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Brief Outline

The Sydney University Stellar Interferometer (SUSI) is a long-baseline optical interferometer located approximately 20km west of the town of Narrabri in northern New South Wales, Australia. SUSI is operated by staff from the Astronomy group (formerly the Chatterton Astronomy Department) within the Institute of Astronomy at the University of Sydney. It is located at the Paul Wild Observatory, alongside the Australia Telescope radio interferometer, a facility operated by the Commonwealth Scientific and Industrial Research Organisation (CSIRO).

SUSI has been developed, based on a successful prototype instrument, to tackle a range of problems in stellar astrophysics including the determination of the effective temperatures of stars, the physical characteristics of binary stars, and Cepheid variable stars. When combined with spectroscopic observations SUSI can be used to determine the masses and parallax (distance) of binary systems independently of other techniques. Similarly, SUSI and spectroscopic observations can be used to find the parallax of Cepheids using the interferometric Baade-Weselink method.

In its current configuration observations are made with a single baseline selected from an array of fixed north-south baselines covering the range from 5 to 640 m. Small apertures, wavefront-tilt correction and rapid signal sampling are employed to overcome the effects of atmospheric turbulence, while optical path equality is maintained by a dynamic optical delay line.

SUSI has two beam-combining systems. The original 'blue' system was designed to operate in the wavelength range 400-540 nm and employs narrow bandwidths (typically a few nanometers). The newer 'red' system is designed to work in the range 500-950 nm. The red system operates with width optical bandwidths of the order of 10% and uses the fringe scanning method to detect and measure the signals.

The red system also provides fringe tracking, enabling the instrument to lock on to the signal. The red and blue systems can be used in parallel: the red system is used to stabilize the fringe signal while the blue system makes narrow band observations.

SUSI seen from the north end of the 640m baseline.

Location : Paul Wild Observatory
approximately 20km from Narrabri
in northern New South Wales, Australia.

Latitude : 30 deg. 19 min. S
Longitude : 149 deg. 33 min. E
Altitude : 210 m above sea level

What is Stellar Interferometry?
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