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Cross-matching the Hubble Legacy Archive

22 July 2010. Nathan Cole (JHU) Tamas Budavari (JHU) Steve Lubow ( STScI ) Alex Szalay (JHU) Brian McLean ( STScI ) Rick White ( STScI ). Cross-matching the Hubble Legacy Archive. 2010 STScI Calibration Workshop. HLA examples. HST_10503_13_ACS_WFC_F606W.

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Cross-matching the Hubble Legacy Archive

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  1. 22 July 2010 Nathan Cole (JHU) TamasBudavari (JHU) Steve Lubow (STScI) Alex Szalay (JHU) Brian McLean (STScI) Rick White (STScI) Cross-matching the Hubble Legacy Archive 2010 STScI Calibration Workshop

  2. HLA examples HST_10503_13_ACS_WFC_F606W HST_10503_18_ACS_WFC_F606W

  3. HLA examples • Absolute astrometry of an image  ~0.3” • Relative astrometry between images  ~0.1” • Different guide stars • Time lapse • Etc… • Many overlapping images • Link sources? • Improve relative astrometry?

  4. Crossmatch and Correction • Crossmatch • Probabilistic algorithm  all matches and probabilities • Budavari and Szalay. 2008, ApJ, 679, 301 • 3-Dimensional rotation • Describes both translation and rotation, locally

  5. Astrometric Correction • Assuming infinitesimal rotation, ω • r = source position, c = current “best guess” position • Solutionis linear • !FAST! • Sum a 3x3 matrix • Sum a vector • Solve!

  6. Procedure Image 1 Image 2 Take all objects with Flag = 0 (Stellar Sources) Match List • Calculate probs, • Matches with prob>0.95, • Best guess position (c) as weighted avg Trimmed Match List • Image 1 positions (r1), • Best guess positions (c) • Image 2 positions (r2), • Best guess positions (c) Transformation (ω1) Transformation (ω2) • r1’ = r1 – r1 x ω1 • r2’ = r2 – r2 x ω2 Updated source list 1 Updated source list 2 • IF: Max change in position > 1e-17

  7. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F606WStep 0

  8. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F606W Step 1

  9. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F606W Step 2

  10. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F606W Step 3

  11. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F606W Step 4

  12. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F606W Step 5

  13. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F606W Step 6

  14. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F606W Step 7

  15. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F606WRelaxed by Golden Ratio

  16. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F606WRelaxed by Golden RatioZoom 0.0034”

  17. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814WStep 0

  18. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814WStep 1

  19. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814WStep 2

  20. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814WStep 3

  21. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814WStep 4

  22. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814WStep 5

  23. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814WStep 6

  24. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814WStep 7

  25. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814WStep 8

  26. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814WRelaxed by Golden Ratio

  27. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814WRelaxed by Golden RatioZoom 0.0020”

  28. Upcoming… • Improved astrometry • Milli-arcsec (sub-pixel) precision • Corrections calculated for complete HLA catalog • New catalog • Link sources between pointings • Link sources between instruments

  29. Cross-matching Algorithm Budavari and Szalay. 2008, ApJ, 679, 301 • wherewhen • where

  30. Astrometric Correction Solution • Assuming small rotation, • where

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