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Date: Wed, 13 Mar 2002 01:21:30 -0700 (MST)
From: Brian Skiff <Brian.Skiff@lowell.edu>
The color terms published by Fabricius will not work in the general
case. I don't have the paper in front of me (it is an ESO conference
proceedings paper), but as I recall he found the color terms with respect
only to Tycho-1 VT, _not_ to standard V. In addition, since you don't
know the color of an individual star, you cannot make other than a generic
correction to a standard passband. If the correction was to Tycho-1 VT,
the magnitude dependence comes from the scale error in Tycho-1 data.
I have never seen any evidence that the GSC magnitudes have a magnitude-
dependent scale error when compared to real photometry. Finally, the
Fabricius color terms take no account of plate-to-plate zero-point shifts,
so will not be useful for much of anything.
In order to preserve what internal precision there is in the GSC
photometry, one would want to make adjustments to the standard passband
closest to whatever the passband of the relevant plates are. Thus in the
south you end up with B magnitudes, and V or R in the north, and V close to
the galactic plane in the south.
\Brian
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