[daip] JMFIT/SAD/ds9 issue with map centered on the NCP

[Eric Greisen]

Hanno Spreeuw wrote:
> Hello, I have been running both JMFIT and SAD on a LOFAR Core Station 1 
> map centered on the NCP:
> http://staff.science.uva.nl/~hspreeuw/
> The bright source at pixel (393, 535) had a peak flux density just over 
> 20 Jy/beam.
> These are the positions that SAD and JMFIT give for this source:
> RA---SIN 06 41 37.3295 DEC--SIN 79 46 02.146
> BLC =   387.00  531.00
> TRC =   399.00  543.00
> (SAD and JMFIT agree accurately).
> However, when loading this image into ds9, there is a difference of 12h 
> in Right Ascension.
> Which is correct?
> There is a dicrepancy in the BPA reported by JMFIT and SAD:
> SAD: 111.9 +- 7 degrees.
> JMFIT: Position angle    =  11.478 +/-  8.009 degrees
> Which is correct?

I am unsure of the answers here and will take a bit of a look at the SAD 
data on PA.  I am glad to see that aips is reasonably consistent on this 
poorly defined image.  The short answer on the fitting is neither is 
correct since your source covers 1/2 the area of the Clean beam and so 
cannot exist in the image.  It is also nearly circular.

I have forwarded your query to Mark Calabretta - he may answer ds9 is 
correct since I suspect it uses his wcslib - but you guys made this 
image so you should know.

Eric Greisen