Aug-Nov, 2008 IAG/USP (Keith Taylor)
Instrumentation Concepts
Ground-based Optical Telescopes
Keith Taylor(IAG/USP)
Aug-Nov, 2008
Aug-Sep, 2008 IAG-USP (Keith Taylor)
Aug-Nov, 2008 IAG/USP (Keith 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?
WFSs
Reference Stars
Telescope
High Altitude Layer
Ground Layer
DM conjugatedTelescope pupil Real Time Computer
Averaged WF..Ground Layer
AltitudeLayers
Laserbeams
Aug-Nov, 2008 IAG/USP (Keith Taylor)
Ex: 50% of the time there is 55% OR LESS turbulence in the 1st 500mMore measurements are being carried out (M. Sarazin)
Does a ground layer exist?
PARANAL OBSERVATORY
Courtesy: M. Sarazin
Aug-Nov, 2008 IAG/USP (Keith Taylor)
Seeing-limited(>90% of Ground-based
Astronomy!)
GroundLayerAdaptiveOptics
Betterseeingin widerfield
• Turbulence profile• Guide star(s)• Gain?
Diffraction limit(full AO or MCAO)
=
Aug-Nov, 2008 IAG/USP (Keith Taylor)
« Ground Layer » Adaptive Optics [GLAO]
GLAO: multi-GS WFS single ground DM correcting average perturbation ~ near ground turbulence
No Correction: Seeing limit
single Ground DMsingle Ground DM
GLAO: reduced apparent seeing
seeing improved and stabilizedin very large FoVgain ~2 in 10 arcmin for NIR VLT obs.
Expected performance:
FoVFoV
Aug-Nov, 2008 IAG/USP (Keith Taylor)
Turbulence Profile and ground layer
Mauna Kea, October 22/23, 2002: G-scidar
0km
5km
10km
15km
Data: J.Vernin, A.Ziad
Aug-Nov, 2008 IAG/USP (Keith Taylor)
Turbulence Profile and ground layerCERRO TOLOLO OBSERVATORY
Courtesy: M. SarazinR. Wilson
Aug-Nov, 2008 IAG/USP (Keith Taylor)
Turbulence Profile and ground layerCERRO TOLOLO OBSERVATORY
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?
Improved seeing, Sr(K) ~ 4% 8’ FOV
Seeing PSF on-axis PSF off-axis
Seeing reducer
Reduced exposure & Telescope time
Better light concentration
Reduced confusion in Stellar populations & Cluster fields
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?
K Band, gain: 100% FWHM
Y Band,Gain: 30%
Seeing
With AO
Aug-Nov, 2008 IAG/USP (Keith Taylor)
GLAO improves Ensquared Energy?
Y Band,gain: 50%
K Band, EE doubled
With AO
Seeing
Pixel: 0.1”
Aug-Nov, 2008 IAG/USP (Keith Taylor)
GLAO reduces confusion?
K Band, gain: 40%
Y Band,Gain: 30%
Seeing
With AO
Yes but more difficult!
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
Tip-tilt limiting magnitude (R-Band)Probability for (top to bottom) 1,2,3 TT NGS
In 1arcmin annular FOV
Tip-tilt limiting magnitude (R-Band)Probability for (top to bottom) 1,2,3 TT NGS
In 2 arcmin annular FOV
1 VIS NGS
Aug-Nov, 2008 IAG/USP (Keith Taylor)
GLAO Gain
MCAO GLAO
Resolution
(K-band)
0.05” 0.2”
Field diameter
1’ 10’
Number of pixels
1.4 Mpix 9 Mpix
+ in the visible!!!
Skycoverage~100%
Aug-Nov, 2008 IAG/USP (Keith Taylor)
GLAO in the visible?
@750nm; FOV=1’
GLAO
Seeing
Aug-Nov, 2008 IAG/USP (Keith Taylor)
Two GLAO systems
S-GLAO 5 sodium LGSs R-GLAO Rayleigh LGS
Aug-Nov, 2008 IAG/USP (Keith Taylor)
MASS/DIMM measures
Aug-Nov, 2008 IAG/USP (Keith Taylor)
Compare S-GLAO with R-GLAO
S-GLAO R-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
~0.5m ~0.7m
Aug-Nov, 2008 IAG/USP (Keith Taylor)
Typical night: Jan 15/16, 2003
Seeing
~0.5m ~0.7m
Aug-Nov, 2008 IAG/USP (Keith Taylor)
Statistics: FWHM25% 50% 75%
Seeing (arcsec)
0.94 1.11 1.33
0.5m 0.38 0.53 0.71
0.7m 0.22 0.31 0.49
1.0m 0.17 0.22 0.30
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
PDR: 2004First light: 2006 (now 9/09)LGS: 2007 (now 9/10)
Aug-Nov, 2008 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!