The HARPS search for southern extra-solar planets

III. Three Saturn-mass planets around HD 93083, HD 101930 and HD 102117

¹ Observatoire de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland e-mail: christophe.lovis@obs.unige.ch
² Laboratoire d'Astrophysique de Marseille, Traverse du Siphon, 13013 Marseille, France
³ Centro de Astronomia e Astrofísica da Universidade de Lisboa, Observatório Astronómico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal
⁴ Physikalisches Institut Universität Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
⁵ Service d'Aéronomie du CNRS, BP 3, 91371 Verrières-le-Buisson, France

Received: 11 February 2005
Accepted: 16 March 2005

Abstract

We report on the detection of three Saturn-mass planets discovered with the HARPS instrument. HD 93083 shows radial-velocity (RV) variations best explained by the presence of a companion of 0.37  orbiting in 143.6 days. HD 101930 b has an orbital period of 70.5 days and a minimum mass of 0.30 . For HD 102117, we present the independent detection of a companion with and orbital period  days. This planet was recently detected by Tinney et al. (ApJ, submitted). Activity and bisector indicators exclude any significant RV perturbations of stellar origin, reinforcing the planetary interpretation of the RV variations. The radial-velocity residuals around the Keplerian fits are 2.0, 1.8 and 0.9 m s^-1 respectively, showing the unprecedented RV accuracy achieved with HARPS. A sample of stable stars observed with HARPS is also presented to illustrate the long-term precision of the instrument. All three stars are metal-rich, confirming the now well-established relation between planet occurrence and metallicity. The new planets are all in the Saturn-mass range, orbiting at moderate distance from their parent star, thereby occupying an area of the parameter space which seems difficult to populate according to planet formation theories. A systematic exploration of these regions will provide new constraints on formation scenarios in the near future.