RESEARCH
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The SOPHIE search for northern extrasolar planets
IV. Massive companions in the planet-brown dwarf boundary

R. F. Díaz, A. Santerne, J. Sahlmann, G. Hébrard, A. Eggenberger, N. C. Santos, C. Moutou, L. Arnold, I. Boisse, X. Bonfils, F. Bouchy, X. Delfosse, M. Desort, D. Ehrenreich, T. Forveille, A.-M. Lagrange, C. Lovis, F. Pepe, C. Perrier, D. Queloz, D. Ségransan, S. Udry, A. Vidal-Madjar

Abstract
Context. The mass domain where massive extrasolar planets and brown dwarfs lay is still poorly understood. Indeed, not even a clear dividing line between massive planets and brown dwarfs has been established yet. This is partly due to the paucity of this kind of objects orbiting close to solar-type stars, the so-called brown dwarf desert, that hinders setting up a strong observational base to compare to models and theories of formation and evolution.
Aims. We search to increase the current sample of massive sub-stellar objects with precise orbital parameters, and to constrain the true mass of detected sub-stellar candidates.
Methods. The initial identification of sub-stellar candidates is done using precise radial velocity measurements obtained with the SOPHIE spectrograph at the 1.93-m telescope of the Haute-Provence Observatory. Subsequent characterisation of these candidates, with the principal aim of identifying stellar companions in low-inclination orbits, is done by means of different spectroscopic diagnostics, as the measurement of the bisector velocity span and the study of the correlation mask effect. With this objective, we also employed astrometric data from the Hipparcos mission and a novel method of simulating stellar cross-correlation functions.
Results. Seven new objects with minimum masses between ∼ 10 MJup and ∼ 90 MJup are detected. Out of these, two are identified as low-mass stars in low-inclination orbits, and two others have masses below the theoretical deuterium-burning limit, and are therefore planetary candidates. The remaining three are brown dwarf candidates; the current upper limits for their the masses do not allow us to conclude on their nature. Additionally, we have improved on the parameters of an already-known brown dwarf (HD137510b), confirmed by astrometry.

Keywords
brown dwarfs – planetary systems – techniques: radial velocities – stars: general

Notes
Based on observations collected with the SOPHIE spectrograph on the 1.93-m telescope at Observatoire de Haute-Provence (CNRS), France, by the SOPHIE Consortium (program 07A.PNP.CONS).
Table 2 is 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/538/A113

Astronomy and Astrophysics
Volume 538, Number of pages A113_1
2012 February

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia