The James Clerk Maxwell Telescope
With a diameter of 15m the James Clerk Maxwell Telescope (JCMT)
is the largest astronomical telescope in the world designed
specifically to operate in the submillimeter wavelength region of
the spectrum. The JCMT is used to study our Solar System,
interstellar dust and gas, and distant galaxies. It is situated
close to the summit of Mauna Kea, Hawaii, at an altitude of 4092m.
It is operated by the United Kingdom and Canada (the Partner
Countries) on behalf of astronomers worldwide. It is managed by
the STFCs Joint Astronomy Centre (JAC) in Hilo, Hawaii. The JAC is
also responsible for the operation of the United Kingdom Infrared
Development and operation of the JCMT is overseen by the JCMT
The 15-metre diameter primary reflector of the JCMT is made up of
276 individual lightweight panels. Each panel consists of a thin
aluminium skin bonded to an aluminium honeycomb and is attached at
three points to the backing structure of the antenna. The
alignment of the mechanical panels can be adjusted by means of
stepper motors at the mounting points. The backing structure is
designed to maintain a parabolic figure as gravity distorts the
antenna as it tips to different elevations. The surface accuracy
is routinely measured and adjustments required to each panel are
calculated by making observations of a coherent millimetre source
located on top of the UKIRT building. The sub-reflector or
secondary mirror can be adjusted in three axes to compensate for
changes in focus as well as changes in the figure of the primary.
In addition, the secondary can be tilted or chopped in two axes in
order to perform sky background cancellation.
The JCMT carousel co-rotates with the antenna and is designed to
protect the telescope from the elements and to provide a safe and
comfortable working environment for astronomers and engineers. An
important feature of the carousel is the membrane which is
deployed in front of the antenna at all times and is transparent
at millimetre and submillimetre wavelengths. In addition to
providing protection from the wind, the membrane performs the
useful function of reflecting the visible and near-infrared
radiation, providing protection from the solar heat which could
damage the antenna, thereby allowing daytime astronomical
observations including direct observations of the Sun itself.
Receivers for the telescope can be located either in one of the
bays of the Cassegrain cabin or on the two Nasmyth platforms
located at the ends of the elevation bearing.
A number of receivers can be and are accommodated on the
telescope at the same time and are selected by a movable tertiary
mirror located in the centre of the Cassegrain cabin. The
heterodyne receivers, covering the atmospheric windows between 215
and 680 GHz, are mounted in the cabin while the continuum
bolometer array instrument, SCUBA-2, and the heterodyne array
receiver, HARP, occupy the Nasmyth platforms.
When observing together with the SMA and the CSO, the JCMT is
part of the Extended Submillimeter Array (eSMA).
Under the terms of the Partnership Agreement, the Partner
Countries jointly undertake the operation, maintenance and
development of the facility with the resources provided for this
purpose in the proportion UK 75% and Canada 25%. In accordance
with the Operating and Site Development Agreement, 11.25% of the
total observing time is set aside for use by the University of
Hawaii (UH). 65% of the UK and CA time is used for the JCMT
Legacy Survey (JLS).
All observing time, except UH, is allocated by ITAC
(International Time Allocation Committee) on the basis of
scientific merit and technical feasibility. Use of the telescope
is not restricted to applicants from partner countries. National
Time Allocation Groups (UK: UKTAG, CAN: CTAC) referee, assess and
nominate allocations for applications from their own countries.
These time allocations are later combined and awarded by the ITAC.
Applications from outside the partner countries are assessed and
nominated by the ITAC. The ITAC is composed of the Chairs of the
national TAGs. The UKTAG is a subcommittee of the PATT
(Panel for the Allocation of Telescope Time).
The international partners set up the James Clerk Maxwell
Telescope Board to oversee the operation of the JCMT, to foster
and develop collaboration between their astronomers in the use of
the facility, and to endeavour to maintain the JCMT in the
forefront of world astronomy. In particular, the JCMT Board (i)
oversees the development of the facility; (ii) determines (with
the advice of users and of the Director JCMT) the programme of
operation and maintenance of the facility; (iii) approves annual
budgets and forward estimates, and (iv) determines the
arrangements for the allocation of observing time.
The JCMT Board comprises three persons appointed by STFC (UK),
two appointed by the NRC (CA), and one appointed by the University