[daip] clean 3bit Ka data

[Eric Greisen]

zadeh wrote:
> Hi Eric,
> We have broad band  data sets at Ka band but the flux of the bright 
> source varies as a function of frequeny as nu^0.3 across the 8GHz of
> bandwidth. How do I clean this data correctly  or even  self-cal this 
> data in aips? Any suggestions would be appreciated.
> 
> Another question. What is the task name to do Faraday depth map and 
> Faradat RM map? We have  images
> at multiple frequencies across the band.

Two excellent - nearly research level - questions.

1. If most of the flux has a single spectral index, then IMAGR will 
allow you to correct it in the UV data work file using IMAGRPRM(2).

   If there is real structure in spectral index that might matter, you 
need to do a multiple step procedure.  First IMAGR the data in spectral 
chunks of modest size.  Take the output images and make a cube with 
MCUBE or FQUBE. then bring the planes of the cube to the same resolution 
(usually just the fattest of your beams) with CONVL.  Then run SPECR on 
that cube.   Take the SPECR output as IN3NAME et al (and perhaps IN4NAME 
if curvature is significant) in an IMAGR that includes all channels/IFs.
Use FQTOL to make this process run faster and also include the primary 
beam (IMAGRPRM(1)) when you do this since it won't cost you anything.

2. RM analysis is definitely a research topic.  The current best answer 
is to run FARS on your P and Q cubes (corrected for spectral index) 
(task SPCOR).  Then run RMFIT.

I am about to go back to work on RMFIT to add another parameter to be 
fit having to do with the thickness of the Faraday screen.  that will 
take a while but you will have much to learn.  The Faraday rotation 
measure synthesis, done with FFTs, has a very fat point-spread function 
(beam) and so is no so useful.  But RMFIT is aided with the FARS output 
and so you must wait for it (FARS is slowwwww).

You may wish to talk to Larry Rudnick (larry at umn.edu) as he is expert on 
the subject.

Eric Greisen