THE UNITED KINGDOM INFRARED TELESCOPE
ANNUAL REPORT 2003-2004

3.4. Established Instrumentation

3.4.1. CGS4 (1-5µm multiple-resolution spectrometer with 256x256 array)

Despite the availability of UIST, CGS4 is still popular, especially for the higher resolution provided by the echelle and its IJ-bandpass functionality. The fault rate is low, although electronic problems led to faults totalling 2.35 hours of lost time in 03A and "negative countdowns" totalling 3.5 hours of lost time in 2004. The former was fixed by cleaning and reseating ALICE transputer boards and the latter by replacing a waveform generator board. CGS4 was warmed up in October 2003 to enable the visiting instrument TIRGO to be mounted; at that time the cold head and cryostat window were replaced and water ice contamination cleared. CGS4 was not available between February and March 2004, when MICHELLE used the North port.

3.4.2. MICHELLE (10-20µm imager and spectrometer)

In April 2003 some engineering work was done by JAC staff to modify MICHELLE for commissioning of its imaging mode on Gemini. Further engineering was done in August 2003 for November commissioning of spectroscopy at Gemini. In 03B the acquisition software was reworked to provide UIST-like imaging acquisition.

In January 2004 MICHELLE was successfully reconfigured for use on UKIRT. The commissioning in February was hampered by poor weather which led to loss of both the "sacrifical" and main instrument windows, most likely due to the sacrifical window not forming a good seal against the main window. The instrument had to be warmed up and the windows replaced. The second attempt at commissioning took place at the end of February but again the weather was bad; an abbreviated commissioning was performed and the instrument made available in mid-March. Despite losses to weather and some faults, numerous PATT-allocated projects were observed. In fact all modes of the instrument were used - imaging, spectroscopy, imaging polarimetry and spectropolarimetry. MICHELLE returned to Gemini on extended loan at the end of April 2004.

3.4.3. UFTI (1-2.5µm camera with 1024x1024 array)

UFTI is more sensitive than UIST in imaging mode and remains in demand. During the primary realuminising in July 2003 new CH₄ and 2.2µm Mauna Kea consortium filters were installed. Also, a nitrogen purging device was fitted to the window, which effectively delays condensation during high humidity conditions. UFTI was not available between April 22nd and May 15th 2004 when both the chiller and cold head failed. 4.5 hours of time were lost during 2004 due to optical issues - external reflections, condensation or other bright patches, latent images from mistakenly exposing while slewing or focussing. Generally the instrument is robust.

3.4.4. UIST (1-5µm imager and spectrometer with 1024x1024 array)

UIST proved to be a very popular instrument, in particular for spectroscopy covering the H and K windows, for its Integral Field Unit, for thermal imaging and for polarimetry of bright sources.

Semester 03A was the first full semester of common-user use of UIST. The instrument was not available during (planned) engineering in March 2003. At that time the IJ and cross-dispersed grisms were replaced but unfortunately the replacements proved to still be not usable. A new KL blocking filter was installed which allows long-K and KL spectroscopy, and the Mauna Kea consortium 2.1, 2.2, Brγ, ice and PAH filters were installed. A larger cold stop increased throughput in the thermal, however the throughput is still lower than expected, most likely due to small (1%) losses at each optical surface of the 11 lenses plus a ~10% deficit in detector QE. Wider slits were provided for poorer seeing conditions. All the wheels were recalibrated and the EPICS screens reworked for the increased number of grism and filter options. The wheel datum switches were adjusted and the grisms realigned to avoid known trouble spots between datums. Vacuum seals and optics were inspected and electronic shielding was improved.

There were software improvements in 03A also: the OT interface was made to look more like UFTI and CGS4, in particular the specification of exposure time, coadds, readout area and mode. Acquisition for spectroscopy was automated. In 03B acquisition was further improved by enabling the telescope to offset automatically using values generated from "pick-object" in GAIA.

In October 2003 vacuum problems began and cryostat temperatures rose. Frequent pumping and LN₂ fills maintained acceptable temperatures until early December when the cold head was replaced. Unfortunately this did not solve the problem and the instrument had to be removed from service in mid-January 2004. Engineering and repair took place in March 2004. During the engineering the non-functional IJ and cross-dispersed HK grisms were removed and returned to Zeiss. At the same time a new "Z" MK consortium filter was installed. Work was done on the thermal performance of the cryostat. Datum problems with a filter wheel and a vacuum leak at a connector delayed recovery from this engineering to the end of March. After the engineering it was found that the dark current on the left side of the detector was elevated. The problem is being controlled by reducing the array temperature and therefore the heater output (which was elevated over its pre-March levels) although the higher counts on the long-wavelength side of the array did compromise one PATT program in 2004. EDICT slave timeouts and slow EDICT reboots led to some lost time in 2004, but mechanically and cryogenically the instrument was robust.

Orders have been placed with Zeiss for a new IJ grism and a JH grism, with similar resolution to the extremely popular HK grism. An order has also been placed with B. Halle for a second Wollaston prism. With the latter we will be in a position to offer spectropolarimetry with all grisms in UIST (at present only 50% of the grisms can be used).

3.4.4. Accessories

In semester 03A three programmes used IRPOL. Two of these had bright sources and used UIST and very short exposure times, the third carried out circular polarimetry with UFTI on Orion. In semester 03B two L-band spectro-polarimetry projects were awarded time. In 2004 four polarimetry projects were awarded time. Two involved spectro-polarimetry with UIST, and circular polarimetry was also requested. UIST spectropolarimetry data reduction scripts were implemented in 03B and pipeline recipes were also adapted to work for circular polarimetry. This facility was advertised at the 2004 Hawaii polarimetry conference.

The Fabry-Perot was not used in 03A or 03B but was successfully used for one Japanese programme in 2004, although the targets were extremely faint.

3.4.5. Visiting Instruments

TIRGO, an 800 GHz heterodyne receiver, was on UKIRT for two weeks in October 2003. The instrument was scheduled from dawn to 10am. An oscillator had to be replaced at the start of the run, which was badly affected by wet weather. Nevertheless, dry mornings showed the instrument to be very sensitive, and some science was achieved. Flexing this instrument with night-time programmes might be a better option for the future, given the tight weather constraints and the difficulty of supporting day observing.