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 Located at Cerro Pachon, Chile Optimized for high angular resolution First light: April 2003

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:

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

Ground layer compensation Rayleigh LGS is better than sodium LGS for ground- layer turbulence sensing

Science case

Resolution: 0.3” and 0.7”

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

Performance 2. High resolution Good seeing, 660 nm, R=12 NGS Good seeing, 660 nm

Performance 3. Low-resolution Stacked PSFs (good seeing, 660 nm) Tip-tilt AO with LGS

Performance 4. Summary FWHM vs. wavelength: median and good seeing More gain for favorable turbulence profiles!

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

Dedicated science instruments InstrumentFormatPixel size, arcsec Field, arcsec CCD, High resol. 2048x x30 CCD, Low resol. 2048x x158 IFU spectrograph 50x and x0.39 and 5x2.6

Deformable mirror Small electrostatic (OkoTech) 35 mm pupil 70 actuators Enough stroke for 1” seeing Biased, R=25 m DM-37 studied

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)

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 micron Transmission at 355 nm 0.74

Spot diagrams (LR mode)

Layout

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 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 mag, 100% sky coverage

Conclusions Astronomy-driven AO for SOAR Cheap AO system Visible-light AO Improved seeing with Rayleigh LGS: test-bed for larger telescopes