The SOPHIE search for northern extrasolar planets - VIII. Follow-up of ELODIE candidates: long-period brown-dwarf companions

Astronomy & Astrophysics, Jan 2016

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 MJup 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.

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The SOPHIE search for northern extrasolar planets - VIII. Follow-up of ELODIE candidates: long-period brown-dwarf companions

A&A Astronomy & Astrophysics F. Bouchy 1 2 D. Ségransan 1 R. F. Díaz 1 2 T. Forveille 0 I. Boisse 2 6 L. Arnold 5 N. Astudillo-Defru 0 J.-L. Beuzit 0 X. Bonfils 0 S. Borgniet 0 V. Bourrier 1 4 B. Courcol 2 X. Delfosse 0 O. Demangeon 2 P. Delorme 0 D. Ehrenreich 1 G. Hébrard 4 5 A.-M. Lagrange 0 M. Mayor 1 G. Montagnier 4 5 C. Moutou 2 3 D. Naef 1 F. Pepe 1 C. Perrier 0 D. Queloz 1 J. Rey 1 J. Sahlmann 8 A. Santerne 6 N. C. Santos 6 7 J.-P. Sivan 2 S. Udry 1 P. A. Wilson 4 0 Université Grenoble Alpes , CNRS, IPAG, 38000 Grenoble , France 1 Observatoire de Genève, Université de Genève , 51 Ch. des Maillettes, 1290 Sauverny , Switzerland 2 Aix-Marseille Université , CNRS , Laboratoire d'Astrophysique de Marseille UMR 7326 , 13388 Marseille Cedex 13 , France 3 Canada France Hawaii Telescope Corporation , Kamuela, HI 96743 , USA 4 Institut d'Astrophysique de Paris, UMR 7095 CNRS, Université Pierre & Marie Curie , 98bis Bd Arago, 75014 Paris , France 5 Aix-Marseille Université, CNRS, Observatoire de Haute-Provence, Institut Pythéas , 04870 St Michel l'Observatoire , France 6 Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto , CAUP, 4150-762 Porto , Portugal 7 Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto , 4150-762 Porto , Portugal 8 European Space Agency, European Space Astronomy Centre , PO Box 78 , Villanueva de la Canada , 28691 Madrid , Spain 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 MJup 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 e ects 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. techniques; radial velocities - binaries; spectroscopic - stars; low-mass - brown dwarfs - stars; general 1. Introduction Brown dwarfs (BD) are substellar objects in the mass range of approximately 13–80 Jupiter masses; they have enough mass to burn deuterium, but are too light to permit hydrogen burning in their inner cores (Burrows et al. 1997; Chabrier & Bara e 2000; Spiegel et al. 2011). BDs constitute intermediate objects between giant planets and low-mass stars, but there is not a complete consensus about their formation mechanisms. The separation between planet and brown dwarf population may not only be related to the mass, but also to the formation scenario. Coreaccretion models predict the formation of objects as heavy as 25 MJup (Mordasini et al. 2009). BD companions orbiting solartype stars with periods of up to about ten years clearly occur less frequently ( 1%) than planetary systems and stellar binaries ? Based on observations made with ELODIE and SOPHIE spectrographs on the 1.93-m telescope at Observatoire de Haute-Provence (CNRS/AMU), France. ?? Tables 5–9 (RV data) are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/585/A46 (e.g., Grether & Lineweaver 2006; Sahlmann et al. 2011; Ma & Ge 2014). Statistical properties of BD companions, such as frequency, separation, eccentricity, and mass ratio distribution, as well as the relation of these properties to their host stars, should permit us to distinguish between di erent formation and evolution models. Most of the brown dwarf companions have been discovered in radial velocity (RV) surveys (e.g., Nidever et al. 2002; Sahlmann et al. 2011; Díaz et al. 2012). In these programs, which were designed to find exoplanets, brown dwarfs are easily detected by their strong RV signatures. However, radial velocity measurements alone do not constrain the orbit inclination and therefore provide only the minimum mass. When available, complementary observational constraints, such as the astrometric motion of the host star, a deep analysis of the spectra to search for a blend or a secondary component, or a photometric transit, are required to attempt determining the true mass or at least to firmly exclude the stellar nature of the companion. So far, only a few brown-d (...truncated)


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F. Bouchy, D. Ségransan, R. F. Díaz, T. Forveille, I. Boisse, L. Arnold, N. Astudillo-Defru, J.-L. Beuzit, X. Bonfils, S. Borgniet, V. Bourrier, B. Courcol, X. Delfosse, O. Demangeon, P. Delorme, D. Ehrenreich, G. Hébrard, A.-M. Lagrange, M. Mayor, G. Montagnier, C. Moutou, D. Naef, F. Pepe, C. Perrier, D. Queloz, J. Rey, J. Sahlmann, A. Santerne, N. C. Santos, J.-P. Sivan, S. Udry, P. A. Wilson. The SOPHIE search for northern extrasolar planets - VIII. Follow-up of ELODIE candidates: long-period brown-dwarf companions, Astronomy & Astrophysics, 2016, pp. A46, 585, DOI: 10.1051/0004-6361/201526347