THE UNITED KINGDOM INFRARED TELESCOPE
ANNUAL REPORT
1995 AND 1996

5. Instrumentation Development

5.3. The UKIRT Imager-SpecTrometer (UIST)

A project team at ROE, led by Suzanne Ramsay Howat as Project Scientist and Mel Strachan as Project Manager, is advancing towards a firm conceptual design for this, the next generation ``workhorse'' 1-5 micron instrument for UKIRT. UIST is intended to utilise the 10241024 InSb ``ALADDIN'' arrays being produced by Santa Barbara Research Corporation, and an attempt is being made to ensure that the design does not exclude the use of future 20482048 InSb devices which may soon be developed for space and other applications. The use of larger arrays allows the possibility of wide spectral coverage at moderately high spectral resolution; this together with improved array performance over the current 256256 arrays and improved optical performance (of both the instrument and the telescope) will lead to significant gains in sensitivity over that of CGS4. Delivery to UKIRT is predicted for the year 2000 or 2001, depending on the funding profile.

UIST is intended to operate as a versatile imager, with pixel fields of view of 0.12 arcsec and 0.06 arcsec, capable of sampling, respectively, good and perfect (diffraction-limited) images at K and possibly also 0.03 arcsec (capable of sampling diffraction-limited images at J which should be achieved in future adaptive optics applications). A camera exchange mechanism will allow plate scales to be changed during the night, to respond to changing atmospheric conditions. In addition, UIST will provide a facility long wished for by CGS4 users: the ability to image the field directly before switching to spectroscopy, thereby removing the need for lengthy peak-up in spectroscopic mode before a spectroscopic observation.

In spectroscopic mode UIST will also offer a long-slit (2 arcmin) and moderate (R1000) and intermediate (R2000-5000) resolutions, the latter to provide the option to observe between the OH lines in the J, H and K windows. A short-slit (probably 20 arcseconds) version of the former, with cross-dispersion, will provide coverage of at least two, and probably all three, of the JHK windows simultaneously. Slit widths matched to two pixels are planned, offering well-sampled spectra without the need to ``step'' the array as is the present practice. Wider slits may be provided for still fuller sampling at the expense of resolution. Note that CGS4 with its echelle will still be required for very high resolution spectroscopy. The dispersing elements for spectroscopy will be grisms. It is hoped that the instrument will include an Integral Field Unit (IFU), if possible ab initio; if not the design will explicitly allow the addition of this option as a future upgrade. The IFU design envisaged at present is a selectable device in the cold fore-optics which would offer a 55 arcsecond FOV at 0.24 arcsecond spatial resolution.