Download - Bright Earth Persistence in NICMOS
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Bright Earth Persistencein NICMOS
Adam Riess
Eddie Bergeron
Acknowledgements: Megan Sosey, Dave Grumm, Helene McLaughlin,Deepashri Thatte, George Chapman, Anton Koekemoer for helpful discussions
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(Another) NICMOS Anomaly
NICMOS Persistence well-known (e.g., CRs post-SAA, planets, etc)
+Limb of the bright Earth (NICMOS has no
shutter)= Bright Earth Persistence (BEP)
What’s new about BEP? Whole field pattern.
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Characterized in SHOES (GO 10802, P.I. Riess)
• SHOES used NICMOS Camera 2 and ACS in parallel
Visit b2, December 2006: large-scale pattern in sky, unlikeDark or Flat
1st dither Last dither
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Diagnosis: Bright Earth Persistence
• SMS: B1 preceded B2, ACS dump to SSR delays NIC dump, NIC transition from “observe” to “operate” and placement of blank. NIC saw bright Earth for 45-70 seconds, array saturated
• “Map” of trap density decays ~20% per 400 sec (consistent with Bergeron & Dickinson 2003)
Good News: BEP can be modeled and removed
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Step 1: Make BEP Frame
Target Field BEP Visit Matching visit w/o BEP
NGC3370_green B2 B1
NGC3021_cyan 6F 6E
NGC1309_cyan2 5D 5J
NGC1309_green 59 5A
NGC4639_cyan 1E 1D
NGC4536_blue 24 25
NGC3982_blue 35 3G
NGC3021_red 62 6H
NGC3021_green 6B 6A
NGC4536_green 27 28
Using 10 clear examples of BEP in SHOES, registersubtract matching frame w/o BEP & w/ sources, produce mean
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BEP in Camera 2
•Level is arbitrary, mean in middle of impacted orbit, 0.047 e/sec, similar to true sky level• Ring median this to remove grot (from dithering, GS reacq)
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Persistence from Various Sources of Excitation
BEP CR’s post-SAA Post Lamp
•CR source different along edges•Signal-to-noise much better in BEP due to saturation, coverage
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BEP Removal• Why? Mottled, irregular sky impacts photometry, source
shapes. And its highly predictable, ~noiseless removal
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δ =(XTX)−1XTY =[sky,persistence]
Image sky persistence BEP noise
Least-squares estimator from matrix inversion
•Different than SAAclean, not local--RMS around CR’s, global-all pixels•Leaves sky, easy to mask out sources pixels (rmedian, threshold, corners)•Run calnica and pedsub first
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Subset of SHOES
Overall ~5% of SHOES orbits impacted, ~10 of 200
PersistenceLevel
Sky level
Fraction ofPixels used
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Before and After
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BEP corrected VS. Unaffected
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Example 2: GO 10258 (P.I. Kretchmer, GOODS NIC+ACS)
2 of 20 visits,09 and 12
PersistenceLevel
Sky level
Fraction ofPixels used
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Result
99.4%Variance removed
Some residual--fit errors,T dependence, angle illum, order of ops
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Other Cameras
Camera 1
Camera 3
Post-SAA CR’s post-Lamp
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In Progress• Looking for examples of BEP in Camera 1 and 3• D. Grumm coded algorithm in pyraf for STSDAS,
D. Thatte experimenting with parameters• First Do No Harm: apply no correction if small or <
50% of pixels useful• Identifying conditions to predict BEP (G. Chapman)• Commanding: GO’s can insert blank, procedural
change?• WFC3 has no shutter and similar detectors…