An Unexpected Hysteresis Effect Seen in Hawaii-2RG Detectors
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Jay Anderson --- TIPS Feb 21, 2008 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 – 55: big enough for all detectors – Good density of stars – Many well-measured stars • More than 100,000 good to 1 mas – Good, but… 1) Not big enough for cross-calibration 2) No IR color information J1
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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 - PowerPoint PPT Presentation
Transcript of An Unexpected Hysteresis Effect Seen in Hawaii-2RG Detectors
Jay Anderson --- TIPS Feb 21, 2008
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– 55: big enough for all detectors– Good density of stars– Many well-measured stars
• More than 100,000 good to 1 mas
– Good, but…1) Not big enough for cross-calibration2) No IR color information
J1
Jay Anderson --- TIPS Feb 21, 2008
Ground-based Observations
• HAWK-I: new IR camera– Being commissioned on VLT at Paranal– 7.57.5 FOV – 22 mosaic of 20482048 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…
J2
Jay Anderson --- TIPS Feb 21, 2008
HAWK-I distortion:Raw residuals
After global correction:
One chip
x
x
x
xx
x
x
x
J3
Jay Anderson --- TIPS Feb 21, 2008
Periodic residuals
Phase Diagram Phase Diagram
•Same throughout detector
•Periodogram
•Square wave removes periodic signature
J4
Jay Anderson --- TIPS Feb 21, 2008
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
J5
Jay Anderson --- TIPS Feb 21, 2008
Why do we care?• 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
AMP#0 AMP#1 AMP#2 AMP#3 AMP#4
All CRs
Odd AmpsEven Amps
inter-pixel capacitance
32 amplifiers
J6
Jay Anderson --- TIPS Feb 21, 2008
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! J7
