The frames within each set were combined.
In this process, values in pixels affected by cosmic-ray-events
The bias level is around 124.2 ADU, but it is not the same in the 6
sets, it varies within
There is a positive gradient in the y-direction,
but the slope is not the same
for the 6 sets, it ranges from 0 to 0.5 ADU over the length of the chip
There is no simple relation between the change of level and gradient,
These two phenomena are illustrated in Figure .
As can also be seen in Figure (left), there are some stripes which run along y (i.e., across x). They are the same in the 6 frames, and are part of the bias image.
All the 6 frames were combined into one (weighting by the number of frames they had been made from). No further processing was done. We would have liked to smooth the image to remove the pixel-to-pixel noise, but since we believe the stripes to be part of the bias image, we could not do that. The mean bias level is 124.2 ADU/pixel. The standard deviation on the final bias image in areas between the vertical stripes is 0.31 ADU/pixel.
Properties of E and S0 Galaxies in the Clusters HydraI and Coma
Master's Thesis, University of Copenhagen, July 1997
Bo Milvang-Jensen (firstname.lastname@example.org)