[daip] UV modelling / UVSUB

[Eric Greisen]

Hans-Rainer Kloeckner wrote:
> Dear Eric,
> 
> I hope you are fine and I also  hope you can help me, please. I'm 
> running into a problem I do not fully understand .
> 
> I try to model a visibility set for a GMRT dataset using UVSUB.
> 
> Now this is what I have done. 
> 
> 1. I have replaced all the real and imaginary values of the visibilities 
> to zero (doing all channels).
> 2. than I have add ONE point source at the phase centre to it, by using 
> UVSUB (7.33473 Jy, DFT,factor -1 ).
> 
> So far so good. Now if I have a look into the visibilities e.g. 
> amplitude versus time,  some of the  
> baselines show a rather strange amplitude behaviour always at the end of 
> the last scan (e.g. 1-29, 1-30). 
> It seems that the flux shouting up. Now the source is above 45 elevation 
> so not sure what causes this jump in amplitude.
> 
> Could that be related to some smoothing etc. ?
> 
> I have attached 2 files:
> 
> Amplitude versus time plot
> JJJ_MODEL_AMP_I.ps_pages file 
> 
> Model visibilities for antenna 1 
> JJJ.FITS
> 
> I hope you might have an idea.
> 
> cheers and thanks for hopefully considering to have a look into it.

I do not find any samples bigger than about 11 in the FITS file that you 
sent - and so no reason why the VPLOT would look as it does.  In fact 
the scatter of the vis is greater than you plot suggests in all 
baselines except the last two whioch seem the same as the previous.
Perhaps you did not send the model data?  The fluxes look like real fluxes.

Eric Greisen