GMOS-S CCD Intervention

The Gemini Multi-Object Spectrograph (GMOS-S) instrument at Gemini South has, for some time, suffered from instabilities in the charge-coupled device (CCD) readout. Since the installation of the Hamamatsu CCDs, they have been performing sub-optimally. In particular, we have seen instances where the charge transfer efficiency became too large, causing smearing on the images, which affects the popular nod-and-shuffle mode of the instrument. We have been planning to tackle this issue by changing the existing electronics board inside the cryostat with one of a better design. This design has been proven to work for the GMOS-N instrument at Gemini North, which does not experience the same smearing effect. The critical and very sensitive intervention was carried out last week. The technical intervention went very well and the first lab tests show very promising results. We expect that GMOS-S will be back in normal operation shortly.