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GMOS-S CCD2 issues

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The repair attempted during July was not successful, and the problem on CCD2 (amplifier #5) persists. On the other hand, the noise patterns on CCD2 and CCD3 are gone.

The situation will remain like this during semester 22B since the only possible solution requires a major intervention, which is not planned for the current semester.

Users are advised to choose an appropriate dither strategy (*) minimizing the effects of the bad amplifier on their science data and/or to place targets or spectral features of interest on other parts of the detector. See this document for further description (note that the noise patterns are gone though, as mentioned above). For MOS and IFU-R, the same strategy can be applied as well. The main additional difficulty is the wavelength calibration since some arc lines are wiped out and the autoidentify task may fail. In this case, the lines identification has to be done interactively. It can also work for IFU-2 in some cases; it was successfully tested with B600. Note that for IFU-2, the situation is more delicate since the lost spectral interval is a bigger portion, therefore the wavelength calibration is more likely to fail for the red slit. 

(*) For dithers we recommend +/-30 arcseconds in P (across the detector columns) in the case of imaging, and for spectroscopy a spectral dither size of at least +/-15nm for B1200, +/-25 nm for R831, +/-30nm for B600, and +/-45nm for R400. For the R150, setting a central wavelength  ~930nm, the full R150 spectral coverage can be accommodated in extensions 6-12 (alternatively, a +/-120nm dither can be used).

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