Viewing the Universe through distorted lenses:

Adaptive optics in astronomy Steven Beckwith

Space Telescope Science Institute & JHU

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Atmospheric turbulence

stratosphere

tropopause

Heat sources within dome

boundary layer ~1 km

10-12 km

wind flow over dome

Log turbulence, Cn2

Windshear

Windshear

-18 -17 -16 -15 -140

10

20

kmCourtesy Claire Max, Center for Adaptive Optics

r0 ~ 40cm (µm)2 vwind ~ 10 m/s

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How are stellar images created?

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

Lick Observatory, 1 m telescope

10s exposure 10ms exposure Diffraction-limit

Speckles (each is at diffraction limit of telescope)

~ 1 arc sec ~ 0.1 arcsec ~ / D

Courtesy Claire Max, Center for Adaptive Optics

Typical time scales ~ 10 ms

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Adaptive Corrections

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Mauna Kea telescopes

Gemini NCFHT

Keck 1&2Subaru

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QuickTime™ and aCinepak decompressor

are needed to see this picture.

The Gemini AO system: movie

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AO correction of a star

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

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ALTAIR: Gemini AO system

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Examples of AO corrected imagesR136, Adonis

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The Center of the Milky Way

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

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Faint companions to starsLiu et al. 2003, Astrophysical Journal, in press

0.06 Msun (48 Mjup) L dwarf companion HR 7672; 14 AU from starGemini/Hokupa’a

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iso10 k

m

Dtel

Isoplanatic angle, iso

Limitations

• Isoplanatic angle: ~30” (µm)2

• Sky coverage: ~2%

• Wavelength range: > 1 µm

Anisoplanatism: image quality deteriorates farther

from guide star

0 50 100

sky coverage (%)

AO now

AO~2009

Space

0

50

100

150

200

arcsec

Field of View

now 2009 HST

r0~40cm (µm)2

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No AO With AO

No AO With AO

Intensity Future promise

• Artificial guide stars: sodium laser-induced fluorescence

• Multi-conjugate adaptive optics (MCAO)

• Adaptive secondary mirrors: simplified optical train

• Very high order corrections: ~10,000 actuator mirrors

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Tomographic reconstruction: multiple stars

X-ray tomography

atmospheric tomography

to use in astronomy