Wide Field Camera 3 Instrument Handbook for Cycle 17

Table of Contents

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Handbook Cover

Acknowledgments

Chapter 1: Introduction to WFC3

1.1 Overview

1.2 Key Features of WFC3

1.3 WFC3 Quick Reference Guide

1.4 Current Instrument Status

1.5 Special Considerations for Cycle 17

1.5.1 WFC3 is Still Under Development

1.5.2 Return to Three-Gyro Mode in Cycle 17

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

2.4 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?

4.2.3 What Aperture or Subarray?

4.2.4 What Overheads and How Many HST Orbits?

4.2.5 Any Special 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

5.5 The WFC3 IR Channel Detector

5.5.1 Overview

5.5.2 IR Detector Basics

5.6 WFC3 IR Readout Formats and Reference Pixels

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 Detector Cosmetics

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

6.4.5 Apertures

6.5 UVIS Spectral Elements

6.5.1 Filter and Grism Summary

6.5.2 Filter Red Leaks

6.5.3 Ghosts

6.6 UVIS Optical Performance

6.6.1 Model PSF and FWHM

6.6.2 Encircled and Ensquared Energy

6.6.3 Other PSF Behavior and Characteristics

6.7 UVIS Exposure and Readout

6.7.1 Exposure Time

6.7.2 ACCUM Mode

6.8 UVIS Sensitivity

6.8.1 Limiting Magnitudes

6.9 Other Considerations for UVIS Imaging

6.9.1 Gain and Full-well Saturation

6.9.2 Cosmic Rays and Hot Pixels

6.9.3 Charge-Transfer Efficiency

6.9.4 Image Persistence

6.9.5 Quantum Yield

6.10 UVIS Observing Strategies

6.10.1 Dithering Strategies

6.10.2 Parallel Observations

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

7.5.2 Filter Blue Leaks

7.5.3 Ghosts

7.6 IR Optical Performance

7.6.1 Model PSF and FWHM

7.6.2 Encircled and Ensquared Energy

7.6.3 Other PSF Behavior and Characteristics

7.7 IR Exposure and Readout

7.7.1 Exposure Time

7.7.2 MULTIACCUM Mode

7.7.3 MULTIACCUM Timing Sequences

7.7.4 Subarray Timing Sequences

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 Hot Pixels

7.9.3 On-orbit Degradation

7.9.4 Image Persistence

7.9.5 The IR Background

7.10 IR Observing Strategies

7.10.1 Dithering Strategies

7.10.2 Parallel Observations

7.10.3 Exposure Strategies

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

Chapter 9: WFC3 Exposure-Time Calculation

9.1 Overview

9.2 The WFC3 Exposure Time Calculator (ETC)

9.3 Sensitivity 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 Background Variations and LOW-SKY

9.7.2 Geocoronal Emission 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: IR Imaging of a Faint Extended Source

Chapter 10: Overheads and Orbit Time Determinations

10.1 Overview

10.2 Observatory Overheads

10.3 Instrument Overheads

10.3.1 Exposure 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 Using the Information in this Chapter

A.2.1 Sensitivity Units and Conversions

A.2.2 Signal-to-Noise Ratio

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

Glossary

Index