As in the case of our FK6,
(using ground based data provided by the FK5 to improve Hipparcos' results),
we also used the
Tycho-2 Catalogue
(TYC2) to increase the number of stars
with such better data: The combination of HIPPARCOS and TYC2 data gives
improved results for 89 908 stars.
This number of objects could be treated as single stars.
The catalogue gives proper motions
with a typical mean error of 0.83 mas/year (about a factor of
1.3 better than Hipparcos for this sample of stars).
