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Issues for the quantitative analysis of Adaptive Optics images

Issues for the quantitative analysis of Adaptive Optics images. Francois Rigaut, Gemini. Workshop on Hokupa’a data acquisition and reduction NOAO, 25-26 February 2001. Presentation “Road-map”. “Quantitative analysis” of AO images : Photometry, Astrometry, Polarimetry

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Issues for the quantitative analysis of Adaptive Optics images

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  1. Issues for the quantitative analysis of Adaptive Optics images Francois Rigaut, Gemini Workshop on Hokupa’a data acquisition and reduction NOAO, 25-26 February 2001.

  2. Presentation “Road-map” • “Quantitative analysis” of AO images: • Photometry, Astrometry, Polarimetry • Differences with Seeing limited case -> Mostly PSF • PSF characteristics • PSF structure, Halo formation, AO Performance • PSF variations & calibration issues • Variations vs FoV, Temporal, GS magnitude • Other issues: • Speckle noise, Artefacts, Sky modulation, … • Limitations of current Data reduction codes Hokupa’a Workshop, NOAO

  3. AO PSF Characteristics High order error Tilt error FWHM = /D x Tip-tilt residuals Narrow Core Artefacts Wide Halo FWHM ~ 50-100% seeing High Contrast / Boost peak intensity Speckle noise Hokupa’a Workshop, NOAO

  4. Strehl vs r0 J H K + Quirc Aberrations + Telescope Shaking ? + Worse seeing ? + …? Hokupa’a Workshop, NOAO

  5. Strehl gain vs D/r0 K H J Hokupa’a Workshop, NOAO

  6. Normalized FWHM vs D/r0 K H J Hokupa’a Workshop, NOAO

  7. FWHM gain vs D/r0 K H J Hokupa’a Workshop, NOAO

  8. Strehl loss vs GS magnitude Hokupa’a Workshop, NOAO

  9. Anisoplanatism • Typical Strehl loss of 50% at zenith: J 17” H 25” K 35” Hokupa’a Workshop, NOAO

  10. Anisoplanatism 18” Hokupa’a Workshop, NOAO

  11. PSF Temporal Variability Example of nightly seeing variations. Data from Paranal, 1998. From ESO Seeing database (Sarazin) Hokupa’a Workshop, NOAO

  12. PSF Temporal Variability Seeing variability: Fractionnal seeing change = relative variation of seeing.Rigaut and Sarazin 1998. Mauna Kea : Racine et al (early 1990). Hokupa’a Workshop, NOAO

  13. PSF Temporal Variability Fractionnal seeing change vs time + Strehl vs D/r0 AO behavior gives Strehl error vs time for given Strehl. Relative Strehl error vs Strehl for various FSC Hokupa’a Workshop, NOAO

  14. Other Issues • Speckle Noise: • Noise in Halo is dominated entirely by “speckle noise” (and quasi-static aberrations), NOT by photon noise • Killer Solution: Dual wavelengths imagers • Artefacts: • Source: Static or quasi-static aberrations that vary with time and/or position in FoV • Solution: Better designed systems (more stable), better Strehl ratio • Sky/FF modulation: Non Problem (DM in pupil plane) Bottom line: Poorly investigated effects, highly statistical phenomena, causes not always understood. Hokupa’a Workshop, NOAO

  15. Photometry with a variable PSF 15x15 arcsec2 J, H and K Fields generated using a GC type stellar distribution but 10% of the crowding only. Completed at faint end. 9000 stars in these images. Classical AO and MCAO at 1.9 airmass under median seeing. Hokupa’a Workshop, NOAO

  16. Photometry with a variable PSF H-K / K , MCAO Hokupa’a Workshop, NOAO H-K

  17. Photometry with a variable PSF H-K / K , AO Hokupa’a Workshop, NOAO H-K

  18. Photometry with a variable PSF J-K / K , AO Hokupa’a Workshop, NOAO

  19. Photometry with a variable PSF J-K / K , MCAO Hokupa’a Workshop, NOAO

  20. Astrometry issues • Potential Field distortion introduced by Optics can be calibrated out • Dynamic Plate Scale effects unchanged w.r.t seeing limited case -> time averaging required (e.g. 2 mas in one mn for median seeing) • Astrometric accuracy in measurements proportional to FWHM -> 10 x gain w.r.t. seeing limited case • Assuming ultimate precision of FWHM/50 -> mas level Hokupa’a Workshop, NOAO

  21. Limitation of current Data Reduction Codes • Code w/ good model for Field Variable PSF missing • Stellar fields: PSF extraction from image • Extended Object: PSF in field or PSF calibration. Deconvolution required ? Limited photometric accuracy. >> Model Fitting << • New stuff around ? Bottom line: • Hit in SNR due to halo • a few 1/100 mag photo. possible with heroic efforts on stars • Blurry situation for blurry objects Hokupa’a Workshop, NOAO

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