms.
- Color dependences
- X-dependences (where X is in the declination direction, perpendicular to
drift scanning)
The corrections were applied in the correct order to get the final numbers.
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