9.1 Overview

Chapter 4 of this Handbook describes the procedures for designing a Phase I WFC3 observing proposal. Two of the steps involved in this process are estimating the exposure times needed to achieve your scientific goals, and then combining these individual exposures with their associated overheads to derive the number of spacecraft orbits that you will request in your Phase I proposal.

This chapter provides guidance on estimating exposure times. The following chapter, Chapter 10, then describes how to include the various overheads so as to determine the total number of spacecraft orbits needed for your program.

You should also refer to the HST Call for Proposals for Cycle 32, which includes information on policies and practices with respect to orbit-time requests. The HST Primer provides specific advice on orbit determination. In particular, please be sure to check the What's New section in the Primer for any late-breaking news. In this chapter, we provide a summary of the WFC3 sensitivities and give several examples that illustrate how to calculate your exposure times for Phase I Proposals.

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WFC3 Instrument Handbook
- • Acknowledgments
- Chapter 1: Introduction to WFC3
  - • 1.1 New for Cycle 32
  - • 1.2. Overview
  - • 1.3 Key Features of WFC3
  - • 1.4 WFC3 Quick Reference Guide
  - • 1.5 Special Considerations for Cycle 32
  - • 1.6 Sources of Further Information
  - • 1.7 The WFC3 Instrument Team at STScI
- Chapter 2: WFC3 Instrument Description
- Chapter 3: Choosing the Optimum HST Instrument
- Chapter 4: Designing a Phase I WFC3 Proposal
  - • 4.1 Phase I and Phase II Proposals
  - • 4.2 Preparing a Phase I Proposal
- Chapter 5: WFC3 Detector Characteristics and Performance
- 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
  - • 6.5 UVIS Spectral Elements
  - • 6.6 UVIS Optical Performance
  - • 6.7 UVIS Exposure and Readout
  - • 6.8 UVIS Sensitivity
  - • 6.9 Charge Transfer Efficiency
  - • 6.10 Other Considerations for UVIS Imaging
  - • 6.11 UVIS Observing Strategies
- 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
  - • 7.5 IR Spectral Elements
  - • 7.6 IR Optical Performance
  - • 7.7 IR Exposure and Readout
  - • 7.8 IR Sensitivity
  - • 7.9 Other Considerations for IR Imaging
  - • 7.10 IR Observing Strategies
- Chapter 8: Slitless Spectroscopy with WFC3
- 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
  - • 9.5 Count Rates: Slitless Spectroscopy
  - • 9.6 Estimating Exposure Times
  - • 9.7 Sky Background
  - • 9.8 Interstellar Extinction
  - • 9.9 Exposure-Time Calculation Examples
- Chapter 10: Overheads and Orbit Time Determinations
  - • 10.1 Overview
  - • 10.2 Observatory Overheads
  - • 10.3 Instrument Overheads
  - • 10.4 Orbit Use Examples
- Appendix A: WFC3 Filter Throughputs
  - • A.1 Introduction
  - A.2 Throughputs and Signal-to-Noise 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
- 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 Overview
  - • E.2 The STScI Reduction and Calibration Pipeline
  - • E.3 The SMOV Calibration Plan
  - • E.4 The Cycle 17 Calibration Plan
  - • E.5 The Cycle 18 Calibration Plan
  - • E.6 The Cycle 19 Calibration Plan
  - • E.7 The Cycle 20 Calibration Plan
  - • E.8 The Cycle 21 Calibration Plan
  - • E.9 The Cycle 22 Calibration Plan
  - • E.10 The Cycle 23 Calibration Plan
  - • E.11 The Cycle 24 Calibration Plan
  - • E.12 The Cycle 25 Calibration Plan
  - • E.13 The Cycle 26 Calibration Plan
  - • E.14 The Cycle 27 Calibration Plan
  - • E.15 The Cycle 28 Calibration Plan
  - • E.16 The Cycle 29 Calibration Plan
  - • E.17 The Cycle 30 Calibration Plan
  - • E.18 The Cycle 31 Calibration Plan
- • Glossary

9.1 Overview

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