SCExAO: the Subaru
Coronagraphic Extreme
AO Project
Frantz Martinache
SCExAO Project Scientist
Subaru Telescope, NAOJ

Adaptive Optics: required but not sufficient!

AO stabilizes the wavefront but cannot do a perfect job
You are at best left with static or slowly varying aberrations thatset contrast detection limits
simulation by James P. LloydTake care of an ill-posed problem

I = O ⊗ PSF

Eliminate the PSF out of the equation

the ADI way...

the exAO way...

Marois et al, 2006, ApJ, 641, 556

Guyon et al, 2009, PASP, 122, 71

SCExAOAngular Differential Imaging
The “state of the art”:
optimized Angular
Differential Imaging
called LOCILOCI led to the obtention of direct images of substellar companions around HR 8799, GJ 758, etc.
Remarkable... but reaches peak performancesomewhere around 0.5 arcsec
Lafreniere et al, 2007, ApJ, 660, 770

example of LOCI observations“conservative” LOCI imageof LkCa 15 by HiCIAO“iconic” LOCI image of theplanetary system orbiting HR 8799

Thalman et al, 2010, ApJL, 718, 87

Marois et al, 2008, Science, 322, 1348

95 %exopolanet f knowns arehere!
!

Marley, Sci. Exp, 10/13/2008

HiCIAO+
fore-optics

HiCIAO+SCExAOSCExAO engineering run September 2011

Internalcalib.
sourceVisible imaging channelsoon to becomepolarimetric NRM interferometry
Pyramid WFS

CommonInjection
moduleIR channel

The SCExAO project
Taking advantage of a series of in house developments (PIAA, CLOWFS) and the existing
infrastructure (AO188 + HiCIAO) to put in the same box:
- a high-efficiency, high-performance PIAA-based coronagraph- all the calibration tools we can think of now (wavefront sensors, active control of the focal
plane image with a DM, post processing techniques, optional NRM)
- simultaneous diffraction limited visible imager
While keeping the design flexible for future improvements.

Optical design
f/14 beamfrom AO 188

SRP

PIAA

tip-tilt
field mirror

50 Hz low-orderwavefront sensor
Subaru
pupil

After
SRP

After
PIAA

Inverse

PIAA

collimated beam
to feed HiCIAO

tip-tilt mounted
deformable mirror

collimated beamfor visible path(science and WFS)

focal planeinternal detector

SRP
dichroic PIAA

apodizerfocal plane
inverse PIAA
mask

beam splitter/fold mirror

Active speckle control
Instead of using a passive approach, andwait for the sky rotation like in ADI, use a
DM with many actuators (~1000) gives
active control of the speckles

Image with flat DM volt-map

Image with dark-hole DM volt-map

Strategy shared with comparable
projects (GPI, SPHERE).
The true advantage of SCExAO isits small IWA
Martinache & Guyon, 2011, AO4ELT
On sky results soon!

High contrast @ 1 lambda with PIAAPIAA optics
on SCExAOFirst on sky demonstration (Sept. 2011)

Martinache & Guyon, 2011, AO4ELTImages by HiCIAO

Active speckle control
Example of PIAA-based coronagraphhigh contrast results (laboratory):
DM diversity identifies “coherent”
fraction of the light in control FOV.
Gains two orders of magnitude overraw contrast
Guyon et al, 2010, PASP, 122, 71

DM wavefront diversity in thepresence of turbulence withSCExAO
Martinache et al, 2012, in prep

SCExAO: the Subaru
Coronagraphic Extreme
AO Project
Frantz MartinacheSCExAO Project Scientist
Subaru Telescope, NAOJ