Instrumentation Concepts for
the 30-meter GSMT
S.C. Barden, M. Liang, K.H. Hinkle, C.F.W. Harmer,
R.R. Joyce (NOAO/NIO)
September 17, 2001
AURA New Initiatives Office
GSMT Point Design Instrument Study
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Develop telescope, AO and instruments as an
integrated system
Design concepts driven by science objectives
– Multi-Object, Multi-Fiber, Optical Spectrograph
MOMFOS (science: tomography of the universe)
– Near IR Deployable Integral Field Spectrograph
NIRDIF (science: tomography of pre-galaxy fragments)
– Mid-IR, High Dispersion, AO Spectrograph
MIHDAS (science: origins of planetary systems)
– MCAO-fed near-IR imager (science: stellar populations)
Build on extant concepts where possible
Define major design challenges
Identify needed technologies
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Multi-Object Multi-Fiber Optical
Spectrograph (MOMFOS)
• 20 arc-minute field at f/1 Prime Focus
• 60-meter fiber cable
• 700 0.7” fibers
• 3 spectrographs, ~230 fibers each
• VPH gratings
• Articulated collimator for different resolution regimes
Resolution
Example ranges with single grating
• R= 1,000
350nm – 650nm
• R= 5,000
470nm – 530nm
• R= 18,000
491nm – 508nm
• Detects 13% - 23% of photons hitting the 30m
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Prime Focus MOMFOS
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MOMFOS
with Prime
Focus
Corrector
Conceptual design
fits in a 3m dia by
5m long cylinder
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MOMFOS Spectrograph
Micro-Lens Relay
500 mm diameter
fiber fed by two
micro-lenses with
spherical surfaces.
Field stop limits
light to 0.72” aperture.
100% of light couples into fiber.
Comparable lens required at fiber output.
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MOMFOS Spectrograph
Fiber Positioner
Positioner based on Echidna positioner
built by AAO for FMOS on Suburu
Echidna prototype image from www.aao.gov.au/local/www/echidna/
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MOMFOS Spectrograph
3 Spectrographs
230 fibers each
R=18000
mode
R=5000
mode
f/4.5 Collimator
f/0.86 Camera
10 VPH gratings
to cover full
optical range
and 3 resolution
modes.
Articulated
collimator
4K by 4K CCD
15 mm pixels
2 pixel binning
R=1000
mode
500mm pupil; all spherical optics
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MOMFOS Spectrograph
Predicted Efficiency
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Spot Diagrams for MOMFOS Spectrograph
On-Axis
R = 5000
1126 l/mm
794-904 nm
28.6°
Fiber Diameter
Half-Field
Full-Field
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Tomography of Individual Galaxies
out to z ~3
GSMT 3 hour, 3s limit
at R=5,000
0.1”x0.1” IFU pixel
(sub-kpc scale structures)
J
26.5
H
25.5
K
24.0
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Near Infra-Red Deployable Integral
Field Spectrograph (NIRDIF)
• MCAO fed
• 1.5 to 2.0 arc-minute FOV
• 1 – 2.5 mm wavelength coverage
• Deployable IFU units
• 1.5 arc-second FOV per IFU probe
• 31 slices per IFU probe (0.048” per slice)
• ~26 deployable units
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Near Infra-Red Deployable Integral
Field Spectrograph (NIRDIF)
Relay optics contained in deployable arm.
1.5 by 1.5 arc-second field of view.
f/38 to f/128 converter from MCAO field to image
slicer.
Telecentric input and output.
Cold stop located within relay.
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Near Infra-Red Deployable Integral
Field Spectrograph (NIRDIF)
f/128 image slicer with 31 slices converted to
f/11.5 for the spectrograph.
Spectrographs
• 2 IFU’s per spectrograph
• ~13 spectrographs
• R = 1000 to 10,000
• Z, J, H, and K spectral coverage
• 2 K detector format assumed
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Near Infra-Red Deployable Integral
Field Spectrograph (NIRDIF)
Image Slicer
Image Relay
Spectrograph
Two Image Slicers per Spectrograph
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Near Infra-Red Deployable Integral
Field Spectrograph (NIRDIF)
Spot diagrams for
NIRDIF spectrograph.
Slice 1
Slice 16
Slice 31
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Origins of Planetary Systems
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Goals:
– Understand where and when planets form
– Infer planetary architectures
via observation of ‘gaps’
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Measurements:
Spectra of accreting
PMS stars
(R~105; l ~ 5, 17 mm)
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Key requirements:
On axis, high Strehl AO;
low emissivity
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Mid-Infrared High Dispersion AO
Spectrograph (MIHDAS)
• Adaptive Secondary AO feed
• On-Axis, Narrow Field/Point Source
• R=120,000
• 3 spectrographs
• 2-5 mm (small beamed, x-dispersed), 0.2 arc-second
slit length
• 10-14 mm (x-dispersed), 1 arc-second slit
• 16-20 mm (x-dispersed), 1 arc-second slit
• 10-14 mm spectrograph likely to utilize same collimator as
16-20 mm instrument. Different Gratings and Camera.
• 2-5 mm spectrograph may require additional AO mirrors.
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Mid-Infrared High Dispersion AO
Spectrograph (MIHDAS)
16-20 mm spectrograph will be large. Diffraction limit
at 20 microns is about ¼ arc-second, comparable to
native seeing limit.
Echelle grating is 1.5 meters in length! Overall
instrument is expected to take up a volume of
about 4 by 2 by 3 meters!
All of which needs to be cryogenically cooled.
Instrument to be located at Cass location and move
with the telescope.
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Mid-Infrared High Dispersion AO
Spectrograph (MIHDAS)
f/18.75 Collimator
f/2 Camera
150 mm by 1500 mm
R10 (84°) Echelle
7 mm/line (0.143 l/mm)
360 mm diameter
cross-disperser
45 l/mm, 26.5° blaze
Off-axis parabolic
collimator
4-mirror camera
1K by 1K Si:As detector
27 mm pixels
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MCAO Near-IR Imager
• f/38 input with 1:1 reimaging optics
• 1.5 to 2 arc-minute field of view
Monolithic imager  5.5 mm/arc-second plate scale!
 0.004 arc-second per pixel sampling
 685 mm sized detector array for 2 arc-min field!
 28K by 28K detector!
 7 by 7 mosaic of 4K arrays
Alternative approach is to have deployable capability for
imaging over a subset of the total field.
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Instrument Locations on Telescope
Fiber-fed
MOMFOS
MCAO-fed
NIRDIF
or
MCAO Imager
Cass-fed
MIHDAS
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Information on AURA NIO activities is
available at:
www.aura-nio.noao.edu
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