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New wide field facility for the AAT

A major upgrade is planned for one of Australia's scientific success stories, the Anglo-Australian Telescope (AAT). At its recent meeting, the bi-national AAT Board approved expenditure of $2 million to equip the 15 year old telescope with a wide angle field of view of two degrees, unique among such telescopes.

With this new wide field capability, the 3.9 metre AAT will maintain its leading role in astronomy. The AAT is the largest optical telescope in Australia and one of the largest and most powerful in the world. However, its supremacy will be challenged before the end of the century by the new generation of giant telescopes, with mirrors up to 10m in diameter, currently being built or planned in several other countries, and by other new facilities such as NASA's Hubble Space Telescope. To stay competitive, the AAT must develop new capabilities.

The wide field system uses optical fibres to enable astronomers to observe several hundred galaxies simultaneously. Thousands of galaxies and quasars are needed to give statistically meaningful results, and wide areas of sky have to be covered to reveal the large scale structure of the Universe. Since each faint galaxy has to be observed for an hour or more to give accurate data, such a programme would require dedicated use of a large conventional single-object telescope for many years. Given the wealth of astronomical projects to be studied and the many astronomers competing to use large telescopes like the AAT, this is not a feasible way to proceed. However, with its wide field of view and multiple optical fibres, the new system will maximise observing efficiency, and increase the rate at which astronomers can explore the Universe.

The AAT equipped with the wide field system will open up new avenues of astronomical research, and promises to yield fundamental answers on the nature and origin of the Universe, as well as the structure of our own Milky Way Galaxy.

Additional technical details

Optical Fibre System During the last few years the Anglo-Australian Observatory (AAO) has pioneered the use of optical fibres, in order to obtain the spectra for many faint stars and galaxies simultaneously. The logical next step is to increase both the field of view and the number of separate fibres.

Using this technique, optical fibres are positioned so that light from hundreds of selected stars or galaxies can travel along separate fibres, to a single spectrograph where it is analysed. Four hundred fibres will be used in the new wide field system, a six-fold increase on the number currently used. The combined effect of the increases in field size and number of fibres is to make the telescope effectively up to sixty times more powerful than it is already for certain crucial types of astronomy.

Robotics Technology The advanced technologies of the robotics industry have been used for the development of the system. A computer controlled robot head picks up and places small magnetic buttons onto the instrument plate, much like attaching magnets to your refrigerator door at home. Each of these buttons carries an optical fibre. To accurately position the button so as to align the fibre with the light from the star or galaxy, a small TV camera is attached to the robot head to observe the position of the button.

Largest Precision Lens System The project will involve the design and construction of one of the largest precision lens systems ever built. The six separate lens elements will have diameters of just under one metre. The entire lens assembly will weigh about 350 kg and will incorporate an atmospheric dispersion compensator, to counteract the effect of the earth's atmosphere.

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© Anglo-Australian Observatory 2004, PO Box 296, Epping NSW 1710 Australia

Roger Bell rb@aaoepp.aao.gov.au
01 Jan 1998