M100 Band3 ACA 4.2.2

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  • Details of the ALMA observations are provided at M100Band3
  • This portion of the guide covers calibration of the raw visibility data. To skip to the imaging portion of the guide, see: M100Band3 Imaging 4.1.

Overview

This part of the M100 Band 3 7m CASA guide will step you through the calibration of the visibility data. We will begin by flagging (marking as bad) data known to be useless before any inspection, for example data where one telescope blocks the line of sight of another. Then we will apply telescope-generated calibration tables to partially correct for atmospheric effects. After inspecting the data, we will flag some additional data that exhibit pathologies. Then we will use observations of the calibrators Titan and 3c279 to derive the phase and amplitude response of individual antennas as a function of time and frequency ("phase", "amplitude", and "bandpass" calibrations). We will apply these to the data and then extract the calibrated source data into a file appropriate for imaging.

The general procedure in this guide follows the other ALMA CASA guides: NGC3256Band3 and TWHydraBand7.

Unpack the Data

Once you have downloaded the M100_Band3_7m_CalibratedData.tgz, unpack the file in a terminal outside CASA using 

tar -xvzf M100_Band3_7m_CalibratedData.tgz

then change directory to the new directory 

cd M100_Band3_7m_CalibratedData

You may wish to type 

ls

to look at the files present. You should see a set of files with extension ".ms". These are CASA measurement set (MS) files. The data have already been converted to MS format from the native ALMA format using the CASA task importasdm. In addition to the data, we provide you with calibration tables containing system temperature (Tsys), water vapor radiometer (WVR), and antenna position information. For Early Science, these tables will either be pre-applied or supplied with the data.

This guide requires Python module analysisUtils. If you have not already installed analysisUtils please follow the link to do so.

To begin, start CASA by typing 

casapy

Be sure that you are using the version indicated at the top of this page.

Confirm your version of CASA

This guide has been written for CASA release 4.1.0. Please confirm your version before proceeding. 

# In CASA
version = casadef.casa_version
print "You are using " + version
if (version < '4.1.0'):
    print "YOUR VERSION OF CASA IS TOO OLD FOR THIS GUIDE."
    print "PLEASE UPDATE IT BEFORE PROCEEDING."
else:
    print "Your version of CASA is appropriate for this guide."

Install Analysis Utilities

Analysis Utilities (or analysisUtils for short) is a small set of Python scripts that provide a number of analysis and plotting utilities for ALMA data reduction. This guide uses a few of these utilities. They are very easy to install (just download and untar). See

http://casaguides.nrao.edu/index.php?title=Analysis_Utilities

for a full description and download instructions. Analysis Utilities are updated frequently so if its been a while since you installed it, its probably worth doing it again. If you are at an ALMA site or ARC, the analysis utilities are probably already installed and up to date.

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