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Oct 30, 2003 PFIS - Student Wkshop 1
The Prime Focus Imaging Spectrograph – Old
Challenges and New OnesK. Nordsieck, Principal Investigator
Jeff Percival, Eric Burgh, Michael SmithUniv of Wisconsin
Ted Williams, Chuck JosephRutgers 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 2
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
Spectrograph
Spectro-polarimeter
Imager
Imaging
Imaging
High-Speed
High-Speed
Oct 30, 2003 PFIS - Student Wkshop 3
Perseus Cluster of Galaxies
Perseus A in Hydrogen Light
Imaging Spectroscopy
Filters
Fabry-Perot etalons(selects wavelength) M
any
wavele
ngths
Oct 30, 2003 PFIS - Student Wkshop 4
Hubble Deep Field
(South)
Up to 100 Spectra
Slitmasks(selects objects)
Filters
VPH Grating(Splits colors)
Multi-Object Grating Spectroscopy
Oct 30, 2003 PFIS - Student Wkshop 5
Optics Design Challenges
• 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
Sodium Chloride (salt)
Sodium
Chloride (salt)
Fused Quartz
Fused QuartzFused Quartz
Fused Silica
Fused S
ilica
Fused S
ilica
Fused S
ilica
Fused S
ilica
Fused S
ilica
Calcium
Fluoride
Calcium
Fluoride
Calcium
Fluoride
Calcium Fluoride
Calcium Fluoride
Calcium Fluoride
Calcium Fluoride
300 nm UV Blue Green Yellow Red Infrared
400
500
600
700
800
900
WavelengthPFIS range
Col
lim
ator
Camera
Tel
esco
pe F
ocus
Grating
CCD detector
Oct 30, 2003 PFIS - Student Wkshop 6
Collimator
Fused Quartz CaF2 Fused Quartz
Fused Quartz CaF2CaF2
CaF2Fused Silica
(NaCl)
Oct 30, 2003 PFIS - Student Wkshop 7
Camera
CaF2Fused SilicaCaF2
CaF2
Fused SilicaNaCl
(Fused Silica)
(Fused Silica)
(Fused Silica)
Oct 30, 2003 PFIS - Student Wkshop 8
Multi-object Spectroscopy with custom masks
• Laser-cut slit masks
• Unique mask cut for each individual observation
• Slit mask magazine will hold 30 multi-object slit masks
• Reload once/ week
Giant Elliptical Galaxy NGC1399
at focus of telescope:
Mask with slits cut in it to let through selected nebulae in galaxy
Oct 30, 2003 PFIS - Student Wkshop 9
New Challenges: on SALT
Prime FocusTracker
Prime FocusSpectrograph
Motion of tracker and illumination of primary mirror as an object sets
The instrument must be:
Oct 30, 2003 PFIS - Student Wkshop 10
Small and Lightweight
DEIMOS on Keck 3x4m, 9000 kg
PFIS on SALT 1.5x2m, 500 kg
Open space frame welded from hollow square tubes of invar (low- expansion stainless steel)
Oct 30, 2003 PFIS - Student Wkshop 11
StiffCAD 3D model of PFIS structure
FEA ("Finite Element Analysis") showing how it bends under gravity
Plus model of how tracker moves and PFIS optics shows how image moves during exposure
Parallel to Dispersion
0
10
20
-80 -60 -40 -20 0 20
Declination (deg)
mic
ron
s/ t
rack Spec
Perpendicular to Dispersion
0
10
20
-80 -60 -40 -20 0 20
Declination (deg)
mic
ron
s/ t
rack
Spec
Oct 30, 2003 PFIS - Student Wkshop 12
Remote control
Filter Jukebox
Grating Jukebox
Shutter
Slitmask Jukebox
Waveplate Rotator
Etalon Insertors
Camera Articulation
Oct 30, 2003 PFIS - Student Wkshop 13
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 14
Astronomical Instrumentation is a exciting business. A big demand for:
Astronomers
Physicists
Optical Engineers
Mechanical Engineers
Software Engineers
...........