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Description
Three fiber feed integral field units (IFU) is being developed in the SAAO fiber-lab for the Robert Stobie Spectrograph's visible arm and the future red arm. The smaller, 200 micron fibre IFU has 309 x 0.9 arcsec diameter spatial elements covering an elongated hexagonal footprint of 18 x 23 arcsec is now being commissioned. The larger, 300 (400) micron fiber IFU has 21 x 1.35 arcsec (178 x 1.8 arcsec) diameter spatial elements covering an on-sky area of 18 x 29 sq. arcsec (21 x 44 sq. arcsec). In all cases there are two groups of 13 fibres offset by roughly 50 arcsec on either side of the primary array to sample sky. The 0.9 arcsec spatial resolution SMIs provide median spectral resolution of
2400 at H-alpha wavelengths in the low resolution mode covering 320 to 740 nm bandpass. At a higher grating angle the SMI will deliver spectral resolution up to 10000 with 200 micron core fiber. In future there will be an additional red-arm which will extend the wavelength coverage up to 900 nm at a median resolution of 6000 for the same IFU. Each IFU sits in its own slit-mask cassette and is referred to as a slit-mask IFU (SMI). These are inserted in the same fashion as the existing long-slit cassettes at the SALT focal plane. Prismatic fold mirrors direct the focal plane into the fiber IFU and then back into the RSS collimator after the fibres are routed 180 deg within the cassette and formatted into a pseudo-slit. Fold-prisms ensure that the spectrograph collimator continues to see the same focal plane. In this paper we update on the laboratory characterization and on-sky commissioning-performance of Slit Mask IFU.
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