[daip] [Fwd: About DBCON]

[Eric Greisen]

Jim Ulvestad writes:

    Please direct queries about AIPS to daip at nrao.edu.  Someone
currently active in the group will attempt to help you.

 > 
 > ---------------------------- Original Message ----------------------------
 > Subject: About DBCON
 > From:    "Miguel Angel Perez-Torres" <torres at iaa.es>
 > Date:    Mon, March 19, 2007 5:34 am
 > To:      "Jim Ulvestad" <julvesta at aoc.nrao.edu>
 > Cc:      "Antxon Alberdi Odriozola" <antxon at iaa.es>
 > --------------------------------------------------------------------------
 > 
 > Dear Jim,
 > 
 > We write you as documentor of program DBCON within AIPS.
 > 
 > We are trying to combine several UV datasets from consecutive VLA-A
 > configurations
 > on NGC 7469, using DBCON.
 > The problem is that the same antenna has different numbers, and even
 > slightly different coordinates, in the antenna files for each epoch.
 > We have tried with different options of adverb DOARRAY within DBCON,
 > without success.

     In the case that you are describing, you should be combining
fully-calibrated, single source files with the NGC 7469 data.  The
correct value for DOARRAY is 0, so that each observation will appear
as a separate subarray in the DBCONed data set.  This completely
solves the fact that the antenna files are different for each epoch.

Do be careful that all data sets before combination are brought to the
same equinox (J2000 presumably).  UVFIX will help with that.

 > 
 > The uv spacings are correct (UVPLT shows that the uv-coverage
 > corresponds to the
 > addition of the files), but not the amplitudes. UVPLT shows
 > amplitudes of hundreds of kiloJansky for a number of baselines, while
 > for the rest, we get the correct flux density
 > (a few tens of mJy).
 > 

However, no setting of DOARRAY should have any affect on the fluxes.
DBCON does not change fluxes at all - if kiloJy come out then kiloJy
went in almost certainly.  I suppose bad things could happen if you
combined multi-source, uncalibrated data with calibration tables and
then attempted to apply the tables to the non-corresponding data,  I
will need to know much more about the data sets that go into the task
and that which comes out to be able to provide you with better
assistance.

Eric Greisen