[daip] UVFIT

[Andy Biggs]

Hi there. Is UVFIT still believed to work? I am finding it difficult to 
get anything sensible out of it. I am using it to fit to VLA data which 
include e.g. about a minute's worth of 3C84 i.e. very nearly a point 
source of 21 Jy. Unless I set dopos=-1, the fluxes are just gibberish 
and usually returns the input guess.

If you'd like to investigate, I have put a dataset at 
ftp://ftp.eso.org/pub/general/abiggs/UVFIT.FITS

The following seem to me to be the basic inputs required for a fit:

source '0319+415' ''
docalib 1
gmax 21 0
go

The other inputs take sensible defaults. In 31DEC16, this just gives me 
back the inputs I gave it. If I set dopos=-1, it at least attempts to 
vary the flux.

Is there something stupid I'm forgetting to do? I've definitely got this 
task to work in the past. IMSIZE has always somewhat baffled me, but I 
thought that leaving it at 0,0 would allow one to fit a point source.

I've been using the difmap modelfitter, but if I could do this in AIPS 
it would make my life so much easier. I'm trying to perform PPA 
calibration using 3C119 on many datasets and at the moment I have to 
SPLIT, FITTP, difmap, extract results from difmap logfile and then run 
CLCOR using an AIPS runfile.

That said, there doesn't seem to be any way to actually use a sane flux 
from UVFIT as input into CLCOR. It would be good if one could have FMAX 
like with JMFIT, but I suppose this is difficult given that UVFIT allows 
one to fit up to 60 components.

I just explored using OMFIT and this actually works, but can't fit to Q 
and U it seems.

Thanks,

Andy

-- 

Andy Biggs
ARC Astronomer, ALMA Regional Centre
European Southern Observatory
Karl-Schwarzschild-Straße 2
D-85748 Garching
Germany

tel. +49 89 3200 6471
fax. +49 89 3200 6898