THE UNITED KINGDOM INFRARED TELESCOPE
ANNUAL REPORT
1999

4.2. Instrumentation Development

The instrumentation programme evolved over the year, as momentum built on the newly-approved UIST imager-spectrometer project, and the design study for the Wide Field Camera (WFCAM) demonstrated that this highly innovative instrument was a genuine option. WFCAM has stimulated widespread interest, and received formal approval in January 2000.

4.2.1. Michelle

The integration phase of the project commenced successfully in late 1998 with verification of optical design performance and array properties which were compatible with multiple readouts to reduce noise, but became seriously delayed by problems with almost all mechanical sub-systems, most notably with the grating exchange drum. Initial ``sticking'' problems associated with ice formation were alleviated by careful outgassing at the start of each cooldown, and the installation of getters at vulnerable locations. However it became clear that design defects were also contributing. A problem-solving ``tiger team'' was assembled in July. They, and the project team, addressed these and other issues including poor vacuum performance, high background light levels on the detector, difficulty in cooling the detector in the fully-assembled cryostat and underpowered stepper motors. In the last case it was found that design changes in these motors had invalidated the standard degreasing procedures for cryogenic operation, leading to demagnetisation. Diversion of effort to Michelle from other projects began. Electrical and thermal short-circuits to the detector mount were identified and rectified, bringing the array temperature low enough for progress to be made in its characterisation. Measured read noise levels within a factor 2 of the delivery goal were measured. The high background fluxes were found by seeking light leaks with a light bulb, correction of these reduced the background levels to a level which allows satisfactory performance for imaging and low-resolution spectroscopy on UKIRT (and Gemini). Further improvememnts were recognised to be essential and efforts were planned for the new year. By November 1999 the project had slipped a total of 43 weeks relative to the baseline set in September 1998 and was approximately £2053 k over budget.

4.2.2. The UKIRT Imager Spectrometer UIST

As noted in the last Annual Report, UIST received formal approval in January 1999 for a cash limit of £2884 k including contingency. Good progress was made early in that year and the cryostat was assembled and successfully vacuum tested in April. Effort availability became a concern in mid-year as the problems with Michelle began to draw resources from the other UKIRT projects. The project continued contracting out sub-systems to the maximum degree, which has stood it in good stead in the climate of effort shortage, but later in the year cost estimates had climbed to a level which appeared close to the cash limit. A re-assessment of ATC accounting processes resulted in the allocation of additional funds, averting the crisis; the pressure on effort later began to make an underspend in FY 1999/00 seem likely. ⁴

Cooldowns commenced in May and the problems identified were solved without major impact on the project schedule. The optics stage reached the desired operating temperature and difficulties in getting the detector array down to optimum working temperature were overcome. Acquisition and operation of an engineering-grade detector allowed verification of the optical performance. Detailed design of the Integral Field Unit was completed and manufacture commenced late in the year. Several measuring runs on UKIRT investigated internal flexure of the Instrument Support Unit, which will not support UIST but will be responsible for feeding it its input beam. (With spectrometer slits as small as 0.25" very little flexure can be tolerated if the goal of continuing observations for at least an hour before checking on pointing is to be realised.) Initial results are encouraging, and major modifications of the ISU may not be necessary. The UIST project entered the new millenium in good shape apart from the unknown impact of Michelle upon its effort requirements.

4.2.3. Wide-Field Camera (WFCAM) and Large-Scale Surveys

WFCAM is a 1-2.5 µm wide-field imager able to cover about 0.25 square degree (900 square arcminutes) in a single exposure. It will utilise its own dedicated topend with articulated ``tip-tilt'' F/9 secondary. The large cryostat will be located ahead of the primary mirror, on the central plug. It uses a Schmidt-type design to feed a corrected image to a mosaic of four 2k square HgCdTe arrays. Up to 8 filters will be available: J, H and K filters (from the new ``Mauna Kea'' filter set) will be the core wavelengths but ``z'' (around 950 nm) and narrow bands, plus a blanking filter, will be included. The facility is expected to be able to provide S/N=3 to K=20 over one square degree in one hour. Design details were firmed up and an advanced Conceptual Design Review (CoDR+), with international participation, was held in Edinburgh in August. The review panel strongly endorsed the scientific potential of the instrument and also the proposed design, recognising its innovative nature but concluding that the proposal was fully practicable. The project team's approach to contingency planning was particularly appreciated. The prospect of WFCAM, which will for several years be the most powerful facility in existence for wide-field IR surveys, has generated extensive interest world-wide. In Japan plans were developed for collaborative involvement, leading to a science meeting at the National Astronomical Observatory of Japan in Tokyo in April. Proposals for surveys were canvassed from the UK and Japanese communities, and by year's end Japanese involvement in both the science and the data processing looks certain. A survey consortium is being the Cambridge Wide Field Astronomy unit. Interest in collaboration was expressed by groups in Canada and Germany. The project was submitted for Council approval at the year's end; approval was received in January 2000 at £4346 k.