Download Ground Layer - IAG-Usp

Instrumentation Concepts
Ground-based Optical
Telescopes
Keith Taylor
(IAG/USP)
Aug-Nov, 2008
Aug-Nov, 2008
Aug-Sep,
2008
IAG/USP (Keith
IAG-USP
(Keith Taylor)
Taylor)
Ground Layer Adaptive Optics
(GLAO)
Thanks to:
Andrei Tokovinin (SOAR)
Norbert Hubin (ESO)
Aug-Nov, 2008
IAG/USP (Keith Taylor)
WHAT IS GROUND LAYER AO?
Laser
beams
Reference Stars
High Altitude Layer
Altitude
Layers
Ground Layer
Telescope
DM conjugated
Telescope pupil
Ground
Layer
Aug-Nov, 2008
WFSs
IAG/USP (Keith Taylor)
Real Time Computer
Averaged WF..
Does a ground layer exist?
PARANAL OBSERVATORY
Courtesy: M. Sarazin
Ex: 50% of the time there is 55% OR LESS turbulence in the 1st 500m
IAG/USP (Keith Taylor)
Aug-Nov, 2008
More
measurements are being
carried out (M. Sarazin)
Seeing-limited
(>90% of Ground-based Astronomy!)
Ground
Layer
Adaptive
Optics
=
Better
seeing
in wider
field
Diffraction limit
(full AO or MCAO)
Aug-Nov, 2008
IAG/USP (Keith Taylor)
• Turbulence profile
• Guide star(s)
• Gain?
« Ground Layer » Adaptive
Optics [GLAO]
GLAO:
 multi-GS WFS
 single ground DM correcting average
perturbation ~ near ground turbulence
Expected
performance:
FoV
single Ground DM
GLAO:
No Correction:
reduced Seeing
apparent
limit
seeing
seeing improved and stabilized
in very large FoV
gain ~2 in 10 arcmin for NIR VLT obs.
Aug-Nov, 2008
IAG/USP (Keith Taylor)
Turbulence Profile and ground
layer
Mauna Kea, October 22/23, 2002: G-scidar
15km
10km
5km
0km
Data: J.Vernin, A.Ziad
Aug-Nov, 2008
IAG/USP (Keith Taylor)
Turbulence Profile and ground
CERRO TOLOLO OBSERVATORY
layer
Aug-Nov, 2008
IAG/USP (Keith Taylor)
Courtesy: M. Sarazin
R. Wilson
Turbulence Profile and ground
CERRO TOLOLO OBSERVATORY
layer
Courtesy: M. Sarazin
Aug-Nov, 2008
IAG/USP (Keith Taylor)
Investigation of Ground layer at
Paranal


Multi Aperture Scintillation Sensor MASS + DIMM: Cn2 profile
SLODAR: Slope Detection and ranging: Higher resolution of ground
layer
Courtesy: R. Wilson
Aug-Nov, 2008
IAG/USP (Keith Taylor)
GLAO as seeing reducer?
Seeing
PSF on-axis
Improved seeing, Sr(K) ~ 4%
PSF off-axis
8’ FOV
Reduced confusion in Stellar populations & Cluster fields
Seeing reducer
Better light concentration
Reduced exposure & Telescope time
Aug-Nov, 2008
IAG/USP (Keith Taylor)
Science with GLAO
Dynamics of galaxies, AGNs (+IFU)
 Stellar populations, clusters (confusion!)
 Supernovae, cepheids
 Weak lensing
 ISM (PNe, jets)
 and more…

GLAO benefits most “classical” astronomical programs
Aug-Nov, 2008
IAG/USP (Keith Taylor)
GLAO as seeing reducer?
Seeing
K Band, gain: 100% FWHM
Y Band,
Gain: 30%
With AO
Aug-Nov, 2008
IAG/USP (Keith Taylor)
GLAO improves Ensquared Energy?
Pixel: 0.1”
With AO
K Band,
EE doubled
Y Band,
gain: 50%
Seeing
Aug-Nov, 2008
IAG/USP (Keith Taylor)
GLAO reduces confusion?
Yes but more difficult!
Seeing
K Band, gain: 40%
Y Band,
Gain: 30%
With AO
Aug-Nov, 2008
IAG/USP (Keith Taylor)
GLAO and full sky coverage?

Need Laser artificial stars for WFS tomography because of:
 Median to bad seeing conditions assumptions
 Science performed down to short λ

Require Natural Guide Star for Tip-tilt correction
1 VIS NGS
Tip-tilt limiting magnitude (R-Band)
Tip-tilt limiting magnitude (R-Band)
Probability for (top to bottom) 1,2,3 TT NGS
Probability for (top to bottom) 1,2,3 TT NGS
IAG/USP (Keith Taylor)
Aug-Nov, 2008In 1arcmin annular FOV
In 2 arcmin annular FOV
GLAO Gain
+ in the visible!!!
MCAO
GLAO
Resolution
(K-band)
Field
diameter
0.05”
0.2”
1’
10’
Number of
pixels
1.4 Mpix
9 Mpix
Aug-Nov, 2008
IAG/USP (Keith Taylor)
Sky
coverage
~100%
GLAO in the visible?
@750nm; FOV=1’
GLAO
Seeing
Aug-Nov, 2008
IAG/USP (Keith Taylor)
Two GLAO systems
R-GLAO Rayleigh LGS
S-GLAO 5 sodium LGSs
Aug-Nov, 2008
IAG/USP (Keith Taylor)
MASS/DIMM measures
Aug-Nov, 2008
IAG/USP (Keith Taylor)
Compare S-GLAO with R-GLAO
R-GLAO
S-GLAO
17% at 8km, 83% at 0.5km
Aug-Nov, 2008
IAG/USP (Keith Taylor)
Further comparison
Aug-Nov, 2008
IAG/USP (Keith Taylor)
Typical night: Jan 11/12, 2003
Seeing
 ~0.5m
 ~0.7m
Aug-Nov, 2008
IAG/USP (Keith Taylor)
Typical night: Jan 15/16, 2003
Seeing
 ~0.5m
 ~0.7m
Aug-Nov, 2008
IAG/USP (Keith Taylor)
Statistics: FWHM
25%
50%
75%
Seeing
0.94
1.11
1.33
0.5m
0.38
0.53
0.71
0.7m
0.22
0.31
0.49
1.0m
0.17
0.22
0.30
(arcsec)
Aug-Nov, 2008
IAG/USP (Keith Taylor)
SAM = SOAR Adaptive Module

Rayleigh LGS

355 nm, 8W, 10km
S-H WFS, 9x9
 Bimorph DM
 CCD imager


FoV = 3’x3’
Visitor instrument
 Collimated space

Aug-Nov, 2008
PDR: 2004
First light: 2006 (now 9/09)
LGS: 2007 (now 9/10)
IAG/USP (Keith Taylor)
Optical design: OAP
•All-reflective
•Excellent quality
•Collimated space
Aug-Nov, 2008
IAG/USP (Keith Taylor)
SAM as adaptor
Aug-Nov, 2008
IAG/USP (Keith Taylor)
GLAO: useful for most astronomical programs








Ground Layer Adaptive Optics = Seeing reducer
Reduced Seeing => reduced exposure & telescope times
Reduced seeing => Reduced confusion in Stellar populations
& Cluster fields
Ground Layer Adaptive Optics = Seeing “stabilizer”
Seeing stabilizer => better percentile seeing for your site!
Seeing reducer is “easily” achievable at all λs (down to vis.)
High Sky coverage GLAO systems will benefit most
astronomical programs
Seeing reducer = light concentration: Sufficient for distant
(“small”) galaxies with low surface brightness (0.2-0.1” pixel
enough)
Aug-Nov, 2008
IAG/USP (Keith Taylor)
Conclusions
GLAO is complementary to AO, MCAO
 Opens “visible” window, all-sky
 Rayleigh LGS is quite good
 SAM _ first implementation, test-bench
 Need data on turbulence in the first km!

Aug-Nov, 2008
IAG/USP (Keith Taylor)