Upgraded UKIRT

The 3.8m UK Infrared Telescope (UKIRT) has been the focus of a programme of upgrades intended to deliver images which are as close as possible to the diffraction limit at ) = 2.2 ,um (FWIIM = O!'12). This programme is almost complete and many benefits are being seen. A high-bandwidth tip-tilt secondary mirror driven by a Fast Guider sampling at 100 Hz effectively eliminates image movement as long as a guide star with R< 16.m5 is available within of the target. Low-order active control of the primary mirror and precision positioning of the secondary, using simple lookup tables, provide telescope optics which are already almost diffraction limited at A = 2 pm. To reduce facility seeing the dome has been equipped with sixteen closable apertures to permit natural wind flushing, assisted in low winds by the building ventilation system. The primary mirror will soon be actively cooled and the concrete dome floor may be thermally insulated against daytime heating if fire safety concerns can be resolved. Delivered images in the K band now have FWHM which is usually O!'8, frequently l O'6 and quite often O!'3. Examples of the latter are shown: these approximate the resolution achieved by NICMOS on the HST. We estimate that the productivity of the telescope has approximately doubled, while its oversubscription factor has increased to > 4.