THE UNITED KINGDOM INFRARED TELESCOPE
ANNUAL REPORT
1998

4.2. Instrumentation Development

4.2.1. UKIRT Fast-Track Imager

As indicated in the previous report, the Imager, under development at Oxford University, suffered several slippages during the year. However, this allowed completion of work in several other areas and, as it turned out, allowing several aspects of software engineering to be more thoroughly addressed. A markedly larger share of the work than was originally planned was, in the event, undertaken at the UKATC and the JAC, thus ensuring that critical system elements were designed and implemented up to the full standard required of a common user instrument, largely by the team that would be responsible for their later maintenance.

In the event UFTI has become the first astronomical instrument to be controlled using the EPICS software running on a VXworks platform; as such it has been a valuable precursor of Michelle and UIST, which will be similarly controlled.

The instrument was shipped to Hawaii in autumn of 1998. Its first light on the telescope occurred on 30 September 1998, and it was rapidly brought into near-routine operation. In October, spectacular images of the Orion ``bullets'' were secured in real time for the official opening of the UKATC by the Minister of Science, Lord Sainsbury. Some problems with image persistence have had to be addressed: it appears that the detector array is about average in this respect, with afterimages at about 0.4% manifesting themselves as areas of enhanced dark current.

4.2.2. Michelle

Michelle is the largest and most complex instrument yet built for UKIRT, and one of the most challenging for any telescope. It will offer fully-sampled imaging, and spectroscopy at low, medium and high spectral resolutions, between 7 and 25 µm, and is to be shared with Gemini.

Most initial hardware manufacture was completed early in 1998, when assembly and testing began. As noted in the last report, a major problem was immediately revealed: porosity of the cast vacuum vessel required its replacement with a fabricated vessel (a manufacturer having by this time been located and designs prepared) around the middle of the year. The first full cool-down of the assembled cryostat took place in August and enabled numerous thermal and optical parameters to be verified. Another important step forward was achieved when it was established that the favoured 320 x 240 Si:As arrays from Raytheon (previously SBRC) could be read without resetting, so that multiple non-destructive reads are possible as a noise reduction strategy. This was a critical issue for the Michelle project and for others hoping to employ these devices.

The main series of cooldowns of the whole assembled cryostat, complete with detector assembly, was commenced late in the year. Problems with cold-operation of mechanisms and detector cooling were encountered, and it became clear that further slippages of this most challenging project were still to come.

4.2.3. The UKIRT Imager Spectrometer UIST

As noted in the last report, a successful Preliminary Design Review was held at ROE in December 1997, when a convincing design for a capable workhorse instrument was presented and agreed.

UIST (the UKIRT Imager-SpecTrometer) is intended to offer imaging at 0.12"/pixel and (possibly later) 0.06" and other pixel scales, long-slit (120 arcseconds) spectroscopy with slit widths from 0.12" to 0.48" at spectral resolutions R (for a 0.24" slit) of 1200 to 4000, the former giving coverage of a complete atmospheric window, the latter about half a window but substantial reduction of the effects of the atmospheric OH features. It will also offer the lower resolution in a cross-dispersed mode, covering two atmospheric windows at once. The cross-disperser alone can be used to give low-resolution (R200) coverage from I through K. An Integral Field Unit (IFU) using an image slicer will also enable spectra to be secured for all pixels (0.36" square: possibly 0.24" square) in a contiguous area of 4.3" x 6.8" on the sky, in any of the long-slit spectroscopic modes. An image rotator allows the slits or IFU to be oriented at any position angle on the sky.

The project makes maximum use of existing subsystem designs at the UKATC, which has been effective both in keeping times short and costs low. However the delays to Michelle, and consequent demands from the Michelle project began to have an effect on UIST and the Project team now uses an unusually high level of outside manufacture, effectively trading effort inside the UKATC for cash spent outside. A Critical Design Review was held on 15 December 1998 and the project secured PPARC formal approval in January 1999, for a cash limit of £2884 k including contingency. At the CDR the excellent imaging performance of the telescope in 1998 led to the decision that UIST should be delivered with both the basic 0.12"/pixel image scale and also the higher-resolution 0.06"/pixel scale to permit it properly to sample the very best images.