[daip] [!5480]: aips - CVEL AIPS 2

[Eric Greisen]

Eric Greisen updated #5480
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              Status: Closed (was: Open)
                 Due: - Cleared - (was: 16 September 2014 10:46 PM)

CVEL AIPS 2
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           Ticket ID: 5480
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/5480
           Full Name: Carolina Rodriguez
               Email: ca.rodriguez at crya.unam.mx
             Creator: User
          Department: AIPS Data Processing
       Staff (Owner): Eric Greisen
                Type: Issue
              Status: Closed
            Priority: Default
      Template Group: Default
             Created: 11 September 2014 10:45 PM
             Updated: 15 September 2014 04:39 PM



Applying CVEL to data taken as you describe causes the emission
to be moved from the channels in which it ended up into the channels
you would prefer.  So long as CVEL works okay, then this is probably
a good thing to do.  But CVEL uses an FFT, so very narrow lines (just
a couple of channels or less) can make all sorts of ringing when FFTed. 
In that case, it is better to fix the velocity labels to put the -17 km/s in the
channel where it ended up and not run CVEL.  Of course, such a labeling
"fix" does not correct for the Earth's rotation during the time of your
observation.  But with narrow lines that is probably preferable to the
ringing.

Note that SETJY now has an option to compute the actual velocity of
the first scan and label the source table properly (multi-source data
before SPLIT).

Eric Greisen




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