Detector

After having performed well since its installation the science array started to malfunction early in the semester when it was found with one of its four quadrants dead. Shortly before that NOTCam had warmed-up, after which it was pumped and re-cooled according to normal procedures. The remaining 3 quadrants performed well and observations were performed with modified dither scripts to keep the targets always inside the three working quadrants. No observing time was lost. After this NOTCam was warmed up and opened for investigation. A number of tests of the various components gave no obvious results and in the warm state none of the quadrants worked well.

Another pump and cool cycle showed that all quadrants were malfunctioning at operating temperature, and it was decided to mount back the engineering grade array and send the science array to Rockwell for further inspection. The Rockwell experts found cracks in the multiplexer in two of the quadrants and some gold bonds lifted. It is not entirely clear what caused the cracks, but neither manufacture errors nor the long-time storage in humid conditions (in the bank deposit box) were excluded by Rockwell.

The Hawaii-I arrays are no longer in production, but Rockwell offered us one of 4 available science grade arrays at a reduced price. We selected the best one according to lab measurements of QE and noise performance. The new array arrived in the beginning of Oct-06 and is currently stored safely and in very dry conditions. It will be mounted in NOTCam after an upgrade of the electronics (see below).

The engineering grade array continues to perform well, but with its limitations in sensitivity, flatness and linearity performance compared to the science array.