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

Kavli Affiliate: Edward H. Morgan

| First 5 Authors: Theron W. Carmichael, Jonathan M. Irwin, Felipe Murgas, Enric Pallé, Keivan G. Stassun

| Summary:

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 $R_b = 1.08 pm 0.03{rm R_J}$, a mass of $M_b = 64.4 pm 2.3{rm M_J}$, an
orbital period of $P = 7.200865 pm 0.00002$ days, and an eccentricity of
$e=0.337pm 0.002$. The host star has a mass of $M_star = 0.53 pm 0.02{rm
M_odot}$, a radius of $R_star= 0.50 pm 0.01{rm R_odot}$, an effective
temperature of $T_{rm eff} = 3621 pm 48{rm K}$, and a metallicity of $rm
[Fe/H]=+0.06pm 0.08$. 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 occupy mass ratios near $q = M_b/M_star approx
0.1$, which separates them from the typical mass ratios for systems with
transiting substellar objects and giant exoplanets that orbit more massive
stars. TOI-2119 is also one of the most active M-dwarf stars known to host a
transiting brown dwarf. 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 $2030pm 84 {rm K}$, which is consistent with predictions by substellar
evolutionary models.

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