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The Prime Focus Imaging Spectrograph – Old Challenges and New Ones K. Nordsieck, Principal Investigator Jeff Percival, Eric Burgh, Michael Smith Univ of Wisconsin Ted Williams, Chuck Joseph Rutgers University Darragh O'Donoghue + SAAO • Old Challenges – What kind of scientific observations? – Big telescope Big instrument optics – Making good use of your observing time • New Ones – The SALT prime focus – New optics: holography Oct 30, 2003 PFIS - Student Wkshop 1 Making a Powerful Astronomical Instrument High-Speed Imager • Efficiency High-Speed – Minimize loss in optics Imaging Spectrograph – Extract maximum data Spectroscopy: composition, motion Imaging Polarimetry: structure, Spectromagnetic field polarimeter – Observe many objects simultaneously • Resolution – Spread out colors more Oct 30, 2003 PFIS - Student Wkshop 2 Imaging Spectroscopy Fabry-Perot etalons (selects wavelength) Filters Perseus A in Hydrogen Light Perseus Cluster of Galaxies Oct 30, 2003 PFIS - Student Wkshop 3 Multi-Object Grating Spectroscopy Filters VPH Grating (Splits colors) Up to 100 Spectra Hubble Deep Field (South) Slitmasks (selects objects) Oct 30, 2003 PFIS - Student Wkshop 4 Optics Design Challenges CCD detector 300 nm 400 UV Blue Camera Grating Collimator Telescope Focus Calcium Fluoride Sodium Chloride (salt) Calcium Fluoride Fused Quartz Fused Quartz Fused Silica Fused Silica Sodium Chloride (salt) Fused Silica Calcium Fluoride Calcium Fluoride Fused Silica Calcium Fluoride Fused Silica Calcium Fluoride Fused Silica 500 600 700 800 Green Yellow Red Wavelength PFIS range 900 Infrared • For highest efficiency: use lenses instead of mirrors • Need many lenses to correct color aberration CAD • Wavelength range: require crystals to work into UV • Lenses need to be very large (up to 25 cm) • Assembled into large holders with coupling fluid Calcium Fluoride Fused Quartz Oct 30, 2003 PFIS - Student Wkshop 5 Collimator Fused Quartz CaF2 CaF2 Fused Quartz Oct 30, 2003 Fused Quartz (NaCl) PFIS - Student Wkshop Fused Silica CaF2 6 CaF2 Camera (Fused Silica) CaF2 Fused Silica (Fused Silica) CaF2 NaCl Fused Silica CaF2 (Fused Silica) Oct 30, 2003 PFIS - Student Wkshop 7 Multi-object Spectroscopy with custom masks at focus of telescope: • Laser-cut slit masks • Unique mask cut for each individual observation • Slit mask magazine will hold 30 multi-object slit masks • Reload once/ week Oct 30, 2003 Giant Elliptical Galaxy NGC1399 PFIS - Student Wkshop Mask with slits cut in it to let through selected nebulae in galaxy 8 New Challenges: on SALT Prime Focus Spectrograph Prime Focus Tracker Motion of tracker and illumination of primary mirror as an object sets The instrument must be: Oct 30, 2003 PFIS - Student Wkshop 9 Small and Lightweight Open space frame welded from hollow square tubes of invar (low- expansion stainless steel) DEIMOS on Keck 3x4m, 9000 kg Oct 30, 2003 PFIS on SALT 1.5x2m, 500 kg PFIS - Student Wkshop 10 Stiff CAD 3D model of PFIS structure Perpendicular to Dispersion Spec microns/ track 20 10 Parallel to Dispersion 0 -80 -60 microns/ track 20 -40 -20 0 20 Declination (deg) Spec 10 0 -80 -60 -40 -20 0 Declination (deg) FEA ("Finite Element Analysis") showing how it bends under gravity Oct 30, 2003 PFIS - Student Wkshop Plus model of how tracker moves and PFIS optics shows how image moves during exposure 11 20 Remote control Grating Jukebox Etalon Insertors Slitmask Jukebox Filter Jukebox Shutter Camera Waveplate Rotator Articulation Oct 30, 2003 PFIS - Student Wkshop 12 Compact New technology: • Grating "grooves" formed by hologram • Interference pattern from two laser beams on gelatin film • Efficient, large, inexpensive custom gratings Oct 30, 2003 PFIS - Student Wkshop 13 Astronomical Instrumentation is a exciting business. A big demand for: Astronomers Physicists Optical Engineers Mechanical Engineers Software Engineers ........... Oct 30, 2003 PFIS - Student Wkshop 14