Detector

There is a recurrence of some low level pick-up noise with the ALFOSC CCD. This has been there in the past and had disappeared, but it has shown up again (be it at a lower level then before). In some exceptional cases this can effect observations. Several tests were made but no obvious cause or solution has been found.

Occasionally also horizontal ``stripes'' are seen in ALFOSC images. The lines appear to have values corresponding to the previous exposure (e.g., a bright ``stripe'' if a bias frame is taken after a flat field image, or a dark ``stripe'' if a flat is taken after a bias frame) and this does not seem to be limited to using either the normal data acquisition program or the fast-photometry program, nor using the corresponding sequencer boards. Investigation the stripes has been inconclusive. Images with the CCD disconnected show no structure implying no problems with the controller or up-stream electronics.