For details on the various frequency and velocity definitions and rest frames used in JCMT heterodyne observations, please see our Velocity Considerations page.
- to convert processed data from the JCMT Science Archive, which is in Barycentric frequency, into radio line-of-sight velocity () in LSRK. You can use the following Starlink commands to do this, assuming you have started with a file named ‘archive_file.fits’. These would be copied into a terminal, after setting up the Starlink software within that terminal. The lines starting with a # symbol are comments.
# Load the convert package to enable conversion from FITS to NDF convert # Convert your archive file into Starlink Data Format (NDF) fits2ndf archive_file.fits archive_file.sdf # Load the KAPPA package (contains many useful routines) kappa # Set the 3rd axis of the coordinate system to be in units of radio velocity wcsattrib ndf=archive_file.sdf mode=set name=system\(3\) newval=vrad # Set the standard of rest to be the LSRK wcsattrib ndf=archive_file.sdf mode=set name=StdofRest newval=LSRK # OPTIONAL: if fits output is required, convert the file back to fits ndf2fits archive_file.sdf archive_file_radiovelocity.fits
- to add together spectral data from moving targets (eg comets) onto a ‘source’ (‘cometocentric’) velocity scale:
makecube <rawdatafile00099> system=GAPPT alignsys=TRUE out=out99.sdf wcsattrib out99.sdf set alignoffset 1 wcsattrib out99.sdf set skyrefis origin wcsattrib out99.sdf set sourceVRF topocentric wcsattrib out99.sdf set stdofrest source wcsattrib out99.sdf set alignstdofrest source wcsattrib out99.sdf set SourceVel <velocity> wcmosaic out*.dat . . .