An eccentric Brown Dwarf eclipsing an M dwarf

TL;DR

This paper reports the discovery and characterization of a highly eccentric brown dwarf transiting an M dwarf, providing insights into its properties, orbit, and potential formation scenarios.

Contribution

It presents the first detailed analysis of an eccentric brown dwarf orbiting an M dwarf, including mass, temperature, and orbital parameters, using combined photometry and velocimetry.

Findings

Brown dwarf has a mass of 67±2 M_J

Orbital eccentricity is 0.3362±0.0005

Brightness temperature is 2100±80 K

Abstract

We report the discovery of a $M=67\pm2~\mathrm{M_J}$ brown dwarf transiting the early M dwarf TOI-2119 on an eccentric orbit ($e=0.3362 \pm 0.0005$) at an orbital period of $7.200861 \pm 0.000005$ days. We confirm the brown dwarf nature of the transiting companion using a combination of ground-based and space-based photometry and high-precision velocimetry from the Habitable-zone Planet Finder. Detection of the secondary eclipse with TESS photometry enables a precise determination of the eccentricity and reveals the brown dwarf has a brightness temperature of $2100\pm80$ K, a value which is consistent with an early L dwarf. TOI-2119 is one of the most eccentric known brown dwarfs with $P<10$ days, possibly due to the long circularization timescales for an object orbiting an M dwarf. We assess the prospects for determining the obliquity of the host star to probe formation scenarios and the possibility of additional companions in the system using Gaia EDR3 and our radial velocities.