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

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 M_⊕ 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 M_⊕ 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.

Based on observations made with HARPS spectrograph on the 3.6-m ESO telescope at La Silla Observatory under the GTO programme ID 072.C-0488. Tables of radial velocities are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/496/527