[vsnet-chat 811] vsnet charts

[aah@nofs.navy.mil]

Thanks to Fraser and Taichi Kato for informing me of the status of
the VSNET chart making software.  I'm pleased that the software is in
that good of shape, and think that the basic approach of a star table
plus local plotting software is a better solution than hand-drawn charts.
My concern was that Lasse Teist Jensen did not seem to have the same
level of software.  Certainly scaling, orientation and magnitude limits
are useful features.  My preference would be to include considerably more
data per star in the table so that you can be more flexible in the future
as to what you plot and how it is done.  Certainly USNO-A has two colors
of information, and future surveys (USNO-B and SDSS come to mind) will be
even more extensive.  You may need to consider a revision of the table
format now rather than later, so that you don't get stuck with supporting
two or more formats in the future.  You've probably discussed this in
gory detail earlier; I'm stepping in very late in the process.
  As for USNO-A magnitudes: any huge catalog has to be produced in an
automated way and must use whatever calibration data is available at its
production time.  USNO-A certainly falls within that category.  There were
no deep, uniformly distributed sequences available when it was made, and
so some regions are not properly calibrated.  In addition, the PMM scanning
machine is designed for astrometry, not photometry, making the photometry
probably the least-well-known aspect of USNO-A.  Use the photometry as
an initial first-guess in sequences, but don't rely on it.
Arne
--------------------------------------------------------------------
Arne Henden                               Instruments/software/CCDs
US Naval Observatory Flagstaff Station    Cepheids/photometry/IR
P.O. Box 1149                             http: ftp.nofs.navy.mil  
Flagstaff, AZ 86002-1149                  Voice: (520)779-5132
aah@nofs.navy.mil                         FAX:   (520)774-3626

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