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A Method for Determining AO Off-Axis PSFs

A Method for Determining AO Off-Axis PSFs. Eric Steinbring (UCSC, UCO/Lick, CfAO, DEEP) Sandra Faber, Sasha Hinkley. Scientific Observations. CFHT Pueo/KIR image of 3C68.2 field (~ 1 square-arcminute FOV) Guide-star is at the faint limits for full correction

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A Method for Determining AO Off-Axis PSFs

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  1. A Method for Determining AOOff-Axis PSFs Eric Steinbring (UCSC, UCO/Lick, CfAO, DEEP) Sandra Faber, Sasha Hinkley

  2. Scientific Observations CFHT Pueo/KIR image of 3C68.2 field (~ 1 square-arcminute FOV) Guide-star is at the faint limits for full correction Scientific target is 20 arcseconds away Suitable PSF stars are rare

  3. Calibration Observations CFHT Pueo MONICA/KIR observations of M5 (~ 1 square-arcminute FOV) Unsaturated image of guide-star in center of field Many PSF stars in field One set of J, H, K images per night

  4. Generating Off-Axis PSFs • Obtain on-axis PSF for each scientific observation • Obtain crowded star-field calibration image • Deconvolve calibration image with its on-axis PSF • Convolve the residual calibration image with the on-axis PSF for the scientific observation

  5. Off-Axis PSFs PSFs at 5, 10, 20, 30 arcseconds off-axis PSFs at 20 arcseconds off-axis at different azimuthal angles

  6. Average Off-Axis PSF The average PSF at 20 arcseconds off-axis Correct mean Strehl and FWHM for scientific observation Does not account for azimuthal anisoplanatism

  7. Improved Test of the Method • Obtain several star-field calibration images with a faint guide-star • Obtain calibration PSFs for bright guide-stars at zenith and star-field airmass

  8. Lick AO/IRCAL Observations of M15 Faint guide-star calibration images in J, H, and K over 2 nights (30 ~ 1 arcminute long) Bright guide-star PSFs at zenith and cluster airmass Estimates of r0 from WFS information (Don Gavel, LLNL)

  9. Isoplanatic Angle Single layer turbulence with D/r0>>1 Obtain on-axis Strehl (J: 4%, H: 6%, K: 10%) and isoplanatic angle (J: 150 arcsec, H: 80 arcsec, K: 60 arcsec) as a function of airmass Obtain estimate of mean altitude of layer (1000 – 3000 m)

  10. Modeling / Simulations Single layer turbulence modeled with a synthetic phase-screen Inputs are r0 and mean altitude of layer Model number of corrected modes, subapertures of WFS and number of degrees of freedom in DM (Sasha Hinkley, UCSC/CfAO)

  11. Summary • A single observation of a crowded star-field can determine off-axis PSF for entire night given on-axis PSF information • A single low-altitude layer is sufficient to explain isoplanatic angle for Lick AO

  12. Future Work • Better determination of Strehl in crowded star-fields • Work repeated with laser guide-stars • More sophisticated simulations (Miska Lelouarn, UCSC/CfAO) • Method would benefit greatly from an independent measurement of mean altitude of turbulence (SCIDAR / DIMM for Lick or Mauna Kea?)

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