[daip] uv coordinates calculation in AIPS

[Eric Greisen]

On 09/18/2017 01:57 AM, Feng Gao wrote:
> Dear Eric,
> 
> Below you can see the header information. As for UVPLT, the parameters I 
> used are: TIMERANGE= 0 4 58 39 0 4 58 41; ANTENNA 3 0;BASELINE 8 0;BCHAN 
> 1;ECHAN 1; DOCALIB -1; APARM 0;BPARM 6 7 1 274305.760 274305.810, 
> 5374.7490 5374.7510 0;
> 
> The frequency difference between the 1st channel and the reference 
> frequency is 4MHz, which I think will cause a much bigger difference. 
> BTW, this data has been run with CVEL before, could this be the reason?
> 
> Thank you.
> 
> Feng
> 
> 
> AIPS 1: Image=J0437+24  (UV)         Filename=blu-V       .av80  .   1
> AIPS 1: Telescope=VLBA               Receiver=VLBA
> AIPS 1: Observer=BB321V0             User #=  100
> AIPS 1: Observ. date=02-DEC-2013     Map date=31-AUG-2017
> AIPS 1: # visibilities    195593     Sort order  TB
> AIPS 1: Rand axes: UU-L-SIN  VV-L-SIN  WW-L-SIN  TIME1  SUBARRAY
> AIPS 1:            INTTIM  GATEID  CORR-ID  ANTENNA1  ANTENNA2  WEIGHT
> AIPS 1:            SCALE
> AIPS 1: ----------------------------------------------------------------
> AIPS 1: Type    Pixels   Coord value     at Pixel     Coord incr   Rotat
> AIPS 1: COMPLEX      1   1.0000000E+00       1.00  1.0000000E+00    0.00
> AIPS 1: STOKES       1   1.0000000E+00       1.00  1.0000000E+00    0.00
> AIPS 1: FREQ         2   2.1900000E+10       0.50  8.0000000E+06    0.00
> AIPS 1: IF           1   1.0000000E+00       1.00  1.0000000E+00    0.00
> AIPS 1: RA           1    04 37 03.684       1.00       3600.000    0.00
> AIPS 1: DEC          1    24 56 06.837       1.00       3600.000    0.00
> AIPS 1: ----------------------------------------------------------------
> AIPS 1: Coordinate equinox 2000.00
> AIPS 1: Rest freq  22235.080         Vel type: OPTICAL wrt LSR
> AIPS 1: Alt ref. value  4.58694E+06  wrt pixel    0.50
> AIPS 1: Maximum version number of extension files of type NX is   1
> AIPS 1: Maximum version number of extension files of type HI is   1
> AIPS 1: Maximum version number of extension files of type FO is   1
> AIPS 1: Maximum version number of extension files of type FQ is   1
> AIPS 1: Maximum version number of extension files of type AN is   1
> AIPS 1: Maximum version number of extension files of type WX is   1
> AIPS 1: Keyword = 'OLDRFQ  '  value =  2.18120000D+10
> AIPS 1: Keyword = 'CORRELAT'  value = 'DIFX    '
> 

Channel 1 is 4 MHz away from the reference pixel at 21900 MHz.  This 
will change the uv values by about 1 part in 5000.  This would be about 
the difference seen.  NOTE that the center of the spectral channel is at 
1.0 while the reference pixel is at the lower edge of the channel.

Eric Greisen