[daip] Combining 2 UV data sets with same correlator and antenna settings but pointing in 2 different directions

[Eric Greisen]

Wasim Raja wrote:
> Dear Eric
>  
>   I would like to know if DBCON is the right task to combine 2
>   uv-datasets observed with exactly the same settings (same
>   Centre-freq, same BW, same nchan, same antenna config)
>   but pointing towards 2 different sources.
> 
>   My goal is to use one of the sources to calibrate the other;
>   unfortunately the data for the 2 sources are in 2 different FITS
>   files. I would also like to add that the 2 sources were observed
>   with their observation times interleaved, ie., every alternate
>   scan corresponds to the same source (the successive scans
>   were put in different FITS-files).
> 
>   I used DBCON to combine the 2 single source files (after having
>   converted them to MULTI-source format using task MULTI) with
>   options:
>   DOARR = +1
>   DOPOS = -1
>  
>   DBCON "appears to have ended successfully" creating the output
>   multi source file. The SU table also seem to get the correct source
>   names, except that their fluxes are all 0.
> 
>   But when I now use UVPLT to plot *one* of these sources I get the
>   following error:
> localh> UVPLT1: Task UVPLT  (release of 31DEC10) begins
> localh> UVPLT1: SOUFIL: ALL SOURCES REJECTED BY SELECTION CRITERIA
> localh> UVPLT1: Purports to die of UNNATURAL causes
> localh> UVPLT1: localhost    31DEC10 TST: Cpu=       0.0  Real=       0
> 
>   However, when I select ALL sources, UVPLT does make the plots
>   successfully -- the 2 sources can also be clearly distinguished by
>   their fluxes.
> 
> 
>   Could you help please? What is the right task for combining uv data
>   on 2 different sources observed with the same correlator settings and
>   the same antenna configuration?
>

DBCON is precisely the correct programs for what you are attempting to 
do.  We need to figure out what has not worked properly so that UVPLT 
source selection is not doing what you want.  Note that the SU table is 
not supposed to have fluxes until they are entered via SETJY and/or 
GETJY.  It is important to check the SU table and your UVPLT adverbs to 
see what the full name, QUAL, and CALCODE of each source might be. 
UVPLT has such adverbs and, for example, if the QUALs do not match your 
QUAL adverb value and your adverb value is not -1, then the sources will 
be rejected.

Eric Greisen