THE UNITED KINGDOM INFRARED TELESCOPE
ANNUAL REPORT
1995 AND 1996

5. Instrumentation Development

5.1. UKIRT Fast-Track Imager (UFTI)

A UKIRT fast-track 1-2.5m imager (UFTI) utilising a 1024 square HgCdTe array is being built at the University of Oxford and is scheduled for first light in 1998. The principal strength and primary function of the new imager is its ability to sample fully the best K-band images UKIRT is expected to deliver in the near future. When the tip/tilt system was brought into operation in August 1996 images down to 0.26 arcseconds FWHM were obtained when the conditions were favourable and the optics had been carefully adjusted. When the Upgrades programme (see § 6) is complete it is expected that such images will be regularly encountered. Already images with FWHM 0.6 arcseconds are frequently seen and 0.4-0.5 arcseconds is not uncommon. As image quality continues to improve compact sources will be seriously undersampled by IRCAM3 with its standard pixel scale of 0.28 arcseconds per pixel. UFTI will have a pixel FOV of 0.09 arcseconds, sufficient to exploit images even better than the best so far encountered.

UFTI will employ a 10241024 HAWAII HgCdTe array with sensitivity from 1 to 2.5 microns. In the interests of a speedy delivery its design is as simple as possible while remaining commensurate with the wide range of science for which it is needed. It does not employ warm fore-optics as the IRCAMs have done: its re-imaging system is internal and cold, so its performance in the K band should be significantly better than that of the IRCAMs. It is equipped with two filter wheels providing locations for up to 14 filters. The filter set includes broad J, H and K filters obtained through the GEMINI-IfA consortium, with optimised bandpasses which are better matched to the atmospheric windows than the ``standard'' JHK set, allowing improved throughput as well as better transformation between systems. They are also made to tighter optical specifications, compatible with the diffraction-limited optics of modern telescopes (and UKIRT). A suite of general-purpose narrow-band filters, also of high optical quality, and a ``Z'' band (0.9 microns) filter, will be provided as well.