The HARPS search for southern extra-solar planets ^*,**

XV. Six long-period giant planets around BD -17 0063, HD 20868, HD 73267, HD 131664, HD 145377, and HD 153950

¹ Laboratoire d'Astrophysique de Marseille, OAMP, Université Aix-Marseille & CNRS, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France e-mail: Claire.Moutou@oamp.fr
² Observatoire de Genève, Université de Genève, 51 ch.des Maillettes, 1290 Sauverny, Switzerland
³ ESO, Alonso de Cordoba 3107, Vitacura Casilla 19001, Santiago, Chile
⁴ Institut d'Astrophysique de Paris, 98bis bd Arago, 75014 Paris, France
⁵ Physikalisches Institut Universität Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
⁶ Centro de Astrofísica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal

Received: 9 September 2008
Accepted: 10 October 2008

Abstract

We report the discovery of six new substellar companions of main-sequence stars, detected by multiple Doppler measurements with the instrument HARPS installed on the ESO 3.6 m telescope, La Silla, Chile. These extrasolar planets orbit the stars BD -17 0063, HD 20868, HD 73267, HD 131664, HD 145377, and HD 153950. The orbital characteristics that reproduce the observed data are presented, as well as the stellar and planetary parameters. Masses of the companions range from 2 to 18 Jupiter masses, and periods range from 100 to 2000 days. The observational data are carefully analysed for activity-induced effects, and we conclude that the observed radial velocity variations are of exoplanetary origin. Of particular interest is the very massive planet (or brown-dwarf companion) orbiting the metal-rich HD 131664 with m₂ sin i = 18.15 M_Jup  and a 5.34-year orbital period. These new discoveries are consistent with the observed statistical properties of exoplanet samples known so far.