Space Telescope Science Institute
ACS Data Handbook V7.2
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Table of Contents

ACS Data Handbook
Preface
How to Use this Handbook
Handbook Structure
Typographic Conventions
Visual Cues
Comments
Acknowledgments
Chapter 1: ACS Overview
1.1 Instrument Design and Capabilities
1.1.1 Detectors
1.1.2 ACS Optical Design
1.1.3 ACS Geometric Distortion
1.1.4 ACS Performance after Servicing Mission 4
1.2 Basic Instrument Operations
1.2.1 Target Acquisitions
1.2.2 Typical ACS Observing Strategies
1.2.3 Data Storage and Transfer
1.2.4 Parallel Operations
Chapter 2: ACS Data Structure
2.1 Types of ACS Files
2.1.1 Data Files and Suffixes
2.1.2 Association Tables
2.1.3 Trailer Files
2.2 ACS File Structure
2.3 Data Storage Requirements
2.4 Headers and Keywords
Chapter 3: ACS Calibration Pipeline
3.1 On The Fly Reprocessing (OTFR)
3.2 Pipeline Overview
3.2.1 calacs: Image Calibration
3.2.2 AstroDrizzle Processing in the Pipeline:
3.2.3 When is OTFR not Appropriate?
3.3 Structure of calacs
3.4 calacs Processing Steps
3.4.1 acsccd
3.4.2 acscte - Pixel-Based CTE Corrections
3.4.3 acsrej
3.4.4 acs2d
3.4.5 acssum
3.5 Manual Recalibration of ACS Data
3.5.1 Requirements for Manual Recalibration
3.5.2 calacs Examples
Chapter 4: ACS Data Processing Considerations
4.1 Read Noise and A-to-D Conversion
4.1.1 Read Noise
4.1.2 A-to-D Conversion
4.2 Bias Issues
4.2.1 Bias Calibration
4.2.2 Bias Jump
4.2.3 Post-SM4 WFC Signal-dependent Bias Shift
4.2.4 Bias Sub-Arrays for WFC and HRC
4.3 Dark Current, Hot Pixels, and Cosmic Rays
4.3.1 Dark Current
4.3.2 Hot Pixels
4.3.3 Cosmic Rays
4.4 Flat-Field Reference Files
4.4.1 Ground Flats (P-flats)
4.4.2 L-flats
4.4.3 Pipeline Flat-Field Files
4.4.4 Earth Flat Verification for the HRC
4.4.5 Sky Flats for the WFC
4.5 Image Anomalies
4.5.1 Dust Motes
4.5.2 Optical Ghosts and Scattered Light
4.5.3 Cross-Talk
4.5.4 Scattered Earth Light
4.5.5 HRC Polarimetry
4.6 ACS/WFC CCD Detector Charge Transfer Efficiency (CTE)
4.6.1 The Issue
4.6.2 Improving CTE: Considerations Before Making the Observations
4.6.3 Improving CTE: Post-Observation Image Restoration
4.7 Generic Detector and Camera Properties
4.7.1 Gain Calibration
4.7.2 Full Well Depth
4.7.3 Linearity at Low to Moderate Intensity
4.7.4 Linearity Beyond Saturation
4.7.5 Shutter Stability
Chapter 5: ACS Data Analysis
5.1 Photometry
5.1.1 Photometric Systems, Units, and Zeropoints
5.1.2 Aperture and Color Corrections
5.1.3 Pixel Area Maps
5.1.4 PSF
5.1.5 CTE
5.1.6 Red Leak
5.1.7 UV Contamination
5.2 Astrometry
5.2.1 Coordinate Transformations
5.2.2 Absolute and Relative Astrometry
5.2.3 Impact of Guide Star Failure
5.3 Polarimetry
5.3.1 Absolute Calibration
5.3.2 Instrumental Issues
5.3.3 Flats
5.3.4 Polarization Calibration
5.4 Coronagraphy
5.4.1 Flat Fielding
5.4.2 PSF Subtraction
5.4.3 Photometry
5.4.4 Ghosting
5.5 Ramp Filters
5.5.1 Introduction
5.5.2 Existing Ground Calibrations
5.5.3 In-Flight Calibrations
5.6 Spectroscopy with the ACS Grisms and Prisms
5.6.1 What to Expect from ACS Slitless Spectroscopy Data
5.6.2 Pipeline Calibration
5.6.3 Slitless Spectroscopy Data and Dithering
5.6.4 Extracting and Calibrating Slitless Spectra
5.6.5 Accuracy of Slitless Spectra Wavelength and Flux Calibration

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