From NAOS to the future SPHERE Extreme AO system

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From NAOS to the future SPHERE Extreme AO system

• T. Fusco1, G. Rousset1,2 , J.-L. Beuzit3, D.
  Mouillet3,
• A.-M. Lagrange3, P. Puget2 and many others
• 1ONERA, Optics Department, Châtillon,
• 2LESIA, Obs. de Paris, Meudon,
• 3LAOG, Obs. de Grenoble

Mail thierry.fusco_at_onera.fr
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Outline

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

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NAOS a multi-purpose AO system

• 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
• gt 80 configurations
• Fine differential tracking refraction, flexure,
  moving object
• Non common path Aberration pre-compensation
• Fully integrated and optimized system

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VLT Nasmyth focus NAOS CONICA

• NAOS

CONICA
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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

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NAOS on-sky performance

• 60 Strehl ratio in K at seeing lt 1 arcsec and
  MVlt10 or MKlt7
• Strehl loss telescope vibrations, calibration
  errors
• Faint NGS 5 Strehl at MV17.5 or MK13.5

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

• First extrasolar planet detection

?K 5 _at_ 0.778 Teff1200/-200K 5-12 Myr,
5/-2 Mjup (Chauvin et al., 20042005) ESO/CNRS/U
CLA

• To go further gt dedicated instrument with
  eXtreme AO

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Requirements for Extra-solar planet detection
Direct detection small separation (1-100 AU)
Large magnitude difference ?m gt 15

• High contrast capability
• Extreme AO (turbulence correction)
• Feed coronagraph with extremely well corrected
  wavefront
• Coronagraphy (removal of diffraction pattern)
• dynamics at short separation lt 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 Vmag10
• Large number of targets

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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 !

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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

C
?
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Nact- Fsamp- Dl the necessary trade-offs
GAINS LOSSES

• Nact
• Fsamp
• Dl (WFS-im)

• Corrected area µNact
• Contrast µ (Nact)8/3
• ä Contrast µ (Fsamp)2
• Noise effects µ Dl-2
• WFS spectral bandwidth
• VIS detector
• Gain in limit mag
• ä contrast

• WFS Flux µ (Nact)
• ð Loss in limit mag
• æ WFS Flux µ(Fsamp)-1
• ð Loss in limit mag
• Chromatism effects
• æ contrast

• Complex trade-offs depends on scientific
  requirements (ultimate contrast, number of
• targets)
  and atmospheric conditions

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AO system (SAXO) the challenges (I)

1 order of magnitude better than NAOS

• Challenging technologies
• DM 185 ? 1370 actuators
• CCD 500 ? 1200 Hz
• ? 5e- ? ? lt 1e-
• RTC gt x10

• 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 ...

NAOS
SAXO
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AO system (SAXO) the challenges (II)

• Non common path aberrations (From dichroic down
  to scientific detectors)
• Reduce SR typically more than 20 of SR_at_1.6
  mm
• Solution Pre-compensation by AO loop
• Phase diversity measurements
• WFS reference modification

• Vibrations
• Main limitation on 10-m class AO systems (NAOS,
  Keck, Altair)
• Solution Kalman Filter
• (predictive control laws)

Test of Kalman filter on ONERA AO bench See C.
Petit et al Optics Letter (submitted)
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Nasmyth focus
Environment static bench, Nasmyth platform
Pupil apodisation Focal masks Lyot, 4-Q Pupil
stop IR-TT sensor for fine centering
0.9 2.3 µm ?/2D _at_ 0.95 µm Differential
imaging 2 wavelengths, R30, FoV 13.5 Long
Slit spectro (grism), R50/500
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Current SPHERE optical design
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Current SPHERE implementation _at_ VLT
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Expected performances

• calibration
• Reference star
• WFS data

• Detection up to 100 pc
• (depending on age and type)
• Masses gt Jupiter
• Distance star-planet gt 0.1
• gt 1 AU at 10 pc

• 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

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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

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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. Conans
  talk)