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This document describes how to calibrate and image interferometric and single-dish radio astronomical data using the CASA (Common Astronomy Software Application) package. CASA is a suite of astronomical data reduction tools and tasks that can be run via the IPython interface to Python. CASA is being developed in order to fulfill the data post-processing requirements of the ALMA and EVLA projects, but also provides basic and advanced capabilities useful for the analysis of data from other radio, millimeter, and submillimeter telescopes.
You have in your hands the latest release of CASA. This package is under active development, and thus there are a number of caveats and limitations for the use of this package. See the release notes (§ 1.1) below for more information, and pay heed to the numerous ALERTs placed throughout this reference. You can expect regular updates and patches, as well as increasing functionality.
This user reference and cookbook is a task-based walk-through of interferometric data reduction and analysis. In CASA, tasks represent the more streamlined operations that a typical user would carry out. The idea for having tasks is that they are simple to use, provide a more familiar interface, and are easy to learn for most astronomers who are familiar with radio interferometric data reduction (and hopefully for novice users as well). In CASA, the tools provide the full capability of the package, and are the atomic functions that form the basis of data reduction. These tools augment the tasks, or fill in gaps left by tasks that are under development but not yet available. See the CASA Toolkit Manual for more details on the tools (available from casa.nrao.edu). Note that in most cases, the tasks are Python interface scripts to the tools, but with specific, limited access to them and a standardized interface for parameter setting. The tasks and tools can be used together to carry out more advanced data reduction operations.
For the moment, the audience is assumed to have some basic grasp of the fundamentals of synthesis imaging, so details of how a radio interferometer or telescope works and why the data needs to undergo calibration in order to make synthesis images are left to other documentation — a good place to start might be Synthesis Imaging in Radio Astronomy II (1999, ASP Conference Series Vol. 180, eds. Taylor, Carilli & Perley).
This reference is broken down by the main phases of data analysis:
- data import, export, and selection (Chapter 2),
- examination and flagging of data (Chapter 3),
- interferometric calibration (Chapter 4),
- interferometric imaging (Chapter 5),
- image analysis (Chapter 6), and
- data and image visualization (Chapter 7).
- single dish data analysis (Chapter 8), and
- simulation (Chapter 9).
These are included for users that will be doing EVLA and ALMA telescope commissioning and software development.
The general appendices provide more details on what’s happening under the hood of CASA, as well as supplementary material on tasks, scripts, and relating CASA to other packages. These appendices include:
- obtaining and installing CASA (Appendix A),
- more details about Python and CASA (Appendix B),
- a discussion of the Hamaker-Bregman-Sault Measurement Equation (Appendix E),
- annotated scripts for typical data reduction cases (Appendix F), and
- CASA dictionaries to AIPS, MIRIAD, and CLIC (Appendix G).
- Writing your own CASA Task (Appendix H).
The CASA User Documentation includes:
- CASA User Reference & Cookbook — this document, a task-based data analysis walk-through and instructions;
- CASA in-line help — accessed using help in the casapy interface;
- The CASA Toolkit Reference Manual — details on a specific task or tool does and how to use it.
- The CASA Task Reference Manual — the information from the inline help and task documentation, available online in HTML.
The CASA home page can be found at:
¿From there you can find documentation and assistance for the use of the package, including the User Documentation. You will also find information on how to obtain the latest release and receive user support.
There is also a CASAGuides Wiki
that contains helpful information on CASA startup, AIPS-to-CASA cheat sheet, example scripts of processing your data in CASA, along with hints and tricks to best use this package.
1.1 About This Release
1.2 Obtaining CASA
1.2.1 What’s New in Release 4.1.0
1.3 CASA Basics — Information for First-Time Users
1.3.1 Before Starting CASA
1.3.2 Starting CASA
1.3.3 Ending CASA
1.3.4 What happens if something goes wrong?
1.3.5 Aborting CASA execution
1.3.6 What happens if CASA crashes?
1.3.7 Python Basics for CASA
1.3.8 Getting Help in CASA
1.4 Tasks and Tools in CASA
1.4.1 What Tasks are Available?
1.4.2 Running Tasks and Tools
1.4.3 Getting Return Values
1.4.4 Running Tasks Asynchronously
1.4.5 Setting Parameters and Invoking Tasks
1.4.6 Tools in CASA
1.5 Getting the most out of CASA
1.5.1 Your command line history
1.5.2 Logging your session
1.5.3 Where are my data in CASA?
1.5.4 What’s in my data?
1.5.5 Data Selection in CASA
1.6 From Loading Data to Images
1.6.1 Loading Data into CASA
1.6.2 Data Examination, Editing, and Flagging
1.6.4 Synthesis Imaging
1.6.5 Self Calibration
1.6.6 Data and Image Analysis
1.6.7 Getting data and images out of CASA
More information about CASA may be found at the CASA web page
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