[vsnet-alert 3575] (fwd) Re: SN 1999ee and others

[Taichi Kato <tkato>]

     With regard to Yamaoka-san's request for improved astrometry of recent
supernovae, I would like to encourage observers to adopt either the GSC v1.2
(not v1.1) or the recently-available GSC-ACT, which was produced by Bill Gray
(Guide/Charon software).  Both versions practically eliminate the sometimes-
large systematic errors (1"-3") that appear in the GSC v1.1 that is in 
common use.  Note that _internal_ errors will remain the same, but the
external tie-in to the ICRS (aka Hipparcos/Tycho) system will be superior.
This has been demonstrated particularly for the GSC-ACT by external tests
against the Sloan equatorial calibration fields (by Jure Skvarc and Hermann
Mikuz in Slovenia) and with southern radio sources with high-precision
VLBI positions (by Paulo Holvorcem in Brazil).  Note also that the mean
scatter in positions derived from these catalogues will be about a factor
or two better than USNO-A2.0, mainly as a result of the more recent epoch
of the GSC source plates.
     Neither catalogue is available as yet 'in toto', although Bill Gray
informs me that GSC-ACT will be placed at the data centers soon.  In the
meantime, small patches of sky suitable for CCD reduction can be obtained
via the Strasbourg 'VizieR' utility (and its mirror copies in the USA and
in Japan):

http://vizier.u-strasbg.fr/cgi-bin/VizieR

Ask for either catalogue I/252 (for GSC v1.2) or I/255 (for GSC-ACT).
     As long as your CCD covers enough area to include at least 8 or 9 GSC
stars, then these catalogues will give more consistent results than either
GSC v1.1 or USNO-A1.0 or A2.0.  It is also helpful for both discoverers and
follow-up astrometrists to measure and report accurate positions for the
nuclei of the host galaxies.  The lack precise positions for most fainter
galaxies leads to the confusions such as Hitoshi has pointed out.

\Brian

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