Fig. 9.

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Two examples of common reflected light artefacts in IGAPS imagery. Left: ghost on image r372056, CCD#4, due to a bright star. We see that the stray-light image even picks up details of protruding cabling at the prime focus of the INT. Part of a much fainter ghost can be seen at the top right. Right: example of a halo around a bright star fooling the HAGRID selection from r541554, CCD#3. Source positions selected by HAGRID are shown as red numbered circles. They crowd into the faint extended halo that is a little offset from the star position. A larger stellar mask for bright stars and the rejection of ‘star-like’ selections as described in Sect. 7.2 helps eliminate these. The blue circles mark identified count minima that are stored as potential sky fibre positions.
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