[daip] VTESS

[Eric Greisen]

rlaing at eso.org writes:
 > Dear Eric et al.
 > 
 > We are comparing some new results with previously published images, and this
 > raised a question about VTESS, specifically the change which was reported in
 > AIPSletter XXIII no 2 (the 2003 Dec 31 release). There, it is reported:
 > 
 > VTESS and the other tessellation tasks were changed to use the standard primary
 > beam routines. The default is now to apply a primary beam correction.
 > 
 > This implies that the previous default was NOT to apply a correction even for
 > VLA data. Looking back at the history files for some of our published images
 > suggests that this was indeed the case, e.g.:
 > 
 >   8510  VTESS  PBCENX( 1), PBCENY( 1) = 1024.41,2049.21 /Pixels
 >   8511  VTESS  NOISE( 1) =   6.300E-06/ Jy/beam
 >   8512  VTESS  /Field  1 : Interferometer  data
 >   8513  VTESS  /Field  1 : No primary beam correction
 > 
 > My questions are:
 > 
 > (1) Is this correct and

         Yes

 > 
 > (2) Does FLUX apply after application of the primary beam correction? The HELP
 >     calls it the zero-spacing flux density, which is ambiguous in this contect,
 >     I think. 

         I do not know whether it is computing the flux internally
before or after a beam correction.  I do know that the FLUX input
adverb works very badly if one attempts to give it an honest zero
spacing flux.  VTESS works much better with FLUX = - real_flux/10
or so which makes the distinction you are asking about moot.

Eric Greisen