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ESO Faint Object Spectrograph and Camera

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CCD#40 Cosmetics

Bad Pixel Map

Shown below is a map of the bad pixels on CCD #40. This plot was generated in the following way:

High intensity normalised flatfields in each of the UBVRi bands (binned 2x2) were filtered to distinguish 2 groups of pixels

the good pixels, with values in the range 0.85 - 1.15 (15% deviation from unity gain). These comprised 97% of all the pixels on the CCD in each of the filters. The pixel intensity histograms of the flat fields were examined; the above limits correspond to the envelope of the central peak of the distribution.
the bad pixels, with values outside the above range. As is obvious from the plot below they are to be found mostly on the margins and along a few well defined "bad-columns".

A "common" bad pixel map for CCD#40 was generated by making a union-set of the 5 individual bad pixel maps. To improve visibility, on this plot, this last image was boxcar-averaged with a 5x5 window.

It may be noted that the above procedure exagerrates the extent and hence improves the visibility of each bad pixel cluster. This was needed to make them visible on a compressed plot. The number of bad pixels in any single filter will be less than in the above combined plot. Further, a rather conservative limit has been chosen to define "good pixels" (within 15% of unity gain).

The Point is: CCD#40 has (but is not just) a pretty face! Apart from a sprinkling of bad pixel clusters, most of which are just 1-5 pixels in size, all the others are concentrated either on 3 (and a quarter) columns or are on the margins.

A more detailed view in each individual filter may be had by downloading the following files :

However the above files are between 2 and 3 MB in size. Listed below is a filtered version of the same (to change real numbers into a small set of integers to reduce the size drastically) which are between 10 and 45 KB in size. The intensity code in the images is as follows :

Intensity range on the flatfield	Corresponding value on the Filtered Image
< 0.55	5
0.55 - 0.65	6
0.65 - 0.75	7
0.75 - 0.85	8
0.85 - 0.95	9
0.95 - 1.05	10
1.05 - 1.15	11
1.15 - 1.25	12
1.25 - 1.35	13
1.35 - 1.45	14
> 1.45	15

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Last modified: Tue Jan 15 20:06:39 CLST 2002