TOI-2155 b: A Massive Brown Dwarf or a Very Low-mass Star?

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Abstract
We present TOI-2155 b, a massive transiting companion, discovered using data from NASA’s Transiting Exoplanet Survey Satellite mission and confirmed with ground-based radial velocity measurements from the Tillinghast Reflector Echelle Spectrograph. We also analyze ground-based follow-up photometric data from the Wendelstein Observatory, Las Cumbres Observatory Global Telescope, and Wild Boar Remote Observatory. TOI-2155 b is a short-period companion with P = 3.7246950 ± 0.0000014 days. The radius and mass of TOI-2155 b are found to be R b = 0.97 2 − 0.008 + 0.009 R J and M b = 80 . 6 − 1.1 + 1.0 M J , respectively, corresponding to a density of ρ b = 10 9 − 3.3 + 3.1 g cm −3 . The F-type subgiant host star has an effective temperature of T eff = 6085 ± 78 K, a radius R ⋆ = 1.70 5 − 0.064 + 0.066 R ⊙ , and a mass M ⋆ = 1.33 ± 0.008 M ⊙ . With a mass close to the hydrogen-burning minimum mass, TOI-2155 b lies at the boundary between brown dwarfs and low-mass stars. Its measured mass, radius, and density place it in a transitional region, where distinguishing between a massive brown dwarf and a very low-mass star is not straightforward. TOI-2155 b therefore provides a valuable benchmark for testing evolutionary models of stellar and substellar structure near the hydrogen-burning limit.
Funding Information
  • University of Sydney (541039110)

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