A 3 degree prime focus field for the AAT

Abstract

The Anglo-Australian Telescope's 2° field 400 fiber prime focus feed for spectroscopy has been very successful. For a new instrument proposal (known as Hector) to provide robotically deployed IFUs at the AAT prime focus, a corrector giving a field 3° in diameter is required to make optimum use of as many as 100 IFUs. Having IFUs with individual field diameters of 10 to 15 arcsec feeding spectrographs allows some relaxation in the tolerances to lateral chromatic aberration and to atmospheric dispersion, since each can be compensated computationally without much loss in efficiency. The AAT has four removable top ends, of which the original prime focus version could be recycled to carry a much larger corrector. Its outer ring passes a field up to 3.3° diameter without vignetting and the dome slit has a little more clearance. A very satisfactory optical design has been developed for a corrector providing 3° field diameter without vignetting, having six elements with three non-spherical surfaces. The diameter of the largest element is 1250 mm. The corrector also works well for direct imaging on a flat field up to 1° diameter.