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AO in AO A daptive O ptics in A stronomical O bservations

AO in AO A daptive O ptics in A stronomical O bservations. Diana R. Constantin ASTRONOMICAL INSTITUTE OF THE ROMANIAN ACADEMY. Why is adaptive optics needed?. Turbulence in earth’s atmosphere makes stars twinkle –which we don’t correct!!

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AO in AO A daptive O ptics in A stronomical O bservations

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  1. AO in AOAdaptiveOpticsin AstronomicalObservations Diana R. Constantin ASTRONOMICAL INSTITUTE OF THE ROMANIAN ACADEMY

  2. 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!

  3. Turbulence arises in many places tropopause 10-12 km wind flow over dome boundary layer ~ 1 km Heat sources w/in dome stratosphere

  4. The solution:Schematic of adaptive optics system

  5. Characterize turbulence strength by quantity r0 Wavefront of light r0 “Fried’s parameter” • “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 Primary mirror of telescope

  6. Adaptive optics increases peak intensity of a point source Lick Observatory No AO With AO Intensity With AO No AO

  7. 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 AO produces point spread functions with a “core” and “halo” Definition of “Strehl”: Ratio of peak intensity to that of “perfect” optical system Intensity x

  8. ATST is able to resolve 30 km structures Simulation: courtesy Stein, Nordlund&Keller Stokes-V Visible(630.2nm) S=0.2 NO-AO ATST median seeing ATST good seeing 4m in space (perfect optics) Input data SRD requirements: S>=0.3 S>=0.6 S=1 (Hinode: S~0.7)

  9. Summit of Mauna Kea, Hawaii AO Applications - Astronomy Subaru 2 Kecks Gemini North

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

  11. Adaptive optics makes it possible to find faint companions around bright stars Another companion? Two images from Palomar of a brown dwarf companion to GL 105 200” telescope With AO No AO Credit: David Golimowski

  12. Uranus with Hubble Space Telescope and Keck AO L. Sromovsky Keck AO, IR HST, Visible Lesson: Keck in near IR has ~ same resolution as Hubble in visible

  13. 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

  14. Defense Systems

  15. Laser guide stars are operating at Lick, Keck, Gemini North, VLT Observatories Keck Observatory Lick Observatory

  16. DLSP Speckle Imager 2kw2k, 25 fps Frame selection Speckle bursts Virtual camera Prototype DFG/NSF Conference

  17. 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 DFG/NSF Conference

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