Journal Article

An Oasis in the Brown Dwarf Desert: Confirmation of Two Low-mass Transiting Brown Dwarfs Discovered by TESS

Carmichael, Theron W, Winn, Joshua N, Latham, David W, Caldwell, Douglas A, Huber, Daniel, Zhang, Elina Yuchen, Murgas, Felipe, Hounsell, Rebekah, Vezie, Michael, Jenkins, Jon M, Palle, Enric, Osborn, Hugh P, Fukui, Akihiko, Seager, Sara, Stassun, Keivan G, Narita, Norio, Calkins, Michael L

2026

Overview

As the intermediate-mass siblings of stars and planets, brown dwarfs (BDs) are vital to study for a better understanding of how objects change across the planet-to-star mass range. Here, we report two low-mass transiting BD systems discovered by TESS, TOI-4776 (TIC 196286578) and TOI-5422 (TI 80611440), located in an underpopulated region of the BD mass–period space. These two systems have comparable masses but different ages. The younger and larger BD is TOI-4776 b with 32.3−1.7+1.8MJup and 1.01 ± 0.05 RJup, orbiting a late-F star about 4.7−2.5+3.1 Gyr old in an ∼10.41 day period. The older TOI-5422 b has 28.0−1.2+1.6MJup and 0.81 ± 0.03 RJup in an ∼5.38 day orbit around a subgiant star about 7.6−2.6+2.5 Gyr old. Compared with substellar mass–radius evolution models, TOI-4776 b has an inflated radius. In contrast, TOI-5422 b is slightly “underluminous” with respect to model predictions, which is not commonly seen in the BD population. In addition, TOI-5422 shows apparent photometric modulations with a rotation period of 10.8 ± 0.5 days found by rotation analysis, and the stellar inclination angle is obtained to be I⋆=76−12+10 deg. Therefore, it is likely that TOI-5422 b is spinning up the host star and its orbit is aligned with the stellar spin axis.

• Publisher: IOP Publishing
• Subject: Brown dwarf stars / Extrasolar planets / F stars / Inclination angle / Public transportation / Rotation / Stars / Subgiant stars