NGTS-19b : A high mass transiting brown dwarf in a 17-day eccentric orbit

TL;DR

NGTS-19b is a newly discovered high-mass brown dwarf transiting a K-star with a 17.84-day eccentric orbit, providing insights into brown dwarf characteristics and the brown dwarf desert.

Contribution

This paper reports the discovery and detailed characterization of NGTS-19b, a high-mass brown dwarf in a long-period eccentric orbit, expanding the known population of transiting brown dwarfs.

Findings

NGTS-19b has a mass of approximately 69.5 M_Jup and a radius of about 1.03 R_Jup.

The system exhibits a high orbital eccentricity of 0.3767.

The brown dwarf appears inflated, inconsistent with age estimates from the host star.

Abstract

We present the discovery of NGTS-19b, a high mass transiting brown dwarf discovered by the Next Generation Transit Survey (NGTS). We investigate the system using follow up photometry from the South African Astronomical Observatory, as well as sector 11 TESS data, in combination with radial velocity measurements from the CORALIE spectrograph to precisely characterise the system. We find that NGTS-19b is a brown dwarf companion to a K-star, with a mass of $69.5 ^{+5.7}_{-5.4}$ M$_{Jup}$ and radius of $1.034 ^{+0.055}_{-0.053}$ R$_{Jup}$. The system has a reasonably long period of 17.84 days, and a high degree of eccentricity of $0.3767 ^{+0.0061}_{-0.0061}$. The mass and radius of the brown dwarf imply an age of $0.46 ^{+0.26}_{-0.15}$ Gyr, however this is inconsistent with the age determined from the host star SED, suggesting that the brown dwarf may be inflated. This is unusual given that its large mass and relatively low levels of irradiation would make it much harder to inflate. NGTS-19b adds to the small, but growing number of brown dwarfs transiting main sequence stars, and is a valuable addition as we begin to populate the so called brown dwarf desert.