viewing the universe through distorted lenses: adaptive optics in astronomy steven beckwith space...
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Viewing the Universe through distorted lenses:
Adaptive optics in astronomy Steven Beckwith
Space Telescope Science Institute & JHU
12/6/03 Astronomical Adaptive Optics 2
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
12/6/03 Astronomical Adaptive Optics 3
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
12/6/03 Astronomical Adaptive Optics 6
QuickTime™ and aCinepak decompressor
are needed to see this picture.
The Gemini AO system: movie
12/6/03 Astronomical Adaptive Optics 7
AO correction of a star
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
12/6/03 Astronomical Adaptive Optics 11
The Center of the Milky Way
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
12/6/03 Astronomical Adaptive Optics 12
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
12/6/03 Astronomical Adaptive Optics 14
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
12/6/03 Astronomical Adaptive Optics 15
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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