TOI-1278 B: SPIRou unveils a rare Brown Dwarf Companion in Close-In Orbit around an M dwarf
\'Etienne Artigau, Guillaume H\'ebrard, Charles Cadieux, Thomas, Vandal, Neil J. Cook, Ren\'e Doyon, Jonathan Gagn\'e, Claire Moutou, Eder, Martioli, Antonio Frasca, Farbod Jahandar, David Lafreni\`ere, Lison Malo,, Jean-Fran\c{c}ois Donati, Pia Cortes-Zuleta, Isabelle Boisse

TL;DR
This paper reports the discovery of a rare brown dwarf companion orbiting an M dwarf star, using TESS photometry and SPIRou radial velocity measurements, revealing a close-in orbit with unique system characteristics.
Contribution
It presents the first detailed characterization of a close-in brown dwarf around an M dwarf using near-infrared spectroscopy, highlighting its rarity and system properties.
Findings
Brown dwarf companion has a mass of 18.5 M_Jup.
Detected a 14.5-day orbital period with RV semi-amplitude of 2306 m/s.
System has a short separation of 0.095 AU with a unique mass ratio.
Abstract
We present the discovery of an M brown dwarf (BD) companion to the M0V star TOI-1278. The system was first identified through a percent-deep transit in TESS 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 (SLS) carried out at the Canada-France-Hawaii Telescope (CFHT) led to the detection of a Keplerian RV signal with a semi-amplitude of m/s in phase with the 14.5-day transit period, having a slight but non-zero eccentricity. The intermediate-mass ratio () is unique for having such a short separation ( AU) among known M-dwarf systems. Interestingly, M dwarf-brown dwarf systems with similar mass ratios…
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