Post-Processing Software
AIPS: The Astronomical Image Processing System, a set of programs for the analysis of continuum and line observations, is widely used with VLBA and VLBI data. These programs are supported on a variety of computer operating systems, including Linux and Mac-OS/X. The AIPS Cookbook (NRAO staff, 2014) includes an entire chapter on reducing VLBI data, including discussion of VLBA calibration, space VLBI, polarimetry, and phase referencing; Appendix C provides a step-by-step guide to calibrating many types of VLBA data in AIPS, including VLBA+VLA datasets.
A new "frozen" version of AIPS is produced each year, and a newer version is updated and made available throughout the calendar year. Observers are encouraged to use a very recent version of AIPS, in order to keep up with ongoing developments in VLBA instrumentation. AIPS home page: http://aips.nrao.edu.
CASA: Common Astronomy Software Applications is the new data reduction package for the Jansky VLA and ALMA. It does not yet offer an end-to-end reduction path for all types of VLBA projects. CASA should not be used for VLBA projects that involve astrometry, polarimetry, or low frequencies (below about 4 GHz). However, CASA does contain imaging and calibration tools that may be of use for most basic phase-referenced VLBI data. CASA home page: http://casa.nrao.edu. CASA VLBA Basic Phase-referencing tutorial (including self-calibration): https://casaguides.nrao.edu/index.php?title=VLBA_Basic_Phase-referencing_Calibration_and_Imaging.
Difmap: Difmap (Shepherd 1997), developed as part of the Caltech VLBI Analysis Programs. Provides editing, imaging, self-calibration, and pipelining capabilities in an interactive package. Development has been frozen, and continued support is limited primarily to assistance in installation. Difmap download site: ftp://ftp.astro.caltech.edu/pub/difmap/difmap.html. Contact: M.C. Shepherd, mcs@astro.caltech.edu.
