The HARPS search for southern extra-solar planets

XLIV. Eight HARPS multi-planet systems hosting 20 super-Earth and Neptune-mass companions^{★,★★,★★★}

¹ Observatoire astronomique de l’Université de Genève, 51 ch. des Maillettes, 1290 Versoix, Switzerland
e-mail: Xavier.Dumusque@unige.ch
² Physikalisches Institut, Universitat Bern, Silderstrasse 5, 3012 Bern, Switzerland
³ Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388, Marseille, France
⁴ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
⁵ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
⁶ Departamento de Física e Astronomia, Faculdade de Cièncias, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
⁷ Instituto de Astrofísica de Canarias, 38025, La Laguna, Tenerife, Spain
⁸ School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS, UK
⁹ Institut d’Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, Bat. B5C, 4000 Liège, Belgium
¹⁰ Canada France Hawaii Telescope Corporation, Kamuela, HI 96743, USA
¹¹ Department of Physics, University of Warwick, Coventry, CV4 7AL, UK

Received: 15 May 2017
Accepted: 16 October 2018

Abstract

Context. We present radial-velocity measurements of eight stars observed with the HARPS Echelle spectrograph mounted on the 3.6-m telescope in La Silla (ESO, Chile). Data span more than ten years and highlight the long-term stability of the instrument.

Aims. We search for potential planets orbiting HD 20003, HD 20781, HD 21693, HD 31527, HD 45184, HD 51608, HD 134060 and HD 136352 to increase the number of known planetary systems and thus better constrain exoplanet statistics.

Methods. After a preliminary phase looking for signals using generalized Lomb-Scargle periodograms, we perform a careful analysis of all signals to separate bona-fide planets from signals induced by stellar activity and instrumental systematics. We finally secure the detection of all planets using the efficient MCMC available on the Data and Analysis Center for Exoplanets (DACE web-platform), using model comparison whenever necessary.

Results. In total, we report the detection of twenty new super-Earth to Neptune-mass planets, with minimum masses ranging from 2 to 30 M_Earth and periods ranging from 3 to 1300 days, in multiple systems with two to four planets. Adding CORALIE and HARPS measurements of HD20782 to the already published data, we also improve the characterization of the extremely eccentric Jupiter orbiting this visual companion of HD 20781.