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WIRCam on the Canada-France-Hawaii Telescope
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Upper
End |
WIRCam mounts on the "old" CFHT prime focus upper end (PFUE),
previously used with the CFH12K and UH8K
cameras (and in much earlier days with photographic plates).
The old optical corrector has been removed (now precluding use
of CFH12K as a backup for MegaPrime),
and CFHT staff has thoroughly renovated the mechanical and electrical
environment of the upper end. In addition to its basic structure, the
PFUE provides a temperature controlled environment for WIRCam and its
readout electronics, and brings the instrument into focus.
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Image
Stabilizing
Unit |
The Image Stabilizing Unit (ISU) has been designed
and built at
Observatoire de Paris.
It is used to produce small corrections of the image position on the focal
plane of WIRCam: a glass plate in the optical beam in front of the camera can
be tilted, to produce a displacement of the image proportional to the small
angle of the tilt. The guiding signal is obtained from the scientific
detectors themselves, on which a small guiding window can be read out at
a high rate. The guiding window can be positioned anywhere within the
detector.
Tip-tilt plate: fused silica
Diameter: 175 mm
Thickness: 20 mm
Motion amplitude: +/- 0.9 degree (or +/- 1.5 arcseconds on the focal
plane)
Image correction bandwidth: up to 5 Hz
Internal loop frequency: >50Hz |
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| Detectors |
The detectors at the heart of WIRCam are
HAWAII-2RG
detectors, produced by
Rockwell Scientific.
| Detector type: HAWAII-2RG
Number of detectors: 4
Detector size: 2040 x 2040 active pixels
(reference pixels border the array and 2048 x 2048 are effectively read)
Pixel size: 18 micrometers
Pixel scale: 0.307 arsecond/pixel
Operating temperature: 80 Kelvin |
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| Optics |
The optics which focuses the infrared light on the WIRCam
detectors was designed and assembled by the Groupe d'Astronomie of
Université de Montréal and the Institut National d'Optique. in
the city of Québec. It consists in 8 lenses plus the cryostat window. To
minimize its own emission the optics is housed inside the WIRCam cryostat. It
is therefore subject to significant thermal contraction, and its large physical
size made this an interesting mounting challenge.
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| Mechanics |
The mechanical structure of WIRCam and its cryogenic
systems were designed by the
Laboratoire d'Astrophysique de Grenoble.
The structure was optimised to have extremely low flexures, and the large
filter wheels to have reliable fast movements in the cold (15s maximum
time for filter changes).
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