James Clerk Maxwell Telescope

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The James Clerk Maxwell Telescope (JCMT) is a 15-metre submillimetre-wavelength telescope at Mauna Kea Observatory in Hawaii. It is the largest astronomical telescope in the world designed specifically to operate in the submillimetre regime (between the far-infrared and the microwave regions of the electromagnetic spectrum). It is used to study our Solar System, interstellar dust and gas, and distant galaxies.

The JCMT is funded by a partnership between the United Kingdom, Canada, and the Netherlands. It is operated by the Joint Astronomy Centre and was named in honour of James Clerk Maxwell. It is located near the summit of Mauna Kea at an altitude of 4092 meters as part of the Mauna Kea Observatory. The JCMT has the second largest telescope mirror on Mauna Kea (largest is the VLBA antenna).

This telescope was combined with the Caltech Submillimeter Observatory to form the first submillimeter interferometer. The success of this experiment was important in pushing ahead the construction of the Submillimeter Array and the Atacama Large Millimeter Array interferometers.

1 History
2 Instrumentation
3 See also
4 External links

[edit] History

In the late 1960s the Astronomy Committee of the UK's Science Research Council (SRC, for forerunner of PPARC) considered the importance of astronomical observations at submillimetre and millimetre wavelengths. A series of proposals and debates led, in 1975, to the SRC millimetre steering committee concluding that it would be possible to construct a 15-metre diameter telescope capable of observing at wavelengths down to 750 µm. The project, then called the National New Technology Telescope (NNTT), was to be an 80/20 per cent collaboration with the Netherlands Organisation for the Advancement of Science. A program of site tests considered Mauna Kea in Hawaii, the Pinaleno Mountains in Arizona, and a site in Chile. Ultimately Mauna Kea was chosen as the preferred site. The NNTT is a unique facility as plans for a similar telescope by the US collapsed in 1982.

The final specifications called for the "world's largest telescope optimised for submillimetre wavelengths." It was to be a parabolic 15-metre antenna composed of 276 individually adjustable panels with a surface accuracy of less than 50 µm. It would be an altitude-azimuth mounted Cassegrain telescope with a tertiary mirror to direct the incoming radiation onto a number of different receivers. The antenna and mountings were to be protected from the elements by a co-rotating carousel with a transparent membrane stretched across the carousel aperture. Building work started in 1983 and went well apart from a small delay caused by the hijacking of the ship carrying the telescope across the Pacific by modern-day pirates. The telescope saw first light in 1987. The name for the final facility was changed to the James Clerk Maxwell Telescope.

The JCMT is currently funded under a tripartite agreement between the United Kingdom (55 per cent), Canada (25 per cent), and the Netherlands (20 per cent). The telescope itself is operated by the Joint Astronomy Centre (JAC), from Hilo, Hawaii. The telescope site agreement with the University of Hawaii provides observer accommodation and infrastructure in exchange for open access to international proposals and 10 per cent of the observing time for the University's own projects. Proposals for telescope usage are submitted to one of the national Telescope Allocation Groups (TAGs) and if successful are awarded time in the next six-monthly semester.

[edit] Instrumentation

The JCMT carries two types of instruments—broadband continuum detectors and heterodyne detection spectral-line receivers.

The older continuum single pixel UKT14 bolometer receiver was replaced in the 1990s by the Submillimetre Common Users Bolometer Array (SCUBA). The SCUBA project was greenlighted in 1987 by the JCMT board and was in development for nearly a decade before it saw first light on the telescope. While it was not the first bolometer-array it was "unique in combining an unparallel sensitivity with an extensive wavelength range and field-of-view" [1].

SCUBA is sensitive to the thermal emission from interstellar dust. This emission is a tracer of star formation in other galaxies and gives astronomers clues to the presence, distance, and evolution history of galaxies other than our own. Within our own galaxy dust emission is associated with stellar nurserys and planet forming solar systems.

SCUBA is ranked second only to the Hubble Space Telescope in terms of publication of high-impact astronomical research. SCUBA was retired from service in 2005. Work is currently underway on SCUBA-2, a replacement for SCUBA, that is expected to see first light in 2006 [2].

The JCMT is also equipped with three heterodyne receivers, which allow submillimetre spectral-line observations to be made. Spectral-line observations can be used to identify particular molecules in the interstellar medium and determine local gas velocity gradients across astronomical objects of interest. The spectral-line mapping capabilities of the JCMT have been greatly enhanced by the commissioning of HARP-B, a 350 GHz, 16 element heterodyne array receiver. HARP-B, and the other heterodyne instruments, can be used in conjunction with the JCMT's new digital autocorrelation spectrometer, ACSIS.