GeminiFocus July 2016 | Page 14

dered our progress on the many programs scheduled for this semester. The good news is that, as reported in the April 2016 issue of GeminiFocus, we have begun adjusting the queue filling to account for the typical pattern of bad weather at Gemini South. So, fortunately, the queue was not overloaded in May as it had been in the past. Figure 2 (left). The new camera cold head (green mechanism, at bottom). Above it is the gate valve baffle, which is employed during MOS mask swaps due to previous thermal background issues. Photo Credit: Gabriel Perez/ Gemini/AURA Figure 3 (right). The MOS wheel (larger segmented black wheel, in front, showing slots for MOS masks) and Dekker wheel (smaller black wheel, behind). Photo Credit: Gabriel Perez/ Gemini/AURA 12 FLAMINGOS-2 Stand-down Completed In May, we removed FLAMINGOS-2 from the Gemini South telescope for a preventative maintenance stand-down. Moving to dedicated instrument stand-downs ensures that key resources and the laboratory environment are available without competing against other important tasks. This has been an issue during other single annual telescope shutdowns. A large team of engineers, technicians, and science staff completed a variety of tasks. First they replaced the instrument’s three coldheads (one is shown in Figure 2), which were approaching the end of their lifetime; indeed, the coldheads should keep the detector at a selectable temperature, but we have seen the temperatures gradually in- GeminiFocus creasing. Replacing coldheads might sound easy, but accessing and replacing them requires dismantling the instrument. Another outstanding issue was addressed by fixing the On-Instrument WaveFront Sensor used to measure distortions at the instrument imaging plane. Careful testing and analysis revealed an electronics problem, which we resolved. We also thoroughly tested all mechanisms, which raised some additional suspicions during the movement of the Multi-Object Spectroscopy (MOS) wheel (Figure 3). Further inspection indicated significant wear in some of the ball bearings, so all were replaced. The team then reassembled and successfully tested the entire mechanism. Finally, the instrument was cooled down, first with liquid nitrogen in the lab, before we connected it to the helium compressors on the telescope. We returned FLAMINGOS-2 to the telescope, tested it during the night, and cleared it for scientific operation. With this success, a large period of intensive work came to an end. The instrument should benefit from reliable operations for the coming semesters, and we can now begin working on the commissioning of the MOS observing mode. Weather permitting, we expect to be commissioning MOS mode in July and August of this year. July 2016