Recent & planned high-contrast work on the WCS and P3K

Gene Serabyn

Nov. 12, 2007

Strehl vs. wavelength

• Go short or go deep• WCS provides P3K ExAO performance now

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ExAO,WCS

ExAOOn WCS

Well Corrected Subaperture (WCS) Relay Optics

• Magnify pupil• Keep pupil location at DM• Center sub-pupil on DM• Maintain F# to AO system

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Potential ExAO Directions • Programs:

– Short wavelength/visible AO– Faint companion observations:

• Coronagraphy• Transit observations• Nulling Interferometry

• Make use of:– High Strehl – Stable PSF– Stable pointing (remove NCP drifts after AO)– Speckle reduction

ExAO Goals and NeedsHigh Strehl Stable

PointingCoronagraphic Masks

Speckle reduction

Short wavelength

Imaging

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Exoplanet transits

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Faint Companion

Coronagraphy

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Nulling Interferometry*

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*Needs 2 good sub-apertures

(Bright) Companion Signal Levels: Brown Dwarfs & Hot Jupiters

• Thermal flux ratio = BplApl/(B*A*) – (in RJ limit = TplApl/T*A*)

• Area ratio 0.01 – (primary transits)

• Temp ratio 0.2• Flux ratio as much as a few 0.1%

– (secondary transits, imaging)• Transit observations:

– Need photometric stability of order 0.1%• Coronagraphic observations

– Need small inner working angle (IWA), low wavefront rms– Need high contrast near IWA

• Best Strehl ratio 0.92-0.94• rms 85 -100 nm• Strehl stability: 1 % rms

Exoplanet Transit Spectroscopy: Strehl Stability

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Exoplanet Transit Spectroscopy• Stabilize ExAO PSF on slit• Difference spectra before and

during transits• Non-common path pointing

drift removal essential– new SSMs

• A handful of targets are bright enough with WCS

• H/K grism will help sensitivity• 5 m collecting area will help

increase target list

Table 1: Best current exoplanet transit sourcesName RA (h) Dec (deg) mV mK SpHD189773 20 22 7.6 5.5 K1-2HD209458 22 18 7.6 6.3 G0VHD149026 16:30 38 8.15 6.75(est) G0 IVHD147506 16:20 41 8.7 7.6 F8/G0HAT-P-1=SAO72884 23 38 10.4 9.0 (est) F8 GL436 (Nep. size) 12 26 10.6 6.3 (est) M2.5

High-Strehl Coronagraphy

FQPM coronagraphy

Pupil plane phase coronagraphy(e.g. coma)

Band-limited masks: linear mask good for binaries

• Need a good wavefront and a good coronagraph• Goal is small inner working angle

• Can partially make up for smaller aperture

“Through–FQPM” image

Peak extinction = 80Mean of 5 short exposures (total time = 21.24s)

Cross-diagonal subtraction

Peak extinction = 235 6 mag

Normal “off-FQPM” image

High-contrast Coronagraphy:The Binary Star HD148112 through a FQPM

• Focal plane phase masks (FQPM, vortex) allow small IWA

Brown Dwarf pair HD130948 at Ks• Broadband: Ks

• Stellar rejection 35:1 Ks = 6.9 ± 0.5 • separation = 2.61 ± 0.08“

• At 7.5 /DLyot Could see it to 1.5 /DLyot

• Looked at fainter, closer BDs 9/06– now 50:1 Ks

• Limitations:– Mask performance – SSM mirror actuator accuracy

• Need to stay on the crosshairs– Long-lived speckles

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Off-axis Performance

“Off-FQPM” PSF“On-FQPM” PSFQuadrant-subtracted PSF

The quadrant subtraction improves the rejection of the peak, but also the halo.

• Below 10-3 at 2/D• Waiting to develop and install new masks• Need to remove long-lived speckles

Pupil Phase Coronagraphy (Coma)• Iscat = (1-S)/N2 4 10-4 • Example: 1.4 waves PV of coma at 2.16 m• Example of pupil phase coronagraphy (Codona et al.)• Generate dark hole on half of image

• Iscat

Ideal 1st ring

Pupil phase (coma) coronagraphy

• Initial trial carried out on the WCS in 9/06• Dark area at the 2 x 10-3 level at 2/D• Saw very long-lived speckles• Require non-common path error reduction/ long-lived speckle reduction• Can move on to more complex phase distributions

Comparison of Coronagraphs

Guyon et al. 2006

Visible AO in the B-band (400-450 nm):

1 pix. = 25.3 mas/D (B) = 59 masStrehl 0.10 – 0.12

• SAO 70505• V = 4.5, 6.0• sep = 0.90 arcsec

• SAO 37735• V = 5.1, 6.3• sep = 0.34 arcsec

• Blue companions to red giants/supergiants • Sirius, O Ceti, etc…

– White dwarf/supergiant flux ratio 10-4 in the red– Much better blue ratio because WDs are very hot– Can move to fainter stars with P3K

• Red/Vis AO

Sensitivity Limitations to WCS • Science camera sensitivity

– Lose factor of ten for area– Lose small factor for transmission (t 0.8) through WCS relay– Gain small factor for Strehl improvement (1.5)– WCS roughly an order of magnitude less sensitive than 5 m aperture

• WFS sensitivity– Also lose first two factors for WFS– WFS cutoff roughly 3 magnitudes higher

• Flexcam sensitivity – Removes non-common path pointing drift– Not the best camera– Same issues as science camera

• Limit for the latter two systems is currently ~ 10th mag– Limit not fundamental for flexcam

P3K Implications/Improvements

• WCS imaging performance for entire 5 m– Coronagraphs– Transits

• Science camera and “flexcam” sensitivities to improve by ~ 3 mag– Fainter sources– Disks as well as companion searches– Can also get better flexcam

• WFS sensitivity loss remains• WFS another 2.5 mag worse with P3K+WCS

• Interesting for very high Strehl coronagraphy and high-Strehl vis AO (red and blue)

Science Goals

• High Strehl stability for transits (HJs)

• High contrast at small IWA for companion searches (BDs, etc.)

• High Strehl for short wavelength AO (WDs)

Prelminary Experiments with the WCS– Extreme AO

• PSF properties/stability in high-Strehl regime• Non-common path error reduction (tip-tilt; higher order)• Dark hole generation• Atmospheric Characterisation• Spatial filtered WFS

– Visible AO• Initial observations of close binaries• Atmospheric properties (isoplanatic angle…)• Laser guide star visible AO?

– High-contrast IR coronagraphy (S > 90%)• FQPM, Pupil-Phase, Band-limited, • Vortex, apodized pupil, etc…• Dark-hole, PSF subtraction, dual- imaging, dual-polarization

imaging…

– Palomar provides an excellent venue for new techniques– Preliminary experiments can accelerate P3K (new SSMs, SF

WFS, speckle reduction…) and help keep the lead

Nulling Interferometry on the 200-inch with a rotating baseline

• Phase the two subapertures to center a dark interference fringe on a bright star • Rotate pupil image or applied phase map to modulate off-axis signals

• Dual subaperture approach 0

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Expected Performance without Phase Control

• Model 100 rotations: top envelope gives avg. null of 0.1 with current AO • Measure bottom envelope shape rapidly• ExAO will lower top envelope to 0.01 and make a huge difference• Phase control between subapertures will also provide improvement