# Cross-matching the Hubble Legacy Archive - PowerPoint PPT Presentation

Cross-matching the Hubble Legacy Archive

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Cross-matching the Hubble Legacy Archive

## Cross-matching the Hubble Legacy Archive

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##### Presentation Transcript

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_F606WRelaxed by Golden Ratio

8. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F606WRelaxed by Golden RatioZoom 0.0034”

9. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814WRelaxed by Golden Ratio

10. HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814WRelaxed by Golden RatioZoom 0.0020”

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

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

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