WFCAM Instrument Overview
The WFCAM is an ambitious instrument which will give the UK and
ESO the most capable IR survey facility in the world. The instrument
consists not only of a cryogenic camera holding four state-of-the-art
detectors, associated electronics and computing, but also large
fore-optics including a new f/9 secondary and a complete autoguiding
system. A substantial data centre and archive will be established
within the UK wide-field astronomy groups.
- Four 2048 x 2048 Rockwell detectors spaced by 94%
- 1-2.5 microns operation (JHKY, narrowband and Z band filters)
- 0.4" pixels giving single-exposure area coverage of 0.19 sq.
- tip-tilt secondary platform to give best possible image quality
- microstepping to ensure proper sampling of the psf
- Forward-Cassegrain quasi-Schmidt camera design
- includes re-imaged pupil and cold stop for maximum K-band sensitivity
- optical rms image quality <0.26 arcseconds rms.
- 1 degree diameter field
- Four Rockwell 2048 x 2048 detectors
- PACE technology rather than MBE for lower cost, less risk.
Electronics and computing
- array-limited read-out times (1-2 seconds).
- design uses four completely parallel channels - one per detector
- 128 channel SDSU system to be used
- will handle 120 GBytes/night (3 Tbyte on-line tape systems currently
- real-time data pipeline processing to fully reduced frames
- object extraction, precision astrometry and photometry to be
done off-line. This will be handled by UK Wide Field Astronomy
groups and is not part of the instrument project.
Focal plane layout
In the preferred configuration four detectors are spaced by 94% of
their active area. Four exposures are then required to achieve a
square. Assuming the baseline pixel size of 0.4 ² per pixel,
then four interleaved exposures give a filled square of 0.865°
on a side (0.75 sq. degrees) as shown in the figure above, and a
single exposure covers an equivalent area of 0.19 sq. degrees.