[daip] FLATN Help

[Eric Greisen]

Julie Grant wrote:
> Hi Eric,
> 
> Thank you for your suggestion.  I have looked through the image headers 
> and I notice that the "Observed RA" is incorrect for the pointings with 
> the weird behaviour.  The actual RA is the value indicated by RA---SIN.  
> The change in the two positions seems to occur after amplitude 
> self-calibration for these pointings.  Any ideas as to why this would 
> happen or how to fix this? 
> 
> AIPS 1: Image=AG768_P1  (MA)         Filename=AG768       .FLATN .   3
> AIPS 1: Telescope=VLA                Receiver=VLA
> AIPS 1: Observer=AG768               User #= 2619
> AIPS 1: Observ. date=20-OCT-2007     Map date=13-MAY-2010
> AIPS 1: Pixel type: FLOATING         Magic value blanking
> AIPS 1: Minimum=-1.24091003E-03      Maximum= 1.34480908E-03 JY/BEAM
> AIPS 1: ----------------------------------------------------------------
> AIPS 1: Type    Pixels   Coord value     at Pixel     Coord incr   Rotat
> AIPS 1: RA---SIN  4096    16 09 24.400    2048.00         -1.000    0.00
> AIPS 1: DEC--SIN  4096    54 02 48.000    2049.00          1.000    0.00
> AIPS 1: FREQ         1   1.4649000E+09       1.00  2.1875000E+07    0.00
> AIPS 1: STOKES       1   1.0000000E+00       1.00  1.0000000E+00    0.00
> AIPS 1: ----------------------------------------------------------------
> AIPS 1: Coordinate equinox 2000.00
> AIPS 1: Map type=NORMAL              Number of iterations=    9193
> AIPS 1: Conv size=   5.02 X   3.82   Position angle=  82.39
> AIPS 1: Observed RA   16 15 37.600    DEC  53 46 46.00

Fixing it is easy - although I am curious about exactly when the error 
arose.

for inse=1:80; keyw='crval1'; geth; keyw='obsra'; puth; end
for inse=1:80; keyw='crval2'; geth; keyw='obsdec'; puth; end

should fix it.  But can you tell when the bad values got in OBSRA and 
where they may have come from?  The bad value looks like it is a real 
value just not the right one.  Did you use a model file with some other 
pointing in the self-cal or ???

Cheers,

Eric Greisen