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 = 0.5m 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