ACS Insturment Handbook for Cycle 24

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Table of Contents

Acknowledgments

Chapter 1: Introduction

Chapter 2: Changes After SM4
and Considerations for Cy24

2.1 SM4 Repair of ACS

2.2 Comparison of ACS/WFC and WFC3/UVIS

2.3 Comparison of ACS/HRC and WFC3/UVIS

2.4 Dithering Considerations

2.5 CTE Considerations

2.6 Revisions to the WFC Subarray Modes

Chapter 3: ACS Capabilities, Design and Operations

3.1 ACS Location in the HST Focal Plane

3.2 Instrument Capabilities

3.3 Instrument Design

3.3.1 Detectors

3.3.2 ACS Optical Design

3.4 Basic Instrument Operations

3.4.1 Target Acquisitions

3.4.2 Typical ACS Observing Sequence

3.4.3 Data Storage and Transfer

3.5 ACS Quick Reference Guide

Chapter 4: Detector Performance

4.1 Overview

4.2 The CCDs

4.2.1 Detector Properties

4.2.2 CCD Spectral Response

4.2.3 Quantum Efficiency Hysteresis

4.2.4 CCD Long-Wavelength Fringing

4.2.5 Readout Format

4.2.6 Analog-To-Digital Conversion

4.2.7 Flat Fields

4.3 CCD Operations and Limitations

4.3.1 CCD Saturation: The CCD Full Well

4.3.2 CCD Shutter Effects on Exposure Times

4.3.3 Read Noise

4.3.4 Dark Current

4.3.5 Warm and hot pixels

4.3.6 Cosmic Rays

4.3.7 Charge Transfer Efficiency

4.3.8 UV Light and the HRC CCD

4.4 The SBC MAMA

4.4.1 MAMA Properties

4.4.2 SBC Spectral Response

4.4.3 Optical Performance

4.5 SBC Operations and Limitations

4.5.1 SBC Scheduling Policies

4.5.2 MAMA Overflow of the 16 Bit Buffer

4.5.3 MAMA Darks

4.5.4 SBC Signal-To-Noise Ratio Limitations

4.5.5 SBC Flatfield

4.5.6 SBC Nonlinearity

4.6 SBC Bright-Object Limits

4.6.1 Overview

4.6.2 Observational Limits

Chapter 5: Imaging

5.1 Imaging Overview

5.2 Important Considerations for ACS Imaging

5.2.1 Optical Performance

5.2.2 CCD Throughput Comparison

5.2.3 Limiting Magnitudes

5.2.4 Signal-To-Noise Ratios

5.2.5 Saturation

5.2.6 Faint Horizontal Striping in WFC CCDs

5.3 Wide Field Optical CCD Imaging

5.3.1 Filter Set

5.4 High-Resolution Optical and UV Imaging

5.4.1 Filter Set

5.4.2 Multiple Electron Events

5.4.3 Red Leaks

5.5 Ultraviolet Imaging with the SBC

5.5.1 Filter Set

5.5.2 Red Leaks

5.5.3 SBC Imaging Filter Shifts

5.6 ACS Point Spread Functions

5.6.1 CCD Pixel Response Function

5.6.2 Model PSFs

5.6.3 Encircled Energy

5.6.4 Geometric Distortions

5.6.5 PSFs at Red Wavelengths and the UV

5.6.6 Residual Aberrations

Chapter 6: Polarimetry, Coronagraphy
and Prism/Grism Spectroscopy

6.1 Polarimetry

6.1.1 Introduction

6.1.2 Performance of ACS Polarizers

6.1.3 Implementation of ACS Polarizers

6.1.4 Challenges and Limitations of ACS Polarimetry

6.2 Coronagraphy

6.2.1 Coronagraph Design

6.2.2 Acquisition Procedure and Pointing Accuracy

6.2.3 Vignetting and Flat Fields

6.2.4 Coronagraphic Performance

6.2.5 Subtraction of the coronagraphic PSF

6.2.6 The Off-Spot PSF

6.2.7 Occulting Spot Motions

6.3 Grism/Prism Spectroscopy

6.3.1 WFC G800L

6.3.2 HRC G800L

6.3.3 HRC PR200L

6.3.4 SBC PR110L

6.3.5 SBC PR130L

6.3.6 Observation Strategy

6.3.7 Extraction and Calibration of Spectra

Chapter 7: Observing Techniques

7.1 Designing an ACS Observing Proposal

7.1.1 Identify Science Requirements and Define ACS Configuration

7.1.2 Available but Unsupported Modes

7.1.3 Determine Exposure Time and Check Feasibility

7.1.4 Identify Need for Additional Exposures

7.1.5 Data Volume Constraints

7.1.6 Determine Total Orbit Request

7.1.7 Charge Transfer Efficiency

7.1.8 Image Anomalies

7.2 SBC Bright Object Protection

7.2.1 Bright Object Violation: SBC Exposures

7.2.2 Policy and Observers’ Responsibility in Phase I and Phase II

7.2.3 Bright-Object Protection for Solar System Observations

7.2.4 Prime and Parallel Observing with the SBC

7.3 Operating Modes

7.3.1 WFC ACCUM Mode

7.3.2 SBC ACCUM Mode

7.4 Patterns and Dithering

7.5 A Road Map for Optimizing Observations

7.6 CCD Gain Selection

7.7 ACS Apertures

7.7.1 WFC Apertures

7.7.2 Ramp-Filter Apertures

7.7.3 The Small Filter Apertures

7.7.4 Polarizer Apertures

7.7.5 HRC Apertures

7.7.6 SBC Apertures

7.8 Specifying Orientation on the Sky

7.8.1 Determining Orientation for Phase II

7.9 Parallel Observations

7.9.1 Parallel Observing

7.10 Pointing Stability for Moving Targets

Chapter 8: Overheads and Orbit-Time
Determination

8.1 Overview

8.2 ACS Exposure Overheads

8.2.1 Subarrays

8.3 Orbit Use Determination Examples

8.3.1 Sample Orbit Calculation 1

8.3.2 Sample Orbit Calculation 2

8.3.3 Sample Orbit Calculation 3

8.3.4 Sample Orbit Calculation 4

Chapter 9: Exposure-Time Calculations

9.1 Overview

9.1.1 The ACS Exposure Time Calculator

9.2 Determining Count Rates from Sensitivities

9.2.1 Imaging

9.2.2 Spectroscopy

9.3 Computing Exposure Times

9.3.1 Calculating Exposure Times for a Given signal-to-noise

9.3.2 Exposure Time Estimates for Red Targets in F850LP

9.4 Detector and Sky Backgrounds

9.4.1 Detector Backgrounds

9.4.2 Sky Background

9.5 Extinction Correction

9.6 Exposure-Time Examples

9.6.1 Example 1: WFC Imaging a Faint Point Source

9.6.2 Example 2: SBC Objective Prism Spectrum of a UV Star

9.6.3 Example 3: WFC VIS Polarimetry of the Jet of M87

9.6.4 Example 4: SBC imaging of Jupiter’s Aurora at Lyman-alpha

9.6.5 Example 5: Coronagraphic imaging of the Beta-Pictoris Disk

9.6.6 Example 6: WFC Imaging: Post-Flash to Mitigate Low Sky

9.7 Tabular Sky Backgrounds

Chapter 10: Imaging Reference Material

10.1 Introduction

10.2 Using the Information in this Chapter

10.2.1 Sensitivity Units and Conversions

10.2.2 Signal-to-Noise

10.2.3 Point Spread Functions

10.3 Throughputs and Correction Tables

10.3.1 Filter Throughputs and Sensitivities

10.3.2 Color Correction Tables

10.4 Geometrical Distortion in the ACS

10.4.1 WFC

10.4.2 HRC

10.4.3 SBC

Glossary

Index