TOI-2119: A transiting brown dwarf orbiting an active M-dwarf from NASA's TESS mission

Abstract

We report the discovery of TOI-2119b, a transiting brown dwarf (BD) that orbits and is completely eclipsed by an active M-dwarf star. Using light curve data from the Transiting Exoplanet Survey Satellite mission and follow-up high-resolution Doppler spectroscopic observations, we find the BD has a radius of $R_b=1.08\pm 0.03{\mathrm{R}}_{\mathrm{J}}$, a mass of $M_b=64.4\pm 2.3{\mathrm{M}}_{\mathrm{J}}$, an orbital period of $P=7.200865\pm 0.00002$ days, and an eccentricity of $e=0.337\pm 0.002$. The host star has a mass of $M_{\star }=0.53\pm 0.02{\mathrm{M}}_{\odot }$, a radius of $R_{\star }=0.50\pm 0.01{\mathrm{R}}_{\odot }$, an effective temperature of $T_{\mathrm{eff}}=3621\pm 48$K, and a metallicity of $[Fe/H]=+0.06\pm 0.08$. TOI-2119b joins an emerging population of transiting BDs around M-dwarf host stars, with TOI-2119 being the ninth such system. These M-dwarf--brown dwarf systems typically occupy mass ratios near $q=M_b/M_{\star }\approx 0.1-0.2$, which separates them from the typical mass ratios for systems with transiting substellar objects and giant exoplanets that orbit more massive stars. The nature of the secondary eclipse of the BD by the star enables us to estimate the effective temperature of the substellar object to be $2030\pm 84$K, which is consistent with predictions by substellar evolutionary models.

14 pages, 13 figures, 4 tables, accepted in MNRAS

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• Improved radius determinations for the transiting brown dwarf population in the era of Gaia and TESS
• HIP 33609 b: An Eccentric Brown Dwarf Transiting a V=7.3 Rapidly Rotating B-Star
• Three low-mass companions around aged stars discovered by TESS
• The OATMEAL Survey. I. Low Stellar Obliquity in the Transiting Brown Dwarf System GPX-1
• The First Spin-Orbit Obliquity of an M dwarf/brown dwarf System: An eccentric and aligned TOI-2119 b
• The Impact of Irradiation on the Radius and Thermal Evolution of Transiting Brown Dwarfs
• The OATMEAL Survey. III. An Aligned Transiting Warm Brown Dwarf and Evidence for Quiescent Brown Dwarf Migration
• A New Brown Dwarf Orbiting an M star and An Investigation on the Eccentricity Distribution of Transiting Long-Period Brown Dwarfs
• Evidence of Radius Inflation Based on 50 Transiting Brown Dwarfs and Low-mass Stellar Companions