[daip] SETJY

[Andy Biggs]

Hi Eric. Here is the IMHEADER:

AIPS 2: Image=MULTI     (UV)         Filename=EGS_N1_NEW  .UVDATA.   1
AIPS 2: Telescope=GMRT               Receiver=GMRT
AIPS 2: Observer=ANDY BIG            User #= 4000
AIPS 2: Observ. date=24-JAN-2008     Map date=05-OCT-2011
AIPS 2: # visibilities   3044130     Sort order  TB
AIPS 2: Rand axes: UU-L-SIN  VV-L-SIN  WW-L-SIN  BASELINE  TIME1
AIPS 2:            SOURCE  FREQSEL
AIPS 2: ----------------------------------------------------------------
AIPS 2: Type    Pixels   Coord value     at Pixel     Coord incr   Rotat
AIPS 2: COMPLEX      3   1.0000000E+00       1.00  1.0000000E+00    0.00
AIPS 2: STOKES       2  -1.0000000E+00       1.00 -1.0000000E+00    0.00
AIPS 2: FREQ       128   6.1000000E+08       0.50 -1.2500000E+05    0.00
AIPS 2: IF           2   1.0000000E+00       1.00  1.0000000E+00    0.00
AIPS 2: RA           1    00 00 00.000       1.00       3600.000    0.00
AIPS 2: DEC          1    00 00 00.000       1.00       3600.000    0.00
AIPS 2: ----------------------------------------------------------------
AIPS 2: Coordinate equinox 2000.00
AIPS 2: Maximum version number of extension files of type HI is   1
AIPS 2: Maximum version number of extension files of type AN is   1
AIPS 2: Maximum version number of extension files of type FQ is   1
AIPS 2: Maximum version number of extension files of type SU is   1
AIPS 2: Maximum version number of extension files of type FG is   4
AIPS 2: Maximum version number of extension files of type CL is   2
AIPS 2: Maximum version number of extension files of type NX is   1
AIPS 2: Maximum version number of extension files of type BP is   1
AIPS 2: Maximum version number of extension files of type PL is1100
AIPS 2: Maximum version number of extension files of type SN is   1

And here is the PRTAB output:

PRTAB2: Task PRTAB  (release of 31DEC11) begins
 pc016987  PRTAB(31DEC11)   4000     12-OCT-2011  20:17:26    Page    1
EGS_N1_NEW  .UVDATA.   1  Disk= 2    FQ Table version   1
Title: AIPS FQ
Created by      TBIN  on 12-OCT-2011 14:47:51
Last written by TBIN  on 12-OCT-2011 14:47:51
Ncol 5  Nrow 1    Sort cols:
    Table has     1 keyword-value pairs:
   NO_IF    =            2
   Table format incompatable with FITS ASCII tables
 
COL. NO.         1              2                3              4              5
     ROW      FRQSEL      IF FREQ           CH WIDTH        TOTAL BAN      SIDEBAND
  NUMBER                  Hz                Hz              Hz
       1         1        0.000000D+00       1.250E+05      1.600E+07          1
       1                  0.000000D+00      -1.250E+05      1.600E+07          1
PRTAB2: Appears to have ended successfully
PRTAB2: pc016987     31DEC11 TST: Cpu=       0.0  Real=       0

I've always slightly worried about the way that I'm reducing these GMRT data. You probably know that the GMRT writes out the IFs into separate files (.lta and .ltb). These can subsequently be merged into a single file using a command line program (ltamerge) and I prefer to do this as it keeps everything together. Some people though recommend that you process them separately, although not for this reason.

Also, the recommended way of flux calibrating GMRT data is to run CALIB on a single channel. If this is done on the 128-channel multi-source file (using ICHANSEL) then I wonder if things will work properly as CALIB and GETJY would need to use the flux density at the particular frequency being used and I doubt if that happens. However, the simple solution would be simply to SPLAT that channel into a separate file. Speaking of which, I just split each IF into a separate file and the same flux density was reported for each when I ran SETJY.

Andy

On 12 Oct 2011, at 16:53, Eric Greisen wrote:

> Can you send me the IMHEADER and a clearer copy of the FQ table PRTAB. I cannot believe that these data are correctly described.  SETJY could I suppose worry about the center frequency of an IF rather than the frequency at the reference pixel which is what I suspect it uses.
> 
> I will look into this.
> 
> Eric Greisen