From NAOS to the future SPHERE Extreme AO system T. Fusco 1, G. Rousset 1,2, J.-L. Beuzit 3, D. Mouillet 3, A.-M. Lagrange 3, P. Puget 2 and many others … 1 ONERA, Optics Department, Châtillon, 2 LESIA, Obs. de Paris, Meudon, 3 LAOG, Obs. de Grenoble Mail:

Outline The NAOS system Extreme AO for direct detection of extrasolar planets The SPHERE instrument and its AO system (SAXO)

On sky since Dec 2001 Consortium: ONERA-LAOG-LESIA Main characteristics  DM: 185 actuators  2 WFS: Visible and IR 14x14 and 7x7 sub-apertures Frequency: 15 to 480Hz > 80 configurations  Fine differential tracking: refraction, flexure, moving object  Non common path Aberration pre-compensation Fully integrated and optimized system NAOS : a multi-purpose AO system

VLT Nasmyth focus: NAOS + CONICA NAOS CONICA

NAOS : a multi purpose AO system On sky since Dec 2001 Consortium: ONERA-LAOG-LESIA Main features  Field de-rotation for CONICA  Spectral range: 0.45  m up to 5  m  Chopping  Off axis NGS selection in 2 arcmin FoV  LGS currently implemented by ESO Fully integrated and automatic system  Full control through VLT software (including CONICA) and configuration selection versus observing conditions  Real time AO performance optimization  Possible storage of AO data for data reduction Off-line preparation of observations

NAOS on-sky performance ~ 60% Strehl ratio in K at seeing < 1 arcsec and M V <10 or M K <7  Strehl loss: telescope vibrations, calibration errors Faint NGS: ~5% Strehl at M V ~17.5 or M K ~13.5

NAOS: example of results (I) NGC 1068 active nucleus (D. Rouan et al., A&A, 2004) 2,2 µm 3,8 µm 4,8 µm Hot dust cloud structures in the nucleus, the arms and to the North

NAOS: example of results (II) First extrasolar planet detection To go further => dedicated instrument with eXtreme AO  K = 0.778’ Teff~1200/+-200K 5-12 Myr, 5+/-2 Mjup ( Chauvin et al., 2004&2005) ESO/CNRS/UCLA

Requirements for Extra-solar planet detection High contrast capability  Extreme AO (turbulence correction) Feed coronagraph with extremely well corrected wavefront  Coronagraphy (removal of diffraction pattern) dynamics at short separation < 0.1”  Differential imaging (removal of residual defects) Calibration of internal system defects  Smart post processing algorithms  Calibration differential aberrations High sensitivity  Optimal correction up to Vmag~10 Large number of targets small separation (1-100 AU) Direct detection : small separation (1-100 AU) Large magnitude difference  m >15 Large magnitude difference  m > 15

Lessons learned from NAOS AO is NOT a separate instrument, it is a sub-system  Global trade-off with focal plane modes (definition and design) In an AO design the simpler is the better ! (as far as possible)  do not try to do everything with a single AO system Stability is a critical issue AO has to correct for :  Turbulence AND system defects (non common path aberrations, vibrations …) Error budget list is always larger than you thought !

Coronagraphic profile and AO error budget Relevant parameter for error budget optimization :  residual variance - SR is not sufficient  Coronagraph profil has to be considered Error budget on coronagraphic contrast: quasi-static terms: create persistent speckles => detection limit !! Dynamic terms: create a “smooth” halo => impact on intregration time (in differential mode) C 

N act - F samp -  : the necessary trade-offs N act F samp  (WFS-im)  Corrected area  N act  Contrast  (N act ) 8/3  Contrast  (F samp ) 2  Noise effects   -2 WFS spectral bandwidth VIS detector  Gain in limit mag  contrast  WFS Flux  (N act )  Loss in limit mag  WFS Flux  (F samp ) -1  Loss in limit mag  Chromatism effects   contrast GAINS LOSSES  Complex trade-offs: depends on scientific requirements (ultimate contrast, number of targets) and atmospheric conditions

Challenging technologies :  DM : 185  1370 actuators  CCD : 500  1200 Hz  = 5e-   < 1e-  RTC : > x10 1 order of magnitude better than NAOS System aspect: System aspect:  Control of 1370 actuators  System calibration  Filtered-SH and pupil stabilisation  L3CCD  Dedicated Tip-Tilt sensor at the level of the coronagraphic mask  Differential aberration calibration  and much more... NAOSSAXO AO system (SAXO): the challenges (I)

AO system (SAXO): the challenges (II) Vibrations  Main limitation on 10-m class AO systems (NAOS, Keck, Altair)  Solution: Kalman Filter (predictive control laws) Class. integrator Kalman filter Vibrations Test of Kalman filter on ONERA AO bench See C. Petit et al Optics Letter (submitted) Non common path aberrations ( From dichroic down to scientific detectors)  Reduce SR : typically more than 20 % of  m  Solution: Pre-compensation by AO loop Phase diversity measurements WFS reference modification no pre-comp after pre-comp SR = 70 % nm Exp. Validation on ONERA AO bench See Sauvage et al., 5903, SPIE 2005

Nasmyth focus Environment: static bench, Nasmyth platform 0.9 – 2.3 µm; 0.95 µm Differential imaging: 2 wavelengths, R~30, FoV = 13.5’’ Long Slit spectro (grism), R~50/500 Common Path High frequency AO correction (41x41 act.) High stability : image / pupil control Refraction correction Visible – NIR, FoV = 13.5’’ Vis AO sensing F-SH WFS in visible, 40x KHz, RON < 1e- Visible Channel (Zimpol) Polarimetry Lyot coronagraph NIR Corono IRDIS Pupil apodisation Focal masks: Lyot, 4-Q Pupil stop IR-TT sensor for fine centering IFS 0.95 – 1.7 µm 1.05 µ m 254x254  lenses Spectral sampling 0.04  m

Current SPHERE optical design Foreoptics ITT DM IR WFS IRDIS ZIMPOL IFS J (phase A) Vis WFS Preliminary instruments optical implantation

Current SPHERE VLT

Expected performances + calibration Reference star WFS data  m = 15 Detection up to 100 pc (depending on age and type) Masses > Jupiter Distance star-planet > 0.1”  > 1 AU at 10 pc 1 2  Assumed defects (conservative):  Seeing variation (obj/ref) = 10 %  Reference decentering = 0.5 mas  Reference Pupil shift = 0.6%  Diff WFE = 10 nm  Additional non turbulent jitter = 3 mas

Conclusion and perspectives NAOS  Multi-purpose system  On sky since 2001  Large number of astrophysical results (more than 75 articles in ref. journals) SPHERE / SAXO  Optimized instrument (and AO system) for exoplanet detection  Extremely challenging system (very tight error budget)  Realization phase has begun (kick off last week)  First light expected in 2010  LAOG-LAM-LESIA-ONERA / ESO / MPIA Heidelberg / Obs de Geneve-Zurich / Obs de Padoue / Univ. of Amsterdam-ASTRON Next step: ELTs  Technical challenges: act. Numbers, comp. time, optics with sub-nm accuracy  Performance challenge: WFE error budget

New requirements in astronomy (1/2) Large field of view observations: Anisoplanatism effect depending on turbulence distribution Images of the Galactic Center, D. Rouan New concepts: Multi Conjugate AO (J.-M. Conan’s talk)