The CCD Hardware: Cooling and Pumping

The CCD system is a SITe back-illuminated 2kx4k chip with 15 micron (1.45 arcsec) pixels, run by a Leach version 2 controller. Its long (4096 pixel) axis is oriented E/W. The CCD reads out through two amplifiers and readout time is about one minute. Gain is fixed and is very close to 2 electrons per ADU. Full well capacity is at least 100,000 electrons. The ADC is 16 bits, ie from 0 to 65K. Bias level is about 7000 counts. Readout noise is around 12 electrons.

There appears to be some cross-talk between the two amplifiers. This will need to be measured, and incorporated into the reduction.

The shutter speed correction is small, less than 0.04s. Paul Harding believes that it has an "odd even" effect due to the direction of the shutter moving.

Pumping down the dewar

Filling the dewar with LN2

Dry Nitrogen Bottles

We use dry nitrogen in the dome for two reasons:
  1. when filling the dewar, it is sometimes necessary to pressurize the liquid nitrogen storage tanks. When the tanks are full there may not be sufficient gas volume to maintain pressure during a fill.
  2. to keep the dewar window free of moisture, dry nitrogen flows across the window. This is only necessary in humid conditions. In this case the flow rate of 0.5 on the flowmeter near the south pier is sufficient.
The main valve on the dry nitrogen tanks downstrairs (located at the bottom of the spiral staircase) should be turned off whenever dry nitrogen is not being used. It is particularly important to remember to turn the main valve off at the end of your observing run.

When the nitrogen tank is empty, mark it empty with chalk or masking tape and pen. Turn off the main valve on the top of the bottle. Use the wrench provided to remove the regulator from the empty bottle, and attach it to the new one.

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