Abstract
Context. Brown dwarfs (BD) are substellar objects intermediate between planets and stars with masses of ~13–80 MJ. While isolated BDs are most likely produced by gravitational collapse in molecular clouds down to masses of a few MJ, a non-negligible fraction of low-mass companions might be formed through the planet-formation channel in protoplanetary discs. The upper mass limit of objects formed within discs is still observationally unknown, the main reason being the strong dearth of BD companions at orbital periods shorter than 10 yr, also known as the BD desert. Aims. To address this question, we aim at determining the best statistics of companions within the 10–100 MJ mass regime and located closer than ~10 au to the primary star, while minimising observation and selection bias. Methods. We made extensive use of the radial velocity (RV) surveys of northern hemisphere FGK stars within 60 pc of the Sun, performed with the SOPHIE spectrograph at the Observatoire de Haute-Provence. We derived the Keplerian solutions of the RV variations of 54 sources. Public astrometric data of the HIPPARCOS and Gaia missions allowed us to constrain the masses of the companions for most sources. We introduce GASTON, a new method to derive inclination combining RVs and Keplerian and astrometric excess noise from Gaia DR1. Results. We report the discovery of 12 new BD candidates. For five of them, additional astrometric data led to a revision of their mass in the M-dwarf regime. Among the seven remaining objects, four are confirmed BD companions, and three others are likely also in this mass regime. Moreover, we report the detection of 42 M-dwarfs within the range of 90 MJ–0.52 M⊙. The resulting M sin i-P distribution of BD candidates shows a clear drop in the detection rate below 80-day orbital period. Above that limit, the BD desert appears rather wet, with a uniform distribution of the M sin i. We derive a minimum BD-detection frequency around Solar-like stars of 2.0 ± 0.5%.
Highlights
According to the classical convention, brown dwarfs (BD) are substellar objects whose masses are too small to maintain hydrostatic equilibrium thanks to hydrogen-based nuclear reactions, while massive enough to ignite Deuterium nuclear reactions in the core, at least for a few million years
In the continuation of the work of Díaz et al (2012) and Wilson et al (2016) which published several new objects in the BD desert with SOPHIE, we present here the latest results of this radial velocity (RV) survey on 54 solar-like sources with spectral types ranging from K5 to F5
In order to gather the largest possible number of BDs in the BD desert, and to be able to compare the BD population to the low-mass star population, we especially focused on sources with companion masses in the broad M sin i range of 20–150 MJ
Summary
According to the classical convention, brown dwarfs (BD) are substellar objects whose masses are too small to maintain hydrostatic equilibrium thanks to hydrogen-based nuclear reactions, while massive enough to ignite Deuterium nuclear reactions in the core, at least for a few million years Following this definition, the BD domain is framed within the mass range of 13–80 MJ. The scarcity of detections of BD companions with orbital periods shorter than 10 yr, the so-called brown dwarf desert (Halbwachs et al 2000; Grether & Lineweaver 2006), is followed by an increase of detection frequency at masses lower than 10 MJ (Marcy & Butler 2000; Udry et al 2002) This shows that giant planets and substellar objects that were formed like stars overlap on a few tens of Jupiter masses
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