[daip] my message to John about his CALIB questions

Sat Jul 29 19:09:33 EDT 2000

Date: Sat, 29 Jul 2000 17:05:38 -0600 (MDT)
From: "[Leonia Kogan]" <lkogan>
Message-Id: <200007292305.RAA09074 at bonito.aoc.nrao.edu>
To: jmonnier at cfa.harvard.edu
Subject: [daip] ANTEN under CALIB
Cc: daip&nrao.edu

John,

You wrote:

> I have an AIPS question.  I was using calib on 3C286 to do (primary) flux
>calibration.  The array was between A and B.  The "Accurate Flux Density
>Bootstrapping" memo on the web indicates that for A (B) array, one should
>use UVRANGE 0,150 and use 3 (all) antennas on each arm.  

>So this leads me to 2 questions.

>1) Why does it matter how many antennas I specify on each arm? If the
>minimum # of antennas is 4 (aparm(0) 4) and uvrange is set, it would
>_seem_ to have little impact, saving minimal computer time. 

You probably have the observation with lambda=2cm.
Yes, the memo says that 3C286 can be considered as a point source if 
the baseline <150 klambda = 3km (lambda=2cm).

The memo says that number of inner antennas (per arm) is 3 for A configuration 
and All for any other configuration. 
That means that only 3 inner antennas create baselines less than 3km.
So this information should be considered as a reminder that even if you include 
all antennas with UVRANGE = 0-150 you'll stil find the solution only 
for 9 antennas (the three for each arm).

I have checked the A configuration and found that the number 3 is almoust 
right although the number 4 or 5 would be better.

APARM(1)=4 controls something different. The number of antennas participating 
at the solution should be >APARM(4).

You wrote:

>2) Under this theory of how CALIB works (and because the array during my
>observation was between A/B), I tried running calib using uvrange 0,150
>and anten 0 (that is, ALL antennas).. Much to my surprise, I got 0 good
>solutions! ("CALIB2: ERROR: NO VALID SOLUTIONS FOUND").

>HOWEVER, when I change my antenna command to 
>anten 2,4,18,22,25,24,21,17,6,7,28,19,14   (which includes basically the
>inner 4 antennas of each arm), then RERUN it -- with uvrange 0,150 --
>then it finds lots of good solutions..

I do not understand that. I'd not expect any difference because UVRANGE 
should select almoust the same baselines.

Send us please the whole list of the input parameters you used at the both 
runs of CALIB

Leonia

----- Begin Included Message -----

>From owner-daip at kochab.cv.nrao.edu Fri Jul 28 16:53 MDT 2000
X-Authentication-Warning: tacks.harvard.edu: jmonnier owned process doing -bs
Date: Fri, 28 Jul 2000 15:46:12 -0400 (EDT)
From: John David Monnier <jmonnier at cfa.harvard.edu>
X-Sender: jmonnier at tacks.harvard.edu
To: aipsmail at cv3.cv.nrao.edu
cc: John David Monnier <jmonnier at cfa.harvard.edu>
Subject: [daip] ANTEN under CALIB
MIME-Version: 1.0
Sender: owner-daip at kochab.cv.nrao.edu
Precedence: bulk
X-Lines: 39
Status: RO

Hello,

 I have an AIPS question.  I was using calib on 3C286 to do (primary) flux
calibration.  The array was between A and B.  The "Accurate Flux Density
Bootstrapping" memo on the web indicates that for A (B) array, one should
use UVRANGE 0,150 and use 3 (all) antennas on each arm.  

So this leads me to 2 questions.

1) Why does it matter how many antennas I specify on each arm? If the
minimum # of antennas is 4 (aparm(0) 4) and uvrange is set, it would
_seem_ to have little impact, saving minimal computer time. 

2) Under this theory of how CALIB works (and because the array during my
observation was between A/B), I tried running calib using uvrange 0,150
and anten 0 (that is, ALL antennas).. Much to my surprise, I got 0 good
solutions! ("CALIB2: ERROR: NO VALID SOLUTIONS FOUND").

HOWEVER, when I change my antenna command to 
anten 2,4,18,22,25,24,21,17,6,7,28,19,14   (which includes basically the
inner 4 antennas of each arm), then RERUN it -- with uvrange 0,150 --
then it finds lots of good solutions..
"CALIB2: Found           28 good solutions
CALIB2: Failed on        2 solutions
CALIB2:                  2 solutions had insufficient data"

I don't understand why it couldn't find this solutions when Anten = 0.
Does ANTEN OVER-RIDE the uvrange command? or is there some other
explanation?

I tried to find my answer looking at the EXPLAIN and HELP pages on CALIB,
but not luck.. I would appreciate any enlightenment...

Regards,
John Monnier

----- End Included Message -----