The Prime Focus Imaging Spectrograph Old Challenges and New Ones K. Nordsieck, Principal Investigato

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The Prime Focus Imaging Spectrograph Old
Challenges and New OnesK. Nordsieck, Principal
InvestigatorJeff Percival, Eric Burgh, Michael
SmithUniv of WisconsinTed Williams, Chuck
JosephRutgers UniversityDarragh 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

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Making a Powerful Astronomical Instrument

• Efficiency
• Minimize loss in optics
• Extract maximum data
• Spectroscopy composition, motion
• Polarimetry structure, magnetic field
• Observe many objects simultaneously

• Resolution
• Spread out colors more

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Imaging Spectroscopy
Filters
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Multi-Object Grating Spectroscopy
Slitmasks (selects objects)
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Optics Design Challenges
CCD detector
Camera
Grating

• 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

Collimator
Telescope Focus
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Collimator
Fused Quartz
CaF2
CaF2
CaF2
(NaCl)
Fused Silica
CaF2
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Camera
Fused Silica
CaF2
CaF2
(Fused Silica)
Fused Silica
NaCl
(Fused Silica)
(Fused Silica)
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Multi-object Spectroscopy with custom masks
at focus of telescope
Giant Elliptical Galaxy NGC1399

• Laser-cut slit masks
• Unique mask cut for each individual observation
• Slit mask magazine will hold 30 multi-object slit
  masks
• Reload once/ week

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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
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Small and Lightweight
DEIMOS on Keck 3x4m, 9000 kg
PFIS on SALT 1.5x2m, 500 kg
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Stiff
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Remote control
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Compact

• New technology
• Grating "grooves" formed by hologram
• Interference pattern from two laser beams on
  gelatin film
• Efficient, large, inexpensive custom gratings

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• Astronomical Instrumentation is a exciting
  business. A big demand for
• Astronomers
• Physicists
• Optical Engineers
• Mechanical Engineers
• Software Engineers
• ...........