[daip] AIPS. VTESS: mem mapping

[Eric Greisen]

On 7/29/2020 2:48 PM, Alexey Nikonov via Daip wrote:
> Hello,
>
> I`m writing to ask help in mem VTESS mapping. Can I?
>
> I`ve self-calibrated and restored image of an extended source 1308+326 
> with CLEAN in DIFMAP. So I know the estimate of noise level from this map.
>
> Loaded to AIPS calibrated UV-file just to do VTESS mem deconvolution. 
> Done IMAGR with 0 iterations to obtain beam and dirty map.
> As I know in CLEAN image results I`ve pick the same cellsize as in 
> DIFMAP and twice image size compared to source area, that can be seen 
> in CLEAN image.
>
> After that VTESS couldn`t find a solution. Instead of extended 
> structure I can see only one Gaussian peak and noise.
>
> I couldn`t find many recommendation to VTESS. Documentation says that 
> noise is crucial parameter, so I played with it, but nothing changed. 
> Also played with FLUX parameter and number of iterations.
>
> Can you please help :)
>
> -- 
> Sincerely yours,
> Aleksei Nikonov
> AstroSpace Center,
> Lebedev Physical Institute,
> Moscow, Russia
>
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VTESS is a peculiar task whose author was never even in the AIPS group.  
It can do nice things but with strange inputs at times. The Y2K test we 
run on a Cygnus A data set sets NOISE=.0024 with is close to the noise 
in the result.  But FLUX is set to -18 (note minus sign!) when the 
actual flux will turn out to be ~200 Jy.  In other words odd inputs are 
needed to kick the task into converging on a good answer.  (It did not 
work when I set FLUX=200 despite the excellent quality of the data.)

Good luck

Eric Greisen




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