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An Empirical Pixel-Based Correction for CTE

An Empirical Pixel-Based Correction for CTE. HST Calibration Workshop 2010 Jay Anderson & Luigi Bedin. 30s, 47 Tuc Outer field. Shuffle. CTE/CTI. Steadily increasing problem for: STIS, ACS’s WFC, … WFC3? Was also bad for WFPC2, HRC Symptoms: Loss of flux Charge trails Cause:

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An Empirical Pixel-Based Correction for CTE

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  1. An Empirical Pixel-BasedCorrection for CTE HST Calibration Workshop 2010 Jay Anderson & Luigi Bedin

  2. 30s, 47 Tuc Outer field Shuffle

  3. CTE/CTI Steadily increasing problem for: • STIS, ACS’s WFC, … WFC3? • Was also bad for WFPC2, HRC Symptoms: • Loss of flux • Charge trails Cause: • Traps within pixels that delay readout • Trap density increases linearly over time readout observed

  4. A New Empirical Approach Will be published in September PASP Inspired by: • Hyper-velocity star project (PI-Oleg Gnedin) • Massey et al. (2010): WPs in COSMOS science data Plan: • Examine WPs in darks • Study two dimensions: • Trail intensity: dependence on WP height • Profile drop-off: dependence on n (distance along trail)

  5. One Raw Dark, post SM4

  6. Stack of 168 Post-SM4 Darks

  7. WP Map

  8. CR Tail Measurement

  9. 100% 1% WP 1 2 3 4 Empirical Trails Faint No “notch” channel apparent! Fractional height greater for fainter WPs Bright

  10. Correction Scheme Start with a readout model • Two parameters: 1) Trap density: (q) 2) Release profile: (n;q) • Shadowing? • Monitor filling/emptying of traps at all charge q levels • PORIG(j) POBS(j) Invert • Find source function that produces observations • Optimize model by varying (q) and (n;q) • Efficiencies… TRAIL INTENSITY TRAIL PROFILE

  11. Faint Corrected WP Trail Residuals Original Corrected Adjust by hand the model parameters 1) density: (q) 2) profile: (n;q) Bright

  12. Corrected WP Deep

  13. The tests… • Aesthetic test: trails gone? • Photometry: is all the flux back? • Astrometry: flux in right place? • Shape: flux really in the right place?

  14. 339s, 47 Tuc Outer field

  15. 30s, 47 Tuc Outer field

  16. 30s, 47 Tuc Outer field

  17. PHOTOMETRY ASTROMETRY 10s -vs- 1200s BKGD ~ 2 e

  18. ComparisonwithChiabergecorrection INSTRUMENTAL MAGNITUDE 

  19. Shape… looks good! AFTER BEFORE

  20. Summary 2-component model (q) and (n;q) based on WPs in darks Tested against stars: • Images with backgrounds of 3 e and 25 e • Trails removed! • Photometry/astrometry generally restored • Shape surprisingly good Remaining issues…

  21. Backup Slides Remaining Issues… • Read-noise mitigation • Time/temperature dependence • X-CTE: present • More exploration of low bkgd levels • short darks coming! • Implications for dark subtraction: darks w/CTE are non-linear • ACS team’s plans • (any day…) PASP paper on site • (continuing) Evaluation of model • (Oct 2010) Come up with stand-alone routine for _flt’s • (Mid2011) Consideration of how/whether to modify the pipeline • Other instruments: • Current: STIS, UVIS • Legacy: HRC, WFPC2 Shape Shadowing Detailed Model

  22. BACKUP SLIDES

  23. SHAPE

  24. Bright What about shape? Faint Corrected

  25. READNOISE MITIGATION

  26. Original “Smoothed” RN Component Decomposition

  27. Original Repaired Original Repaired Modified Actual Change

  28. Change for Original Change for RN-Smoothed Just the change

  29. SERIAL CTE

  30. Serial CTE

  31. Serial CTE linear trends FIRST PIXEL 2ND PIXEL

  32. Serial CTE Parameters

  33. DETAILED MODEL EXAMPLE

  34. Detailed Model Example

  35. SHADOWING

  36. WP~5000 What about Shadowing? Yes! Shadowing is essentially “perfect”! WP~2500 WP  ? C R X ? C R

  37. Total Power in Tails TOTAL IN TAIL WP INTENSITY

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