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The Giant Magellan Telescope

The Giant Magellan Telescope. AAS San Diego January 11, 2005. Matt Johns. The GMT Institutions. Carnegie Observatories Harvard University Smithsonian Astrophysical Observatory Massachusetts Institute of Technology University of Arizona University of Michigan University of Texas, Austin

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The Giant Magellan Telescope

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

  2. 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

  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 -> 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. 8.4 m, f/1.14 LBT surface, 24 nm rms 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. 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 Test tower LOG 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> 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)

  13. 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 elongation as seen through the off-axis 1.5-meter telescope. (Right) With dynamic refocus, the images become nearly circular. FWHM 6.4 arcsec H 2.7 arcsec V FWHM 2.8 arcsec 15w laser 20-30 km DR off 20-30 km DR on 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. Magellan (Manqui) Campanas Pk. Alcaino Pk. Ridge (Manquis) 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. 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

  27. 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

  28. Rms wavefront error summed over all 6 orders. bavg = average of all 5 LGS signals

  29. GMT cophasing of 7 segments (Lloyd Hart) Quarter-wave piston error PSF Sub-pupil MTFs • 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.)

  30. Test configuration

  31. 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

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