[daip] [!6921]: AIPS - VLBA continuum data reduction----three questions

[Amy Mioduszewski]

Amy Mioduszewski updated #6921
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                 Due: - Cleared - (was: 26 August 2015 12:34 AM)

VLBA continuum data reduction----three questions
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           Ticket ID: 6921
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/6921



Hi Hui,

If those baselines were there when you do not apply the CL table with the FRING solutions, but disappear once you apply that CL table, then the reason they aren't there is because of the FRING solutions.  One way to see this is to plot the SNR  from FRING SN table solutions with SNPLT, the "failed" solutions will have an SNR of 0.  If there is a failed solution then that flags the data from the time.  Looking at the SNR will also tell  you if you are barely detecting fringes and if occasionally the SNR goes below the detection threshold.   The phase coherence on 0219+428 do not look particularly good, so I am not surprised you got some failed/poor solutions.

GC441 looks like a *terrible* phase calibrator in the plot you sent me.  You need to have some reasonable phase coherence for FRING to find solutions.    This source looks like it cannot be used as a phase reference source at all.  As for why it is a bad calibrator, probably it is too faint, as to why it is too faint I cannot tell you.   See the left  side of figure 9.1 of the AIPS Cookbook, this is what a calibrator should look like, it can look a little worse or better than this but this will give you an idea.




Amy Mioduszewski
NRAO

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