THE UNITED KINGDOM INFRARED TELESCOPE
ANNUAL REPORT 2003-2004

3.3. Telescope and Enclosure

3.3.1. Telescope and Dome Control

The telescope performed well in semester 03A although there were some guider losses at relatively low windspeeds, and we started to see crosshead problems that would worsen in later semesters. Between June and July 2003 the primary was realuminised and the pneumatic mirror supports were checked for leaks with one leaky valve being replaced. The mirror plug and covers were modified to accommodate WFCAM, and a new Uninterruptable Power Supply was installed. In 03B the dome drives were replaced. Software improvements included improvements to UIST spectroscopy acquisition and enabling alt-az coordinates to be used in the Observing Tool.

During spring 2004 the telescope suffered from an unusually large number of problems. A fast guider rotation bearing and the brake on the crosshead failed, and a low control voltage to the slew rate relay caused a prolonged period of extremely slow slews. Another problem occurred in the crosshead controller, which can hang, leading to lost time due to pointing errors. This is being worked around by being more careful when datuming. Oscillations in the telescope mount servo led to elongated images in the far North; work on this was delayed into 2005.

3.3.2. Emissivity

During 03A the emissivity was measured with CGS4 to be quite high at 17-19%. A gradual increase was seen over the five years since the last primary realuminising. After the primary was realuminised in July 2003 the emissivity still appeared quite high at 15%, and it was thought that this was possibly compromised by a degraded CGS4 window. The range in emissivity between the various dichroics was measured to be 13% for that with a gold coating and 15-17% (depending on age) for those with silver-dielectric coatings. In semester 04A the gold-coated dichroic was installed so that Michelle observations could benefit from the lowest possible emissivity. Disappointingly, Michelle observations implied an emissivity of 20% but this was likely due to a degraded Michelle window as the UIST emissivity values were measured at 12% in March 2004.

3.3.3. Image Quality

Image quality was sometimes compromised due to the oscillation problems mentioned above, however in summer 2004 UKIRT delivered 0.22 arcsecond images and fundamentally the telescope optical performance is sound.

3.3.4 Dome

The dome extension roof was damaged in stormy weather in early 2004. The roof was repaired in September 2004.