Pat Roche (Oxford) is currently building an infrared camera for the WHT, based on the design of UKIRT's IRCAM-3, and using the dewar from UKIRT's IRCAM-1. Although primarily intended as the detector for a Martini-like Adaptive Optics system (currently being built at Durham), it will also be offered as a common-user instrument for imaging. (Unfortunately none of the WHT spectrographs would be suited to IR spectroscopy with this camera.) Initially WHIRCAM will be mounted at GHRIL, as it's closed-cycle cooling pump exchanges heat with high pressure helium delivered via a flexible hose from a compressor. This means that to mount the IR camera at cassegrain will require a special hose-feeder, as the cassegrain cable wrap is too small for the minimum curvature limits of the He hose.
WHIRCAM: The dewar/cryostat is that of UKIRT's old IRCAM-1, but with a doublet lens mounted in an extended cold `snout'. The doublet (40 mm diam) collimates an expanding f/11 input beam, producing a 16 mm diameter cold stop at the secondary image (lyot stop), located between the filter wheels [ I J H K L' K-short plus K-narrow band at S(1), H and Br() lines] and a triplet lens. The triplet converts the collimated beam to f/5.5, giving an image scale on the detector of 0.27 arcsec/pix, and a FOV of 68x68 arcsec. [With Martini-3, a pair of mirrors prior to the telescope's focal plane will f-convert from f/11 to f/55, resulting in a 3.3 mm diameter cold stop, achieved with a small aperture in the second filter wheel, and an image scale of 0.05 arcsec/pix --- the WHT diffraction limit is 0.13 arcsec at K and 0.08 arcsec at J.] The cold snout is about 130 mm long and attaches to the front of the dewar. The front of the snout is 137 mm beyond telescope focus, and the detector is 316 mm beyond the front of the cold snout. The dewar itself is 380x380x240 mm (XYZ), with the optical axis 100 mm above the bottom of the dewar. Preamps are mounted in a 100 mm cubed box attached to the rear of the dewar. The closed-cycle coolant pump is about 400x400x480 mm, and attaches to the top of the dewar. The dewar plus c-c-c pump weigh 67 kg. Heat from the c-c-c pump is extracted by compressed He attached to the pump via two flexible hoses attached to a compressor (a cube about 400 mm per side, which consumes about 1.5 kW).
Detector: 256x256 InSb array, 30m pixels, cooled to 35K by a closed cycle high pressure He cooling system. Typically, qe 80%, dark current = 1 e/s, readout noise = 30 e, and wavelength range = 0.8 - 5.5 m (if the thermal background of WHT is too high for this to be possible, imaging will be restricted to a wavelength range = 0.8 - 2.3 m = J to K).
Electronics: The readout/detector control is a virtual copy of the ALICE rack built for UKIRT's IRCAM-3 (and CGS-4), which is controlled by a DEC VAXstation 4000 via Ethernet. The chip can also be continuously displayed via 3 coax cables to an RGB monitor. Control software is a copy of UKIRT's IRCAM-3, except for the stepping motor controllers (two filter wheels and one focus) and the telescope interface (for writing coords, etc to the headers).
Timescale: WHIRCAM is expected to be completed by December 1994, and ready for commissioning on the WHT in February and June 1995.
Magnitude Limits: Based on the performance of IRCAM3 on UKIRT (courtesy of Colin Aspin, JAC), and assuming the same sky brightness and extinction as at Mauna Kea, estimates of saturation and limiting magnitudes are (but note that these are rough estimates only):
For a minimum exposure time of 0.12s, observing point source with 0.5 arcsec seeing, and assuming a bias-subtracted linear-well capacity of 60K e)
Minimum exposure times needed for noise due to sky to dominate the readout noise (40 e), assuming gain of 6 eDN.
For point source with 0.8 arcsec seeing and a 2 arcsec aperture to 5 (20%) photometry.