The SOPHIE search for northern extrasolar planets

XI. Three new companions and an orbit update: Giant planets in the habitable zone^⋆

¹ Observatoire Astronomique de l’Université de Genève, 51 Chemin des Maillettes, 1290 Versoix, Switzerland
e-mail: rodrigo.diaz@unige.ch
² Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
³ Institut d’Astrophysique de Paris, UMR 7095 CNRS, Université Pierre & Marie Curie, 98bis boulevard Arago, 75014 Paris, France
⁴ Observatoire de Haute Provence, CNRS, Aix Marseille Université, Institut Pythéas UMS 3470, 04870 Saint-Michel-l’ Observatoire, France
⁵ Université Grenoble Alpes, IPAG, 38000 Grenoble, France
⁶ CNRS, IPAG, 38000 Grenoble, France
⁷ Canada-France-Hawaii Telescope Corporation, 65-1238 Mamalahoa Hwy, Kamuela, HI 96743, USA
⁸ Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE, UK
⁹ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
¹⁰ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
¹¹ European Space Agency, European Space Astronomy Centre, PO Box 78, Villanueva de la Canada, 28691 Madrid, Spain

Received: 17 February 2016
Accepted: 12 April 2016

Abstract

We report the discovery of three new substellar companions to solar-type stars, HD 191806, HD 214823, and HD 221585, based on radial velocity measurements obtained at the Haute-Provence Observatory. Data from the SOPHIE spectrograph are combined with observations acquired with its predecessor, ELODIE, to detect and characterise the orbital parameters of three new gaseous giant and brown dwarf candidates. Additionally, we combine SOPHIE data with velocities obtained at the Lick Observatory to improve the parameters of an already known giant planet companion, HD 16175 b. Thanks to the use of different instruments, the data sets of all four targets span more than ten years. Zero-point offsets between instruments are dealt with using Bayesian priors to incorporate the information we possess on the SOPHIE/ELODIE offset based on previous studies. The reported companions have orbital periods between three and five years and minimum masses between 1.6 M_Jup and 19 M_Jup. Additionally, we find that the star HD 191806 is experiencing a secular acceleration of over 11 m s^-1 per year, potentially due to an additional stellar or substellar companion. A search for the astrometric signature of these companions was carried out using Hipparcos data. No orbit was detected, but a significant upper limit to the companion mass can be set for HD 221585, whose companion must be substellar. With the exception of HD 191806 b, the companions are located within the habitable zone of their host star. Therefore, satellites orbiting these objects could be a propitious place for life to develop.