The SOPHIE search for northern extrasolar planets^⋆

VIII. Follow-up of ELODIE candidates: long-period brown-dwarf companions ^⋆⋆

¹ Aix-Marseille Université, CNRS, Laboratoire d’Astrophysique de Marseille UMR 7326, 13388 Marseille Cedex 13, France
² Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland
³ Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁴ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, 4150-762 Porto, Portugal
⁵ Aix-Marseille Université, CNRS, Observatoire de Haute-Provence, Institut Pythéas, 04870 St Michel l’ Observatoire, France
⁶ Institut d’Astrophysique de Paris, UMR 7095 CNRS, Université Pierre & Marie Curie, 98bis Bd Arago, 75014 Paris, France
⁷ Canada France Hawaii Telescope Corporation, Kamuela, HI 96743, USA
⁸ European Space Agency, European Space Astronomy Centre, PO Box 78, Villanueva de la Canada, 28691 Madrid, Spain
⁹ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, 4150-762 Porto, Portugal

Received: 17 April 2015
Accepted: 13 October 2015

Abstract

Long-period brown dwarf companions detected in radial velocity surveys are important targets for direct imaging and astrometry to calibrate the mass–luminosity relation of substellar objects. Through a 20-yr radial velocity monitoring of solar-type stars that began with ELODIE and was extended with SOPHIE spectrographs, giant exoplanets and brown dwarfs with orbital periods longer than ten years are discovered. We report the detection of five new potential brown dwarfs with minimum masses between 32 and 83 M_Jup orbiting solar-type stars with periods longer than ten years. An upper mass limit of these companions is provided using astrometric Hipparcos data, high-angular resolution imaging made with PUEO, and a deep analysis of the cross-correlation function of the main stellar spectra to search for blend effects or faint secondary components. These objects double the number of known brown dwarf companions with orbital periods longer than ten years and reinforce the conclusion that the occurrence of such objects increases with orbital separation. With a projected separation larger than 100 mas, all these brown dwarf candidates are appropriate targets for high-contrast and high angular resolution imaging.