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A Pot Pourri: AO vs HST, the Gemini MCAO and AO for ELTs

A Pot Pourri: AO vs HST, the Gemini MCAO and AO for ELTs. Francois Rigaut, Gemini GSMT SWG, IfA, 12/04/2002. IRS8 (bow shock). Very high extinction clouds. 4’. 40”. 5”. Bow shock. >10 stars per arcsec 2 at K~18. >220 stars in 5”x5”. UH-88”, Courtesy W.Brandner, 0.65” seeing. IRS7.

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A Pot Pourri: AO vs HST, the Gemini MCAO and AO for ELTs

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  1. A Pot Pourri: AO vs HST, the Gemini MCAO and AO for ELTs Francois Rigaut, Gemini GSMT SWG, IfA, 12/04/2002

  2. IRS8 (bow shock) Very high extinction clouds 4’ 40” 5” Bow shock >10 stars per arcsec2 at K~18 >220 stars in 5”x5” UH-88”, Courtesy W.Brandner, 0.65” seeing IRS7 SgrA* • Filters: • H • K’ • CO • CO cont. GSMT SWG

  3. Arches Cluster 2.2 micron image. Young Star cluster in Galactic center region (10 Million years old) • Up-left: HST/NICMOS • Up-right: Gemini/Hokupa’a • Lower-right: Gemini/seeing 0.5” GSMT SWG

  4. Gemini goes ~ 5-10x deeper • Angular Resolution : • HST = 0.19” • Gemini = 0.13” Luminosity Function GSMT SWG

  5. HST/NICMOS Gemini/Hokupa’a GSMT SWG

  6. GSMT SWG

  7. GSMT SWG

  8. Guyon This figure shows a ten minute exposure of GG tau using this technique compared to the HST/NICMOS image from Silber et al. (2000). The Hokupa'a image comfirms the suspected gap in the disk that fell in the diffraction spikes of HST/NICMOS as well as revealing new structure in the disk. GSMT SWG

  9. MPE Group: GC results GSMT SWG

  10. NAOS results GSMT SWG

  11. MCAO Performance SummaryEarly NGS results, MK Profile Classical AO MCAO No AO 2 DMs / 5 NGS 1 DM / 1 NGS 165’’ 320 stars / K band / 0.7’’ seeing Stars magnified for clarity GSMT SWG

  12. Effectiveness of MCAO Numerical simulations: • 5 Natural guide stars • 5 Wavefront sensors • 2 mirrors • 8 turbulence layers • MK turbulence profile • Field of view ~ 1.2’ • H band GSMT SWG

  13. PSF Characteristics Most of area is here ! 3x 10x 0.7 mag IFU: > 1 mag • H Band • [16,17,8] actuators • Median seeing, CP • 200 PDE/sub/ms for H.Order WFS • Least square FWHM [arcsec] Strehl ratio MCAO AO Distance off-axis [“] Distance off-axis [“] 0.1” Slit Coupling 50% Enc.En. [“] GSMT SWG Distance off-axis [“] Distance off-axis [“]

  14. The Gemini MCAO in brief... • Baseline system (17,19,12) actuators across beams, 3DMs, 5 WFS+LGS (125 PDE/subaperture/frame ~ 10W) • Field average Strehl under median seeing conditions at zenith (no NGS noise) Band AO-only S Overall S * FWHM Limiting mag† J 41% 20% 0.032’’ 26.3 H 60% 40% 0.042’’ 25.0 K’ 75% 60% 0.057’’ 24.9 *includes mostly low order aberrations from telescope and instrument, and AO calibration errors. †5 sigma in 1 hour, extrapolated from the Hokupa’a results • H band Sky Coverage : 15% (b=90o), 70% (b=30o) GSMT SWG

  15. MCAO, CAO, HST & NGST Sensitivities Limiting magnitudes, 5, 3600sec, aperture = 2x2pixels Median seeing No AO MCAO HST NGST R~5 [magnitude (nJy)] 2.1 mm 23.2 (370) 24.9 (76) 23.7 (230) 28.0 (4.4) 1.25 mm 24.8 (190) 26.3 (50) 26.0 (66) 28.6 (6.0) R~10000 [magnitude (mJy)] 2.1 mm 20.4 (4.8) 20.3 (4.8) 17.2 (92) 20.1 (6.1) 1.25 mm 21.3 (4.7) 20.5 (9.7) 17.9 (107) 20.5 (9.7) slit width (at K) 0.4” 0.066” 0.22” 0.066” • Chun et al: • confirmed spectroscopy 1 < l < 2.5 mm will be detector limited • Nearly half (11/25) of the DRM’s can be started and explored by Gemini • The MCAO Science Case workshop GSMT SWG

  16. Various AO modes and first order performance GSMT SWG

  17. Relative Gain of groundbased 20m and 50m telescopes compared to NGST Imaging Velocities ~30km/s Groundbased advantage NGST advantage GSMT SWG

  18. ELT-AO Fundamental Challenges 90 km Path diff. and “Missing” Data Sky Coverage (independent of D) S.C. 0.1% (V), 2% (K), 20% (L-M) Solutions: Laser Guide Stars  Multiple faint Natural GSs LGS Cone effect: S  exp[- (D/d0)5/3] Scone(1 m) = 0.5 (8-m), < 0.01 (50-m) Solution: Multiple beacons Open-loop measurements of off-axis LGS (large dynamic range, sensitivity loss) Solution: Multi-Conjugate AO GSMT SWG

  19. Scaling and Orders of magnitude versus D  FoV  1 2 3 #DM - -1.2  3 6 6 #act/DM D2-2.4 (1+a)2 300030000125000 #WFS/GS - - (1+b)2 56 6 #pix/s/WFS D2-3.6 - 5.1065.1072.108 Computing Pow. D4-6 (1+c)2 100GF30PF800PF Laser power* -/D/D2-3.6 - 50W80W160W 1: D=30 m, S~30% @ =1 m, FoV= 1’ 2: D=50 m, S~30% @ =0.5 m, FoV= 2’ 3: D=100 m, S~30% @ =0.5 m, FoV= 2’ >>> Fundamental limits: #DM (, ), #GS > #DM <<< Fov = 2’, ~ 6 DM / FoV = 4’, 15 DMs ! (at ~ 1 micron) * no smart tricks GSMT SWG

  20. Sample Numerical Results(CP Turbulence, 3 DM’s) GSMT SWG

  21. Critical Technology to develop • Deformable Mirrors : • Deformable secondaries (butable) • Dense / Compact DMs (d=1mm? 8’ waffers / 5mm Xinetics) • High speed CCD arrays for WFS • Fast computers/Alternative control schemes • “segmented pupil” • Layer oriented WFSs • Lasers (short pulses) Cost: $50 to $100M. To be started ASAP. AO defines the ELT’s critical path ! GSMT SWG

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