THE UNITED KINGDOM INFRARED TELESCOPE
ANNUAL REPORT
1998

3.3. Telescope and Enclosure

Pointing and tracking accuracy remained close to the excellent levels reported in all of the semesters since the top-end upgrade (1.5" r.m.s. pointing, 1-2 arcseconds per hour blind tracking accuracy). General reliability of the telescope has been excellent, even with the additional complexity of the numerous Upgrades subsystems. This reliability was emphasized by the failure on September 8 of the Canada-France-Hawaii Telescope's hour angle drive, which resulted in a 4 week shut-down. The UKIRT gearboxes are in good physical condition with only minor wear; this was borne out by tests of gearbox grease samples.

To aluminize the 3.8-metre primary mirror took some 15 days, mostly because of the great complexity of dismantling UKIRT's bottom end. Experience gained this year should make future realuminizing quicker.

Apparent variations in emissivity were causing concern near the end of the reporting period. A scatterometer was purchased late in semester 98B, which allows an independent check on the primary's surface, and a consistent series of emissivity measurements were underway.

A specialist filter was developed to reduce the HA oscillation that has plagued UKIRT since it was built. The telescope's construction places a limit to the amount of improvement that can be achieved, but significant gains were made.

The dome ventilation system gave occasional problems in the winter of 1998; the watertight enclosures (WTEs) were found to be prone to sticking open in freezing and high-humidity conditions (such as had not occurred in the previous - el Niño - winter).