With its 3.8 meter primary mirror (150 inches), The United Kingdom Infrared Telescope (UKIRT) is one of the largest infrared telescopes in the world, covering a wavelength range from 1 to 30 micrometers. The telescope is located on Maunakea, on the Big Island of Hawaii, and is part of the Maunakea Observatories. UKIRT is currently funded by NASA and operated under scientific cooperation between Lockheed Martin Advanced Technology Center, the University of Hawai’i, and the U.S. Naval observatory. The initial Manunakea Comprehensive Management Plan targeted UKIRT for decommissioning if and when the Thirty Meter Telescope becomes operational on Maunakea.
UKIRT is a reflecting, Cassegrain telescope with a thin primary mirror – roughly two-thirds thinner than contemporaneous telescopes – that weighs only 6.5 tonnes. This large mirror sits on 80 computer-controlled aluminum pistons that allow for accuracy consistent with a much thicker primary. This accuracy is possible because the pistons cancel out stresses, mimicking a thicker mirror’s behavior and improving optical performance.
The mirror itself is held in place by 20 tonnes of steel, linked to supports by Serrurier Trusses, a type of construction used in telescope tube assembly.
It is crucial to reduce background heat to a minimum due to the wavelength of UKIRT observations. In order to reduce residual heat from the mirror, UKIRT uses power motors and control systems that create less heat.
The telescope itself sits in an English Equatorial mount atop ball-bearings, which themselves sit on steel piers. The use of this mount allows the telescope to swing east-west and rotate north-south. Furthermore, the advantage of this mount is incredibly accurate pointing, as the telescope is sturdy and free of deformation. However, the downside is that access to objects between +60 and -40 in declination is limited.
The entire structure is held in place by more giant ball-bearings that are held rigid by shear pins. The pins protect against damage to the telescope during earthquakes.
Built between 1975 and 1978, UKIRT was initially known as the ‘Infrared Flux Collector.’ Dunford Hadfields Limited of Sheffield built UKIRT’s mechanical systems and Grubb Parsons of Newcastle built the optics. Operations officially began in 1979.
A major triumph of the UKIRT telescope is the UKIRT Infrared Deep Sky Survey (or UKIDDS), which began in 2004 using the wide-field imager (WFCAM). Initially, the UKIDSS survey used 80% of the available wide-field time (out of the 60-40 split between wide-field observations and other Cassegrain instruments). However, as of December 2008, UKIRT switched to wide-field operations full time.
In December 2010, UKIRT switched to a full-time minimalist operation mode with no observers present and currently operates from the Institute for Astronomy building on the Big Island of Hawai’i.
As explained in the previous section, UKIRT is currently devoted to wide-field operations; however, it also has four Cassegrain instruments (not including WFCAM). Three of the four Cassegrain instruments can be on the telescope simultaneously, with WFCAM placed forward of the Cassegrain focus. A list of UKIRT instruments is as follows:
- CGS4 is a cooled-grating spectrometer with a 90” slit. It has spectral resolutions ranging between 1000 and 30,000.
- Michelle is a 320X240 pixel mid-infrared imager/spectrometer. It operates between 10 and 20 micrometers.
- UFTI is a 1024X1024 pixel imager. It operated between 0.8 and 2.5 micrometers.
- UIST is a 1024X1024 pixel imager/spectrometer operating between 0.8 and 5 micrometers. It offers an integral field mode 3”X6” in size.
- WFCAM is a wide-field imager with four 2048X2048 arrays, each of which covers a field of 13.6′ on each side. It boasts a total field of view of about 0.2 square degrees.
UKIRT was inexpensive to initially build and has undergone extensive upgrades since it saw first light. Improvements made to image performance between 1990 and 1998 were considerable, meaning that by 2001 UKIRT delivered a median infrared seeing of 0.8″ at dusk to 0.5″ in the early morning.
UKIRT undertook two major software projects between 1998 and 2003. The first was ORAC, which provided a significant upgrade to the user interface and allowed for automation of the telescope. The second was the OMP that provides a broad observing database and data feedback system.
Thanks in part to these software upgrades, since 2003, UKIRT has carried out highly efficient flexible scheduling and can tailor observation to weather conditions. A Telescope System Specialist (TSS) selects observations from a database that provides available observations according to several metrics. These include current seeing, atmospheric water vapor, sky transparency, and a science priority. The telescope time allocation committee allocates the priority.
On 16th December 2009, the announcement came that UKIRT was “subject to discussion leading to managed withdrawal.” Following this announcement, UKIRT became earmarked for an end of 2013 shutdown; however, transfer was considered an alternative. Thankfully, in 2014 shutdown of the telescope was prevented by transfer of ownership to the University of Hawai’i.
Currently, UKIRT operates under a Scientific Cooperation Agreement that includes the University of Arizona, the University of Hawai’i, and the Lockheed Martin Advanced Technology Center (LM-ATC). The NASA Orbital Debris Program office provides funding for the observatory, and UKIRT shares observing time between these groups.
Steward Observatory at the University of Arizona is responsible for the daily operations and scientific productivity of UKIRT. Until August 2020, East Asian Observatory (EAO) provided technical support (EAO is the successor to Joint Astronomy Center that once operated UKIRT and the James Clark Maxwell Telescope (JCMT)). Since August 2020, the UKIRT offices, including the remote observing room, have transitioned to the Institute for Astronomy building.
The UK continues to provide support for data pipelines and archives for WFCAM. As a result, the UK receives a share of observing time for survey projects with a shared interest.