[daip] question about BPASS (specifically, about the CHN_SHIFT field)

[Craig Walker]

Could someone answer this?  I presume CHN_SHIFT has something to do with
the shifting that can happen with CVEL, but it is likely that Lebach is
dealing with continuum data and not using CVEL.  In any case, I don't have
a clue why the number should be -1000 occasionally when it is normally 
much less than 1.

Craig




----- Begin Included Message -----

>From del at gyro.harvard.edu Wed Dec 13 16:15 MST 2000
Date: Wed, 13 Dec 2000 18:14:59 -0500 (EST)
To: aipsmail at cv3.cv.nrao.edu
Subject: question about BPASS (specifically, about the CHN_SHIFT field)
Cc: cwalker at zia.aoc.NRAO.EDU, dgg at leo.gsfc.nasa.gov,
        michael at polaris.phys.yorku.ca, ransom at polaris.phys.yorku.ca
From: Daniel Lebach <dlebach at cfa.harvard.edu>
Content-Type: text
Status: RO


Hello,

I have noticed that for certain non-VLBA sites, when I run BPASS, I
sometimes get values of -1.0D+03 for the CHN_SHIFT field (indicating
some kind of problem?) even though weights (WEIGHT field) and phases
(REAL and IMAG fields) look fine (nonzero weights and phases) and I
know of no problems with the data.  Can you explain why this
happens?  Need I be concerned?

In the most recent experiment I looked at (BR063C, obs. on 1999
Sept. 18-19), I got CHN_SHIFT values of -1.0D+03 for the VLA most of
the time but not all the time, depending on the epoch and timerange.
For example, when I specified one particular epoch via TIMERANGE and
ran BPASS, I got reasonable values of CHN_SHIFT for the VLA (about
1.9D-02 for all elements), but for a different epoch I got CHN_SHIFT
values of -1.0D+03, and when I used TIMERA 0, I got CHN_SHIFT values
of -1.0D+03 at all epochs for the VLA, including the epoch for which
it was not that value with a single-epoch timerange.  I found that
very worrisome.  Just how is this field used, anyway?  The weights
and phases looked fine in all cases.

-- Dan Lebach

--------------------------------------------------------------------------
| Daniel E. Lebach         ! Harvard-Smithsonian Center for Astrophysics |
| dlebach at cfa.harvard.edu  ! 60 Garden Street, MS 42                     |
| Voice: (617) 495-7150    ! Cambridge, MA  02138                        |
| Fax:   (617) 495-7345    ! USA                                         |
--------------------------------------------------------------------------


----- End Included Message -----