Transcript Document

AO in AO
Adaptive Optics
in
Astronomical Observations
Diana R. Constantin
ASTRONOMICAL INSTITUTE OF THE ROMANIAN
ACADEMY
Page 1
Why is adaptive optics needed?
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
Even the largest ground-based astronomical
telescopes have no better resolution than an 8" telescope!
Page 2
Turbulence arises in many places
stratosphere
tropopause
10-12 km
wind flow over dome
boundary layer
~ 1 km
Heat sources w/in dome
Page 3
The solution:
Schematic of adaptive optics system
Page 4
Characterize turbulence strength by
quantity r0
Wavefront
of light
r0
“Fried’s parameter”
Primary mirror of telescope
• “Coherence Length” r0 : distance over which optical phase
distortion has mean square value of 1 rad2 (r0 ~ 15 - 30 cm at
good observing sites)
• PSF is |FT(wavefront@pupil)|  FWHM
λ/D → λ/r0
• Easy to remember: r0 = 10 cm  FWHM = 1 arc sec at l = 0.5m
Page 5
Adaptive optics increases peak
intensity of a point source
Lick
Observatory
No AO
With AO
Intensity
No AO
With AO
Page 6
AO produces point spread functions with a
“core” and “halo”
Intensity
Definition of “Strehl”:
Ratio of peak intensity to
that of “perfect” optical
system
x
• The GOOD: When AO system performs well (good seeing), more energy in core
––space quality imaging!!
• The BAD: When AO system is stressed (poor seeing), halo contains larger fraction of
energy (diameter ~ r0)
• The UGLY: Ratio between core and halo varies during night and in particular during
the day
Page 7
ATST is able to resolve 30 km structures
Simulation: courtesy Stein, Nordlund&Keller
Stokes-V Visible(630.2nm)
S=0.2
NO-AO
SRD
requirements:
ATST median
seeing
S>=0.3
ATST good
seeing
S>=0.6
4m in space
(perfect optics)
Input data
S=1 (Hinode: S~0.7)
AO Applications Astronomy
Subaru
2 Kecks
Gemini North
Summit of Mauna Kea, Hawaii
Page 9
European Southern Observatory:
four 8-m Telescopes in Chile
Page 10
Adaptive optics makes it possible to find
faint companions around bright stars
Two images from Palomar of a brown
dwarf companion to GL 105
200” telescope
No AO
With AO
Another companion?
Credit: David Golimowski
Page 11
Uranus with Hubble Space Telescope
and Keck AO
L. Sromovsky
HST, Visible
Keck AO, IR
Lesson: Keck in near IR has ~ same resolution as Hubble in visible
Page 12
AO Applied to Free-Space Laser
Communications
• 10’s to 100’s of gigabits/sec
• Example: AOptix
• Applications: flexibility, mobility
– HDTV broadcasting of sports events
– Military tactical communications
• Between ships, on land, land to air
Page 13
Defense Systems
Page 14
Laser guide stars are operating at Lick,
Keck, Gemini North, VLT Observatories
Keck Observatory
Lick Observatory
Page 15
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“, Thomas Rimmele
June 10-12, 2007
DFG/NSF Conference