[vsnet-id 689] Re: [vsnet-chat 5437] Precise position of TZ Vel

[Brian Skiff <Brian.Skiff@lowell.edu>]

     In many cases it's worth checking VizieR to see what shows up.
Here the MSX detection was useful in that the positions are usually good
to a few arcsec (versus ~20" but rather variable for IRAS positions),
and the UCAC entry.  Generally a star won't appear in UCAC unless it is
uncrowded, since the aim with this catalogue is a clean astrometric
reference net.  For the general plate-scan catalogues like GSC, USNO-x.x,
and GSC-2.2, you really have to be cognizant of their various limitations
and when one is better than the other.  Also there was the old Astrographic
Catalogue entry, which would have been from plates with short exposures
so that crowding by faint stars would not have interferred.  The quirks
of various catalogues is sometimes infuriating, but also leads to real
astronomical insight (sometimes!).

\Brian

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