A very eccentric brown dwarf coplanar to a warm Jupiter and a hot super Earth

TL;DR

This paper reports the discovery of a unique multi-planet system with a hot super-Earth, a warm Jupiter, and an eccentric brown dwarf, revealing insights into planetary formation and system architecture.

Contribution

It presents the longest-period transiting brown dwarf characterized via RVs, coplanar with inner planets, and discusses formation scenarios of the system.

Findings

Brown dwarf has an eccentricity of 0.622 and a mass of about 16 Jupiter masses.

The system includes a hot super-Earth, a warm Jupiter, and a coplanar eccentric brown dwarf.

The brown dwarf's orbit is the longest-period transiting object characterized via RVs.

Abstract

In transiting planetary systems, where planetary sizes are accurately determined from transit observations, the presence of transit timing variations (TTVs), especially when combined with radial velocity (RV) data, provides powerful constraints on masses and orbital eccentricities. Together, these measurements offer crucial insights into system architecture, formation mechanisms, and dynamical evolution. We present long-term RV and transit/TTV monitoring of the active and young star (age $\sim$1 Gyr) TOI-201, revealing an exceptional multi-planet system composed of a hot super-Earth (SE) transiting every 5.8 days, a warm Jupiter (WJ) on a 53-day orbit, and an eccentric (e = 0.622) low-mass brown dwarf (BD) on an approximately 8-year orbit, with an estimated mass of M$_{\rm BD}$ $\sim$ 16 Jupiter masses. The BD is the longest-period transiting object ever characterized via RVs, and the only one known to be coplanar with inner planets. The architecture of this system suggests that the SE was formed isolated and in the innermost region of the gaseous disc. On the other hand, the orbital configuration of the outer companions suggests a nearly in-situ formation of both objects, with the WJ forming in a dense inner disc. Alternatively, the BD might have formed farther out and migrated inward, while inflating its eccentricity due to interactions with the disc.