RSS-NIR: a Versatile New Near-Infrared Instrument for the 11-meter Southern African Large Telescope

Type Conference Paper
Names Ryan L. Doering, A. I. Sheinis, M. J. Wolf
Proceedings Title Bulletin of the American Astronomical Society
Conference Name American Astronomical Society, AAS Meeting #215, #441.30
Volume 42
Pages 406
Date January 1, 2010
Short Title RSS-NIR
Library Catalog NASA ADS
Abstract The near infrared (NIR) upgrade to the Robert Stobie Spectrograph (RSS) will be commissioned on the 11-meter Southern African Large Telescope (SALT) in 2012. The versatile instrument provides high throughput, low- to medium-resolution long-slit and multi-object spectroscopy with broadband, spectropolarimetric, and Fabry-Perot imaging modes over an 8′ × 8′ field of view. In spectroscopy mode the instrument is expected to have a throughput > 35% and reach a limiting Vega magnitude of H=19 with S/N=10 in a 1 hour exposure at R 7000. A dichroic beamsplitter allows RSS-NIR to be used with the existing optical spectrograph to simultaneously cover the spectral range from 3200 Å to 1.7 μm, a rare instrumentation capability among 8-11 meter class telescopes. Both the NIR and optical arms incorporate an articulated camera design to extend the performance range of the suite of highly efficient volume phase holographic gratings. The NIR camera utilizes a HAWAII-2RG detector with an Epps optical design consisting of 7 spherical elements and providing images with ensquared energy of 90% within a 2 × 2 pixel Nyquist sampled box (0.5″ on a side) over all wavelengths and field angles. The RSS-NIR is semi-warm, sharing a common slit plane and partial collimator with the optical spectrograph. During NIR spectroscopic observations the slit plane will be cooled to 20-30 degrees below the ambient temperature. To lower the remaining thermal background of the instrument, a pre-dewar, cooled to -40 °C, houses all of the optical elements upstream of the NIR pupil: the dispersing optics, filters, and the first five camera optics. The last two camera optics, long-wavelength blocking filters, and the HAWAII-2RG detector and SIDECAR electronics are housed in a dewar cryogenically cooled to approximately 120 K. We present an overview of the instrument's design and discuss its expected performance.
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