[daip] forwarded w/o attachments

[Eric Greisen]

From: Preeti Kharb <pxkpcia at cis.rit.edu>
To: Eric Greisen <egreisen at nrao.edu>
Subject: Radio imaging problem
Date: Tue, 29 Nov 2005 10:52:57 -0500 (EST)

Hullo Eric,

I was wondering if you could help me with an AIPS-related problem ?

I am basically trying to combine VLA L-band data from different arrays
into one dataset and then making 1 final image of the same. This is
usually not a problem and I have used DBCON for this purpose.

However, for some datasets where there is a slight difference in the
central frequencies of the 2 datasets being combined (for eg., 1504.9 &
1425.0 MHz), I get 2 slightly shifted images in the final map. I get this
even after I choose DOPOS(1,1)= 1 & DOPOS(2,1)= -1 in DBCON.

I have enclosed 4 images with this mail. These are maps of 3C470 with the
A-array, B-array and then combined A+B array data. You can see in the
combined image (3C470ABL.ICL001.23) that the northern hotspot has 2
shifted images. The positions of the 2 datasets being combined match
perfectly. So the problem has to do with frequency alone.

I dont think it is a bandwidth smearing problem. I attempted to do
bandwidth synthesis, and that didnt improve things.

I also tried UVFIX to make the central frequencies the same for both the
datasets being combined (just as an exercise - I am sure it is not the
best thing to do). The 4th image (3C470ABL.ICL001.24) enclosed with this
email is the output from that attempt.

Can you think of any obvious problem with my approach ?

Hoping to hear from you

Thanks !

Preeti