[daip] forwarded message from Eric Greisen

[Eric Greisen]

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From: Eric Greisen <egreisen at nrao.edu>
To: Johnny Metelsky <johnny at astro.columbia.edu>
Subject: Re: [daip] aips_gripe
Date: Wed, 25 Aug 2004 13:44:47 -0600

Johnny Metelsky writes:
 > {25-AUG-2004 15:21:36}
 > {iolanthe     UN-REGISTERED!!!!!!!}
 > {  920  31DEC03  SOL}
 > {Johnny}
 > {Columbia University, Pupin Hall}
 > {1(212)854-8927}
 > {I can't get an image with IMAGR.
 >  I get this message:
 >  IMAGR1: Field   1 Sum of gridding weights =  1.74374E+10
 >  IMAGR1: Field   1 Beam min = -487.7 MilliJy, max =    1.0      Jy
 >  IMAGR1: FITBM: SOLUTION FOR RESTORING BEAM FAILED
 >  IMAGR1: Field   1 fit FWHM =    4.710 x    4.710      arcsec, PA=   45.0
 >  IMAGR1: CLBHIS: minimum component 0.500 of current peak
 >  I'm trying to image a SNR from data in A array, 6cm.
 >  I think it could be a calibration issue.
 >  When I try to run CALIB with UVRANGE 0 25 for 3C286, I get no solutions.
 >  I haven't had this problem before, when I had an unlimited UVRANGE.
 >  I'm not sure what the problem is.
 >  Thanks
 >  Johnny
 >   }
 > {Can't properly calibrate using 3C286 in A array, 6cm even when UVRANGE 0 25.}
 > {johnny at astro.columbia.edu}
 > { }

What is failing is the attempt to fit a Gaussian to the beam.  It has
nothing to do with the values in the data nor does it have anything to
do with CALIB directly.  The UVRANGEs listed in the CookBook for
sources such as 3C286 are for their use as a calibration source and
have nothing to do with imaging them.  If you are in the A array there
may simply not be enough data on 3C286 to use it as a flux calibrator
unless you apply a source model.  We supply source models for 3C286 at
higher frequencies but not yet at 6 cm (see CALDIR verb, CALRD task).

I do not understand what you think you are doing - you are talking
about calibration and using IMAGR which is an imaging task.

The parameters shown in the IMAGR output suggest that you have only
verty few data points or that the cellsize is really wrong or
something.  Beam fitting will fail if the cell size is way wrong.

Try SETFC on these data starting with CELLSIZE=0; IMSIZE=0.  How many
samples are going in to the image?  Your message does not include
enough info to comment.

Eric Greisen
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