an empirical pixel-based correction for cte
DESCRIPTION
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: - PowerPoint PPT PresentationTRANSCRIPT
An Empirical Pixel-BasedCorrection for CTE
HST Calibration Workshop 2010
Jay Anderson & Luigi Bedin
30s, 47 Tuc Outer field
Shuffle
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
CTE/CTI
readout
observed
A New Empirical ApproachWill 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)
One Raw Dark, post SM4
Stack of 168 Post-SM4 Darks
WP Map
CR Tail Measurement
Empirical Trails
Faint
Bright
No “notch”channel apparent!
WP 4321
1%
100%
Fractionalheight greaterfor fainter WPs
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…
Correction Scheme
TRAILINTENSITY
TRAILPROFILE
Corrected WP Trail
Residuals
Faint
Bright
Adjust by handthe model parameters1) density: (q)2) profile: (n;q)
Original
Corrected
Corrected WP Deep
The tests…
1) Aesthetic test: trails gone?
2) Photometry: is all the flux back?
3) Astrometry: flux in right place?
4) Shape: flux really in the right place?
339s, 47 Tuc Outer field
30s, 47 Tuc Outer field
30s, 47 Tuc Outer field
10s -vs- 1200s
ASTROMETRYPHOTOMETRY
BKGD ~ 2 e
Comparisonwith
Chiabergecorrection
INSTRUMENTAL MAGNITUDE
Shape… looks good!
AFTER BEFORE
Summary2-component model (q) and (n;q) based on WPs in darksTested against stars:
– Images with backgrounds of 3 e and 25 e
– Trails removed!– Photometry/astrometry generally restored– Shape surprisingly good
Remaining issues…
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
– (Mid2011) Consideration of how/whether to modify
the pipeline
• Other instruments: – Current: STIS, UVIS
– Legacy: HRC, WFPC2
BackupSlides
Shadowing
Detailed Model
Shape
BACKUP SLIDES
SHAPE
What about
shape?
Bright
Faint
Corrected
READNOISE MITIGATION
Original
Decomposition
“Smoothed” RN Component
Actual Change
Original Repaired Original Repaired Modified
Just the change
Change for Original Change for RN-Smoothed
SERIAL CTE
Serial CTE
Serial CTE linear trends
2NDPIXEL
FIRSTPIXEL
Serial CTE Parameters
DETAILED MODEL EXAMPLE
Detailed Model Example
SHADOWING
WP
C R
C R
WP~2500
WP~5000What about Shadowing?
?
?
Yes! Shadowing is essentially “perfect” !
X
Total Power in
Tails
WP INTENSITY
TO
TA
L I
N T
AIL