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
Finer-scale
CTE-losstrends Flat?
monotonic
Line
ar g
row
th N
trap
s α
Nq
Line
ar g
row
th N
trap
s 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
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
DeepStack (700s)
A: 22 electrons above skyB: 28 electrons above skyC: 65 electrons above skyD: 13 electrons above sky
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)