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

E. Artigau, G. Hébrard, C. Cadieux, T. Vandal, N. J. Cook, R. Doyon, J. Gagné, C. Moutou, E. Martioli, A. Frasca, F. Jahandar, D. Lafrenière, L. Malo, J.-F. Donati, P. Cortés-Zuleta, I. Boisse, X. Delfosse, A. Carmona, P. Fouqué, J. Morin, J. F. Rowe, G. Marino, R. Papini, D. Ciardi, M. B. Lund, J. H. C. Martins, S. Pelletier, L. Arnold, F. Bouchy, T. Forveille, N. C. Santos, X. Bonfils, P. Figueira, M. M. Fausnaugh, G. R. Ricker, D. W. Latham, S. Seager, J. N. Winn, J. M. Jenkins, E. B. Ting, G. Torres, J. Gomes da Silva

Abstract
We present the discovery of an 18.5 ± 0.5 MJup 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 s−1 in phase with the 14.5 day transit period, with a slight but nonzero eccentricity. The intermediate-mass ratio (M/Mcomp ∼ 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.

Keywords
Brown dwarfs; Radial velocity; Transit photometry; Transits; M dwarf stars; Astrophysics - Solar and Stellar Astrophysics; Astrophysics - Earth and Planetary Astrophysics

The Astronomical Journal
Volume 162, Number 4
2021 October

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