|
Optical fibres are now regularly being used at the AAO for multiple object spectroscopy. The first prototype FOCAP system, built in late 1981, comprised a three metre bundle of 24 polymer-clad silica (PCS) fibres with core diameters of 200 microns. This linked an aperture plate at the auxiliary Cassegrain focus with the main intermediate dispersion spectrograph (known as the RGO spectrograph). Using the Image Photon Counting System as a detector, it was then possible to simultaneously record the spectra of up to 25 separate objects within the 12 arcmin field of the auxiliary focus. This system had a throughput of 40-50%, the major source of loss being focal ratio degradation (FRD). Intended as a trial, this first FOCAP bundle was used successfully in various observing programs on a total of 12 nights in 1982. Following on from the experience gained from this observing, new FOCAP bundles were developed using new all-silica (AS) type fibre which showed much less FRD. Bundles of 50 fibres were built, employing a faster f/6 collimator to collect more of the fibre output beam. With these improvements, the FOCAP system transmission was increased to 60-70%. A total of 15 nights were scheduled in the first three quarters of 1983 to use this system in a wide variety of multi-object spectroscopic observing programs. As an example of the substantial savings in telescope time that are possible with this system, during a recent run of three nights, spectra were obtained for a total of 400 objects with an average exposure of two hours. Other developments that are planned or in progress include a fibre feed to the low--dispersion faint object red spectrograph (FORS) and an aperture plate system to access the full 40 arcmin field available at the AAT's Cassegrain focus. This paper reports on this work and outlines possible future developments.
|
