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How Post-Flashing Can Improve CTE in Some UVIS images

How Post-Flashing Can Improve CTE in Some UVIS images. Jay Anderson John MacKenty Sylvia Baggett Kai Noeske. Background on CTE. Understanding evolving , improving Photometric corrections Pixel-based corrections Corrections never perfect Better… Minimize losses in first place

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How Post-Flashing Can Improve CTE in Some UVIS images

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  1. How Post-Flashing Can ImproveCTE in Some UVIS images Jay Anderson John MacKenty Sylvia Baggett Kai Noeske

  2. Background on CTE • Understanding evolving, improving • Photometric corrections • Pixel-based corrections • Corrections never perfect • Better… • Minimize losses in first place • Place source close to amplifier • Maximize signal (fewer exposures) • Avoid low backgrounds • UVIS charge-injection • Post-flash options

  3. WP CTE TRAILS: ACS-vs-UVIS(May 2012) 0 1 2 3 4 5

  4. The magic of short-long dark studies… WP LOSSESDOWNCHIP:ACSUVIS −5% 1000s −75% 100s

  5. Finer-scale CTE-losstrends

  6. Finer-scale CTE-losstrends monotonic Linear growth Ntraps α Nq Linear growth Ntraps α Nq Flat?

  7. Way to think about it… 18 total 6 in head 12 in trail ✕ Number of traps encountered is proportionalto the cross-section area Transfer out of board Want to spread out Prefer to squeeze rather than go up Prefer to go up and squeeze more

  8. Way to think about it… 18 total 6 in head 12 in trail 18 total Above bkgd 6 in bkgd

  9. New Observations Omega Cen center, from SM4-calibration --- F336W Two Kinds of Obsns 1) 10s + 700s at same pointing with varbkgd 2) three 9pt dither stacks: (a) 700s deep (b) 10s (no bkgd) (c) 10s (12 e-bkgd)

  10. DeepStack (700s) A: 22 electrons above sky B: 28 electrons above sky C: 65 electrons above sky D: 13 electrons above sky

  11. Short UnflashedStack (10s)

  12. Short Post-FlashedStack (10s)

  13. DeepStack (700s) A: 22 electrons above sky B: 28 electrons above sky C: 65 electrons above sky D: 13 electrons above sky

  14. Trends from~5×5-pixel Aperture Photometry on ×2-Sampled Stacks

  15. Losses as a Function of Background:Survival of a 100 e- source at top of chip = sweet spot!

  16. Next steps… • UVIS • Help users re-plan Phase-II’s to hit sweet spot • Use observations to calibrate losses-vs-bkgd • Constrain model better • Take more long/short darks-vs-background • ACS • Following in UVIS’s footsteps • No sweet spot: compromise • Add noise, preserve signal • More complicated analysis for us and users • Post-flash issues: • 50% variation across field • 25% dependence on shutter (A or B)

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