Jay Anderson --- TIPS

1
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 JWSTs 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

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

J2
3
HAWK-I distortion
After global correction
Raw residuals
?x
?x

• One chip

?x
?x
?x
?x
?x
?x
J3
4
Periodic residuals
Phase Diagram
Phase Diagram

• Same
• throughout
• detector
• Periodogram
• Square wave
• removes
• periodic
• signature

J4
5
Why do we care?

• Rockwell Scientific
• HAWAII-2RG
• Prototype for JWST!
• Very important to
• understand the source
• Geometric, like HST?
• WFPC2s 34-row effect
• ACS/WFCs 68-column effect
• Check flat fields
• No evidence

WFC FLAT FIELDS
HAWK-I
J5
6
Why do we care?
32 amplifiers ?
AMP0
AMP1
AMP2
AMP3
AMP4

• 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
Odd Amps
Even Amps
inter-pixel capacitance
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!

J7