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AO AO inin AO AOAAdaptivedaptive OOpticsptics

in in

AAstronomicalstronomical OObservationsbservations

Diana R. Constantin

ASTRONOMICAL INSTITUTE OF THE ASTRONOMICAL INSTITUTE OF THE ROMANIAN ACADEMYROMANIAN ACADEMY

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Why is adaptive optics needed?Why is adaptive optics needed?

Even the largest ground-based astronomical telescopes have no better resolution than an 8"

telescope!

Even the largest ground-based astronomical telescopes have no better resolution than an 8"

telescope!

Turbulence in earth’s atmosphere makes stars twinkle –which we don’t correct!!

More importantly, turbulence spreads out light; makes it a blob rather than a point

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Turbulence arises in many placesTurbulence arises in many places

stratosphere

tropopause

Heat sources w/in dome

boundary layer~ 1 km

10-12 km

wind flow over dome

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The solution:The solution:Schematic of adaptive optics systemSchematic of adaptive optics system

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Characterize turbulence Characterize turbulence strength by quantity rstrength by quantity r00

• “ “Coherence Length” rCoherence Length” r0 0 : distance over which optical : distance over which optical phase distortion has mean square value of 1 radphase distortion has mean square value of 1 rad22 (r (r00 ~ ~ 15 - 30 cm at good observing sites)15 - 30 cm at good observing sites)

• PSF is |FT(wavefront@pupil)| PSF is |FT(wavefront@pupil)| FWHM FWHM λλ/D → /D → λλ/r/r00

• Easy to remember: rEasy to remember: r0 0 = 10 cm = 10 cm FWHM = 1 arc sec at FWHM = 1 arc sec at = 0.5= 0.5mm

Primary mirror of telescope

r0 ““Fried’s parameter”Fried’s parameter”

Wavefront of light

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Adaptive optics increases Adaptive optics increases peak intensity of a point peak intensity of a point sourcesource

Lick Observatory

No AO With AO

No AO With AO

Intensity

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AO produces point spread functions AO produces point spread functions with a “core” and “halo”with a “core” and “halo”

• The GOOD: When AO system performs well (good seeing), more energy in core The GOOD: When AO system performs well (good seeing), more energy in core

–––space quality imaging!!space quality imaging!!

• The BAD: When AO system is stressed (poor seeing), halo contains larger The BAD: When AO system is stressed (poor seeing), halo contains larger fraction of energy (diameter ~ rfraction of energy (diameter ~ r00))

• The UGLY: Ratio between core and halo varies during night and in particular The UGLY: Ratio between core and halo varies during night and in particular during the dayduring the day

Inte

nsity

x

Definition of “Strehl”:Ratio of peak intensity

to that of “perfect” optical system

Simulation: courtesy Stein, Nordlund&Keller

Input data4m in space (perfect optics)

ATST good seeing

ATST median seeing

S>=0.3 S>=0.6 S=1 (Hinode: S~0.7)

S=0.2

ATST is able to resolve 30 km structures

Stokes-V Visible(630.2nm)

SRD requirements:

NO-AO

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Summit of Mauna Kea, HawaiiSummit of Mauna Kea, Hawaii

Subaru

2 Kecks

Gemini North

AO Applications -Astronomy

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European Southern Observatory: European Southern Observatory: four 8-m Telescopes in Chile four 8-m Telescopes in Chile

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Adaptive optics makes it possible to Adaptive optics makes it possible to find faint companions around bright find faint companions around bright starsstars

Two images from Palomar of a brown Two images from Palomar of a brown dwarf companion to GL 105dwarf companion to GL 105

Credit: David Golimowski Credit: David Golimowski

200” telescope

No AONo AO With AOWith AO

Another companion?

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Uranus with Hubble Space Uranus with Hubble Space Telescope and Keck AOTelescope and Keck AO

HST, Visible Keck AO, IR

L. Sromovsky

Lesson: Keck in near IR has ~ same resolution as Hubble in visibleLesson: Keck in near IR has ~ same resolution as Hubble in visible

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AO Applied to Free-Space Laser AO Applied to Free-Space Laser CommunicationsCommunications

• 10’s to 100’s of gigabits/sec10’s to 100’s of gigabits/sec• Example: AOptixExample: AOptix• Applications: flexibility, mobilityApplications: flexibility, mobility

– HDTV broadcasting of sports eventsHDTV broadcasting of sports events– Military tactical communicationsMilitary tactical communications

• Between ships, on land, land to airBetween ships, on land, land to air

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Defense SystemsDefense Systems

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Keck Observatory

Laser guide stars are operating at Laser guide stars are operating at Lick, Keck, Gemini North, VLT Lick, Keck, Gemini North, VLT ObservatoriesObservatories

Lick Observatory

June 10-12, 2007 DFG/NSF Conference

DLSP Speckle Imager

2kw2k, 25 fps

Frame selection

Speckle bursts

Virtual camera Prototype

June 10-12, 2007 DFG/NSF Conference

Books

"Adaptive Optics for Astronomy", Francois Roddier (ed.), Cambridge University Press, 1999

"Adaptive Optics for Astronomical Telescopes", John W. Hardy, Oxford Books, 1998

"A Field Guide to Adaptive Optics" Robert K. Tyson and Benjamin W. Frazier, SPIE Press

"Introduction to Adaptive Optics" Robert K. Tyson and Benjamin W. Frazier, SPIE Press

"Principles of Adaptive Optics", Robert K. Tyson, Academic Press, 1997

"Imaging Through Turbulence", Michael C. Roggemann & Byron Welsh, CRC Press, 1996

SPIE Proceedings – tons of it (literally)CFAO web site and list of tutorials there

““(Solar) Observations with Adaptive Optics“, (Solar) Observations with Adaptive Optics“, Thomas Rimmele