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Rich Dekany, Ralf Flicker, Mike Liu, Chris Neyman, Bruce MacintoshRich Dekany, Ralf Flicker, Mike Liu, Chris Neyman, Bruce MacintoshNGAO meeting #6, 4/25/2007NGAO meeting #6, 4/25/2007
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Contrast budget - summary
• Contrast performance budget still incomplete• Combining 2 analysis tools• Need more science input to complete
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Goal and Science requirements
• Goal of Contrast WFE budget (WBS 3.1.1.10):– Development of a companion sensitivity performance budget, based on
a strawman coronagraph approach meeting the science requirements. Develop a contrast-driven spatio-temporal wavefront error budget that includes not just AO performance but realistic values for static/internal effects, so that we can see what instrument design choices (e.g. optics quality) are important now
• From the System Requirements Document (KAON 456):a) ≥ 4 magnitudes at 0.055” at 1-2.5 m for Galactic Center
b) ≥ 10 mags at 0.5” (0.7-3.5 m) for 30% sky cov. & ≤ 20” object diam.• These are insufficient specifications for contrast performance budget
evaluation: more detailed observing scenario required to calculate actual contrast for specific cases.
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High-C science case recap
• Principal NGAO high-contrast science cases:– Direct imaging and spectroscopy of
• Planets around low-mass stars and brown dwarfs• Resolved debris disks and protostellar envelopes
• NGAO high-contrast selling points:– LGS tomography is the primary AO mode of interest
• Large sky coverage• Fainter stars = many more targets +
– Provided by B. Macintosh (derivative of GPI tool)– Fast to evaluate– Parameterizes speckle noise effects– Observing scenario implicit– We do not have good analytical models for some terms
• Dynamic/static telescope aberrations (Keck pupil diffraction not included)
• LGS effects
• Tomography error (approximate power law for now)
– Does not produce PSFs
• Numerical AO simulations– YAO Monte Carlo AO simulation package (F. Rigaut)– Computationally expensive (more than ~30 s real time unreasonable)– Obtain AO PSFs at multiple wavelengths with & w/o coronagraph simultaneously– Contrast for a given observation scenario must be evaluated separately
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Contrast tool (1) - Wavefront budget
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Contrast tool (2) - PSD modeling
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Contrast tool (3) - Observing scenario
• “Contrast” depends on:– Smoothness of host star halo
– Host star magnitude
– Companion magnitude and position (angular distance from host)
– Exposure time (speckle noise, dark current)
• Complete observing scenario required in order to calculate contrast