[daip] offset between HDF New VLA and old VLA data

[Glenn Morrison]

Well, the "offset" is back. UVFIX was run on all the data before it  
was DBCON.

This offset was not seen after UVFIX for one day of the 2006 A-array  
data but I did not check all days.

--Glenn

Begin forwarded message:

> From: Mark Dickinson <med at noao.edu>
> Date: April 2, 2008 11:15:29 AM HST
> To: Glenn Morrison <morrison at cfht.hawaii.edu>
> Cc: Mark Dickinson <med at noao.edu>
> Subject: you'll feel better if you delete this message
>
> Hi Glenn -
>
> I'm finally getting back to looking at the VLA vs. other astrometry  
> using the newest
> catalogs that you sent me on January 16.    I'm sorry to say that if  
> I compare these new
> radio positions to the old Richards 2000 positions or the Biggs &  
> Ivison 2006 catalog
> (from the same data as Richards 2000), I'm still seeing evidence for  
> systematic
> astrometric offsets with a pattern that looks very much like it did  
> before you did all
> of the work to rereduce the data.  I'm very surprised by this  
> because I really thought
> you had fixed this & checked the results - but somehow the pattern  
> still seems to be there!
>
> See the attached plots.  The first one (vlagm08_ab06) compares your  
> new positions
> (from the January 16 catalog) to the Biggs & Ivison 2006 catalog.   
> The second plot
> comes from July 31 2007 and shows the old ABCD-array reduction  
> (before you
> had rereduced the data) compared to B&I'06.   You'll see that they  
> look very similar.
> I think the new residuals are slightly smaller than the old ones,  
> but overall the same
> systematic pattern is visible.  Comparing to Richards 2000 instead  
> shows the same thing.
>
> I could *swear* that you showed me plots that indicated you had  
> fixed the
> rotation/offset problem - so do you know how it could have crept  
> back in again?
>
> 	Mark
>
>

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