Tycho2 catalog fits

[<aah@nofs.navy.mil>]

For those of you that are interested in using the
Tycho2 catalog for photometric as well as astrometric
calibration, here are the results from my latest fits
vs. Landolt standards (about 270 stars, V brighter than
10.5, B-V bluer than 1.8):
U = Bt - 0.325 + 0.8034*(Bt-Vt)
B = Bt + 0.018 - 0.2580*(Bt-Vt)
V = Vt + 0.008 - 0.0988*(Bt-Vt)
R = Vt - 0.014 - 0.5405*(Bt-Vt)
I = Vt - 0.039 - 0.9376*(Bt-Vt)

U has terrible systematics; I has systematics as well.
The BVR fits are quite good.  For these fits, I have
not made any discrimination on luminosity class and have
assumed a purely linear relationship.
Arne