Star mapper photometric calibrations
The star mapper photometric calibration split into four cases, depending on slit group and field of view. The model used is relatively simple, with up to second order dependencies in colour and across-scan coordinate. There is considerably less loss of transmission through radiation damage here (see figure below), as there is very little optics involved.
Examining the dependencies of the calibration on the colour index V-I, it is clear that there are small passband differences between the raw data as collected by the different combinations of slit group and field of view, as shown in the figure below. It is possible that the short-time-scale variations in the calibration are linked to colour coverage by the calibration stars rather than actual variations in the instrument.
Epoch observations for star mapper data can be linked to calibration values using the orbit numbers.