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 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.

2. AO Time Line

3. 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

4. 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

5. Demonstration of Concept Error Budgets 180nm:

6. Demonstration of Concept Error Budgets 120nm:

7. 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

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

9. 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

10. 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

11. 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.