Keck Precision Adaptive Optics

1
Keck Precision Adaptive Optics Authors
Christopher Neyman1, Richard Dekany2, Mitchell
Troy3 and Peter Wizinowich1. 1 W.M. Keck
Observatory,2California Institute of Technology,
Jet Propulsion Laboratory3.
Abstract Keck Observatory, with the guidance of
the Keck Adaptive Optics (AO) Working Group, has
recently embarked on a conceptual design for the
Observatorys next-generation AO facility. This
Keck Precision Adaptive Optics (KPAO) system is
envisioned as delivering stable high Strehl ratio
infrared images in moderate field-of-view areas
throughout the sky. Such a system would allow
Keck to take the lead in general use
high-precision AO, in which many of the
scientific advances in high-resolution imaging
are currently thought to be. The top-level KPAO
requirements are very demanding and are in many
ways similar to those for future 30-m AO systems
especially the total rms wavefront error budget
of 120 nm.
2
AO Time Line
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• Unique Features of KPAO
• High Strehl AO, S0.8 (1-2 mm wavelength)
• High sky coverage
• Moderate field of view, anisoplanatism limited.
• Larger fields from a mosaic of several images
  (Not MCAO)
• See example of mosaic image with current LGS
  system (Galactic Center Observations, Keck LGSAO
  team, this Conference)
• Still have good PSF knowledge over FOV
• Automatic optimization and calibration
• Facility class AO system

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• KPAO Science
• Global Changes on Pluto
• Smaller icy solar system objects outside range of
  current AO, Pluto is the prototype object, Pluto
  in only 0.1 arcsec.
• Planetary rotation plus PSF stability needed for
  a reliable map
• Complimentary to HST UV maps
• Too faint for NGS X-AO
• Low Mass stars in Binaries and Clusters.
• Companion searches with current AO limited by
  Stehl stability
• Too faint for NGS X-AO
• Need precise photometry (Stable Strehl and Good
  Calibration)
• Low mass limit in clusters can be pushed to
  Jupiter masses and lower
• Star formation in quasar host
• Young stellar population in QSO hosts, role of
  mergers between galaxies
• First gen. LGS AO likely to have highly variable
  PSF
• Cant reliably separate host galaxies from QSO
• High Strehl stability plus LGS
• See PSF simulation below

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Demonstration of Concept Error Budgets 180nm
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Demonstration of Concept Error Budgets 120nm
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• Error Budgets Assumptions
• Scaling laws only, no Monte Carlo simulations
• Set Tip/tilt guide star to visual magnitude 17,
• NGS is on axis,
• At present no wind shake,
• Exact details for faintness limits not
  investigated at this time
• Used CELT report No. 34 (Green Book) for multiple
  LGS error,
• The Green Book Tomography error assumes LGS at
  infinity
• No modeling of laser saturations effect
• Only a first cut at optimization

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KPAO Point Design
Comparison of key system parameters for current
Keck LGS system and KPAO
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• KPAO Requirements Document
• Keck Precision Adaptive Optics Technical
  Requirements and Constraints 7/13/2003 (KAON
  237) See Handouts.
• The Authors along with Keck AO working group
  began the process of investigating and
  documenting the top-level requirements for KPAO.
  We discuss list some preliminary design goals.
  We then discuss a number of design constraints
  (additional requirements) imposed by the
  implementation of a KPAO system at Keck
  Observatory.
• Summary of high level requirements
• High IR Strehl
• High Strehl Stability
• Moderate FOV
• Near Complete Sky Coverage
• Good Knowledge of the Delivered PSF
• Facility Class Instrument

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• PSF Simulation
• Simulated PSF from empirical model of AO
  corrected phase structure function.
• Phase structure function should be Kolmogorov at
  low spatial frequencies and flat at high
  frequencies if AO system was perfect. Empirical
  model fits these two extreme cases.
• Point spread function calculated from Fourier
  transform of system optical transfer function.

Comparison Strehls for KECK AO KECK NGS AO, S
0.6 K band 260nm RMS (Marcos Van Dam), Keck
LGS AO S0.23 K band 425nm RMS (Antonin
Bouchez) KPAO 120 nm S 0.77 KPAO 180 nm S
0.89
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• Future
• WMKO support FY05 2.5 FTE includes fulltime lead
  (1st author)
• Collaborations with CfAO and TMT including
• TMT and CfAO funded Postdoc position
• (Advertised Sept. 2004 see handout and
  http//www2.keck.hawaii.edu/jobs/index.html)
• Coordination of TMT, GMT and KPAO
  simulation/analysis and sharing of information
• Determination of Keck Specific parameters, such
  as
• telescope wavefront errors (segment warping,
  stacking and phasing)
• windshake
• vibrations
• Seeing, Outerscale and Cn2 profile.
• Full Simulation of KPAO
• Modeled with ARROYO
• compared to equivalent MCAO systems
• Conceptual level design by October 2005.