HEAsoft is a Unified Release of the FTOOLS and XANADU Software Packages:

XANADU - High-level, multi-mission tasks for X-ray astronomical spectral, timing, and imaging data analysis

FTOOLS - General and mission-specific tools to manipulate FITS files

When you login, your environment should automatically be set up correctly to use this software. You can verify this by using the printenv command and grepping its output for the word HEADAS.

On a 32-bit system:

$ printenv | grep HEADAS

On a 64-bit system:

$ printenv | grep HEADAS

If for some reason the correc environment isn't set up automatically, you can set it up with the following commands: For bash/64-bit systems:

source "${HEADAS}/headas-init.sh"

For bash/32-bit systems:

source "${HEADAS}/headas-init.sh"

For tcsh/64-bit systems:

setenv HEADAS  /usr/local/headas-6.8/x86_64-unknown-linux-gnu
source ${HEADAS}/headas-init.csh

For tcsh/32-bit systems:

setenv HEADAS  /usr/local/headas-6.8/i686-pc-linux-gnu-libc2.5
source ${HEADAS}/headas-init.csh

Please see http://heasarc.gsfc.nasa.gov/docs/software/lheasoft/ for more information. There are links to user documentation at the bottom of this page.