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Flatfield Features

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GMOS-N flatfield features introduced with the Hamamatsu CCDs

There are a number of new flatfield features seen in the GMOS-N Hamamatsu CCDs commissioned in 2017A.  There is currently less dust visible in the field than with the previous arrays, and there is no longer a "dust bunny" feature (see below).

GMOS-N flatfield features introduced during August 2006 shutdown

August 30, 2006

GMOS-N was removed from the telescope July 31, 2006 as part of an extensive Gemini North shutdown period. GMOS-N was mounted on the telescope (port 5, same as previously) again on August 9. The first science data was obtained the evening of August 16 (UT August 17).

Unfortunately, at some point during this time a large flatfield feature was introduced into the GMOS-N optical path. A series of tests has determined that this feature:

  • extinguishes ~2.5-3% of the incident light at the darkest point
  • is present in all filters
  • does not move around with either telescope position or cass rotator angle
  • is located within GMOS-N somewhere downstream of the grating/mirror turret
  • is not located on the detector package
  • is most likely located within the GMOS-N camera
  • appears to flatfield out quite well when appropriate twilight flats are used
  • does not flatfield out when domeflats are used

It is very important that GMOS-N users take care to use appropriate baseline twilight flats when reducing their data: All GMOS-N data taken since and including August 17, 2006 UT should be flatfielded with twilight flats also obtained after and including August 17, 2006 UT.

Further details and images are provided below. Please note that, while we suspect that this feature arises from dust somewhere in the camera, the affectionate term "dustbunny" is not intended to imply that we actually are aware of the nature of the substance causing the new GMOS-N flatfield feature as yet.

Gemini Observatory Participants