THE UNITED KINGDOM INFRARED TELESCOPE
ANNUAL REPORT
2000

3.3. Telescope and Enclosure

3.3.1. Telescope and Dome Control

The telescope systems performed very reliably throughout 2000. Counter-weighting provisions in preparation for Michelle were installed in the summer. The dome ventilation system (DVS) worked reliably through this year. Due to staff shortages, work to fix the dome seals and skirts could not be accommodated this financial year and was deferred until 2001/2002.

3.3.2. Emissivity

Emissivity is routinely measured at the end of each night using CGS4. Work on these measurements revealed that averaging over a narrow band of echelle data produced an overestimated emissivity. By extracting the complete spectrum, a region of minimal atmospheric emissivity was identified. A reduction in the inferred emissivity resulted; emissivity was measured as below 10%, close to the theoretical minimum for the current telescope components. Some features of the relationship between emissivity and photometric zeropoints imply that an emissivity plateau exists.

The calibration between the emissivity measured with the 150 l/mm grating and with the echelle was determined when the gratings were switched in early summer 2000. In a further attempt to understand the UKIRT emissivity, the TRISPEC aluminized patch was used with the 150 l/mm grating in early 2001 to calibrate measurements taken with the commonly used float-glass dichroic. The results were encouraging: the inferred echelle-mode emissivity is 8%, slightly lower than the prediction of the standard telescope model. In all but the thermal infrared, there is no advantage to using an opaque aluminized patch, and whether or not to do so was still under debate at the end of the year.

To maintain low emissivity and high throughput, dichroics were exchanged in March when it became clear that the surface had degraded, and the primary was cleaned in December 2000.

3.3.3. Image Quality

As a result of concerted monitoring of UKIRT's seeing performance, a number of advances were made in understanding its behaviour as a function of conditions both inside and outside the observatory. Poor seeing is correlated with low wind speed; above 5 miles per hour the dome ventilation system allows the wind to blow away the dome seeing as demonstrated in Figure 3 , which shows the seeing disk size as a function of wind speed. Note the improvement in seeing for windspeeds greater than 5 mph. The seeing has been interpolated from the focus z values.

In October 2000, primary mirror cooling was attempted for the first time; early results show that the system is capable of producing excellent seeing when the flow temperature is suitably regulated relative to the dome temperature. Figure 4 shows the dependence of seeing on the temperature difference between mirror cooling flow and dome air, where the data taken between 7 pm and 9 pm on 11th October 2000. Further work on primary mirror cooling was delayed by staff shortages into early Semester 01A (by the end of 2000, significant effort remained to have the flow air track dome temperature accurately and without intervention).

3.3.4. Telescope Control System

A new interface to the UKIRT telescope control system (TCS) was installed in time for initial ORAC commissioning in May. The longer-term goal was to be ready for the JCMT portable telescope control system (PTCS) but in the interim this system provided the functionality required by ORAC. Web pages were provided which describe the peakup process under the new system, and the key case (faint source with very accurate position but unknown guide star position) was an early demonstrator that the entire instrument aperture concept works well. The TCS was stable from August on, with minor changes and improvements to the interim interface. Work commenced on bringing the PTCS to UKIRT from the JCMT (this is a requirement for UIST and will also remove our reliance on VAXes).

3.3.5. User Environment

There were no major changes to the control-room environment. Further large screens were installed as part of the ORAC commissioning, bringing the total of 21-inch monitors to eight. Flat screens were under consideration for ergonomic reasons, but were ruled out due to their poor performance with Solaris workstations.