James Clerk Maxwell Telescope - Overview

Contents

Introduction

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, Canada and the Netherlands (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 Telescope (UKIRT). Development and operation of the JCMT is overseen by the JCMT Board.

Telescope

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.

Carousel

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.

Instruments

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).

Tripartite Agreement

Under the terms of the Tripartite 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: 55%, Canada: 25% and the Netherlands: 20%. In accordance with the Operating and Site Development Agreement, 10% of the total observing time is set aside for use by the University of Hawaii (UH).
55% of the UK, CA, and NL time is used for the JCMT Legacy Survey (JLS).

Time Allocation

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, NL: NL-PC, Ca: 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 JCMT Board

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), two appointed by the NWO (NL), and one appointed by the University of Hawaii.

See also JCMT Telescope Technical Details

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