Detection and Characterisation of 54 Massive Companions with the SOPHIE Spectrograph

Brown-dwarfs are substellar objects with masses intermediate between planetsand stars within about 13-80Mjup. While isolated BDs are most likely producedby gravitational collapse in molecular clouds down to masses of a few Mjup, anon-negligible fraction of low-mass companions might be formed through theplanet formation channel in protoplanetary disks. The upper mass limit ofobjects formed within disks is still observationally unknown, the main reasonbeing the strong dearth of BD companions at orbital periods shorter than 10years, a.k.a. the BD desert. To address this question, we aim at determiningthe best statistics of secondary companions within the 10-100Mjup range andwithin 10 au from the primary star, while minimising observational bias. Wemade an extensive use of the RV surveys of FGK stars below 60pc distance to theSun and in the northern hemisphere performed with the SOPHIE spectrograph atthe Observatoire de Haute-Provence. We derived the Keplerian solutions of theRV variations of 54 sources. Public astrometric data of the Hipparcos and Gaiamissions allowed constraining the mass of the companion for most sources. Weintroduce GASTON, a new method to derive inclination combining RVs Keplerianand astrometric excess noise from Gaia DR1. We report the discovery of 12 newBD candidates. For 5 of them, additional astrometric data led to revise theirmass in the M-dwarf regime. Among the 7 remaining objects, 4 are confirmed BDcompanions, and 3 others are likely in this mass regime. We also report thedetection of 42 M-dwarfs within 90Mjup-0.52Msun. The resulting Msin(i)-Pdistribution of BD candidates shows a clear drop in the detection rate below80-day orbital period. Above that limit, the BD desert reveals rather wet, witha uniform distribution of the Msin(i). We derive a minimum BD-detectionfrequency around Solar-like stars of 2.0+/-0.5