Adaptive optics for SOAR

Andrei Tokovinin (CTIO)

More information:

SOAR niche
SOAR, Blanco and Gemini as a system

Science case for AO at SOAR

The case for high angular resolution is evident! See images with 0.3" and 0.7" resolution.

Improved seeing in a large (3') FOV

Diffraction limit, small (10") FOV

Seeing at Cerro Pachon

Source: Gemini RPT-AO-G0094

Revised seeing

r0 at zenith at 0.5 micron

  • Median: 15 cm (FWHM 0.67")
  • Good (25%): 20 cm (FWHM 0.50")
  • 75%: 10.7 cm (FWHM 0.94")

Finite turbulence outer scale

~25 m

  • Less tip-tilt (compared to standard theory)
  • Better uncompensated seeing
  • More improvement in the IR
  • Less improvement from tip-tilt

Revised "isokinetic patch"

4 m/ 16 km = 51"

Mean turbulence profile at Cerro Pachon

Mean turbulence profile at Cerro Pachon (1998, 22 nights).

Seeing improvement with AO

Improve wave-front coherence at r0 scale .

Idea 1: Low-order compensation = incoherent combination of 1 m sub-apertures. Example: CFHT+PUEO. Gain in FWHM: ~2 times. Small FOV.

Idea 2: Compensate only low layers. Gain in FWHM: ~2 times. Large FOV.

PSFs: uncompensated, tip-tilt, AO+LGS
PSFs under good seeing at 0.67 micron:

Full line: uncompensated (leftmost) and with tip-tilt.

Dashed line: AO+LGS at 10 km.

Diffraction-limited AO

Improve wave-front coherence across full aperture.

PSFs: uncompensated, compensated

PSFs under good seeing at 0.67 micron with 12m NGS. The leftmost PSF is for uncompensated image under same conditions.

Strehl vs. NGS magnitude

Limiting magnitude?

Strehl ratio on-axis and at 4" off-axis versus NGS R-magnitude. Good seeing, 0.67 micron.

PUEO: 1-m sub-apertures -> 15m

SOAR: 0.5-m sub-apertures -> 13m?

AO modes

Comparing tip-tilt, seeing improvement and full AO

Performance: FWHM

FWHM on-axis, median seeing

FHWM: median seeing

Good match between seeing-improved resolution in the visible and seeing limit in the IR.

FWHM on-axis, good seeing

FHWM: good seeing

Performance: Central intensity = Strehl

Fried resolution: median seeing

Performance: Encircled energy

Half encircled energy diameter: median seeing

System concept

Optical concept

Implementation plan


2002 - NOAO internal (design study)

2003-2005: NOAO+SOAR? $500K?

Summary: We want to design a USEFUL system which combines unique high-resolution capability in the optical with seeing improvement mode. It must be cheap!

Road map for SOAR AO