Detector

MOSCA ran for almost two years without problems and then the intermittent failure of one of the CCDs returned. The detector stopped working at specific orientations of the instrument. During tests in the lab it was found the error could be reproduced by simply moving the internal dewar wires to the CCD.

In April 2009 it was finally decided to get replacement wires, which were made in Copenhagen sent down and installed. In the 10 observing nights following the installation the problem has not returned. It was also interesting to note that after the new wires were installed another problem associated with a variable bias level for the same CCD seems to have corrected itself and returned to the post-commissioning value.