NGAO Companion Sensitivity NGAO Companion Sensitivity Performance Budget (WBS 3.1.1.10)Performance Budget (WBS 3.1.1.10)

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 +

relaxed contrast requirements• Multi-band studies: optical & near-IR

~5 MJup?

~25 MJup

(images from M. Liu ppt NGAO m1)

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Analysis tools• Contrast budget spread sheet (analytical model)

– 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

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Contrast tool (4) - Contrast budget

• Sample contrast budget– 142 nm RMS WFE = 0.3”

– m(J) = 16

– r0 = 0.18 cm

– N = 48x48 sub-ap.

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Using the contrast tool

• [R,I,J,H,K,L] band (color/psym)• 142 nm (“Exo-Jupiter”) NGAO WFE budget (solid lines)• 158 nm (30° zenith angle) (dot-dashed lines)

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Numerical simulation tool

• 5-LGS (@ 90 km) quincunx asterism– Optimized for on-axis Strehl

• 36x36 sub-apertures across pupil• 2-DM MCAO system

– DM2 @ 10 km

• Bright NGS case– Used 4 tip/tilt NGS for null-mode

correction; could have used only1 NGS (2x2) measuring Z2-Z6

• Frame rate 1 kHz– LOWFS @ 250 Hz

• CN-M3 turbulence model– r0 = 18 cm

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Lyot coronagraph model

Slide borrowed fromthe Lyot Project

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Apodized Lyot coronagaph

0.7 m 1.0 m 1.25 m 1.65 m 2.2 m

0.92” 1.32” 1.65” 2.18” 2.90”

0.14% light though10 /D occ. spot

1.5% light through6 /D occ. spot

No occulting spot

• Implemented in YAO numerical AO simulation• 160 nm (36x36 quincunx MCAO shown below)

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Radial average PSFs

• No static/dynamic telescope aberrations• 160 nm RMS residual wavefront error• No coronagraph (left) ; 6/D occulting spot (right)

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Radial average PSFs

• No static/dynamic telescope aberrations• 160 nm RMS residual wavefront error• No coronagraph (left) ; 10/D occulting spot (right)

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Radial average PSFs

• 180 nm input (segment figure + windshake)• 170 nm RMS residual wavefront error• No coronagraph (left) ; 10/D occulting spot (right)

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Conclusions / recommendations

1. Spread sheet contrast tool:– Needs to be validated/anchored against numerical simulation

2. Numerical simulations:– Will returns contrast estimates given observing scenarios

• Host magnitude• Companion position & magnitude• Exposure time

– Would like to include optical quality requirements(maybe not feasible within current study)

3. Observing scenarios:– Need to be better defined