[vsnet-alert 5727] Re: Possible nova in Sgr: astrometry

[Brian Skiff <bas@lowell.edu>]

     I note that Kadota-san's position is 0".4 from a moderately-bright
USNO-A2.0 star (which looks real on the DSS image) at:

17 54 40.413  -26 14 15.38 (2000)

When reporting astrometry from CCD images, it would be best if several
images were used to make the determination, particularly if the target were
moved somewhat between frames, so that the reference net would also be
shifted.  The scatter in say three or four measurements would give a much
better idea of the true uncertainty in the position than would a single
frame using only the error in the fits to the reference stars.

\Brian

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