TOI-1278 B: SPIRou Unveils a Rare Brown Dwarf Companion in Close-in Orbit around an M Dwarf

We present the discovery of an 18.5 ± 0.5 M_(Jup) brown dwarf (BD) companion to the M0V star TOI–1278. The system was first identified through a percent-deep transit in Transiting Exoplanet Survey Satellite photometry; further analysis showed it to be a grazing transit of a Jupiter-sized object. Radial velocity (RV) follow-up with the SPIRou near-infrared high-resolution velocimeter and spectropolarimeter in the framework of the 300-night SPIRou Legacy Survey carried out at the Canada–France–Hawaii Telescope led to the detection of a Keplerian RV signal with a semi-amplitude of 2306 ± 10 m sâ»Â¹ in phase with the 14.5 day transit period, with a slight but nonzero eccentricity. The intermediate-mass ratio (M⋆/M_(comp) ∼ 31) is unique for having such a short separation (0.095 ± 0.001 au) among known M-dwarf systems. Interestingly, M-dwarf–BD systems with similar mass ratios exist with separations of tens to thousands of astronomical unit. ; © 2021. The American Astronomical Society. Received 2021 March 16; revised 2021 June 7; accepted 2021 June 7; published 2021 September 16. Based on observations obtained at the Canada–France–Hawaii Telescope, which is operated from the summit of Maunakea by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. The observations at the Canada–France–Hawaii Telescope were performed with care and respect from the summit of Maunakea, which is a significant cultural and historic site. This work has been carried out within the framework of the National Centre of Competence in Research PlanetS supported by the Swiss National Science Foundation. J.F.D. acknowledges funding from the European Research Council under the H2020 research & innovation program (grant #740651 NewWorlds). This work was supported by FCT—Fundação para a Ciência e a Tecnologia through national funds and by FEDER through COMPETE2020—Programa Operacional ...