THE UNITED KINGDOM INFRARED TELESCOPE
ANNUAL REPORT
1998

3.4. Instruments

3.4.1. CGS4 (1-5 µm multiple resolution spectrometer with 256 x 256 array)

CGS4 continued to operate successfully with only 0.3% of clear time lost to faults in Semester 98A, and 0.94% in 98B. The 2-pixel wide slit has shown some signs of deterioration in the reproducibility of its position (orientation). The new wedged CVFs for use with the echelle grating were installed in CGS4 in September 1998. These were designed to remove the ripple pattern that the old CVFs introduced into high-resolution spectra. It appears that in previous echelle spectra there were two components to the ripple pattern, one of which was removed by the new CVFs. The residual pattern is periodic and can be largely removed during data reduction. The new CVFs also allow observations at all wavelengths between 0.93 and 5.2 microns. In addition a new ``IJ'' filter covering 0.85-1.05 µm was installed for use with the lower-resolution gratings.

The policy of switching between echelle and 150 gratings on an approximately 9-month timescale was maintained. The 40 line per mm grating remained the workhorse. The spectral tilt caused by this grating was cured by shimming in May 1998.

3.4.2. IRCAM3 (1-5 µm camera with 256 x 256 array)

IRCAM3 was used for 35% of the PATT nights in Semester 98A and for one third of the PATT nights in Semester 98B. The main sources of lost time with IRCAM were problems relating to communications (e.g. the BDS error problem, which was starting to be associated with a temperature effect during the 1998-9 winter). In general, IRCAM performed reliably, with less than 5% lost time over the semester. Baking out the array while doing a filter change resulted in a smattering of dark spots. These flat-field out perfectly and there was no obvious effect on users' data.

It became clear that the default pixel scale of 0.28"/pix undersamples the typical image; as reported in the 1997 Annual report, the 2 x magnifier was becoming increasingly popular. However, it was clear that the camera should be modified to a smaller pixel scale in order to keep up with the image quality as well as improve its thermal-infrared sensitivity.

3.4.3. UFTI (1-2.5 µm camera with 1024 x 1024 array)

UFTI arrived in Hilo in September 1998, and received first light in October 1998. Its pixel scale of 0.09/pixel properly samples the UKIRT PSF, in most conditions. A problem with the filter wheels that had been present since assembly eventually resulted in a hard failure of the filter mechanisms in January 1999, and the instrument was subjected to re-engineering of all three motor mechanisms (2 filter wheels and shutter). Early imaging results with UFTI were encouraging, with the UKATC opening ceremony and the 20th anniversary of UKIRT being celebrated with UFTI imaging of the Orion nebula in molecular hydrogen. Data were relayed back to the ATC via the worldwide web, and displayed in real time to an audience including the science minister, Lord Sainsbury.

It was quickly apparent that the instrument's focussing requirements were stringent, and attempts were under way to devise a strict focussing protocol. Photometric calibration of UFTI was commenced at the end of 1998. Polarimetry and Fabry-Perot operations remained to be done.

3.4.4. Accessories

Both the 350 km/s Fabry-Perot interferometer and IRPOL operated very successfully during Semesters 98A and B.

3.4.5. Visitor Instruments

The MPIA thermal imager, MAX, had two observing runs at UKIRT early in Semester 98A. The first was seriously affected by numerous instrument problems, but the April 1998 run was much better and excellent data were obtained. Two further runs were undertaken in the winter of 1998/9. The first of these was moderately successful, but the second was lost to poor weather and instrument problems.

MICS, the Japanese ten-micron imager/spectrometer, was used moderately successfully for one 3-night run in April 1998 and a 4-night run in August. The measured sensitivity during the latter observing run was somewhat lower than advertised, although still considerably better than CGS3. Due to commitments to the Subaru COMICS camera, the MICS team were not able to provide effort to support the instrument into semester 99A.

COHSI, an OH-suppressing spectrometer/IFU, saw its first UKIRT time in 1998. After working through their originally-scheduled observing time in 1998. After working through their originally-scheduled observing time in June 1998, the COHSI team reported that the instrument's throughput, which had been rather low, was sufficiently improved to make a further run worthwhile. Time was allocated in November to commission the instrument and allow the throughput to be confirmed in time for PATT to consider an allocation for multi-object spectroscopy in the summer of 1999. In the event, the run was largely (though not entirely) cloudy, and did not give a clear demonstration of improvement.