WFC3 Instrument Handbook for Cycle 24

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Table of Contents

Wide Field Camera 3 Instrument Handbook for Cycle 24

Table of Contents

Acknowledgments

Chapter 1: Introduction to WFC3

1.1 What’s New for Cycle 24

1.2 Overview

1.3 Key Features of WFC3

1.4 WFC3 Quick Reference Guide

1.5 Special Considerations for Cycle 24

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?

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

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 PSF Width and Sharpness

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 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 Photometric Calibration

6.11 Other Considerations for UVIS Imaging

6.11.1 Gain and Full-Well Saturation

6.11.2 Cosmic Rays and Hot Pixels

6.11.3 Image Persistence

6.11.4 Shutter-Induced Vibration

6.11.5 Droplets

6.11.6 Optical Anomalies

6.12 UVIS Observing Strategies

6.12.1 Dithering Strategies

6.12.2 Parallel Observations

6.12.3 Spatial Scans

6.12.4 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

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

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

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 H-alpha

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 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

E.8 The Cycle 22 Calibration Plan

E.9 The Cycle 23 Calibration Plan

Glossary