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Australian–European Southern Observatory Positioner

AESOP is the fibre positioner unit for the 4MOST instrument planned for the 4-metre European Southern Observatories VISTA telescope in Chile.

The 4MOST project, led by the Astrophysical Institute Potsdam (Germany), involves a number of European partners. The AAO component, AESOP, deploys 2400 optical fibres to required positions on the curved focal surface of the telescope. Each fibre can be deployed anywhere within a fixed patrol area. Field reconfigurations are achieved in an iterative closed-loop process with positional feedback from a metrology system. Optical fibres are connectorised at their exit from the positioner system, where they feed a fibre bundle terminated a series of optical spectrographs. The proposed design for AESOP is an evolution of the AAO’s tilting spine technology, first designed and implemented in the FMOS-Echidna instrument for the Subaru telescope.

The AESOP instrument deploys 2436 science fibres and 12 guide fibre bundles, each consisting of a spine at one end and a fibre connector at the other. Fibres from spectrographs will be terminated with similar fibre connectors and will be plugged into the AESOP fibre connector adaptors.
Light coming from the sky (grey beam) travels through the telescope optics into the science fibres onto the focal surface. The science fibres transmit the light to the Fibre Feed Connectors which connect via long science fibres to the spectrographs. The light from the Spectrograph Back Illumination system travels from the far ends of the fibres to the Metrology Camera.
AESOP mounted on the Vista telescope (spines not shown here).
Close-up of AESOP showing modules with guide spines only.