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Eli Rykoff, 10/31/2013 04:58 PM


On the Bias Jumps

-Eli Rykoff

Something strange is going on with the bias jumps at 2048...

I'm taking as an example 180985, CCD 41, somewhat arbitrarily.

I use swarp to subtract the sky and rebin to a 2" scale to highlight the sky levels. This is the finalcut image which shows the problem:

But if we go back to the raw_obj image (same scaling) which has had DECam_crosstalk run on it then it looks fine! (Well, it could use a good flat-fielding).

Similarly, the raw-raw image looks fine (though it's hard to get the scaling right because of the dynamic range).

So this is being inserted into the image somewhere along the line...Alex suspects the flat field...

Looking at the flat field applied to this image:

https://desar2.cosmology.illinois.edu:7443/DESFiles/desardata/OPS/red/20130725170742_20130217t0227/flatcor/flatcor_i_41.fits

And rebinning we see:

A-ha! A bias jump made its way into the flat field and has now corrupted the downstream images.