CASA-VLBI Scripts

Scripts to assist VLBI data reduction in CASA. These scripts focus on the a-priori (initial) gain calibration of the different VLBI antennas, and the a-priori flagging commands, both provided by the EVN Data Archive.

All scripts can run as a standalone program or being called within the CASA environment.

To install these scripts, run the following command:

git clone https://github.com/jive-vlbi/casa-vlbi

After the initial install, use the following command to update to the latest version of the scripts:

git pull https://github.com/jive-vlbi/casa-vlbi

A-priori gain calibration

The a-priori gain calibration sets the initial gains of each antenna based on their gain curves and the recorded system temperatures during the observation.

To prepare the data in order to be able to apply the gain calibration in CASA you will need to run two steps before the FITS-IDI files are converted into a Measuarement Set (MS) format.

Appending the system temperatures to the FITS IDI files

You can run it either via the following standalone command:

append_tsys.py  {antabfile}  {idifiles}

or via the Python module:

import casavlbitools.fitsidi
casavlbitools.fitsidi.append_tsys(antabfile, idifiles)

This will append Tsys measurements from the file named by antabfile (which should be in AIPS ANTAB format or VLBA VLOG format) to the FITS-IDI file named by idifiles. If an observation is split into multiple FITS-IDI files, idifile should be a list of file names.

The functionality of the append_tsys.py, gc.py and flag.py scripts is also available in Python modules. The following interfaces are available:

Appending the Gain Curve and sensitivity to the FITS IDI files

You can run it either via the standalone command:

append_gc.py  {antabfile}  {idifiles}

or via the Python module:

import casavlbitools.fitsidi
casavlbitools.fitsidi.append_gc(antabfile, idifile)

This will append gain curves and sensitivity information from the file named by antabfile (which should be in AIPS ANTAB format) to the FITS-IDI file named by idifile.

Create the Gain Curve calibration table

-- Note that if you already appended the system temperatures and the gain curves into the FITS-IDI files before convert it to a MS file, you can directly run gencal in CASA with such information without requiring this step. --

To create an external gain curve calibration table with the responses for each antenna:

gc.py {antabfile}  {gc}  --min-elevation=0.0  --max=elevation=90.0

or via the Python module:

import casavlbitools.casa
casavlbitools.casa.convert_gaincurve(antabfile, gc, min_elevation=0.0, max_elevation=90.0)

This creates a gaincurve table with name gc from gain curves from the file named by antablfile (which should be in AIPS ANTAB format or VLBA gains format). The gain curves are sampled between min_elevation and max_elevation, which should be specified in degrees, and then refitted.

Convert the file format or the a-priori flagging

If you have a flag file in AIPS UVFLG format, you can convert it into a CASA FLAG format with the following standalone command:

flag.py  {infile}  {idifiles}

or using the Python module:

import casavlbitools.fitsidi
casavlbitools.fitsidi.convert_flags(infile, idifiles, outfp=sys.stdout, outfile=None)

This converts the flag file named by infile (which should be in AIPS UVFLG format) into a format that can be used by CASA. The name of the FITS-IDI files corresponding to the observation should be passed in idifiles. By default the converted output is written to stdout. Output is written to a file named outpufile instead if that parameter is provided.