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WFC3 – Critical Science Review

WFC3 – Critical Science Review. Science Driven CEIs Requirements. The “Critical Science Metric”. The “Critical Science Metric”. Science Driven CEIs Requirements. CEIS - Sect. 4. 4.3 Optical Performance 4.4 Spectral Performance 4.5 UVIS Channel Shutter Performance

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WFC3 – Critical Science Review

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  1. WFC3 – Critical Science Review Science Driven CEIs Requirements

  2. The “Critical Science Metric”

  3. The “Critical Science Metric”

  4. Science Driven CEIs Requirements CEIS - Sect. 4 • 4.3 Optical Performance • 4.4 Spectral Performance • 4.5 UVIS Channel Shutter Performance • 4.6 UVIS Channel Detector Requirements • 4.7 CCD Detector Thermal Control • 4.8 IR Channel Detector Requirements • 4.9 HgCdTe Detector Thermal Control • 4.10 Observational Requirements • 4.11 Calibration

  5. Science Driven CEIs Requirements • an “astronomer friendly” view: • UVIS Detectors • IR Detector • Optics • Filters • Operations

  6. 1. UVIS DETECTORS

  7. UVIS Detectors – specs (1/2) • Number of detectors 2 • Type CCD Backside Illuminated UV Coated Supplementary Buried Channels (SBC) • Producer Marconi (former EEV) • Format 2048  4096 • Quantum Efficiency • Range and absolute valuesee viewgraph • Stability 0.2 %/hr 1s 1.0 %/month (2% @ l< 300nm) • Read-out noise 4.0 e/read (3e goal) @ 4.27 min R.O.time • Dark current <25 e/hr/pix @ -83C for 90% of the pixels • Operability >99% good pixels • Bias stability <2 e rms during read

  8. UVIS Detectors – specs (2/2) • Linearity >95%, correctable to >99.7% • Full well capacity 50,000 e/pix (85,000 goal) • Charge-transfer efficiency > 5E-6 @ 1620 and 40,000 e/pix • (see viewgraphs) • Pixel-to pixel response • uniformity better than 2%; 1% @ 400-850nm(0.5% goal) • stability<0.2 % over 1 hr (see Q.E.) • Radiation hardness • Absolute sensitivity <2,000 e/event • Stability (SAA) <0.1/e/s/pix after 5min > 90%

  9. MARCONI CCD – Q.E. 200-400nm optimized

  10. The CCD context

  11. CTE anomaly: STIS data SITe 1024  1024 CCD thinned backside NGC 6752, 8  20s, ‘D’ amp at the top Courtesy R. Gilliland (STScI)

  12. CTE anomaly: STIS data NGC 6752, 8  20s, ‘B’ amp at the bottom Courtesy R. Gilliland (STScI)

  13. CTE losses in WF/PC2 “…preliminary evidence for accelerating growing rate.” (“Charge Transfer Efficiency in the WF/PC2 CCD Arrays” J. Biretta et al., June 2000 AAS)

  14. Improving CTE for WFC3

  15. Improving CTE for WFC3 M. Robbins (Marconi Apple.Tech.): “Possibility of limiting the radiation damage effects in CCDs”, in CCD Detector CTE workshop, STScI, January 2000 (http://www.stsci.edu/instruments/acs/ctewg/cte_papers.html)

  16. 2. IR Detectors - specs (1/2) • Number of detectors 1 • Type HgCdTe/ZnCdTe MBE on WFC3-1R MUX • Producer Rockwell Science Center • Pixel size 18 mm • Format 1014 1014 • Quantum Efficiency • Range and absolute value see viewgraph • Stability 0.5 %/hr p-p; 1.0 %/month Minimum | Target | 100% Incentive • Read-out noise 17-20 | 15-17 | <15 e/pix/read @ 100KHz • Dark current 0.3-0.4 | 0.2-0.3 | <0.2 e/pix/s @ 150K • Operability 94-96 | 96-98 | >98 % • Bias stability <2 e rms during read

  17. IR Detectors - specs (2/2) • Amplifier glow <10 e/pix/read at the center • <400 e/pix/read at the border (<5%) • Linearity >95%, correctable to >99.7% • Full well capacity 100,000 e/pix (150,000 goal) • Pixel-to pixel response • uniformity better than 2%; 1% @ 1000-1800nm(0.5% goal) • stability<0.2 % over 1 hr ; <1% over 2 months • Radiation hardness • Absolute sensitivity <1,000 e/event • Stability (SAA) <0.1/e/s/pix after 5min > 90%

  18. IR detector Q.E.

  19. Improvements over NICMOS • Amplifier glow • Vignetting • Filter ghosts • Persistence • Column • new MUX design (WFC3-1R) > NGST development • no optical misalignment • detector tilted with respect to the chief ray 240 s later • HgCdTe on ZnCdTe provide better lattice matching • new Conexant 0.5mm capability

  20. Improvement over NICMOS Residual bias (pedestal) Variable DC offset, thermally driven and 1/f time variable, reduces the sensitivity. Present in NICMOS and in first generation of Hawaii detectors. • Solved with new MUX design (WFC3-1R) using reference pixels 1014  1014 active pixels 1014  5 reference pixels

  21. 3. UVIS Optics specs • Range 200-1000 nm (200-400nm emphasis) • Field of view 162”  160” • Pixel separation/scale 39.6 mas (nominal); f/31 • Field distortion see viewgraph; correctable to .2pix • Induced polarization <6.5% (<5% goal) • Image quality • encircled energy see viewgraph • jitter < 3 mas (1/13 pix) 1s over 1300sec • drift < 10 mas (1/4 pix) p-p over 2 orbits • Optics see viewgraph

  22. UVIS Channel – field distortion

  23. UVIS channel encircled energy

  24. IR Optics specs • Range 850-1700 nm (700-1900nm emphasis) • Field of view 123” 139” • Pixel size 0.121” 0137” • Field distortion see viewgraph; correctable to .2pix • Induced polarization <5% • Image quality • encircled energy see viewgraph • jitter < 6 mas (1/20 pix) 1s over 1300sec • drift < 20 mas (1/5 pix) p-p over 2 orbits • Optics see viewgraph

  25. IR Channel – field distortion

  26. IR channel encircled energy

  27. Optics and coating

  28. Throughput specs vs. actual

  29. Pupil image and OTA throughput Footprints of ray bundles from nine field points 0.5 mm in front of the pupil image. The cold stop allows an annular transmission region and the hatched areas indicate areas that block light due to the oversized cold stop. The throughput efficiency of this cold mask is 95%. We add 10% for spiders, M1 pods, diffraction effects and alignment tolerances. • 15% throughput loss due to the HST obstructions, plus • 15% throughput loss due to the cold stop and pupil masking

  30. WFC3 subsystems throughput WFC3 optics OTA detectors

  31. WFC3 overall throughput Photon flux OTA WFC3optics detectors

  32. 4. Filter specs UVIS IR • Total number of spectral components: 48 16 • Very Broad Band 4 - • Broad Band 13 5 • Medium Band 8 3 • Narrow Band 17 6 • Narrow Band Quad Elements 5  4 - • UV Prism 1 - • Grisms - 2

  33. UVIS filters

  34. IR filters

  35. Operations • Standard observing mode IMAGING MULTIACCUM (1+15) • Integration time • Minimum (readout/buffer) 2 min. @ 4 ampli 3s @ 4 ampli • Longer 1 orbit (~3000 s) • Readout schemes • Subarray Y Y • Rebinning 2  2 N/A • Gain setting 1, 2, 4, 8 e/bit 1/2/4/8 e/bit • Overheads • Filter change max 60 s • Channel change 150 s (except power conserving mode) • Data Buffer 2 UVIS images OR 2 IR ramps (IR reads) • Calibration: on-board flat/field simulators between 2000A and 2micron must provide… • Uniformity within a factor 2 over both fields of view • Stability >99% /hr and >95% /yr • Flux >10,000e/10min (all filters) UVIS IR

  36. The end

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