A dark exposure made in mpp+ mode at -100^\;
C is shown in figure
10. The image has not been bias subtracted. Along the edges,
dark current is increased where the CCD is not thinned, as here is
more Silicon in which a spontaneous free electron can appear.
Almost no cosmic hits appear as single pixel events, due to the MTF
problem.
A group of hot pixels are around (1388,1190), also increasing the level of
the column at this location.
In mpp+ mode, the dark current is measured to 1e
/hour, while in
mpp- mode the dark current increases to 6e
/hour.
Figure 10:
A 20 minute dark exposure. Outside the thick edges and the single hot
column, dark current is low and uniform. Cosmic hits appear stellar-like
due to the poor MTF.