[daip] CLCOR/POLR fails on VLA cont. snapshot dataset

[Chris Flatters]

Michael Rupen <mrupen at aoc.nrao.edu> writes:

> running CLCOR to correct the R-L phase offset in standard VLA continuum
> (snapshot) observations fails, with the following error message:
> 
>   CLCOR1: Task CLCOR  (release of 31DEC99) begins
>   CLCOR1: TABKEY: TABLE KEYWORD POLTYPE  NOT FOUND
>   CLCOR1: ANTCOR: ERROR 21 FINDING POL. SOLUTION TYPE KEYWORD
>   CLCOR1: Purports to die of UNNATURAL causes
>   CLCOR1: mithril      31DEC99 TST: Cpu=       0.0  Real=       0
> 
> Using version OLD (15APR99) gives the identical error.  Since this is a
> fairly standard thing to do, I suspect the error results because I have NOT
> run PCAL -- the parallactic angle coverage is very small, and it seemed
> silly to try to determine ant. pol'n parameters.  I *would* like to
> roughly correct the R-L phase offset however, which doesn't seem
> unreasonable, so I hoped CLCOR would work.  Any thoughts?  Is the lack of
> PCAL actually the problem, or is this a red herring?

The lack of PCAL is the problem: CLCOR wants to adjust the polarization 
solutions for the change in the relative phases of R and L.

For the VLA, parallactic angle change only distinguishes the polarization
contribution of the calibrator from those of the antennas so a limited
range of parallactic angles should not be a problem for PCAL if you know
the polarization of your calibrator.

	Chris Flatters
	cflatter at nrao.edu