Detection and characterisation of 54 massive companions with the SOPHIE spectrograph

Abstract

Context. Brown-dwarfs (BD) are substellar objects with masses intermediate between planets and stars within about 13-80 M J . While isolated brown-dwarfs are most likely produced by gravitational collapse in molecular clouds down to masses of a few M J , a nonnegligible fraction of low-mass companions might be formed through the planet formation channel in protoplanetary disks. The upper mass limit of objects formed within disks is still observationnally unknown, the main reason being the strong dearth of BD companions at orbital periods shorter than 10 years, a.k.a. the brown-dwarf desert. Aims. We aim at determining the best statistics of secondary companions within the 10-100 M Jup range within ∼10 au from the primary star, while minimising observational bias. This can help determining the mass limit separating planet-formed from star-formed browndwarfs. Moreover, the exact shape of the BD desert in a mass-period space is still underdetermined, and can strongly constrain the companion-star interactions mechanisms at work in close binary systems at small mass ratio. Methods. We made an extensive use of the radial velocity (RV) surveys of FGK stars below 60 pc distance to the Sun and in the northern hemisphere performed with the SOPHIE spectrograph at 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 deriving direct astrometric solution of orbital motion and constraining the mass of the companion for most sources. We introduce GASTON, a new method to derive inclination combining RVs Keplerian and astrometric excess noise from Gaia DR1. Results. We report the discovery of 12 new BD candidates. For 5 of them, additional astrometric data led to revise their mass in the M-dwarf regime. Among the 7 remaining objects, 4 are confirmed BD companions, and 3 others are likely also in this mass regime. Moreover, we report the detection of 42 objects in the M-dwarf mass regime 90 M J -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 reveals 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%.

Discovery and characterization of the exoplanets WASP-148b and c

“…It is well known that stellar blended configurations can mimic planetary transits, including undiluted eclipsing binaries with low-mass stellar companions or diluted eclipsing binaries (e.g., Almenara et al 2009). The astrometric excess noise of WASP-148 measured by Gaia is 0.7 mas, which is below its detection limit (Kiefer et al 2019), thus showing no signatures for contamination or a blend caused by a possible massive companion. This agrees with the lack of companion detection in the images obtained for photometry (Sect.…”

Determining the true mass of radial-velocity exoplanets with Gaia

“…It also led to the corrected mass of planet candidates beyond the deuterium-burning limit; these include HD 38529 b, with a mass in the BD regime of 17 M J (Benedict et al 2010); and HD 33636 b, with an M-dwarf mass of 140 M J (Bean et al 2007). HIPPARCOS data were also extensively used to that purpose (Perryman et al 1996;Mazeh et al 1999;Zucker & Mazeh 2001a;Sozzetti & Desidera 2010;Sahlmann et al 2011a;Reffert & Quirrenbach 2011;Díaz et al 2012;Wilson et al 2016;Kiefer et al 2019) but only yielded masses in the BD to M-dwarf regime. More recently, Gaia astrometric data were used for the first time to determine the mass of RV exoplanet candidates; various methods were used, for example, based on astrometric excess noise for HD 114762 b, showing this object is stellar in nature (Kiefer 2019) and by comparing Gaia proper motion to HIPPARCOS proper motion in the case of Proxima b, confirming its planetary nature (Kervella et al 2020).…”

“…In the present study, we aim to assess the nature of numerous RV-detected exoplanet candidates publicly available in exoplanets catalogs using the astrometric excess noise from the first data release (DR1) of the Gaia mission (Gaia Collaboration 2016). We use the recently developed method called Gaia Astrometric noise Simulation To derive Orbit iNclination (GASTON; Kiefer et al 2019;Kiefer 2019) to constrain, from the astrometric excess noise and RV-derived orbital parameters, the orbital inclination and true mass of these companions.…”

“…The most recent Gaia DR2 release cannot be used similarly because it is based on a different definition of the astrometric excess noise and moreover cursed by the so-called DOF bug, directly affecting the measurement of residual scatter (Lindegren et al 2018). For that reason, from Kiefer et al (2019) it was decided to rely the GASTON analysis, even though this analysis uses preliminary Gaia DR1 data.…”

“…Moreover, the distribution of binary companions in the BD to M dwarf domain, with orbital periods of 1-10 4 d, from which exoplanet candidates could be originating, is not well described. Detections are still lacking in the BD regime -the socalled BD desert (Marcy & Butler 2000) -although this region is constantly being populated (Halbwachs et al 2000;Sahlmann et al 2011a;Díaz et al 2013;Ranc et al 2015;Wilson et al 2016;Kiefer et al 2019). Our sparse knowledge of the low-mass tail of the population of stellar binary companions does not allow us A&A 645, A7 (2021) Table 1.…”