Space Telescope Science Institute
WFC3 Instrument Handbook
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Table of Contents

Wide Field Camera 3 Instrument Handbookfor Cycle 22
Acknowledgments
Chapter 1: Introduction to WFC3
1.1 What’s New for Cycle 22
1.2 Overview
1.3 Key Features of WFC3
1.4 WFC3 Quick Reference Guide
1.5 Special Considerations for Cycle 22
1.5.1 Current Instrument Status
1.5.2 Ongoing Calibration
1.5.3 New Capabilities
1.6 Sources of Further Information
1.7 The WFC3 Instrument Team at STScI
Chapter 2: WFC3 Instrument Description
2.1 Optical Design and Detectors
2.2 Field of View and Geometric Distortions
2.3 Spectral Elements
2.3.1 The Filter Selection Process
2.3.2 Filter and Grism Summaries
2.3.3 Shutter Mechanism
2.4 Detector Read-Out Modes and Dithering
Chapter 3: Choosing the Optimum HST Instrument
3.1 Overview
3.2 Choosing Between Instruments
3.3 Comparison of WFC3 with Other HST Imaging Instruments
3.3.1 Wavelength Coverage
3.3.2 Field of View
3.3.3 Detector Performance
3.3.4 System Throughputs and Discovery Efficiencies
Chapter 4: Designing a Phase I WFC3 Proposal
4.1 Phase I and Phase II Proposals
4.2 Preparing a Phase I Proposal
4.2.1 Which WFC3 Channel(s) and Filter(s)?
4.2.2 What Exposure Times?
Dithering and Mosaicking
Bright Targets
UVIS Exposures
IR Exposures
4.2.3 What Aperture or Subarray?
4.2.4 What Overheads and How Many HST Orbits?
4.2.5 Any Special Calibration Observations?
4.2.6 What is the Total Orbit Request?
Chapter 5: WFC3 Detector Characteristics and Performance
5.1 Overview of this Chapter
5.2 The WFC3 UVIS Channel CCD Detectors
5.2.1 Basics of CCD Operation
5.2.2 The WFC3 CCDs
5.3 WFC3 CCD Readout Formats
5.3.1 Full-frame Readout
5.3.2 Subarrays
5.3.3 On-Chip Binning
5.4 WFC3 CCD Characteristics and Performance
5.4.1 Quantum Efficiency
5.4.2 Multiple-Electron Events at Short Wavelengths
5.4.3 Flat Fields
5.4.4 Long-Wavelength Fringing
5.4.5 Linearity and Saturation
5.4.6 Gain
5.4.7 Read Noise
5.4.8 Dark Current
5.4.9 Bad Pixels
5.4.10 Cosmic Rays
5.4.11 Charge Transfer Efficiency
5.4.12 Crosstalk
5.5 The WFC3 IR Channel Detector
5.5.1 Overview
5.5.2 IR Detector Basics
5.6 WFC3 IR Readout Formats
5.6.1 Full-Frame Readouts and Reference Pixels
5.6.2 Subarrays
5.7 WFC3/IR Detector Characteristics and Performance
5.7.1 Quantum Efficiency
5.7.2 Dark Current
5.7.3 Read Noise
5.7.4 Flat Fields
5.7.5 Linearity and Saturation
5.7.6 Count Rate Non-Linearity
5.7.7 Detector Cosmetics
5.7.8 Crosstalk
5.7.9 Image Persistence
Chapter 6: UVIS Imaging with WFC3
6.1 WFC3 UVIS Imaging
6.2 Specifying a UVIS Observation
6.3 UVIS Channel Characteristics
6.4 UVIS Field Geometry
6.4.1 Field of View and Pixel Size
6.4.2 Geometric Distortion
6.4.3 Coordinate Systems
6.4.4 Subarrays and On-Chip Binning
Subarrays
On-Chip Binning
6.4.5 Apertures
6.5 UVIS Spectral Elements
6.5.1 Filter and Grism Summary
UV Filters
Ultra-Wide Filters
Wide-Band Filters
Medium-Band Filters
Narrow-Band Filters
Quad Filters
Grism
6.5.2 Filter Red Leaks
6.5.3 Ghosts
Window Ghosts
Filter Ghosts
6.6 UVIS Optical Performance
6.6.1 PSF Width and Sharpness
6.6.2 Encircled and Ensquared Energy
6.6.3 Other PSF Behavior and Characteristics
Temporal Dependence of the PSF: HST Breathing
Pixel Response Function
PSF Characteristics
6.7 UVIS Exposure and Readout
6.7.1 Exposure Time
6.7.2 ACCUM Mode
Overscan Regions
6.8 UVIS Sensitivity
6.8.1 Limiting Magnitudes
6.9 Charge Transfer Efficiency
6.9.1 Overview
6.9.2 CTE-Loss Mitigation Before Data Acquisition: Observation Planning
6.9.3 CTE-Loss Mitigation After Data Acquisition: Post-Observation Image Corrections
6.10 Other Considerations for UVIS Imaging
6.10.1 Gain and Full-Well Saturation
6.10.2 Cosmic Rays and Hot Pixels
6.10.3 Image Persistence
6.10.4 Shutter-Induced Vibration
6.10.5 Droplets
6.10.6 Optical Anomalies
6.11 UVIS Observing Strategies
6.11.1 Dithering Strategies
6.11.2 Parallel Observations
6.11.3 Spatial Scans
6.11.4 PSF Subtraction
Chapter 7: IR Imaging with WFC3
7.1 WFC3 IR Imaging
7.2 Specifying an IR Observation
7.3 IR Channel Characteristics
7.4 IR Field Geometry
7.4.1 Field of View and Pixel Size
7.4.2 Geometric Distortion
7.4.3 Coordinate Systems
7.4.4 Subarrays
7.4.5 Apertures
7.5 IR Spectral Elements
7.5.1 Filter and Grism Summary
Wide-Band Filters
Medium-Band filters
Narrow-Band Filters
Grisms
7.5.2 Filter Blue Leaks
7.5.3 Ghosts
7.6 IR Optical Performance
7.6.1 PSF Width and Sharpness
7.6.2 Encircled and Ensquared Energy
7.6.3 Other PSF Behavior and Characteristics
Temporal Dependence of the PSF: HST Breathing
Intra-Pixel Response
Inter-Pixel Capacitance
7.7 IR Exposure and Readout
7.7.1 Exposure Time
7.7.2 MULTIACCUM Mode
7.7.3 MULTIACCUM Timing Sequences: Full Array Apertures
RAPID Sequence
SPARS Sequences
STEP Sequences
7.7.4 MULTIACCUM Timing Sequences: Subarray Apertures
7.8 IR Sensitivity
7.8.1 Limiting Magnitudes
7.9 Other Considerations for IR Imaging
7.9.1 Gain and Full-Well Saturation
7.9.2 Cosmic Rays and Snowballs
7.9.3 On-Orbit Degradation
7.9.4 Image Persistence
7.9.5 The IR Background
7.9.6 Blobs
7.9.7 Optical Anomalies
7.10 IR Observing Strategies
7.10.1 Dithering Strategies
7.10.2 Parallel Observations
7.10.3 Exposure Strategies
7.10.4 Spatial Scans
7.10.5 PSF Subtraction
Chapter 8: Slitless Spectroscopy with WFC3
8.1 Grism Overview
8.2 Slitless Spectroscopy with the UVIS G280 Grism
8.3 Slitless Spectroscopy with the IR G102 and G141 Grisms
8.3.1 IR G102
8.3.2 IR G141
8.4 Sensitivities and Exposure-Time Estimation
8.5 Extraction and Calibration of Spectra
8.6 Slitless Spectroscopy with Spatial Scanning
Chapter 9: WFC3 Exposure-Time Calculation
9.1 Overview
9.2 The WFC3 Exposure Time Calculator (ETC)
9.3 Calculating Sensitivities from Tabulated Data
9.4 Count Rates (Imaging)
9.4.1 Point Source
9.4.2 Diffuse Sources
9.4.3 Emission-Line Sources
9.5 Count Rates (Slitless Spectroscopy)
9.6 Estimating Exposure Times
9.6.1 S/N Reached in a Given Exposure Time
9.6.2 Exposure Time to Reach a Given S/N
9.6.3 Exposure Time Estimates for Red Targets in F850LP
9.7 Sky Background
9.7.1 Zodiacal Light, Earth Shine, and LOW-SKY
9.7.2 Geocoronal Emission, Airglow, and SHADOW
9.8 Interstellar Extinction
9.9 Exposure-Time Calculation Examples
9.9.1 Example 1: UVIS Imaging of a Faint Point Source
9.9.2 Example 2: UVIS Imaging of a Faint Source with a Faint Sky Background
9.9.3 Example 3: IR Imaging of a Faint Extended Source
9.9.4 Example 4: Imaging an HII region in M83 in Hα
Chapter 10: Overheads and Orbit Time Determinations
10.1 Overview
10.2 Observatory Overheads
10.3 Instrument Overheads
10.3.1 Exposure Overheads
Dumping of the WFC3 Buffer
UVIS Parallel Buffer Dumps
IR Parallel Buffer Dumps
Filter and Channel Select Overheads
10.3.2 Reducing Overheads with Subarrays and Binning
10.4 Orbit Use Examples
10.4.1 Example 1: UVIS, 1 Orbit, 1 Filter
10.4.2 Example 2: UVIS, 1 Orbit, Short Exposures
10.4.3 Example 3: IR, 1 Orbit, 2 Filters
10.4.4 Example 4: UVIS, Dithering, 2 Orbits, 1 Filter
10.4.5 Example 5: IR, 1 Orbit, Grism
Appendix A: WFC3 Filter Throughputs
A.1 Introduction
A.2 Throughputs and S/N Ratio Data
UVIS/F200LP
UVIS/F218W
UVIS/F225W
UVIS/F275W
UVIS/F280N
UVIS/F300X
UVIS/F336W
UVIS/F343N
UVIS/F350LP
UVIS/F373N
UVIS/F390M
UVIS/F390W
UVIS/F395N
UVIS/F410M
UVIS/F438W
UVIS/F467M
UVIS/F469N
UVIS/F475W
UVIS/F475X
UVIS/F487N
UVIS/F502N
UVIS/F547M
UVIS/F555W
UVIS/F600LP
UVIS/F606W
UVIS/F621M
UVIS/F625W
UVIS/F631N
UVIS/F645N
UVIS/F656N
UVIS/F657N
UVIS/F658N
UVIS/F665N
UVIS/F673N
UVIS/F680N
UVIS/F689M
UVIS/F763M
UVIS/F775W
UVIS/F814W
UVIS/F845M
UVIS/F850LP
UVIS/F953N
UVIS/FQ232N
UVIS/FQ243N
UVIS/FQ378N
UVIS/FQ387N
UVIS/FQ422M
UVIS/FQ436N
UVIS/FQ437N
UVIS/FQ492N
UVIS/FQ508N
UVIS/FQ575N
UVIS/FQ619N
UVIS/FQ634N
UVIS/FQ672N
UVIS/FQ674N
UVIS/FQ727N
UVIS/FQ750N
UVIS/FQ889N
UVIS/FQ906N
UVIS/FQ924N
UVIS/FQ937N
IR/F098M
IR/F105W
IR/F110W
IR/F125W
IR/F126N
IR/F127M
IR/F128N
IR/F130N
IR/F132N
IR/F139M
IR/F140W
IR/F153M
IR/F160W
IR/F164N
IR /F167N
Appendix B: Geometric Distortion
B.1 Overview
B.2 UVIS Channel
B.3 IR Channel
B.4 Summary
Appendix C: Dithering and Mosaicking
C.1 Why Mosaicking and Dithering are Needed
C.2 WFC3 Patterns
Appendix D: Bright-Object Constraints and Image Persistence
D.1 UVIS Channel
D.2 IR Channel
Appendix E: Reduction and Calibration of WFC3 Data
E.1 The STScI Reduction and Calibration Pipeline
E.2 The SMOV Calibration Plan
E.3 The Cycle 17 Calibration Plan
E.4 The Cycle 18 Calibration Plan
E.5 The Cycle 19 Calibration Plan
E.6 The Cycle 20 Calibration Plan
E.7 The Cycle 21 Calibration Plan
Glossary

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