[daip] (AIPS) question about the Y2K HUGE IMCLN image

[Eric Greisen]

Samuel R Conner writes:
 > To Whom it may concern (I suspect Eric or Patrick),
 > 
 >    The Y2KHIMCLN image is a lovely X-Band image of Cygnus A, J2000 coordinates
 > and rotated 23 degrees counterclockwise.
 > 
 >    I would like to have a high resolution spectral index image of this source
 > between X and C bands --- I'm interested in what this source might look like if
 > observed at different frequencies (and it if notionally were more distant).
 > Chris Carilli has kindly provided me with a good C-band (B1950) image. REGRD
 > and OGEOM have given me excellent alignment of the two images.
 > 
 >    The reduction history of Y2KHIMCLN in its image header looks conventional and
 > I am wondering whether I can trust this image to have the right flux scale for
 > my spectral index (and, ultimately, observation simulation) purposes.
 > 
 >    Any advice?
 > 
I took these data from Perley and Carilli as well and so the original
calibration should be quite good.  I did however in the Huge case do a
multi-scale Clean which was probably not done on the C band image.
This may affect the low-brightness but significant fluxes from
extended regions.  Note that the primary beam has not been corrected
and is quite significant in the X band image.  In fact, pointing is
what limits the dynamic range since both hot spots are down about 20%
on the primary beam.

Eric Greisen