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

[Robert H Gray]

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): Eric Greisen
                Type: Issue
              Status: Open
            Priority: Default
                 SLA: NRAO E2E
      Template Group: Default
             Created: 03 April 2015 02:54 PM
             Updated: 06 April 2015 12:27 AM
      Resolution Due: 13 April 2015 02:54 PM (7d 14h 26m)



Hi!

Thanks for looking at the apparently spurious SAD source example I sent.  The most recent example of an apparently spurious ‘source’ is below, where SAD reported 1114 mJy in channel 3216 at Xpixel 929, Ypixel 1013, but ISPEC finds nothing over 100 mJy (and mostly just noise) at that position.  

If you would be willing to take a look, the data is indicated below and you are welcome to do anything you deem apppropriate:
Account: nm-7005  pwd: g0g0g0g0 (zeros)
Node: nmpost050 
UV file slot 45, source ‘M31 Center  (no closing quote)
Image file (8192 channels) slot 328, source ‘M31 Center (no closing quote)

Below is what I got from SAD with NGAUSS 200.  The position is very close to the edge of the image, and I see that often but not always in these cases.  

Thanks for any suggestions you can provide!  I’ll be chugging through 350 GB of data with AIPS until April 24, when my account expires.  Hope you have a good vacation!

Best wishes,

Bob Gray 


SAD excerpt:
      nmpost05   SAD  (31DEC15)    1111               05-APR-2015   11:04:42               Page    1
M31-HI-CTR-C.ICL001.      2     Disk  1     Plane 3216     User    1111
 
 
Window BLC   10   103216   1  1  1  1 TRC 1014 10143216   1  1  1  1
Sources found down to  0.131065 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  0.03238
Reference Center: 00 42 44.0000  41 16 09.001
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 *    1.114(  0.032)    0.095(  0.014) 00 41 29.7873  41 32 47.224(   0.079   0.014)    6.442   1.077  86.9(  0.187  0.031   0)
    2    166.336( 32.375)   92.426( 38.581) 00 42 46.5299  41 13 25.075(   1.043   0.480)   13.478   3.344  68.7(  2.623  0.651   4)

...
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    6.44    1.08   86.9       ---     ---     ---  U     ---     ---     ---      ---     ---     ---   929.1 1013.5   0.08281
    2   13.48    3.34   68.7       ---     ---     ---  U     ---     ---     ---      6.50    0.00   96.1   497.7  430.9   0.09048

Procedure that’s run on image cubes, typically invoked like “SRCS(4, 1, 8192, 1024)” for a 4-sigma ‘source’ threshold, processing channels 1 to 8192, for a 1024-pixel image:

AIPS 1:  1 PROC SRCS( SIGMAMIN, CH1, CH2, IMAGESIZ )
AIPS 1:  2 SCALAR CHAN, CH1, CH2, SIGMAMIN, IMAGESIZ, IMAGEBDR
AIPS 1:  3 SCALAR CPARM1, CPARM2, CPARM3, CPARM4, CPARM5
AIPS 1:  4 INEXT 'MF'; INVERS -1; EXTDEST;
AIPS 1:  5 IMAGEBDR = 10
AIPS 1:  6 IF IMAGESIZ = 512 THEN
AIPS 1:  7 NGAUSS=100
AIPS 1:  8 END
AIPS 1:  9 IF IMAGESIZ =1024 THEN
AIPS 1: 10 NGAUSS = 200
AIPS 1: 11 END
AIPS 1: 12 IF IMAGESIZ =2048 THEN
AIPS 1: 13 NGAUSS = 400
AIPS 1: 14 END
AIPS 1: 15 FOR CHAN = CH1 TO CH2
AIPS 1: 16 BLC IMAGEBDR IMAGEBDR CHAN
AIPS 1: 17 TRC IMAGESIZ-IMAGEBDR IMAGESIZ-IMAGEBDR CHAN
AIPS 1: 18 GO IMSTAT
AIPS 1: 19 TASK 'SAD'
AIPS 1: 20 CPARM1 = PIXSTD * SIGMAMIN*3
AIPS 1: 21 CPARM2 = PIXSTD * SIGMAMIN*2
AIPS 1: 22 CPARM3 = PIXSTD * SIGMAMIN*1.5
AIPS 1: 23 CPARM4 = PIXSTD * SIGMAMIN*1.25
AIPS 1: 24 CPARM5 = PIXSTD * SIGMAMIN*1
AIPS 1: 25 CPARM = CPARM1, CPARM2, CPARM3, CPARM4, CPARM5, 0
AIPS 1: 26 GO SAD
AIPS 1: 27 WAIT SAD
AIPS 1: 28 END
AIPS 1: 29 FINISH


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