The Giant Magellan Telescope
Matt Johns
AAS San Diego
January 11, 2005
The GMT Institutions
Carnegie Observatories
Harvard University
Smithsonian Astrophysical
Observatory
Massachusetts Institute of
Technology
University of Arizona
University of Michigan
University of Texas, Austin
Texas A&M University
+ …OTHERS TBD
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
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
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
GMT Optical Design
GMT Structure
Design goal: Compact, stiff Structure
Low wind cross-section
Maximize modal performance
Minimum swing radius -> 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
Exploits 8.4 m experience
• Large 8.4m diameter subapertures of
well-corrected wavefront.
– Co-phasing not needed for seeing-limited
imaging at l<5 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 < 1
hour
• Existing production facilities &
technology exists within the consortium
at SOML.
8.4 m, f/1.14 LBT
surface, 24 nm
rms
Preparations
for Casting
GMT 1
8.4-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
Stressed Lap Polishing Machines at SOML
Test
tower
LPM
Stressed
lap
LOG
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.
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.
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 > 0.8 m
– Field of view: > 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)
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).
Figure 89. (Left) Five beams projected on a 1 arcmin radius from a single 15–Watt laser using a custom hologram.
The beams are seen here on the bottom of cloud. (Center) Images of the Rayleigh beacons gated between 20 – 30
kilometers without dynamic refocus. The streaking is caused by perspective
FWHMelongation as seen through the off-axis
1.5-meter telescope. (Right) With dynamic refocus, the images become
circular.
6.4nearly
arcsec
H
2.7 arcsec V
15w laser
20-30 km DR off
FWHM
2.8 arcsec
20-30 km DR on
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.
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 AOImager
5-25
5-5000
30”
LTAO
Coronagraph/IFU/TF
Concepts under development
GMT Instrument Platform (IP)
Rotator
GLAO Guider
Folded port
instruments
Echelle
Small-intermediate
NIR AO imager
sized intstruments
NIR Echelle
Rapid exchange
Gregorian
instruments
capacity
Optical
MOS
6.4 m Dia.
Near-IR
MOS
7.6 m high
Mid-IR 25
Spectrograh
ton
GMT Enclosure Concept
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
Site Testing
Magellan (Manqui)
Campanas Pk.
Alcaino Pk.
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
Ridge (Manquis)
Decadal Survey Key Problems
1. Large-Scale properties of the Universe, Matter,
Energy, Expansion History
2. First Stars and Galaxies
3. Formation and Evolution of Black Holes
4. Formation of Stars and Planetary Systems
5. Impact of Astronomical Environment on the Earth
“Astronomy & Astrophysics in the New Millennium”
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
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
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
Schedule
www.gmto.org
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
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
Rms wavefront error summed over all 6 orders.
bavg = average of all 5 LGS signals
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.)
Quarter-wave
piston error
Sub-pupil
PSF
MTFs
Absolute piston measurement
Piston misregistration has unique effects
on the MTF of three partially nonredundant 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.)
Test configuration
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