Zhang, Elina Yuchen; Carmichael, Theron W.; Huber, Daniel; Stassun, Keivan G.; Fukui, Akihiko; Narita, Norio; Murgas, Felipe; Pall茅, Enric; Latham, David W.; Calkins, Michael L.; Seager, Sara; Winn, Joshua N.; Vezie, Michael; Hounsell, Rebekah; Osborn, Hugh P.; Caldwell, Douglas A.; Jenkins, Jon M. (2026).听.听Astronomical Journal, 171(2), 62.听
Brown dwarfs (BDs)聽are objects with masses between planets and stars, making them useful for understanding how properties change across this range. In this study, researchers report the discovery of two such objects鈥�TOI-4776 b听补苍诲听TOI-5422 b鈥攊dentified using data from the TESS space telescope. Both are聽transiting systems, meaning the brown dwarf passes in front of its host star, causing a small, measurable dip in brightness that reveals its size and orbit. Although the two objects have similar masses, they differ in age and physical properties.
TOI-4776 b is younger and larger, orbiting its star every ~10 days, and appears聽鈥渋苍蹿濒补迟别诲鈥�鈥攊ts radius is bigger than expected based on standard models of how brown dwarfs evolve. In contrast, TOI-5422 b is older, smaller, and orbits more quickly (about every 5 days). It appears slightly聽鈥涡苍诲别谤濒耻尘颈苍辞耻蝉,鈥�聽meaning it emits less light than models predict, which is unusual for objects like this.
The study also found that the star hosting TOI-5422 b shows brightness variations linked to its rotation, suggesting the brown dwarf may be influencing the star鈥檚 spin. The alignment between the star鈥檚 rotation and the brown dwarf鈥檚 orbit indicates a close dynamical relationship. Overall, these two systems provide valuable examples for testing and refining models of how brown dwarfs form and evolve over time.
Figure 1.聽Detrended TESS light curve of TOI-5422 shown as dark blue points. The star was observed at 10 minute cadence in TESS Sectors 43, 44, and 45, and 2 minute cadence in Sectors 71 and 72. Removed TESS data in Sectors 43鈥�45 are shown as gray points. The binning shown here as yellow points uses bin sizes of 90 minutes. This star also exhibits photometric variations likely due to stellar rotation; these effects have been removed for the transit analysis. The red line is the fitted model from聽EXOFASTv2.