[daip] Re: AIPS MOMNT bug freq axis

[Eric Greisen]

Krzysztof Chyzy writes:
 > Dear Eric,
 > 
 > It seems to me that I have found a bug in AIPS (ver. DEC03 and earlier):
 > 
 > task MOMNT:
 >   - moment maps created by momnt do not have an axis with frequency (velocity)
 >     which is needed for PBCOR. XMOM is doing that well from the same data cube.
 >     Creating axis by hand is inconvenient.

Perhaps I am not following your English and do not understand your
comment.  XMOM does not make a frequency axis on output in its normal
usage.  XMOM does moments on the 1st axis and then deletes that axis.
If that axis is frequency, velocity et al then no frequency remains.
The point of that is, of course, that moments over frequency no longer
have a unique frequency and hence no longer have a unique primary beam
for PBCOR to correct.  If primary beams are important in your
observation, then you must run PBCOR before either XMOM or MOMNT.
This does cause the noise to become a function of distance from the
pointing position and XMOM now offers the option to adjust the cutoff
levels for this effect.  MOMNT does not have that option.

Eric Greisen