Pupil Scrambling Integral Field Unit (PSI) for the Robert Stobie Spectrograph on SALT

Abstract

We propose to build an integral field unit (IFU) for the Robert Stobie Spectrograph (RSS) on the Southern African Large Telescope (SALT). This IFU (PSI) will employ the scrambling properties of fibers to address fundamental problems in achieving photon-limited sky subtraction due to variations in pupil illumination during observations. PSI will be fully encapsulated with a compact folding scheme in a standard long slit mask—far thinner than any previous fiber-based implementation. The IFU will cover 14 x 24 arcsec on sky, achieving spectral resolution R ≡ λ/δλ up to 6200 and photon-limited sky subtraction for studies of faint extended gas around galaxies beyond the reach of current 4m-class instruments. It will incorporate new-technology octagonal shaped fiber cores coupled by telecentric, pupil-imaging lenslets to fully optimize pupil scrambling and provide 100% integral sky coverage.