1 WFC3 – Critical Science Review Science Driven CEIs Requirements

2 The “Critical Science Metric” High-z Universe Nearby Galaxies Resolved Stellar Pop. Stars & ISM Solar System Detectors Spectral coverage Q.E. Read Out Noise Dark Current C.T.E. and pedestal Radiation Hardness Cosmetics Optics Field and Sampling PSF: encircled energy PSF: stability PSF: uniformity Throughput Ghosts and Stray light Filters

3 The “Critical Science Metric” High-z Universe Nearby Galaxies Resolved Stellar Pop. Stars & ISM Solar System Operations Readout modes I.T. Range Readout time Overheads Saturation limit Subarrays and rebinning Mechanical stability Calibration

4 Science Driven CEIs Requirements 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 CEIS - Sect. 4

5 Science Driven CEIs Requirements an “astronomer friendly” view: 1. UVIS Detectors 2. IR Detector 3. Optics 4. Filters 5. 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 value see viewgraph –Stability  0.2 %/hr 1   1.0 %/month < 300nm) Read-out noise 4.0 e/read (3e 4.27 min R.O.time Dark current< C 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 > 1620 and 40,000 e/pix (see viewgraphs) Pixel-to pixel response – uniformity better than 2%; nm (0.5% goal) – stability <0.2 % over 1 hr (see Q.E.) Radiation hardness – Absolute sensitivity <2,000 e/event – Stability (SAA) 90%

9 MARCONI CCD – Q.E nm optimized

10 The CCD context

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

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

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 (

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  m 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 | | <15 100KHz Dark current | | < K Operability | | >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%; nm (0.5% goal) – stability <0.2 % over 1 hr ; <1% over 2 months Radiation hardness – Absolute sensitivity <1,000 e/event – Stability (SAA) 90%

18 IR detector Q.E.

19

20 Improvements over NICMOS 1.Amplifier glow 2.Vignetting 3.Filter ghosts 4.Persistence 5.Column new MUX design (WFC3-1R) > NGST development HgCdTe on ZnCdTe provide better lattice matching new Conexant 0.5  m capability 240 s later no optical misalignment detector tilted with respect to the chief ray

 5 reference pixels 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  1014 active pixels Solved with new MUX design (WFC3-1R) using reference pixels

22 3. UVIS Optics specs Range nm ( nm 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) 1  over 1300sec – drift < 10 mas (1/4 pix) p-p over 2 orbits Optics see viewgraph

23 UVIS Channel – field distortion

24 UVIS channel encircled energy

25 IR Optics specs Range nm ( nm 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) 1  over 1300sec – drift < 20 mas (1/5 pix) p-p over 2 orbits Optics see viewgraph

26 IR Channel – field distortion

27 IR channel encircled energy

28 Optics and coating

29 Throughput specs vs. actual

30 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

31 WFC3 subsystems throughput WFC3 optics OTA detectors

32 WFC3 overall throughput Photon flux OTA WFC3optics detectors

33 4. Filter specs Total number of spectral components:48 16 Very Broad Band 4 - Broad Band135 Medium Band 83 Narrow Band17 6 Narrow Band Quad Elements 5  4 - UV Prism 1- Grisms -2 UVISIR

34 UVIS filters

35 IR filters

36 Operations Standard observing modeIMAGING MULTIACCUM (1+15) Integration time –Minimum (readout/buffer)2 4 4 ampli –Longer 1 orbit (~3000 s) Readout schemes –SubarrayYY –Rebinning2  2N/A –Gain setting1, 2, 4, 8 e/bit1/2/4/8 e/bit Overheads –Filter changemax 60 s –Channel change150 s (except power conserving mode) –Data Buffer2 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) UVISIR

37 The end