The Sydney University Stellar Interferometer -- I. The instrument

ABSTRA C T The Sydney University Stellar Interferometer (SUSI) is a new long-baseline optical interferometer located in northern New South Wales, Australia. SUSI has been developed to tackle a range of problems in stellar astrophysics, and its design is based on a successful prototype instrument. In its initial 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, and optical path equality is maintained by a dynamic optical delay line. The planned astrophysical programmes, the resulting design criteria, the instrument and its current status are described.