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Policy on Skyflats (A. Walker)

Regulations (10-Nov-2012)

The DECam CCDs can be damaged by exposure to very bright light. Tests indicate that only the daytime sky should be bright-enough to cause the problem. Three photodiodes on the focal plane monitor the amount of light and will cause the CCD electronics to be powered off in the event that the CCDs are exposed to a bright sky. However, because CCD 61 (N30) appears to be damaged shortly after a bright morning skyflat we are providing the following regulations.

Note that it has been shown that the DECam dome flats are as good as the sky flats on the scale that the sky is uniform.

  1. Twilight sky flats (evening or dawn) are forbidden.
  2. On-sky observing will start no earlier than 30 minutes after sunset and will finish no later than 30 minutes before sunrise. The telescope operator will advise the astronomer of these times.
  3. Before the dome is opened, at any day time between the above limits, the person opening the dome will check on the DECam Guis whether VSUB is OFF and the blank filter is in the beam. This includes opening the dome to allow the telescope dome to ventilate prior to observing, and when extra light is needed in the dome for daytime work.
  4. Before turning on the lights in the dome, check that no calibrations are underway and that the shutter is closed and VSUB is OFF.
  5. Please use the "Calibrations warning signs" on the console and in the elevator. Any calibrations running in the morning after observing must finish before 08:00 a.m. unless arrangements have been made with the TelOps Manager the previous day.

Any questions, please ask me.

Thank you for your cooperation.

Alistair