[daip] AIPS Query

[dbgob at brandeis.edu]

Hello,

After this conversation with Eric yesterday I realized I missed the  
appendix on Line mode, which was most helpful. I have 2 more questions  
which I hope for good answers to.

1.) I tried using CLIP and CLIPM. CLIP does not let me select a source  
and seems to work on all sources, creating a CLIP file, but seems to  
not have flagged data. When I used CLIPM I gave it parameters based on  
uncalibrated data I wanted to flag but no matter what inputs I give it  
(only gave it min/max for parallel/cross) it seems to flag everything.  
Ideas?

2.) Recently we have started to work with BLCAL in the office. This  
works great for a strong source like 3C48 and so I wanted to take it  
to data sets with just pointy phase calibrators. I choose a set I was  
working on recently which had data washed out by symmetry noise from  
the array. I calibrated my data, read it out of AIPS, cleaned and  
selfcaled the phase calibrator in Difmap, then brought the fits file  
back into AIPS, and used it as the model for BLCAL on the phase  
calibrator. The manual says I need at least 100:1 to do this and by my  
estimates this source has 3000:1 and should work fine. Splitting off  
the primary source using my new BL table I was able to get rid of the  
noise that was pestering me before, but I am troubled that the UV plot  
looks very distorted. Have I done something wrong? Is my source  
fidelity not good enough? Improper use of the task?

Thanks much.

~Doug

----- Forwarded message from egreisen at nrao.edu -----
     Date: Mon, 8 Oct 2007 13:46:18 -0600
     From: Eric Greisen <egreisen at nrao.edu>
Reply-To: Eric Greisen <egreisen at nrao.edu>
  Subject: Re: AIPS Query
       To: dbgob at brandeis.edu
       Cc: daip at aoc.nrao.edu

dbgob at brandeis.edu writes:
  > Eric,

     Please use daip at nrao.edu for quieries - I do go on vacation
sometimes
  >
  > I just pulled in some archival data from the NRAO and it was done in
  > Line Mode. I did a quick perusal of the AIPS manual but have not found
  > a good walk through on how to work with data with the VLA in this
  > mode. Do you have any good suggestions? Chapter 8 discusses some of
  > this as well as 4.7. I have also tried to just run with the normal
  > calibration laid out in chapter 4 and then pushing to Difmap but run
  > into some interesting problems. Thoughts?

      There is quite a bit about spectral-line reduction including a
whole appendix.  If these are pseudo-continuum data with multiple
channels only to avoid bandwidth smearing, then life is rather easy.
One still calibrates with CALIB either with a channel-0 data set of
with the average of channels directly specified in CALIB.  A bandpass
cal is a good thing even in this mode.  difmap is easier in some ways
to use but IMAGR offers a great deal more capability.


  > Also, when using task 'uvflg' why am I not allowed to flag data by
  > using aparm? For example, I will choose a source and then specify
  > aparm 100 200 0 to say to remove points lower than 100 and higher than
  > 200. I continually receive:
  >
  > UVFLG1: Task UVFLG  (release of 31DEC07) begins
  > UVFLG1: NO AMPL. OR WGT. CLIPPING WITH FLAG TABLES
  > UVFLG1: NOTE THAT MULTI-SOURCE FILES MUST USE FLAG TABLES
  > UVFLG1: Purports to die of UNNATURAL causes
  > UVFLG1: galaxy       31DEC07 TST: Cpu=       0.0  Real=       0
  > AIPS 1: Resumes
  >
  >
  > Thoughts?

Yes - use the task designed to do this - CLIP is you have the latest
version of AIPS or CLIPM with an older version (including older
31DEC07).

UVFLG is really mostly for single-source files in some of its off-beat
modes.

Eric Greisen


----- End forwarded message -----