Space Telescope Science Institute
ACS Instrument Handbook
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Table of Contents

Advanced Camera for Surveys Instrument Handbook for Cycle 22
Acknowledgments
Chapter 1: Introduction
Chapter 2: Changes After SM4 and Considerations for Cy22
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
Chapter 3: Introduction to ACS
3.1 ACS Location in the HST Focal Plane
3.2 Instrument Capabilities
3.3 Instrument Design
3.3.1 Detectors
The WFC & HRC CCDs
The SBC MAMA
3.3.2 ACS Optical Design
Filter Wheels
Calibration-Lamp Systems
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
WFC Properties
HRC
4.2.2 CCD Spectral Response
4.2.3 Quantum Efficiency Hysteresis
4.2.4 CCD Long-Wavelength Fringing
4.2.5 Readout Format
WFC
HRC
4.2.6 Analog-To-Digital Conversion
4.2.7 Flat Fields
WFC
HRC
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
WFC
HRC
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
Global
Local
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
WFPC2 and Johnson-Cousins filters
Sloan Digital Sky Survey filters
Narrow Band filters
Ramp filters
Polarizer filters
Grism and Prism
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
Imaging
Special Uses
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
Policy on Observations Which Fail Because they Exceed Bright-Object Limits
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
WFC CCD Subarrays
Ramp Filters
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
WFC Ramp Filter Apertures
HRC 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
ACS Coordinated Parallels
ACS Pure Parallels
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
Point Source
Diffuse Source
Emission Line Source
9.2.2 Spectroscopy
Point Source
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
Background Variations and LOW-SKY
Geocoronal Emission and Shadow
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
WFC/F435W
WFC/F475W
WFC/F502N
WFC/F550M
WFC/F555W
WFC/F606W
WFC/F625W
WFC/F658N
WFC/F660N
WFC/F775W
WFC/F814W
WFC/F850LP
WFC/G800L
WFC/CLEAR
HRC/F220W
HRC/F250W
HRC/F330W
HRC/F344N
HRC/F435W
HRC/F475W
HRC/F502N
HRC/F550M
HRC/F555W
HRC/F606W
HRC/F625W
HRC/F658N
HRC/F660N
HRC/F775W
HRC/F814W
HRC/F850LP
HRC/F892N
HRC/G800L
HRC/PR200L
HRC/CLEAR
SBC/F115LP
SBC/F122M
SBC/F125LP
SBC/F140LP
SBC/F150LP
SBC/F165LP
SBC/PR110L
SBC/PR130L
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

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