Bright Earth Persistencein 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, unlikeDark 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

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

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

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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

Subset of SHOES

Overall ~5% of SHOES orbits impacted, ~10 of 200

PersistenceLevel

Sky level

Fraction ofPixels used

Before and After

BEP corrected VS. Unaffected

Example 2: GO 10258 (P.I. Kretchmer, GOODS NIC+ACS)

2 of 20 visits,09 and 12

PersistenceLevel

Sky level

Fraction ofPixels used

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…