[daip] Re: question about XMOM

[Eric Greisen]

Ashley Zauderer writes:

 > I am trying to use the task 'XMOM' to get the 1st order moment, but
 > am getting output that doesn't make sense (ie. only two perpindicular 
 > lines of data, instead of an image similar to the orignial image).
 > 
 > Is there anything tricky that I might be missing?  I put the velocity axis 
 > first in the data cube.

    Transposing with TRANS to make the velocity axis first is
essential (if you want moments on that axis).  It is also good to have
it be a velocity rather than a frequency axis - the fractional change
of frequency wrt the central frequency strains the range of floating
point numbers.

    FLUX and ICUT are important, they could be the cause of only a few
pixels getting through.  I often use BLANK on the data cube first to
blank out the areas I am sure have no emission and then let XMOM
compute with most of the remaining numbers.

If this does not work out, let me see the inputs and IMHEADER and
maybe put the image somehwre I can get to it.

 > Furthermore, does XMOM do any unit conversions?  I read all the help files 
 > and was still a bit unclear...
 > 

Not that I can think of.  Of course the higher moments have odd units
but they are just compounds of what are already there.

Cheers,

Eric Greisen