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

XVII. Super-Earth and Neptune-mass planets in multiple planet systems HD 47 186 and HD 181 433

¹ Institut d'Astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis Bd Arago, 75014 Paris, France e-mail: bouchy@iap.fr
² Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland
³ Physikalisches Institut Universitat Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
⁴ Service d'Aéronomie du CNRS, BP 3, 91371 Verrières-le-Buisson, France
⁵ Laboratoire d'Astrophysique, Observatoire de Grenoble, Université J. Fourier, BP 53, 38041 Grenoble, Cedex 9, France

Received: 24 July 2008
Accepted: 20 November 2008

Abstract

We report on the detection of two new multiple planet systems orbiting solar-like stars HD 47 186 and HD 181 433. The first system contains a hot Neptune of 22.78 with a 4.08-day period and a Saturn of 0.35 M_JUP with a 3.7-year period. The second system contains a Super-Earth of 7.5 with a 9.4-day period, a 0.64 M_JUP with a 2.6-year period, and a third companion of 0.54 M_JUP with a period of about 6 years. These detections increase to 20 the number of close-in low-mass exoplanets (below 0.1 M_JUP) and strengthen the fact that 80% of these planets are in multiple planetary systems.