Bright Earth Persistence
in NICMOS
Adam Riess
Eddie Bergeron
Acknowledgements: Megan Sosey, Dave Grumm, Helene McLaughlin,
Deepashri Thatte, George Chapman, Anton Koekemoer for helpful discussions
(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.
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, unlike
Dark or Flat
1st dither
Last dither
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
Step 1: Make BEP Frame
Using 10 clear examples of BEP in SHOES, register
subtract matching frame w/o BEP & w/ sources, produce mean
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
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)
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
BEP Removal
• Why? Mottled, irregular sky impacts photometry, source
shapes. And its highly predictable, ~noiseless removal
yi  s Pxi  ni
Image sky persistence BEP noise
y1  1 x1 
n1 
       
y2  1 x2  s  n2 
    P  
   
 
yN  1 xN 
nN 
Least-squares estimator from matrix inversion
  (X X) X Y
T
1

T
=[sky,persistence]
•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
Subset of SHOES
Persistence
Level
Sky level
Fraction of
Pixels used
Overall ~5% of SHOES orbits impacted, ~10 of 200
Before and After
BEP corrected VS. Unaffected
Example 2: GO 10258 (P.I. Kretchmer,
GOODS NIC+ACS)
Persistence
Level
Sky level
Fraction of
Pixels used
2 of 20 visits,
09 and 12
Result
99.4%
Variance
removed
Some residual--fit errors,T dependence, angle illum, order of ops
Other Cameras
Camera 1
Camera 3
Post-SAA CR’s
post-Lamp
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…