The Giant Magellan Telescope

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The Giant Magellan Telescope
AAS San Diego January 11, 2005
Matt Johns
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The GMT Institutions
Carnegie Observatories Harvard University Smithson
ian Astrophysical Observatory Massachusetts
Institute of Technology University of
Arizona University of Michigan University of
Texas, Austin Texas AM University OTHERS TBD
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The GMT Organization

• Memorandum of Understanding
• Conceptual design phase funding.
• Work toward GMT incorporation agreement
• Governing bodies
• GMT Board each institution has two members
• Science Working Group
• Project Scientists Working Group
• AO Instrumentation Groups
• Project Office

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GMT Design

• Alt-az structure
• Seven 8.4-m primary mirrors
• Cast borosilicate honeycomb
• 25.3-m enclosed diameter
• 24-m diffraction equivalent
• 21.5-m equivalent aperture
• 3.2-m adaptive Gregorian secondary mirror
• Instruments mount below M1 at the Gregorian focus

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GMT Optical Design

• Primary Mirror
• D1 25.3 meter
• R1 36.0 meters
• K -0.9983
• f/0.7 primary mirror overall
• Gregorian secondary mirror
• D2 3.2 meter
• R2 4.2 meter
• K2 -0.7109
• Segments aligned with primary mirrors
• Combined Aplanatic Gregorian focus
• f/8.2 final focal ratio
• Field of view 24 - 30 arc-min.
• BFD 5.5 meters
• M2 conjugate 160 m above M1

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GMT Structure
Design goal Compact, stiff Structure Low wind
cross-section Maximize modal performance Minimum
swing radius -gt cost Model parameters Analysis
includes telescope structure, optics,
instrument load Height 36.1 meters Moving mass
991 metric tons Lowest vibration mode 5.1 Hz
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Exploits 8.4 m experience

• Large 8.4m diameter subapertures of
  well-corrected wavefront.
• Co-phasing not needed for seeing-limited imaging
  at llt5 mm
• Thick cross section (0.7m) resists surface
  deflection under wind loading.
• Developed technology
• Active supports maintain figure accuracy
  alignment in the telescope.
• Thermal Control ? Settling time 1/e lt 1 hour
• Existing production facilities technology
  exists within the consortium at SOML.

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Preparations for Casting GMT 18.4-m off-axis
segment
Primary mirror production Pacing item for GMT
completion Requires development of off-axis
technology Modification of test tower
Prototype mirror Casting contract signed December
2004 Projected casting date July 05
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Stressed Lap Polishing Machines at SOML
LOG
Test tower
LPM
Stressed lap
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3.2-m Segmented Adaptive Gregorian Secondary
Mirror
64 cm MMT AO secondary mirror
Technology developed for MMT LBT 7 2-mm thick
facesheets aligned with Primary mirror segments
attached to a single reference body. 4700 voice
coil actuators total Laser projector rides on top.
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Adaptive Optics Modes

• First Generation AO Capabilities
• Ground layer AO (GLAO)
• Laser tomography AO
• Second Generation capabilities
• Extreme (high contrast) AO (ExAO)
• Ref. J. Codona, SPIE 5490-51.
• Multi-conjugate AO (MCAO)
• Adaptive secondary mirror is the first deformable
  element in all AO systems.

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Ground Layer AO (GLAO) with GMT

• Emerging technology.
• Low altitude turbulence correction.
• Secondary conjugation at 160m above primary.
• Natural guide stars or lasers.
• Performance goals
• l gt 0.8 m
• Field of view gt 10
• Factor of 1.5-2 reduction in image size.
• GLAO test at Magellan (A. Athey, SPIE 5490-179)
• GLAO at MMT

Modeled using Cerro Pachon turbulence profile.
(M-L Hart 2003)
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LTAO

• Laser Tomography AO
• Single conjugate AO with the AO secondary mirror
  multiple lasers.
• Diffraction limited imaging over full sky in the
  NIR.
• Fields of view limited by tilt anisotropy
• Prototype systems under development at 1.5m
  telescope MMT
• Rayleigh beacons with dynamic re-focusing (DR)
  (Stalcup,SPIE 5490-29).
• Sodium lasers will be required to scale up to GMT
  (Angel, SPIE 5490-31).

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Extreme AO
Radial average of GMT diffraction-limited PSFs
with a bandpass of 1.57 to 1.73 microns. Blue
dash is the normal profile. Red line is with
apodization of individual segments. Green line is
150-degree average of the PSF formed by phase
compensation applied to the adaptive secondary.
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Candidate First Generation Instruments
Instrument Wavelength (µm) Resolution R FOV AO Mode Observing Modes
1 Optical MOS 0.4-0.95 (0.3-1.0) 500-2500 (250-5000) 50 (150) sq. arcmin (GLAO) MOS/IFU/TF/Imager
2 Near-IR MOS 1.0 -2.5 (0.8 -2.5) 500-3500 (250-10K) 25 (100) sq. arcmin GLAO MOS/IFU/TF/Imager
3 Echelle 0.3-1.0 30k-50K 3 slit Natural seeing Single Obj/Fiber-fed MOS/I cell
4 MIR Spectrograph 5.0-25 (3-25) 30K (100K) 3 slit LTAO Single Object
5 NIR AO imager 1.0-2.5 1500 (3500) 20 (30) LTAO (ExAO, MCAO) Coronagraph/IFU/TF/ Imager
6 MIR AO-Imager 5-25 5-5000 30 LTAO Coronagraph/IFU/TF
Concepts under development
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GMT Instrument Platform (IP)
Rotator
GLAO Guider
Folded port instruments
Echelle NIR AO imager NIR Echelle
Small-intermediate sized intstruments Rapid
exchange
Gregorian instruments
capacity 6.4 m Dia. 7.6 m high 25 ton
Optical MOS Near-IR MOS Mid-IR Spectrograh
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GMT Enclosure Concept
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Enclosure Structure
Height 60 m Diameter 54 m Structure design
cost study complete 12/04 Thermal flow
studies On-site Facilities design mid-2005
M3 Engineering
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Site Testing

• Northern Chile location
• GMT conducting tests at 4 LCO sites
• Coordinate/share data with other projects
• Test equipment
• Differential Image Motion Monitors (DIMM)
• Multi-aperture Scintillation Sensor (MASS)
• Meteorological stations

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Decadal Survey Key Problems

• Large-Scale properties of the Universe, Matter,
  Energy, Expansion History
• First Stars and Galaxies
• Formation and Evolution of Black Holes
• Formation of Stars and Planetary Systems
• Impact of Astronomical Environment on the Earth
• Astronomy Astrophysics in the New Millennium

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GSMT Key Science Areas

• Origin of Large-Scale Structure
• Building of the Milky Way and Other Galaxies
• Exploring Other Solar Systems

Frontier Science Enabled by a Giant Segmented
Mirror Telescope
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GMT Science Priorities

• Physical Studies of Exoplanets
• Star Formation the Origin of the IMF
• Stellar Populations Chemical Evolution
• The Nature of Dark Matter and Dark Energy
• Galaxy Assembly
• Black Hole Growth
• First Light Reionization of the Universe

The Giant Magellan Telescope Opening a New
Century of Cosmic Discovery
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GMT Science Technology in Context

• The GMT Scientific priorities and capabilities
• Address the key decadal survey goals
• Are aligned with the GSMT science priorities
• The GMT design will readily
• Adapt to new discoveries evolving priorities
• Enhance value of ALMA, JWST, other existing and
  planned facilities

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Schedule
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www.gmto.org
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Reaching the diffraction limit of the GMT with
adaptive optics
The central peak of the GMT PSF contains 65 of
the total incident flux, compared to 84 for a
filled circular aperture. FWHM is the same as
for 24 m filled aperture 40 mas FWHM at 5 mm
8 mas FWHM at 1 mm
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Ground layer measured with laser at MMT 9/28/04
Telescope measurement of ground layer
seeing (Michael Lloyd Hart et al) 5 Rayleigh
beacons in 2 arcminute circle 30W 532 nm YAG
laser Centered around natural star in 0.7 seeing
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Rms wavefront error summed over all 6 orders.
bavg average of all 5 LGS signals
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GMT cophasing of 7 segments (Lloyd Hart)

• phase information for closed loop operation will
  come from a natural star.
• A single NGS can sense the 6 relative pistons in
  addition to regular tip/tilt. (Need 8 modes from
  7x8.4 m mirrors better than 2 modes from 1x8.4 m
  on current large telescope with LGS, so should
  not at all compromise sky cover.)

• Absolute piston measurement
• Piston misregistration has unique effects on the
  MTF of three partially non-redundant arrays made
  from the full pupil.
• Each M1 segment is used exactly twice.
• Ideal PSFs are shown in second column.
• A quarter wave of piston on either an edge or
  center segment will affect two of the three MTFs.
  
• (N.B. MTFs are shown at much higher resolution
  than would actually need to be sampled.)

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Test configuration
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New test tower at Mirror Lab
Needed for 8.4 m off-axis segments Long 36
m radius of curvature (LBT 20 m) Requires
diffraction limited 4 m folding spherical mirror
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