From tvcawthorne@uclan.ac.ukFri May 23 16:34:35 2003
Date: Wed, 21 May 2003 17:04:40 +0100 (BST)
From: Tim Cawthorne <tvcawthorne@uclan.ac.uk>
To: vlbiobs@cv3.cv.nrao.edu
Subject: BC127/C/D/E/F schedule substituting VLA1 for PT.


Hi - Thanks for your note. We believe that a single VLA dish can
be substituted for PT without any serious consequences and so 
a .key file with VLA1 substituted for PT is attached.

I was worried about the phase referencing scans, since I thought
that VLA slews more slowly than PT. However sched seems to throw up
no problems. It might be a good thing if you could check this on
your software. 

With best wishes

Tim Cawthorne.

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From tvcawthorne@uclan.ac.ukFri May 23 16:35:18 2003
Date: Fri, 23 May 2003 18:55:22 +0100 (BST)
From: Tim Cawthorne <tvcawthorne@uclan.ac.uk>
To: "VLBI Observers (Aspen only)" <vlbiobs@cv3.cv.nrao.edu>
Subject: Re: BC127/C/D/E/F schedule substituting VLA1 for PT.


Dear Lisa, thanks for your note. 

I've taken a look through the .sum file you sent and its clear that
the time taken for VLA1 to slew between the phase reference
(BL~Lac) and the `target' source (2151+431) is always about the same
as the time we've allowed on 2151 at 43GHz (about 20 secs). To avoid all
this
needless slewing I've edited VLA1 out of the 2151 43GHz scans. This means
that we lose the phase-reference information for VLA at 43GHz,
unfortunately.  

We would prefer to have PT, obviously, but we also want to try and achieve
even coverage for our experiment, ie. observations every 2 months or so. 
If substituting VLA1 for PT helps to get the data regularly then I guess
we'd sacrifice the 43GHz referencing at one antenna. 

I've attached the edited file. 

(Note that we're doing a kind of `reverse referencing' here - the target
source is really BLLac but we're trying to locate its position on the
sky with reference to the weak nearby source 2151.)

I hope this all makes sense. Thanks again for your help.

Kind regards, Tim Cawthorne. 


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