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We search for the astrometric signatures of planets and brown dwarfs knownfrom radial velocity surveys in the improved Hipparcos intermediate astrometricdata provided by van Leeuwen (2007a). Our aim is to put more significantconstraints on the inclination and the longitude of the ascending node than waspossible before, resulting in unambiguous companion masses. We fitted theastrometric orbits of 310 substellar companions around 258 stars to theHipparcos intermediate astrometric data. Even though the astrometric signaturesof the companions cannot be detected in most cases, the Hipparcos data stillprovide lower limits on the inclination for all but 67 of the investigatedcompanions, which translates into upper limits on the masses of the unseencompanions. For nine companions the derived upper mass limit lies in theplanetary and for 75 companions in the brown dwarf mass regime, proving thesubstellar nature of those objects. Two of those objects have minimum massesalso in the brown dwarf regime and are thus proven to be brown dwarfs. Theconfirmed 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 HD147513 b. The confirmed brown dwarfs are HD 137510 b and HD 168443 c. In 20cases, the astrometric signature of the substellar companion was detected inthe Hipparcos data. Of these 20 companions, three are confirmed as planets orlightweight brown dwarfs (HD 87833 b, iota Dra b, and gamma Cep b), two asbrown dwarfs (HD 106252 b and HD 168443 b), and four are low-mass stars (BD -04782 b, HD 112758 b, rho CrB b, and HD169822 b). Of the others, many are eitherbrown dwarfs or very low mass stars. For epsilon Eri, we derive a solutionwhich is very similar to the one obtained using Hubble Space Telescope data.

astronomy and astrophysics

Mass constraints on substellar companion candidates from the re-reduced  Hipparcos intermediate astrometric data: Nine confirmed planets and two  confirmed brown dwarfs