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!