Karl G. Jansky VLA Tutorials

Disclaimer: These tutorials provide guidelines to help users become familiar with VLA data reduction in CASA. They offer examples for common general-use cases such as spectral line, continuum, linear polarization, and mosaicking. However, the results demonstrated here are specific to the given data sets. The VLA is an extremely flexible instrument, and the techniques presented here may not apply equally to every individual VLA data set, especially if the type of observations, quality of data, or imaging analysis are particularly different or complicated. More details about CASA and its tasks and tools are available in the Online CASA Documentation. Further assistance with VLA data reduction is available through the NRAO HelpDesk.

For data reduction of pre-EVLA upgrade VLA data, we provide separate, pre-upgrade VLA data reduction tutorials

In addition to the current VLA CASA Guides below, we also provide links to older versions of the VLA CASA guides.

Introduction

The Karl G. Jansky Very Large Array (VLA) Tutorials are meant to guide the observer through some common types of data analysis, using example datasets, and including explanations of the individual steps. These analyses will be broadly applicable to many VLA data sets.

If you are new to CASA, you may start with

VLA Data Reduction Tutorials

High frequency (36GHz), spectral line data reduction: Carbon Star IRC+10216

• IRC+10216 Tutorial (CASA 6.2.0)

• This tutorial requires to download a dataset 1.1GB in size

Calibrate and make image cubes of the line emission from this asymptotic giant branch star. This is a high-frequency VLA dataset. Includes:

• Inspecting data; basic flagging & calibration
• Subtracting continuum emission
• Imaging the spectral lines
• Imaging the continuum
• Image analysis
• Self-calibration

6cm Continuum Imaging, Mosaicking: Supernova Remnant 3C391

• 3C391 Tutorial (CASA 6.4.1)

• This tutorial requires to download a dataset 3.1GB in size

Calibrate VLA continuum data, image a mosaic of the region in Stokes I. Includes:

• Inspecting data; basic flagging
• Calibration
• Image Analysis
• Self-calibration

Polarization Calibration based on CASA pipeline standard reduction: The radio galaxy 3C75

• Polarization Calibration based on CASA pipeline (3C75) (CASA 6.5.4)

• This tutorial requires to download a dataset 10GB in size

This tutorial demonstrates continuum calibration with the standard VLA pipeline and focuses on linear polarization calibration based on pipeline products, as well as full Stokes wide-field imaging and analysis. It includes:

• Instructions on how to execute the VLA pipeline
• How to modify pipeline products for polarization calibration
• Linear Polarization Calibration
• Wide-field Polarization Imaging
• Self-calibration
• Analysis of Polarization Products

P-band continuum imaging data reduction tutorial: 3C129

• 3C129 P-band Tutorial (CASA 6.4.1)

• This tutorial requires to download a dataset 26GB in size

This low frequency VLA tutorial for the observation of radio galaxy 3C 129 focuses on low frequency wide-fractional-bandwidth data in the sub GHz regime and demonstrates multi-frequency synthesis imaging with w-projection. This includes:

• Basic flagging and evaluation
• Automatic RFI Excision
• Ionospheric Calibration
• Self - Calibration
• Widefield imaging

MG0414+0534 P-band Spectral Line Tutorial

• MG0414+0534 P-band Spectral Line Tutorial (CASA 6.5.2)

• This tutorial is based on an archival data-set of 142 GB in size, but we will extract only a 33GB portion of this data-set to work on.

This VLA P-band tutorial is aimed at calibrating and making an image cube of line-emission centered on 390.6 MHz. It includes:

• P-band spectral-line observing strategies
• Basic flagging options
• Low-frequency calibration and self-calibration
• Spectral-line imaging

HI 21 cm Spectral Line Data Reduction Tutorial

• HI 21cm Spectral Line (CASA 6.5.2)

• This tutorial is based on an archival data-set of 85 GB in size.

This HI 21cm spectral line tutorial is aimed at calibrating and making an image cube of the dwarf galaxy LEDA4 4055. It includes:

• Finding the HI 21 cm spectral line in LEDA 44055
• Basic flagging
• Splitting out the HI Line
• Spectral-line imaging
• Continuum Subtraction

VLA Topical Guides

Flagging VLA Data in CASA

• Topical Guide: Flagging VLA Data (CASA 6.4.1)

• This tutorial requires to download a dataset 4.9GB in size

This tutorial describes different flagging techniques, including:

• Identifying Problematic Antennas from the Operator Logs
• Online Flags
• Shadowing, zeroes, quacking, flagmanager, Hanning smoothing
• Automatic RFI excision (TFCrop, RFlag)
• Interactive Flagging (plotms, msview)
• Flagging Summary & Report

Imaging VLA Data in CASA

• Topical Guide: Imaging VLA Data (CASA 6.5.2)

• This tutorial requires to download a dataset 1.2GB in size

The Imaging topical guide shows annotated examples of different imaging techniques that are applicable to different science applications. This tutorial includes:

• An Introduction to the CLEAN algorithm, data and imaging weights, primary and synthesized beams
• Clean Output Images
• Dirty Image, Regular CLEAN & RMS Noise, CLEAN with different Weights
• Multi-Scale CLEAN
• Multi-Scale, Wide-Field CLEAN (w-projection)
• Multi-Scale, Multi-Term Frequency Synthesis
• Multi-Scale, Multi-Term Frequency, Widefield CLEAN
• Imaging Outlier Fields
• Primary Beam Correction
• Imaging Spectral Cubes, Beam per Plane
• Image Header, Image Conversion

Self-calibration of VLA Data

• Topical Guide: VLA Self-calibration Tutorial (CASA 6.4.1)
• This tutorial requires to download a dataset 19GB in size

This tutorial demonstrates how to perform self-calibration on a VLA data set, covering aspects such as how to choose the time interval, signal-to-noise ratio, and combination over spectral windows and polarizations.

VLA Multi-Configuration Data Combination

• Topical Guide: VLA Data Combination Guide (CASA 6.5.4)
• This tutorial requires to download a dataset 3.0GB in size

The VLA Data Combination Tutorial provides guidance on the combination of multi-configuration VLA data sets (in this case VLA A, B, C and D configurations). The data are re-weighted in two different ways, combined, and imaged.

Source Subtraction in VLA data

• Topical Guide: Source Subtraction in VLA data (CASA 6.4.1)
• This tutorial requires to download a dataset 1.4GB in size

This topical guide demonstrates how to remove a time variable source from the visibility data.

Correcting for a Spectral Index in Bandpass Calibration

• Topical Guide: Correcting for a Spectral Index in Bandpass Calibration (CASA 6.5.4)
• This tutorial requires to download a dataset 3.4GB in size

This tutorial explains how to obtain a bandpass solution when the bandpass calibrator is a source with an unknown spectral index. This is typically encountered at high frequency observations, where the standard VLA flux density calibrators are too weak for high signal-to-noise bandpass solutions.

VLA CASA Simulation Guide

• VLA Protoplanetary Disk Simulation Guide (CASA 6.5.4)
• This tutorial does not require any download.

The VLA Protoplanetary Disk Simulation Guide shows examples on how to simulate VLA data based on model images. The tutorial will explain the main simulation tools, apply different parameters to simulations, and compares the results to the VLA exposure calculator.

VLA CASA Pipeline Guide

• VLA CASA Pipeline Guide (CASA 6.5.4)
• This tutorial does not require any download.
• The guide contains a link to Frequent VLA problems and how to address them within a pipeline run.

The VLA CASA Pipeline Guide provides an example of a VLA CASA pipeline run. Whereas the VLA Pipeline Web Page describes the pipeline structure, requirements, execution options including restoration, pipeline output products, and pipeline modifications, this CASA guide is a detailed walkthrough of the weblog and provides interpretations of pipeline plots, tables, and Quality Assurance (QA) metrics.