Three low-mass companions around aged stars discovered by TESS

Abstract

We report the discovery of three transiting low-mass companions to aged stars: a brown dwarf (TOI-2336b) and two objects near the hydrogen burning mass limit (TOI-1608b and TOI-2521b). These three systems were first identified using data from the Transiting Exoplanet Survey Satellite (TESS). TOI-2336b has a radius of 1.05 ± 0.04 RJ, a mass of 69.9 ± 2.3 MJ and an orbital period of 7.71 days. TOI-1608b has a radius of 1.21 ± 0.06 RJ, a mass of 90.7 ± 3.7 MJ and an orbital period of 2.47 days. TOI-2521b has a radius of 1.01 ± 0.04 RJ, a mass of 77.5 ± 3.3 MJ and an orbital period of 5.56 days. We found all these low-mass companions are inflated. We fitted a relation between radius, mass and incident flux using the sample of known transiting brown dwarfs and low-mass M dwarfs. We found a positive correlation between the flux and the radius for brown dwarfs and for low-mass stars that is weaker than the correlation observed for giant planets. We also found that TOI-1608 and TOI-2521 are very likely to be spin-orbit synchronized, leading to the unusually rapid rotation of the primary stars considering their evolutionary stages. Our estimates indicate that both systems have much shorter spin-orbit synchronization timescales compared to their ages. These systems provide valuable insights into the evolution of stellar systems with brown dwarf and low-mass stellar companions influenced by tidal effects.

TOI-1994b: A Low-mass Eccentric Brown Dwarf Transiting A Subgiant Star

“…We report the discovery of TOI-1994b, a low-mass brown dwarf with moderate eccentricity transiting an evolved star. TOI-1994b is one of only six known brown dwarf companions transiting an evolved star (Carmichael et al 2021;Lin et al 2023;Psaridi et al 2022). The moderate eccentricity of TOI-1994b may present a discrepancy with previous attempts to define brown dwarfs using eccentricity distributions to determine formation mechanisms.…”

“…In addition to planets, TESS is able to detect transiting brown dwarf companions. Out of the 39 confirmed transiting brown dwarf companions currently known, TESS has discovered almost half (Grieves et al 2021;Cañas et al 2022;Carmichael et al 2022;Lin et al 2023;Psaridi et al 2022;Sebastian et al 2022;Vowell et al 2023). The use of TESS to detect transiting brown dwarf companions enables the determination of precise radii, and may therefore illuminate the brown dwarf desert and associated formation mechanisms.…”

Verification of Gaia Data Release 3 Single-lined Spectroscopic Binary Solutions With Three Transiting Low-mass Secondaries

“…TESS light curves have been exhaustively searched for candidate transiting planets (Guerrero et al 2021). Now in its Second Extended Mission, TESS data has led to the discovery of thousands of eclipsing binaries (Prša et al 2022) and over a dozen transiting very-low-mass stars and brown dwarfs (e.g., Grieves et al 2021;Carmichael et al 2022;Psaridi et al 2022;Lin et al 2023;Vowell et al 2023). The population of TESS-discovered eclipsing or transiting systems is biased toward periods shorter than about 10 days due to TESS's observing strategy and the smaller transit probabilities of systems with longer periods.…”