Context : The recently completed re-reduction of the Hipparcos data by van Leeuwen ( 2007a ) makes it possible to search for the astrometric signatures of planets and brown dwarfs known from radial velocity surveys in the improved Hipparcos intermediate astrometric data .

Aims : Our aim is to put more significant constraints on the orbital parameters which can not be derived from radial velocities alone , i.e .
the inclination and the longitude of the ascending node , than was possible before .
The determination of the inclination in particular allows to calculate an unambiguous companion mass , rather than the lower mass limit which can be obtained from radial velocity measurements .

Methods : We fitted the astrometric orbits of 310 substellar companions around 258 stars , which were all discovered via the radial velocity method , to the Hipparcos intermediate astrometric data provided by van Leeuwen .

Results : Even though the astrometric signatures of the companions can not 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 , resulting in reasonable constraints on inclination and ascending node .
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 .

Conclusions :