[Comm2011] VST rotator offset

[Konrad Kuijken]

Dear all,

I've visually gone through the observations since June 10 that I have - about 860 frames, to look for rotator misalignment. Procedure very simple:
Put chips 73 and 80 (left and right edges of the mosaic) side by side, overplot catalogue positions of stars based on the WCS in the headers, and look for a misalignment.

The result is attached as a long list - a filename without comment shows no rotation, an 'r' means obvious rotation (about 1 degree) and a '.' means I could not measure it.

It is clear the effect was already there in June, and it seems to be related to presets. It really is bimodal: either there is an offset of about 1 degree, or there is not. I have not found examples of serious trailing (strong elongation of the stars) that would come from an error in rotator tracking.

Hope this is useful in diagnosing and fixing the problem.

Attached: the list of results, and a couple of inspect images - one showing rotation, one not.

Konrad


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