a visible-light ao system for the 4.2 m soar telescope
DESCRIPTION
A visible-light AO system for the 4.2 m SOAR telescope. A. Tokovinin, B. Gregory, H. E. Schwarz, V. Terebizh, S. Thomas. Outline of the talk…. Case for visible-light AO at SOAR Performance estimates System concept. SOAR telescope. Built and operated by a consortium - PowerPoint PPT PresentationTRANSCRIPT
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A visible-light AO system for the 4.2 m SOAR telescope
A. Tokovinin, B. Gregory, H. E. Schwarz, V. Terebizh, S. Thomas
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Outline of the talk…
• Case for visible-light AO at SOAR
• Performance estimates• System concept
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SOAR telescope
• Built and operated by a consortium• Located at Cerro Pachon, Chile• Optimized for high angular
resolution• First light: April 2003
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Drivers for visible-light AO
SOAR should complement 8-m Gemini (IR-optimized) and 4-m Blanco (wide field): high angular resolution in the visible is required!
Lack of bright guide stars for AO Small isoplanatic field and cone effect Competition with Hubble Space Telescope Competition with Gemini, VLT in the IR
Problems:
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Concept for SOAR AO
•High-resolution mode: NGS up to 12 mag., small field, diffraction-limited resolution, 3-D spectroscopy
•Low-resolution mode: ground layer compensation (improved seeing) with Rayleigh LGS, 3 arcmin. field, 100% sky coverage
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Ground layer compensation
Rayleigh LGS is better than sodium LGS for ground-layer turbulence sensing
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Science case
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Resolution: 0.3” and 0.7”
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Performance 1. Seeing at Pachon
• Median seeing: 0.67” (r0=15cm at 500nm)
• Good seeing: 0.50” (r0=20cm)
• Outer scale 25m• Average profile (65%
near the ground)• >25000 profiles at
CTIO with MASS A good night: June 20, 2002
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Performance 2. High resolution
Good seeing, 660 nm, R=12 NGS
Good seeing, 660 nm
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Performance 3. Low-resolution
Stacked PSFs (good seeing, 660 nm)
Tip-tilt
AO with LGS
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Performance 4. Summary
• FWHM vs. wavelength: median and good seeing• More gain for favorable turbulence profiles!
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AO instrument concept
• Compensation order 10 (40-cm sub-aperture size)• Dedicated science instruments
(not adaptive secondary)• Small Deformable Mirror (DM)• Shack-Hartmann WFS• Compact refractive optics• UV laser
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Dedicated science instruments
Instrument Format Pixel size,arcsec
Field,arcsec
CCD, High resol.
2048x2048
0.015 30x30
CCD,Low resol.
2048x2048
0.077 158x158
IFU spectrogra
ph
50x26 0.015 and 0.1
0.75x0.39 and 5x2.6
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Deformable mirror• Small
electrostatic (OkoTech)• 35 mm pupil • 70 actuators• Enough stroke
for 1” seeing• Biased, R=25 m• DM-37 studied
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Wave-front sensor
• Shack-Hartmann type• 10x10 format (8 pixels per sub-
aperture)• CCD-39 from E2V corp. most likely• No offsets resp. to science instruments• 4 TTS for LGS (APD-based)
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Optical design• Refractive design (cheap, compact)• Field lens, collimator, DM, camera• Two cameras: low and high resolution• Low Res.: FWHM <0.1” over 3 arcmin.• High Res.: diffraction-limited• Wavelength range 0.4-1 micron• Transmission at 355 nm 0.74
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Spot diagrams (LR mode)
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Layout
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Laser Guide Star
• Solid-state Nd:YAG laser, 355 nm• Power from 1 to 8 W• Focused at 10 km, range gate 1 km• Flux 400-3000 photons per sub-
aperture per millisecond• Small launch telescope behind the
SOAR secondary• No danger to airplanes and satellites• Tip-tilt on 2-4 stars to 18-19 mag,
100% sky coverage
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Conclusions
• Astronomy-driven AO for SOAR• Cheap AO system• Visible-light AO• Improved seeing with Rayleigh
LGS: test-bed for larger telescopes