How Post-Flashing Can Improve CTE in Some UVIS images
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How Post-Flashing Can Improve CTE in Some UVIS images Jay Anderson John MacKenty Sylvia Baggett Kai Noeske
description
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 - PowerPoint PPT Presentation
Transcript of How Post-Flashing Can Improve CTE in Some UVIS images
How Post-Flashing Can ImproveCTE in Some UVIS images
Jay AndersonJohn MacKentySylvia Baggett
Kai Noeske
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
CTE TRAILS:
ACS-vs-UVIS(May 2012)
WP
0 1 2 3 4 5
WP LOSSESDOWNCHIP:ACSUVIS
The magic ofshort-long
dark studies…
1000s
100s
−5%
−75%
Finer-scale
CTE-losstrends
Finer-scale
CTE-losstrends Flat?
monotonic
Linea
r gro
wth
Ntra
ps α
Nq
Linea
r gro
wth
Ntra
ps α
Nq
Way to think about it…
12 in trail
18 total
6 in head
✕ Transfer out of board
Number of traps encountered isproportional to
the cross-sectionarea
Want to spread out
Prefer to squeeze rather than go up
Prefer to go up and squeeze more
Way to think about it…
18 totalAbove bkgd
6 in bkgd
12 in trail
18 total
6 in head
New ObservationsOmega Cen center, from SM4-calibration --- F336W
Two Kinds of Obsns
1) 10s + 700s at same pointing with var bkgd
2) three 9pt dither stacks: (a) 700s deep (b) 10s (no bkgd) (c) 10s (12 e- bkgd)
DeepStack (700s)
A: 22 electrons above skyB: 28 electrons above skyC: 65 electrons above skyD: 13 electrons above sky
Short UnflashedStack (10s)
Short Post-FlashedStack (10s)
DeepStack (700s)
A: 22 electrons above skyB: 28 electrons above skyC: 65 electrons above skyD: 13 electrons above sky
Trends from ~5×5-pixel Aperture
Photometry on ×2-Sampled Stacks
Losses as a Function of
Background:
Survival of a 100 e- source at top of chip
= sweet spot!
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)
