TOI-2490b- The most eccentric brown dwarf transiting in the brown dwarf desert

TL;DR

This paper reports the discovery of TOI-2490b, the most eccentric transiting brown dwarf in the brown dwarf desert, providing insights into its formation and orbital characteristics through multi-method observations.

Contribution

It presents the first detailed characterization of an extremely eccentric brown dwarf in the desert, combining TESS, radial velocities, and photometry to analyze its properties.

Findings

TOI-2490b has an eccentricity of 0.78.

The brown dwarf's radius appears inflated compared to models.

It is one of only two known highly eccentric brown dwarfs in the desert.

Abstract

We report the discovery of the most eccentric transiting brown dwarf in the brown dwarf desert, TOI02490b. The brown dwarf desert is the lack of brown dwarfs around main sequence stars within $\sim3$~AU and is thought to be caused by differences in formation mechanisms between a star and planet. To date, only $\sim40$ transiting brown dwarfs have been confirmed. \systemt is a $73.6\pm2.4$ \mjupnospace, $1.00\pm0.02$ \rjup brown dwarf orbiting a $1.004_{-0.022}^{+0.031}$ \msunnospace, $1.105_{-0.012}^{+0.012}$ \rsun sun-like star on a 60.33~d orbit with an eccentricity of $0.77989\pm0.00049$. The discovery was detected within \tess sectors 5 (30 minute cadence) and 32 (2 minute and 20 second cadence). It was then confirmed with 31 radial velocity measurements with \feros by the WINE collaboration and photometric observations with the Next Generation Transit Survey. Stellar modelling of the host star estimates an age of $\sim8$~Gyr, which is supported by estimations from kinematics likely placing the object within the thin disc. However, this is not consistent with model brown dwarf isochrones for the system age suggesting an inflated radius. Only one other transiting brown dwarf with an eccentricity higher than 0.6 is currently known in the brown dwarf desert. Demographic studies of brown dwarfs have suggested such high eccentricity is indicative of stellar formation mechanisms.