  We search for the astrometric signatures of planets and brown dwarfs known
from radial velocity surveys in the improved Hipparcos intermediate astrometric
data provided by van Leeuwen (2007a). Our aim is to put more significant
constraints on the inclination and the longitude of the ascending node than was
possible before, resulting in unambiguous companion masses. We fitted the
astrometric orbits of 310 substellar companions around 258 stars to the
Hipparcos intermediate astrometric data. Even though the astrometric signatures
of the companions cannot be detected in most cases, the Hipparcos data still
provide lower limits on the inclination for all but 67 of the investigated
companions, which translates into upper limits on the masses of the unseen
companions. For nine companions the derived upper mass limit lies in the
planetary and for 75 companions in the brown dwarf mass regime, proving the
substellar nature of those objects. Two of those objects have minimum masses
also in the brown dwarf regime and are thus proven to be brown dwarfs. The
confirmed planets are the ones around Pollux (beta Gem b), epsilon Eri b,
epsilon Ret b, mu Ara b, upsilon And c and d, 47 UMa b, HD 10647 b and HD
147513 b. The confirmed brown dwarfs are HD 137510 b and HD 168443 c. In 20
cases, the astrometric signature of the substellar companion was detected in
the Hipparcos data. Of these 20 companions, three are confirmed as planets or
lightweight brown dwarfs (HD 87833 b, iota Dra b, and gamma Cep b), two as
brown dwarfs (HD 106252 b and HD 168443 b), and four are low-mass stars (BD -04
782 b, HD 112758 b, rho CrB b, and HD169822 b). Of the others, many are either
brown dwarfs or very low mass stars. For epsilon Eri, we derive a solution
which is very similar to the one obtained using Hubble Space Telescope data.
