Keck Precision Adaptive Optics Authors: Christopher Neyman 1, Richard Dekany 2, Mitchell Troy 3 and Peter Wizinowich 1. 1 W.M. Keck Observatory, 2 California Institute of Technology, Jet Propulsion Laboratory 3. Abstract: Keck Observatory, with the guidance of the Keck Adaptive Optics (AO) Working Group, has recently embarked on a conceptual design for the Observatory’s 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.

AO Time Line

Unique Features of KPAO High Strehl AO, S~0.8 (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

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 Can’t reliably separate host galaxies from QSO High Strehl stability plus LGS See PSF simulation below

Demonstration of Concept Error Budgets 180nm:

Demonstration of Concept Error Budgets 120nm:

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

Comparison of key system parameters for current Keck LGS system and KPAO KPAO Point Design:

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

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 S~0.23 K band 425nm RMS (Antonin Bouchez) KPAO 120 nm S= 0.77 KPAO 180 nm S= 0.89

Future WMKO support FY FTE includes fulltime lead (1 st author) Collaborations with CfAO and TMT including: TMT and CfAO funded Postdoc position (Advertised Sept see handout and 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 C n 2 profile. Full Simulation of KPAO Modeled with ARROYO compared to equivalent MCAO systems Conceptual level design by October 2005.