[daip] Source correction with CLCOR

[Andrew Biggs]

Hi there. I'm trying to correct the position of a phase calibrator in a
global VLBI observation using CLCOR. The positions are:

correlated - 01:32:44.1275    43:25:32.675
actual -     01:32:44.1268050 43:25:32.661270

The shifts are small, but I want to combine the target data with multiple
epochs and these were observed with different phase cal positions. The
above are the J2000 coordinates and so I've run CLCOR using:

OPCOD='ANTC'
clcorprm(5) = -6.95e-4 * 15 * cos(43+((25+(32.675/60))/60))
clcorprm(6) = -0.01373


After running CLCOR, LISTR shows that the position is now exactly as
requested:

2 P0128           : 0000         01:32:44.1268  43:25:32.661  625185


However, the CLCOR corrections are huge i.e. the phase wraps incredibly
quickly thus preventing the data from being fringe fitted. I then noticed
that when I ran CLCOR, it gave the following message:

CLCOR1 13:05:49 SOUMOD: change in Epoch    RA,DEC -7.57132E-03
-1.37300E-02 asec
CLCOR1 13:05:49 SOUMOD: change in Apparent RA,DEC  1.18498E+02
5.90945E+01 asec

The changes in the apparent RA and Dec seem to be far too large and are
presumably the origin of my problem. Any idea why this might be? It almost
sounds as if it isn't using an epoch of J2000. I'm using 31DEC12 that was
midnight job'd this morning.


By the way, there's a small inconsistency in the documentation. The
explain text below the inputs describes how CLCORPRM(7) needs to be set
although this is apparently no longer being used.

Thanks.

Andy