Robert Stobie Prime Focus Imaging Spectrograph

1. Robert StobiePrime Focus Imaging Spectrograph • Science Rationale • Modes • Fabry-Perot Spectral Imaging • Grating Spectroscopy; VPH Gratings, MOS • Spectropolarimetry • Mode table • Status SALT Workshop UKZN

2. What science should RSS do? • SALT features • very large aperture • good field of view (8 arcmin) • excellent ultraviolet throughput • queue scheduling • modest imaging • RSS: emphasize unique observing modes that do not require excellent imaging • UV spectroscopy down to 3200 Ǻ (rare on large telescopes) • higher resolution: high-throughput grating 3200 - 9000 Ǻ; Fabry-Perot 4300 - 9000 Ǻ (Visible Beam); later - 1.7 μm (NIR) • polarimetry (circular and linear) (very rare) • high-speed detector mode (very rare) SALT Workshop UKZN

3. Optics • All-refractive UV optics for high throughput • At prime focus for UV and full-field access • NIR upgrade path: simultaneous 3200 Ǻ – 1.7 μ SALT Workshop UKZN

4. Mechanisms 6-Grating Magazine Polarizing Beamsplitter(slide) 40-Slitmask Magazine 2 Fabry-Perot Etalons (slides) 3 CCD Mosaic Detector Shutter Camera Articulation 0 - 100° 2 Polarimeter Waveplates (slides) 20-Filter Magazine SALT Workshop UKZN

5. RSS on SALT Detector Camera Articulation Rail Etalons Collimator SALT Workshop UKZN

6. Fabry-Perot etalons (scans wavelength) Many wavelengths Perseus A in Hydrogen Light Perseus Cluster of Galaxies Imaging/ Fabry-Perot Spectroscopy Filters SALT Workshop UKZN

7. Filters "VPH" Grating disperses wavelengths Up to 40 Spectra Hubble Deep Field (South) Multi-Object Grating Spectroscopy Slitmasks selects objects SALT Workshop UKZN

8. Beamsplitter splits 2 polarizations Hubble Deep Field (South) Waveplate rotates polarization Spectropolarimetry Submode Polarization of 20 Spectra Also works in Imaging/ Fabry-Perot Modes SALT Workshop UKZN

9. = λ/Δλ High Efficiency with Volume Phase Holographic Gratings Resolution vs wavelength for 1.2 arcsec slit Constant Efficiency Contours SALT Workshop UKZN

10. How VPH Gratings Work • Created by exposing holograph material (“DiChromated Gelatin") to interference pattern from laser • Index of refraction of DCG is modulated in space • Large; inexpensive; custom design; efficient at high groove density SALT Workshop UKZN

11. One RSS VPH 1300 gr/ mm VPH SALT Workshop UKZN

12. Laser-cut slit masks Standard set of longslits Unique mask cut for each individual MOS observation Slit mask magazine will hold 10 longslits, 30 MOS masks Reload once/ week Mask with slits cut in it to let through selected nebulae in galaxy "Longslit" mask to get spectrum along one position angle Multi-Object Spectroscopy with custom masks at focus of telescope: Giant Elliptical Galaxy NGC1399 SALT Workshop UKZN

13. MOS Test Field Courtesy: Petri Vaisanen SALT Workshop UKZN

14. Position Reference Stars HII and PNe MOS Test Run Spectra 4080 A 7180 A NGC6822 – Oct 20 SALT Workshop UKZN

15. 17 PFIS Modes Tried: 6 Team Commissioned: 9 User Commissioned: 8 SALT Workshop UKZN

16. Status • On telescope Nov 2005 - Oct 2006 • longslit mode, polarimetry commissioning • other mode tests • on-sky throughput tests • Off telescope Nov 2006 - present • improving UV throughput, ghosts • Measured throughput to be 75 - 100% of design, sensitivity comparable or better than design throughput of other large telescope spectrographs • Back on telescope for further commissioning April 2008 SALT Workshop UKZN