[daip] [!7748]: AIPS - Wrong definition of position angle in IRING

[Luis Rodriguez]

Luis Rodriguez updated #7748
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              Status: Open (was: Closed)

Wrong definition of position angle in IRING
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           Ticket ID: 7748
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/7748
           Full Name: Luis Rodriguez
               Email: l.rodriguez at crya.unam.mx
             Creator: User
          Department: AIPS Data Reduction
       Staff (Owner): Eric Greisen
                Type: Issue
              Status: Open
            Priority: Default
      Template Group: Default
             Created: 19 December 2015 09:15 PM
             Updated: 24 December 2015 02:33 AM



Hi Eric: Thank you for looking into this.
It’s good to know that you are behind AIPS because we
keep needing your package so much. As you know well, even
for JVLA and ALMA data, we do the calibration in CASA but then
have to move to AIPS to do many things not yet available in CASA.

Here is what I did with IRING:
I produced a FITS file with an elliptical donut, that has
its major axis at PA = 0.0 degrees.The inclination is 60 degrees.
The peak value of the donut is 1.62829757E-01 Jy/beam.

You can find this image and the other FITS images mentioned here in
ftp://ftp.crya.unam.mx/pub/l.rodriguez/eric/

The elliptical donut is ELLDONUT.FITS.
I used IRING with

APARM  0  0  0 60
CPARM  0  3  0.1  0  1

But in the table (or resulting figure) I do not get the maximum for
the donut. To get the maximum I just change

aparm(3)=90

and everything seems fine. I interpret this to mean that the PA has a +-90 degrees shift.

Then I used the same elliptical donut, but with a blob located at PA=0 degrees.
This image is ELLDONUT1B1.FITS.

Then I run IRING with

APARM  0  0 0 60 10 0
CPARM  0.5 1.5 1.0 0 1
 
and loop
APARM(6)=10,20,30,40,.., 360

This gives strange values for the average intensity. Again,
if you change

aparm(3)=90

everything works fine (see attached plot ELLDONUTBFX.eps).

Finally, I use the elliptical donut but with two blobs, one at PA=0 degrees
and the other at PA=90 degrees (file ELLDONUT2B.FITS).

I use

APARM  0  0 90 60 10 0
CPARM  0.5 1.5 1.0 0 1

and loop
APARM(6)=0,10,20,30,40,.., 360

Things work OK, except that the second peak appears at APARM(6)=270
and not at APARM(6)=90 as expected if PA increases
counterclockwise (see Figure ELLDONUT2B.eps). I interpret this to mean that 
APARM(6) increases clockwise, when counterclockwise is expected.

Finally, if one uses

APARM  0  0 90 60 10 360.0
CPARM  0.5 1.5 1.0 0 1

and loops
APARM(6)=360, 350, 340, 330, …, 0

the output is the expected one for a definition of PA
with 0 to the north and increasing counterclockwise.

Please let me know if I can do something else.

Regards, Luis.



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