[daip] KNTR

[Robert Laing]

On Mon, 27 Nov 2006, Eric Greisen wrote:

> I think you sent daip a message about KNTR.  The MailMan system is
> messing things up, causing approved messages to disappear in some way
> or other.  Can you resend the message to me directly?
>
> Sorry,
>

Dear Eric

I was wondering why daip had refused to post my message quoting "no 
reason".

Here it is:

Dear Eric et al.

I think that there is an inconsistency between the polarization vector
information printed out by KNTR and what is actually plotted for the case 
in
which the pol line length for a pixel is given

The two attached plots are for KNTR with the same set of input images for 
ltype
= 3 and 4. The pixel size is 0.05 arcsec:

The two attached plots are for KNTR with the same set of input images for 
ltype
= 3 and 4. The pixel size is 0.05 arcsec:

AIPS 1: Image=SS433     (MA)         Filename=SS433 SC7   .I 0.4 .   1
AIPS 1: Telescope=VLA                Receiver=VLA
AIPS 1: Observer=AF403               User #=    5
AIPS 1: Observ. date=11-JUL-2003     Map date=17-NOV-2006
AIPS 1: Minimum=-7.57716261E-05      Maximum= 3.25772434E-01 JY/BEAM
AIPS 1: ----------------------------------------------------------------
AIPS 1: Type    Pixels   Coord value     at Pixel     Coord incr   Rotat
AIPS 1: RA---SIN  1024    19 11 49.563     512.00      -0.050000    0.00
AIPS 1: DEC--SIN  1024    04 58 57.783     513.00       0.050000    0.00
AIPS 1: FREQ         1   4.8601000E+09       1.00  1.0000000E+08    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=    3459
AIPS 1: Conv size= 0.40000 X 0.40000   Position angle=   0.00
AIPS 1: Observed RA   19 11 49.566    DEC  04 58 57.84
AIPS 1: Phase shifted in X     -0.051  in Y     -0.057
AIPS 1: Rest freq      0.000         Vel type: OPTICAL wrt YOU
AIPS 1: Alt ref. value  0.00000E+00  wrt pixel    1.00
AIPS 1: Maximum version number of extension files of type CC 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 PL is   6
AIPS 1: Keyword = 'WTNOISE '  value =  1.206694E+00
AIPS 1: Keyword = 'CCFLUX  '  value =  5.098795E-01
AIPS 1: Keyword = 'CCTOTAL '  value =  5.098795E-01
AIPS 1: Keyword = 'PARANGLE'  value =  7.517672E+00
AIPS 1: Keyword = 'ZENANGLE'  value =  2.937325E+01

and factor = 10.

ltype = 3 gives 1 arcsec = 1 Jy/beam (actually a ratio in this case)
         4       1 pixel  = 0.1 Jy/beam, or
                 1 arcsec = 2 Jy/beam


I believe that the scaling from arcsec to vector length for ltype = 3 is 
correct
(there are no vectors with ratio > 0.9 in the ratio image), although I 
would
have expected factor = 10 to give 1 pixel = 0.1 Jy/beam from the
documentation. pcntr gives the scaling in arcsec for both ltypes, 
consistent
with ltype = 3 for kntr.

In the code for kntr (and similarly for pcntr), there is the segment:

C                                       polarization
          IF (PI.GT.0) THEN
             CALL GPOS (X0, Y0, IWBUFF, IRET)
             IF (IRET.NE.0) GO TO 980
             CALL H2CHR (8, 1, PCATH(KHBUN,PI), CHTMP)
             VECTOR = 1.0 / FACTOR
             WRITE (SPRTXT(1),1050) VECTOR, CHTMP
C                                       Arc seconds instead
             IF ((AXTYP(LOCNUM).EQ.1) .AND. (PCATR(KRCIC,PI).NE.0.0)
      *         .AND. (PCATR(KRCIC+1,PI).NE.0.0)) THEN
                TEMP = MAX (ABS(PCATR(KRCIC,PI)), ABS(PCATR(KRCIC+1,PI)))
     *            * 3600.0
                VECTOR = VECTOR / (2.0 * TEMP)
                IF (TEMP.GT.0.01) THEN
                   WRITE (SPRTXT,1051) VECTOR, CHTMP
                ELSE
                   VECTOR = VECTOR / 1000.0
                   WRITE (SPRTXT,1052) VECTOR, CHTMP
                   END IF
                END IF
             INCHAR = ITRIM (SPRTXT(1))
             CALL GCHAR (INCHAR, IANGL, DCX, DCY, SPRTXT(1), IWBUFF,
      *         IRET)


I wonder whether the factor of 2 in

                VECTOR = VECTOR / (2.0 * TEMP)


is responsible for the difference?

Regards

Robert
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