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More on scattered light

Early polarimetric tests showed the presence of a considerable scattered component with some structure. We have conducted experiments to identify the source of the scattered light, with a view to eliminating it. We identified several distinct modes of scattering, each of which can be quantified to a large extent from our data. They include:

Since CCDs are preferentially red-sensitive, one is more likely to run into scattered-light problems when observing in the blue, particularly if the source is strong in the red. The evidence indicates that light just longward of where the recorded spectrum stops is the worst culprit. At present this is all the guidance we can give, but the question is being actively pursued. For quantitative estimates and detailed structure of the scattered light, we obtained (in February 1991) over 400 CCD frames under various conditions of illumination and spectrograph settings. This database is slowly being analysed and is available to users via the LPO archive at RGO; it includes an ASCII observing log.


next up previous contents
Next: How to measure CCD Up: No Title Previous: Dekkers

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Tue Oct 7 17:34:45 BST 1997