[daip] [!6413]: aips - SAD Question 2015-04-03

Fri Apr 3 10:54:20 EDT 2015

Robert H Gray updated #6413
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SAD Question 2015-04-03
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           Ticket ID: 6413
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/6413
           Full Name: Robert H Gray
               Email: roberthansengray at gmail.com
             Creator: User
          Department: AIPS Data Processing
       Staff (Owner): -- Unassigned --
                Type: Issue
              Status: Open
            Priority: Default
                 SLA: NRAO E2E
      Template Group: Default
             Created: 03 April 2015 02:54 PM
             Updated: 03 April 2015 02:54 PM
                 Due: 07 April 2015 02:54 PM (4d 0h 0m)
      Resolution Due: 13 April 2015 02:54 PM (10d 0h 0m)

Hi Eric,

I’ve had repeated problems with SAD reporting strong sources in clean 8192-channel image files, which don’t appear to really be there when I investigate the pixel positions (with ISPEC), or visually inspect the image for that channel (with FitsView).   Any idea of what might be going on?  I’m including some results below as an example of that I’m seeing.

Thanks for any thoughts you have on this!

Bob Gray

SAD item #1 below appears to be a 49 sigma Peak in channel 3920, assuming these conversions are right: “*    1.535” means 1535 mJy, and “RMS  0.03132” means 31.32 mJy (or alternatively, assuming both values are in Jy).   

But, ISPEC shows no big feature in the spectrum at that pixel position in the clean 8192-channel image file (pixels 339.5  332.7), and IMEAN reports 376 mJy as the maximum value anywhere in the file (IMEAN1: Maximum= 3.7606E-01 at  511  455 8169    1).  

      nmpost04   SAD  (31DEC15)    1111               28-MAR-2015   18:14:20               Page    1
M33-HI-CTR-C.ICL001.      2     Disk  1     Plane 3920     User    1111

Window BLC   10   103920   1  1  1  1 TRC  502  5023920   1  1  1  1
Sources found down to  0.092844 in JY/BEAM
Reject components peak <  0.00000 in JY/BEAM
Reject components flux <  0.00000
Reject components outside window >   0.0 cells
Reject components outside image >    0.0 cells
Reject residual flux >   0.00000 with gain 0.100
Fluxes expressed in units of milliJY/BEAM
NOTE: Fluxes marked by * have been divided by 1000.
Errors determined by theory from RMS  0.03132
Reference Center: 01 33 51.0000  30 39 37.000
All source widths, width errors, and both coordinate errors are in arc seconds
NO corrections for bandwidth smearing have been made
Source peaks and fluxes NOT corrected for primary beam

    #      Peak    Dpeak     Flux    Dflux       RA---SIN      DEC--SIN    Dx      Dy        Maj     Min     PA    Dmaj   Dmin  Dpa
    1 *    1.535(  0.031)    0.137(  0.014) 01 32 59.1081  30 35 00.038(   0.020   0.079)    9.102   2.267 178.3(  0.186  0.046   0)
    2    145.125( 31.242)  164.603( 58.905) 01 33 20.7367  30 45 30.150(   1.372   1.888)   22.784  11.528 150.7(  4.905  2.482  12)
...

Component widths & PA: fit, deconvolved at fit and  1.30 sigma low and high from fit
   #  MAJ-fit MIN-fit PA-fit    MAJ-dec MIN-dec PA-dec  R  MAJ-low MIN-low PA-low    MAJ-hi  MIN-hi  PA-hi    Xpix   Ypix   MAXresid

    1    9.10    2.27  178.3       ---     ---     ---  U     ---     ---     ---      ---     ---     ---   399.5  197.8   0.07447
    2   22.78   11.53  150.7      14.74    0.00  154.0  U     ---     ---     ---     23.84    6.34  178.8   339.5  332.7   0.08415

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