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Lucky imaging - Life in the visible after HST

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Lucky imaging - Life in the visible after HST

  1. 1. Lucky Imaging Life in the visible after HST Tim Staley Southampton Seminar Series February 2012 WWW: timstaley.co.uk 1 / 73
  2. 2. Outline 1 Atmospheric effects 2 High spatial resolution astronomy 3 Adaptive optics 4 Lucky imaging 5 Lucky imaging + AO 2 / 73
  3. 3. Outline 1 Atmospheric effects 2 High spatial resolution astronomy 3 Adaptive optics 4 Lucky imaging 5 Lucky imaging + AO 3 / 73
  4. 4. Coping with weather 4 / 73
  5. 5. Atmospheric structure 5 / 73
  6. 6. Boundary layers 6 / 73
  7. 7. Kelvin-Helmholtz instability –> turbulence 7 / 73
  8. 8. Wavefront perturbations Planar wavefronts: Resolution ∝ λ D 8 / 73
  9. 9. Wavefront perturbations Perturbed wavefronts: Resolution ∝ λ r0 (long exposure on a large telescope) 9 / 73
  10. 10. 10 / 73GOODS North, Subaru @ 0.8” seeing Hubble UDF
  11. 11. Outline 1 Atmospheric effects 2 High spatial resolution astronomy 3 Adaptive optics 4 Lucky imaging 5 Lucky imaging + AO 11 / 73
  12. 12. Why bother? 12 / 73
  13. 13. Exoplanets 13 / 73
  14. 14. Exoplanets Keck II - AO using angular differential imaging 14 / 73 HR8799 — Marois et al., 2010
  15. 15. Globular clusters 15 / 73 HST mosaic of M53 (spot the blue stragglers!)
  16. 16. 16 / 73
  17. 17. The cost of space astronomy HST: ≈ $2 billion at launch (1990) $9.6 billion lifetime cost, including servicing missions 17 / 73 Image: ESA Source: NY Times: “Refurbishments Complete, Astronauts Let Go of Hubble”
  18. 18. Ground based astronomy VLT: $330 Me to build $16.9 Me annual running costs ‘Expensive’ is relative 18 / 73 Image: ESA Source: www.eso.org
  19. 19. Outline 1 Atmospheric effects 2 High spatial resolution astronomy 3 Adaptive optics 4 Lucky imaging 5 Lucky imaging + AO 19 / 73
  20. 20. AO: The basic idea 20 / 73
  21. 21. Guide stars and sky coverage Isoplanatic patch = area for which perturbations roughly the same Require rmag ≤ 10 star within 5” – 40”, depending on observation wavelength and atmospheric conditions 21 / 73 See e.g. Racine, 2006
  22. 22. Laser guide stars 22 / 73 Image: G. Hudepohl / ESO
  23. 23. Laser guide stars 23 / 73 Image: R. Tyson - An introduction to AO (2000)
  24. 24. Laser guide stars Still require a tip-tilt NGS of rmag ≤ 14 within ≈ 40” of science target. Good quality sky coverage ≈ 10% at 30◦ galactic latitude. (Strehl ≥ 0.3, J band) 24 / 73 Davies et al., 2008 Ellerbroek and Tyler, 1998
  25. 25. (Strehl?) The ratio of peak intensity compared to a perfect telescope (0 to 1) HST Strehl near 1, but suffers pixellation effects. AO Strehl usually varies from around 0.2 – 0.6 Seeing “Strehl” depends on the telescope, but is typically ≈ 0.01 on medium size telescopes in the visible. 25 / 73
  26. 26. Outline 1 Atmospheric effects 2 High spatial resolution astronomy 3 Adaptive optics 4 Lucky imaging 5 Lucky imaging + AO 26 / 73
  27. 27. Seeing isn’t stable How often will we get a ‘good’ frame? 27 / 73
  28. 28. Fried’s probabilities Probability of a lucky exposure (near diffraction limited): P ≈ 5.6 exp − 0.1557(D/r0)2 28 / 73 Fried, 1978
  29. 29. Fried’s probabilities D/r0 Probability 2 0.986 ± 0.006 3 0.765 ± 0.005 4 0.334 ± 0.014 5 (9.38 ± 0.33) × 10−2 6 (1.915 ± 0.084) × 10−2 7 (2.87 ± 0.57) × 10−3 10 (1.07 ± 0.48) × 10−6 15 (3.40 ± 0.59) × 10−15 29 / 73 Fried, 1978
  30. 30. How to take advantage of this? Cross-correlate speckle image with an Airy psf model Cross-correlation values provide a proxy for Strehl Cross-correlation positions give a good estimate of brightest speckle Select desired frames, then shift and add. 30 / 73
  31. 31. Early tests 31 / 73
  32. 32. Early tests 2.5m Nordic Optical Telescope 512 sq. pixel detector 185Hz frame rate 810nm observing wavelength Faint limit at 6th magnitude 32 / 73
  33. 33. Early tests Seeing width ≈ 0.4” 33 / 73 Baldwin et al., 2001
  34. 34. Early tests ζ Bootis, Seeing width ≈ 0.8” 34 / 73 Baldwin et al., 2001
  35. 35. Fast imaging with EMCCD’s 35 / 73 Cost: Around £15K
  36. 36. Fast imaging with EMCCD’s Conventional CCD: SNR= M√ M+σ2 N EMCCD: SNR= M√ 2M+(σN /gA)2 36 / 73
  37. 37. Fast imaging with EMCCD’s Calibration: 37 / 73
  38. 38. Fast imaging with EMCCD’s Calibration: 38 / 73
  39. 39. Fast imaging with EMCCD’s Calibration: 39 / 73
  40. 40. Fast imaging with EMCCD’s Limited pixel size, 1K2 Can only get 30 sq. arcseconds Nyquist sampled on 2.5m telescope. Readout electronics are a bottleneck on the frame rate 40 / 73
  41. 41. 2009 — LuckyCam goes wide field 41 / 73
  42. 42. 2009 — LuckyCam goes wide field 42 / 73
  43. 43. 2009 — LuckyCam goes wide field 43 / 73
  44. 44. 2009 — LuckyCam goes wide field 44 / 73
  45. 45. 2009 — LuckyCam goes wide field 45 / 73
  46. 46. Wide fields of view: M13 120 x 30 arcsecond FoV @ 33mas per pixel Challenging data storage and processing requirements Astrometric calibration is non-trivial 46 / 73
  47. 47. Wide fields of view: M13 Zoom — 6.7 arcseconds across this FoV Conventional imaging 50% frame selection 47 / 73
  48. 48. Wide fields of view: M13 0 10 20 30 40 50 60 Distance from guide star in arcseconds 100 200 300 400 500 FWHMinmilliarcseconds 10% selection 100% selection Seeing FWHM 48 / 73
  49. 49. Guiding on a faint reference: the Einstein cross Guiding on a 17th mag. star — FWHM≈ 0.1” 49 / 73
  50. 50. Science at the faint limit: thresholding Read out noise still 0.1 electrons. Faint limit around 23rd magnitude on a 2.5m telescope (good seeing) Thresholding eliminates read noise But for now we are limited by CIC 50 / 73
  51. 51. Science at the faint limit: thresholding 51 / 73
  52. 52. Science at the faint limit: thresholding 52 / 73
  53. 53. Applications Stellar binarity surveys 53 / 73
  54. 54. Applications High resolution surveys (e.g. microlensing in crowded field) 54 / 73
  55. 55. Applications High resolution surveys (e.g. microlensing in crowded field) Cheap high resolution follow-up (stellar transits, etc) 55 / 73
  56. 56. Applications High resolution surveys (e.g. microlensing in crowded field) Cheap high resolution follow-up (stellar transits, etc) Planetary imaging 56 / 73
  57. 57. Applications High resolution surveys (e.g. microlensing in crowded field) Cheap high resolution follow-up (stellar transits, etc) Planetary imaging Potentially better faint limits that conventional imagers in future? (esp. for bright sky) 57 / 73
  58. 58. Applications High resolution surveys (e.g. microlensing in crowded field) Cheap high resolution follow-up (stellar transits, etc) Planetary imaging Potentially better faint limits that conventional imagers in future? (esp. for bright sky) But still limited to smaller telescopes. 58 / 73
  59. 59. Outline 1 Atmospheric effects 2 High spatial resolution astronomy 3 Adaptive optics 4 Lucky imaging 5 Lucky imaging + AO 59 / 73
  60. 60. Lucky + AO Adaptive optics systems are not stable. 60 / 73 Gladysz et al., 2008
  61. 61. Lucky + AO 61 / 73 Gladysz et al., 2008
  62. 62. Lucky + AO 62 / 73 Gladysz et al., 2008
  63. 63. Lucky at Mt. Palomar 63 / 73 Law et al., 2009
  64. 64. Lucky at Mt. Palomar 5m Palomar “200 inch” Hale telescope 512 sq. pixel EMCCD detector First generation AO system (since upgraded) 64 / 73 Law et al., 2009
  65. 65. Lucky at Mt. Palomar Field of view: 65 / 73
  66. 66. Lucky at Mt. Palomar Comparison with HST: 66 / 73
  67. 67. Lucky at Mt. Palomar Comparison with HST: 67 / 73
  68. 68. Lucky + AO: Applications Probing binarity in GC cores 68 / 73
  69. 69. Lucky + AO: Applications Probing binarity in GC cores Exoplanet direct imaging (See e.g Gladysz 2010) 69 / 73
  70. 70. Lucky + AO: Applications Probing binarity in GC cores Exoplanet direct imaging (See e.g Gladysz 2010) Resolving close stars (Kervella 2009) 70 / 73
  71. 71. Lucky + AO: Applications Probing binarity in GC cores Exoplanet direct imaging (See e.g Gladysz 2010) Resolving close stars (Kervella 2009) Cheap visible wavelength AO on 4m class telescopes 71 / 73
  72. 72. Lucky + AO: Applications Probing binarity in GC cores Exoplanet direct imaging (See e.g Gladysz 2010) Resolving close stars (Kervella 2009) Cheap visible wavelength AO on 4m class telescopes Expanding AO sky coverage 72 / 73
  73. 73. Summary Standard lucky imaging can now go wide and faint This gives HST class capabilities at very low cost EMCCD’s are pretty good and still improving AO astronomers should consider fast imaging to get the most from their systems 73 / 73

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