NOT CCD4 (HiRAC), details:

Notices:

25 Feb 1999: The flat field of this CCD appears to have changed as of 15th Feb 1999. Because the CCD requires O₂ flooding as part of the backside passivation, the flat field is not absolutely stable from run to run (or, more precisely, from cool-down to cool-down). Normally, any changes will be invisible except upon dividing one run's flat field by that of another and even then the effects may be negligible. However, as of February 1999, an unusual pattern has appeared in the upper right corner of the CCD flat field. The quantum efficiency of the region is reduced by approximately 10%. Its qualitative appearance suggests that it may be the result of contamination of the detector. At the time of writing, we are investigating possible causes. The affected area is small and unlikely to affect observations.

Summary of properties:

Oxygen Soaking

• Preparing CCD#4
• Failed O₂ Soak

Because this device uses the PPt passivation technology, it requires soaking in oxygen before cooling in order to achieve the best possible QE sensitivity and uniformity. Occasionally, this can fail. In this case, the flat field will be very non-uniform with a number of sensitive patches distributed over a much reduced overall sensitivity. For sample images, look here. Normally this will be caught before the observer arrives at the telescope to use the instrument.

Other Literature:

• In situ test results
• Pre commissioning report (HTML).
• Pre commissioning report (gzipped postscript).

Links

• Steward Observatory CCD Lab - where the device was thinned.