The Giant Magellan Telescope

1
The Giant Magellan Telescope
AAS San Diego January 11, 2005
Matt Johns
2
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
3
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

4
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

5
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

6
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
7
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.

8
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
9
Stressed Lap Polishing Machines at SOML
LOG
Test tower
LPM
Stressed lap
10
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.
11
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.

12
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)
13
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).

14
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.
15
Candidate First Generation Instruments
Concepts under development
16
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
17
GMT Enclosure Concept
18
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
19
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

20
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

21
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
22
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
23
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

24
Schedule
25
www.gmto.org
26
(No Transcript)
27
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
28
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
29
Rms wavefront error summed over all 6 orders.
bavg average of all 5 LGS signals
30
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.)

31
Test configuration
32
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
at top