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An Unexpected Hysteresis Effect Seen in Hawaii-2RG Detectors

17". An Unexpected Hysteresis Effect Seen in Hawaii-2RG Detectors. Background Distortion calibration important for JWST Coronagraphy, MSA, slits Self-calibration will be difficult ACS field observed in 2006 In LMC, in JWST’s CVZ 5 5: big enough for all detectors Good density of stars

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An Unexpected Hysteresis Effect Seen in Hawaii-2RG Detectors

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  1. 17" An Unexpected Hysteresis Effect Seen in Hawaii-2RG Detectors • Background • Distortion calibration important for JWST • Coronagraphy, MSA, slits • Self-calibration will be difficult • ACS field observed in 2006 • In LMC, in JWST’s CVZ • 55: big enough for all detectors • Good density of stars • Many well-measured stars • More than 100,000 good to 1 mas • Good, but… • Not big enough for cross-calibration • No IR color information Jay Anderson --- TIPS Feb 21, 2008 J1

  2. Ground-based Observations • HAWK-I: new IR camera • Being commissioned on VLT at Paranal • 7.57.5 FOV • 22 mosaic of 20482048 NIR detectors • “Active optics” • Luigi Bedin (STScI) observed the JWST field • For them: exquisite distortion solution • For us: IR photometry & larger field • We got an additional benefit… Jay Anderson --- TIPS Feb 21, 2008 J2

  3. HAWK-I distortion: After global correction: Raw residuals x x One chip x x x x x x Jay Anderson --- TIPS Feb 21, 2008 J3

  4. Periodic residuals Phase Diagram Phase Diagram • Same throughout detector • Periodogram • Square wave removes periodic signature Jay Anderson --- TIPS Feb 21, 2008 J4

  5. Why do we care? • Rockwell Scientific HAWAII-2RG • Prototype for JWST! • Very important to understand the source • Geometric, like HST? • WFPC2’s 34-row effect • ACS/WFC’s 68-column effect • Check flat fields • No evidence WFC FLAT FIELDS HAWK-I Jay Anderson --- TIPS Feb 21, 2008 J5

  6. 32 amplifiers  Why do we care? AMP#0 AMP#1 AMP#2 AMP#3 AMP#4 • Rockwell Scientific HAWAII 2RG • Prototype for JWST! • Very important to understand the source • Geometric? No! • Readout artifact? • HAWK-I Readout • CTE-like hysteresis • PSF asymmetry? • Look at CRs… • Likely cause • pixel dwell time All CRs Even Amps Odd Amps inter-pixel capacitance Jay Anderson --- TIPS Feb 21, 2008 J6

  7. Possible Implications for JWST • JWST will have four amplifiers • four 512-pixel zones • Not clear if effect comes before or after the amplifiers… Really a problem? • How to deal with hysteresis? • Mild deconvolution? (will amplify noise) • Leave in, but model • Similar to the inter-pixel capacitance • Effective PSF will treat it implicitly as (x,y) • Need to study impact on: • subarray mode, guider, spectra, dithering, noise model • Early NIRCam/U.AZ tests • encouraging! Jay Anderson --- TIPS Feb 21, 2008 J7

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