TOI-2490b- The most eccentric brown dwarf transiting in the brown dwarf desert (2408.04475v1)

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.

• The paper reports the discovery of TOI-2490b with an extreme eccentricity of 0.78, marking it as the most eccentric brown dwarf identified in the brown dwarf desert.
• It utilizes TESS transits, radial velocity measurements, and NGTS data to accurately determine its mass of 73.6 MJ, radius of 1.00 RJ, and a 60.33-day orbit.
• The study challenges existing formation models by revealing age inconsistencies between the host star and the brown dwarf, suggesting minimal tidal interactions and prompting future observational research.

An Insight into TOI-2490b: The Most Eccentric Brown Dwarf in the Brown Dwarf Desert

The research paper explores the discovery and comprehensive analysis of TOI-2490b, an extraordinarily eccentric brown dwarf located within a parameter space notoriously coined as the "brown dwarf desert." This term refers to the observed paucity of brown dwarfs found orbiting main-sequence stars within approximately 3 AU, a region where the dynamical occurrence of planets and stars dramatically diverges. The investigation was led by Beth A. Henderson and a diverse collaboration of international astronomers who adopted observational and analytical methods to characterize this unique sub-stellar companion.

Key Findings

TOI-2490b distinguishes itself by exhibiting an eccentricity of $e = 0.77989 \pm 0.00049$, marking it as the most eccentric brown dwarf identified in this desert region. It possesses a mass of $73.6 \pm 2.4 \ M_J$ and a radius of $1.00 \pm 0.02 \ R_J$, orbiting a G-type star with a period of 60.33 days. Noteworthy is the fact that its host star exhibits characteristics that suggest an old age of around 8 billion years, yet the corresponding model isochrones for TOI-2490b propose a far younger age, implying a potential discrepancy between stellar age assessments and sub-stellar evolutionary models.

The observational data collection spanned various methods, predominantly leveraging the Transiting Exoplanet Survey Satellite (TESS) and supplemented by radial velocity datasets acquired using the FEROS instrument. Further validation was achieved through the Next Generation Transit Survey (NGTS), illustrating robust cross-methodological validation that defines the contours of TOI-2490b’s orbit and physical properties.

Implications and Theoretical Context

This discovery challenges our current understanding of the brown dwarf formation mechanisms, especially given its high eccentricity, which typically suggests origins tied more to stellar rather than planetary processes. Furthermore, the lack of orbital circularization within the system implies minimal tidal interactions, proposing the persistence of primordial characteristics or external dynamical influences during its formation and evolution.

The paper speculates about the evolutionary path of TOI-2490b, contrasting the isochrone age discrepancies with stellar metallicity effects and atmospheric tidal heating. It opens discussions on potentially inflated radii due to high-energy stellar interactions at periastra—a condition that draws parallels yet maintains distinctions with systems such as HD 80606b, a benchmark for high-eccentricity, long-haul hot Jupiters.

Prospective Directions in Research

Moving forward, the paper proposes the necessity of further observational campaigns, particularly at varied wavelengths, to refine transit depth measures and dissect the atmospheric profiles under contrasting radiation conditions. Such follow-ups might elucidate the atmospheric components and energy dissipation mechanisms responsible for the perceived inflated radius, further contributing to our understanding of sub-stellar boundary objects in comparable environments.

In sum, this research not only presents a precise characterization of a unique celestial object but also questions the assumptions underlying brown dwarf population demographics and evolutionary pathways. By embedding TOI-2490b within a broader spectrum of stellar and sub-stellar objects, this work underscores the complex interdependencies of formation, evolution, and potential habitability within the expanses of planetary and stellar science.