[daip] [!7577]: AIPS - IRING

[Lynn Matthews]

Lynn Matthews updated #7577
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IRING
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           Ticket ID: 7577
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/7577
           Full Name: Lynn Matthews
               Email: lmatthew at haystack.mit.edu
             Creator: User
          Department: AIPS Data Reduction
       Staff (Owner): -- Unassigned --
                Type: Issue
              Status: Open
            Priority: Default
                 SLA: NRAO E2E
      Template Group: Default
             Created: 10 November 2015 06:02 PM
             Updated: 10 November 2015 06:02 PM
                 Due: 13 November 2015 06:02 PM (3d 0h 0m)
      Resolution Due: 19 November 2015 06:02 PM (9d 0h 0m)



I have some questions about values reported by IRING.
I find that results differ depending on whether one specifies the aperture radius in pixels versus arcseconds.

Example: I have an image with 10" pixels and I want to integrate over a circular aperture with radius 50".

For APARM 0; CPARM 0, 50, 50, 0, 2, 0  (i.e., integrating over 50" radius circle) it reports:

IRING1: Beam area  31.50 pixels, correlation correction  31.35 pixels
IRING1: Ring  Inner  Outer  Points    Average     Sigma     Cumul. Flux
IRING1:          (arcsec)    Not 0    (JY/BEAM )  (JY/BEAM ) (JY      )
IRING1:   1     0.0   50.0       69  -3.4950E-04  7.8234E-04 -7.6549E-04

But for APARM 0; CPARM 0, 5, 5, 0, 2, 1 (i.e., 5-pixel radius = 50") it reports:

IRING1: Ring  Inner  Outer  Points    Average     Sigma     Cumul. Flux
IRING1:          (pixels)    Not 0    (JY/BEAM )  (JY/BEAM ) (        )
IRING1:   1     0.0    5.0       69  -3.4950E-04  1.3972E-04 -2.4116E-02

I note also:
(1) for the "pixel" case only, the reported "Sigma" becomes smaller as the radius is increased 
(2) no units are quoted for the cumulative flux for the "pixel" case
(3) the quoted "number of points not zero" (which I take to be the number of pixels within the aperture)
is consistent with a radius of ~4.6 pixels, not 5.0 pixels, and is smaller than when one creates a circular aperture of radius 5 pixels with IMSTAT (IMSTAT reports measuring over 81 pixels).

Lynn Matthews


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