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Bright Earth Persistence in NICMOS

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)

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Bright Earth Persistence in NICMOS

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  1. Bright Earth Persistencein NICMOS Adam Riess Eddie Bergeron Acknowledgements: Megan Sosey, Dave Grumm, Helene McLaughlin, Deepashri Thatte, George Chapman, Anton Koekemoer for helpful discussions

  2. (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.

  3. 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

  4. 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

  5. Step 1: Make BEP Frame Using 10 clear examples of BEP in SHOES, register subtract matching frame w/o BEP & w/ sources, produce mean

  6. 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)

  7. Persistence from Various Sources of Excitation Post Lamp BEP CR’s post-SAA • CR source different along edges • Signal-to-noise much better in BEP due to saturation, • coverage

  8. BEP Removal • Why? Mottled, irregular sky impacts photometry, source shapes. And its highly predictable, ~noiseless removal Image sky persistence BEP noise Least-squares estimator from matrix inversion =[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

  9. Subset of SHOES Persistence Level Sky level Fraction of Pixels used Overall ~5% of SHOES orbits impacted, ~10 of 200

  10. Before and After

  11. BEP corrected VS. Unaffected

  12. 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

  13. Result 99.4% Variance removed Some residual--fit errors,T dependence, angle illum, order of ops

  14. Other Cameras Camera 1 Camera 3 Post-SAA CR’s post-Lamp

  15. 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…

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