Wide-Field Adaptive Optics for ground based telescopes ...€¦ · Wide-Field Adaptive Optics for...
Transcript of Wide-Field Adaptive Optics for ground based telescopes ...€¦ · Wide-Field Adaptive Optics for...
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Wide-Field Adaptive Optics for ground
based telescopes:
First science results and new challenges
Edinburgh– 25th March 2013 Presented by B. Neichel
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A brief Introduction to Adaptive
Optics (AO) and Wide Field AO
GeMS: the Gemini MCAO
system
Tomography & Calibrations
First science results with
WFAO
New challenges
Outline
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A brief Introduction to
Adaptive Optics (AO) and
Wide Field AO (WFAO)
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Adaptive Optics
Earth’s
atmosphere
Spatial
resolution is
lost…
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Wave-Front
Sensor
Earth’s
atmosphere
Spatial
resolution is
restored
Adaptive Optics
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Resolucion
spatial esta
restaurada
Wave-Front
Sensor
Earth’s
atmosphere
Adaptive Optics
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Resolucion
spatial esta
restaurada
Adaptive Optics works
close to a bright
guide star
Wave-Front
Sensor
Earth’s
atmosphere
Adaptive Optics
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Resolucion
spatial esta
restaurada
Adaptive Optics works
close to a bright
guide star
Wave-Front
Sensor
Earth’s
atmosphere
Adaptive Optics
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Anisoplanatism
High atmosphere’s layers are not
sensed when looking off-axis
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Anisoplanatism
High atmosphere’s layers are not
sensed when looking off-axis
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Anisoplanatism
High atmosphere’s layers are not
sensed when looking off-axis
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Tomography
High atmosphere’s layers are not
sensed when looking off-axis
Solution => Combine off-axis
measurements
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Tomography
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Many different flavors of 3D phase reconstruction:
LSE, MMSE, MV, L&A, FRIM, POLC, Neuronal Network, …
Usually done in 2 steps (1) Reconstruction ; (2) projection
Tomography
How to combine the WFSs measurements to do the tomography ?
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=> Combine off-axis
measurements
=> Add deformable mirrors
MCAO
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MCAO
Good
correction in a
larger FoV !
=> Combine off-axis
measurements
=> Add deformable mirrors
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How many Guide Stars are available ?
Sky Coverage
Adaptive Optics works
close to a bright
guide star
3 stars with R < 16 in a
2 arcmin FoV
10%
0.1%
1%
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When no guide star are available, we can create one
Laser Guide Star
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Laser Guide Star
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Laser Guide Star
22 January 2011
First LGS
constellation at
Gemini South
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BUT requires LGS
(We’ll see some of the LGS issues latter in this talk)
Tomography
Tomography for Astronomy means:
(1) Access to larger FoV
(2) Access to better sky Coverage
- In summary -
Where the first AO systems are limited to small and bright objects, new WFAO system
opens the way to a multitude of new science cases.
(We’ll see some nice images at the end of this talk)
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All the ELTs are based on multi-LGS WFAO
systems
WFAO challenges
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Introduction to GeMS –
The Gemini MCAO
system
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GeMS Intro.
GeMS = Gemini
(South) MCAO system
GeMS = Facility
instrument delivering
AO corrections in the
NIR, and over a
2arcmin diameter FoV
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50W Laser
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50W Laser
Beam Transfer Optics
(BTO)
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50W Laser
Beam Transfer Optics
(BTO)
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Beam Transfer Optics
(BTO)
50W Laser
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Beam Transfer Optics
(BTO)
50W Laser
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Picture of BTOOB
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Picture of BTOOB
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DM9
DM4.5
DM0
TTM
VISIBLE
NIR
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Instruments fed by GeMS
GSAOI
0.9 - 2.4 µm wavelength
2 x 2 mosaic Rockwell HAWAII-2RG 2048 x
2048 arrays
85" x 85" field-of-view
Pix. scale of 0.02"/pixel
Flamingos-2
Near-Infrared wide field imager and multi-
object spectrometer
Near-Infrared wide field imager
0.95-2.4 µm wavelength
FoV = 120" diameter
Pix. Scale 0.09 arcsec/pix
Long Slit (slit width from 1 to 8 pixels)
MOS (custom masks)
R = 1200-3000
GMOS
0.36-0.94 µm (New Hamamatsu-Red-Sensitive CCDs)
Imaging, long-slit and multi-slit spectroscopy
FoV = 2.4 arcminute diameter.
Integral Field Unit (IFU) - pix = 0.1arcsec - FoV = 17arcsec - R150 to 1200
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GeMS’s Tomography
Calibrations & Limitations
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GeMS’s Tomography
Calibrations & Limitations
Tomography is easy, calibrations are difficult…
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GeMS’s Tomography
Calibrations & Limitations
Tomography is easy, calibrations are difficult…
Differential aberrations between WFSs
Fratricide effect
Non-Kolmogorov turbulence
Quasi-static aberrations
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Impact of differential aberrations between WFSs
WFS differential aberrations
WFS1
WFS2
WFS3
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Impact of differential aberrations between WFSs
WFS differential aberrations
WFS1
WFS2
WFS3
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Origin of differential aberrations between WFSs ?
Registration Look-Up Table
Static aberrations - Centroiding gains
Laser Spots
Differential LGS focus
Non-linear effects
WFS differential aberrations
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Origin of differential aberrations between WFSs ?
Registration Look-Up Table
Static aberrations - Centroiding gains
Laser Spots
Differential LGS focus
Non-linear effects
WFS differential aberrations
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LUTs are everywhere…
WFS differential aberrations
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LUTs are everywhere…
Ex: LGS WFS zoom mechanisms
WFS differential aberrations
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LGSWFS LUT versus elevation / temperature
When elevation / temperature /
flexure change, need to keep
the registration and
magnification right on each
LGSWFS.
WFS differential aberrations
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LGSWFS LUT versus elevation / temperature
LUT is built with
calibrations sources
moved to different LGS
range.
8 mechanisms in the
LGSWFS are adjusted to
keep registration /
magnification right.
WFS differential aberrations
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LGSWFS LUT versus elevation / temperature
Need to be done daily when observing.
No ways to check while observing, “ Trust the LUT ”
(Can do some on-sky checks, but “science destructive”)
Would require non-destructive, on-line calibration tools !
WFS differential aberrations
(Cf. ESO AOF ?)
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Origin of differential aberrations between WFSs ?
Registration Look-Up Table
Static aberrations
Centroiding gains - Laser Spots
Differential LGS focus
Non-linear effects
WFS differential aberrations
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No NCPA == SR of 50 (±10)% (H-band) in the field.
Static tomography for NCPA
Science
Camera
Goal:
find slope offsets that
would provide the best
image quality in the
science path.
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No NCPA == SR of 50 (±10)% (H-band) in the field.
Static tomography for NCPA
Science
Camera
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Static tomography for NCPA
[Rigaut et al. AO4ELT2
Gratadour et al. AO4ELT2]
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No NCPA == SR of 50 (±10)% (H-band) in the field.
Static tomography for NCPA
Science
Camera
Goal:
find slope offsets that
would provide the best
image quality in the
science path.
=> Static differential aberrations
between WFS should be absorbed
by NCPA.
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Origin of differential aberrations between WFSs ?
Registration Look-Up Table
Static aberrations
Centroiding gains - Laser Spots
Differential LGS focus
Non-linear effects
WFS differential aberrations
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Quad-cells transfer function & centroid gain
Laser related
A
B C
D A
B C
D
Centroid gain depends on spot size.
Spot size changes with seeing / sodium layer characteristics
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Quad-cells transfer function & centroid gain
Laser related
A
B C
D A
B C
D
Centroid gain depends on spot size.
Spot size changes with seeing / sodium layer characteristics
An error on the centroid gains can produce:
Wrong loop gain in CL (minor effect) (What in OL ?)
Wrong NCPA (major effect if NCPA are large)
Differential aberrations between the WFSs and wrong tomography
=> Centroid gains need to be calibrated on-line
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Quad-cells transfer function & centroid gain
Laser related
=> Centroid gains need to be calibrated on-line
Insensitive to vibrations
Not (really) seen by the WFSs, so not
corrected
Small amplitude required (20nm rms)
Would create satellite spot on the
images, but lost in noise.
Method: Apply a “sine wave” on the DM at a given frequency
and do a lock-in detection.
Seems to be working, but no direct way to cross-check results
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Origin of differential aberrations between WFSs ?
Registration Look-Up Table
Static aberrations
Centroiding gains - Laser Spots
Differential LGS focus
Non-linear effects
WFS differential aberrations
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Differential focus introduced by Na-layer transversal
variations
WFS differential aberrations
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Differential focus introduced by Na-layer transversal
variations
WFS differential aberrations
For 8m, differential focus does not seem to be an issue.
But large error bars.
Could be few hundreds of nm for 30-m telescopes
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Origin of differential aberrations between WFSs ?
Registration Look-Up Table
Static aberrations
Centroiding gains - Laser Spots
Differential LGS focus
Non-linear effects
WFS differential aberrations
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Non-linear effects
WFS differential aberrations
Lasers not properly centered
LGS spot Clipping ?
Field stop Vignetting ?
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WFS differential aberrations
And telescope field aberrations !!
2 DMs DM0 only
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GeMS’s Tomography
Calibrations & Limitations
Tomography is easy, calibrations are difficult…
Differential aberrations between WFSs
Fratricide effect
Non-Kolmogorov turbulence
Quasi-static aberrations
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Fratricide Effect
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Fratricide Effect
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Fratricide Effect
224 subapertures lost (~20% of the subapertures !)
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Fratricide Effect
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Fratricide Effect
Impact of “Fratricide Leaks”
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GeMS’s Tomography
Calibrations & Limitations
Tomography is easy, calibrations are difficult…
Differential aberrations between WFSs
Fratricide effect
Non-Kolmogorov turbulence
Quasi-static aberrations
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Covariance matrix
Ground layer
turbulence
(h = 0 m)
High layer
turbulence
(h = 9 km) Covariance map
Sub-map,
ground layer
Sub-map,
9 km layer
GeMS’ SLODAR
[Cortes et al. – MNRAS – 2012]
2040
330
Theoretical
covariance maps are
built from realistic
simulations (yorick/
yao model of GeMS)
Profile is retrieved by
fitting the data with
the theoretical maps
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Some examples of on-sky data:
GeMS’ SLODAR
0 1 2 3 4 5 6 7 8 9
hours
Altitude, Km
20
16
12
8
4
0
Turbulence profile at Pachón, April 16th 2013
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GeMS’ SLODAR
Limitations of the method: presence of strong dome seeing
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GeMS’ SLODAR
Limitations of the method: presence of strong dome seeing
measured
theoretical
noise
[Guesalaga et al. AO4ELT3]
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GeMS’ SLODAR
Limitations of the method: presence of strong dome seeing
measured
theoretical
noise
noise
Non-
Kolmogorov
turbulence!!
[Guesalaga et al. AO4ELT3]
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Non-Kolmogorov (or non stationary) turbulence does exists !
What is the impact on tomographic performance ?
However:
Wind speed and direction can be predicted and measured.
Frozen Flow assumption holds for long enough for predictive
reconstructors.
GeMS’ wind profiler
[Guesalaga et al. – MNRAS – 2014]
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GeMS’s Tomography
Calibrations & Limitations
Tomography is easy, calibrations are difficult…
Differential aberrations between WFSs
Fratricide effect
Non-Kolmogorov turbulence
Quasi-static aberrations
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Quasi-static aberrations
Cf. CANARY
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Science with MCAO
WFAO is opening new
opportunities for a large range of
science cases
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Filters:
Mol. Hydrogen (H2) - 2.122 µm (orange)
[Fe II] - 1.644 µm (blue)
Ks continuum - 2.093 µm (white)
3.9
arc
min
3arcmin
Exposure Time per field:
H2 = 12min
[Fe II] = 10min
Ks continuum = 10min
3 Fields:
OMC1 – North
OMC1 – Center
OMC1 – South-East
<FWHM> :
H2 = 90mas
[Fe II] = 100mas
Ks continuum = 90mas
Natural seeing:
0.6” to 1.1” @ 550nm
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NACO
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NACO
GeMS
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NACO
GeMS
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FWHM=0.75” FWHM=0.33” FWHM =0.08”
Courstesy M. Schirmer
Star Clusters
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Star Clusters
NGC1851
SV406 – A. McConnachie
80mas
50mas
ISOCHRONES from Dotter et al. 2007 WEBsite
Z=0.001 age=10Gyrs
P. Turri – PhD thesis
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Pulsar Isolated galaxy Quasar
MCAO for Sky Coverage
SV412 – R. Mennickent SV411 – P. McGregor SV409 – D. Flyod
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Pulsar
MCAO for Sky Coverage
SV412 – R. Mennickent
Filter = Ks
FWHM = 80mas
Exposure time = 1900s
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Pulsar Isolated galaxy Quasar
MCAO for Sky Coverage
SV412 – R. Mennickent SV411 – P. McGregor SV409 – D. Flyod
1 arcsec
FWHM = 0.13 arcsec
Filter = Ks
Exposure Time = 92min
SV411 P. McGregor
Clumpy K-band
continuum structure
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N
E
Abell 780 – z ~ 0.1
85” ~ 150kpc
SV403
R. Carrasco & I. Trujillo
Filter = Ks
1h on-source
<FWHM> = 77mas
2 NGS only
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New challenges for
WFAO
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AO Facility
2015
WFAO challenges
Current WFAO science instruments:
SOAR Adaptive Module
Near future WFAO
science instruments: Current WFAO demonstrators:
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All the ELTs are based on multi-LGS WFAO
systems
WFAO challenges
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All the ELTs are based on multi-LGS WFAO
systems
WFAO challenges
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Conclusions
WFAO is opening new opportunities for a large range of science cases
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Static tomography for NCPA
Tomographic phase diversity: The classical PD approach can be extended to process data over an
extended field of view.
Instead of solving for a 2D phase, solve for a 3D phase (discrete or
continuous). E.g 2-3 phase planes + a tomographic projector
Naturally more overconstrained/robust than PD in individual direction +
tomographic reconstruction (assuming # of field positions/images is larger
than the # of phase planes).
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1 2 3 4 40
60
80
100
IterationS
tre
hl o
ve
r fie
ld [
%]
Static tomography for NCPA
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1 2 3 4 40
60
80
100
IterationS
tre
hl o
ve
r fie
ld [
%]
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1 2 3 4 40
60
80
100
IterationS
tre
hl o
ve
r fie
ld [
%]
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1 2 3 4 40
60
80
100
IterationS
tre
hl o
ve
r fie
ld [
%]
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Static tomography for NCPA
( NCPA issues for wide-field AO systems: Impossibility to compensate for anything
that’s not close to a DM conjugation altitude ! )
(NCPA optimizes the wave-front in the science beam, but may degrade it severely in
the NGSWFS path ! )
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Time-delayed cross correlation between two wave front sensors, WFSA and WFSB, is :
),(
)()(),,(
, ,,
vuO
ttStS
tvuTvu
B
vvuu
A
vuAB
ΔΔ
Δ+⋅=ΔΔΔ∑ Δ+Δ+
: X and Y slopes of the WFS in subaperture (u,v) at time t )(, tSWFS
vu
),( vuO ΔΔ : overlapping illuminated subapertures for offset
: is a multiple of the acquisition time tΔ
GeMS’ wind profiler
Wind profiler method (Wang et al. 2008)
]][][[ /FTFTFT1
ATAB−
),(
)()(
2
1
),(
)()(
2
1),(
, ,,, ,,
vuO
tStS
vuO
tStS
vuAvu
B
vvuu
B
vuvu
A
vvuu
A
vu
ΔΔ
⋅+
ΔΔ
⋅=ΔΔ
∑∑ Δ+Δ+Δ+Δ+
A is the average of the autocorrelations of WFSA and WFSB
Signal is retrieved by deconvolution
[Co
rtes e
t al. –
MN
RA
S –
2012]
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For T = 0 s, the turbulence profile in altitude is extracted from the baseline
For T > 0, the layers present can be detected and their velocity estimated
GeMS’ wind profiler [C
orte
s e
t al. –
MN
RA
S –
2012]
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For T = 0 s, the turbulence profile in altitude is extracted from the baseline
For T > 0, the layers present can be detected and their velocity estimated
GeMS’ wind profiler [C
orte
s e
t al. –
MN
RA
S –
2012]
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GeMS’ wind profiler
Cross-Check with wind predictions
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GeMS’ wind profiler
Wind profiler solves the “negative Cn2” issue
[Guesalaga et al. – MNRAS – 2014]
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GeMS’ wind profiler
Wind profiler solves the “negative Cn2” issue
Also allows to study the Frozen Flow hypothesis
!
wind speed = 8.8 m/s
wind direction = 187.1°
m = -1.33 s-1
time, s
dec
ay r
atio
[Guesalaga et al. – MNRAS – 2014]
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SV413 – H. Plana RCW41 Star Clusters
SV402 – R. Blum
R136
NGC1851
SV406 – A. McConnachie
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Star Clusters
Low mass cluster
Age estimation based on PMS
~ 10Myr cluster
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MCAO for Astrometry
Why MCAO is good for astrometry ?
Active control of plate scales
Large FoV => more reference stars
PSFs are uniform over the field
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MCAO for Astrometry
Why MCAO is good for astrometry ?
Active control of plate scales
Large FoV => more reference stars
PSFs are uniform over the field
0.4mas
Rigaut, Neichel et al. 2012
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MCAO for Astrometry
Why MCAO is good for astrometry ?
Active control of plate scales
Large FoV => more reference stars
PSFs are uniform over the field
But astrometry is challenging:
Distortions in Science plane are
difficult to calibrate.
Multi-epoch astrometric
performance is ~ 1 mas
For crowded fields, it can be calibrated
For sparse fields, looking for hardware
solutions
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MCAO for Astrometry
Diffraction grid for high-precision astrometry programs
Guyon+12
Bendek+12
Ammons+12.