Benchmark brown dwarfs -- I. A blue M2 + T5 wide binary and a probable young [M4 + M4] + [T7 + T8] hierarchical quadruple

TL;DR

This paper reports the discovery of two new multiple systems with T dwarf companions, including a wide binary with a mildly metal-poor M2 dwarf and a hierarchical quadruple system, enriching the sample of benchmark brown dwarfs for model calibration.

Contribution

It presents the identification and characterization of two new benchmark systems containing T dwarfs, including a rare mildly metal-poor binary and a probable planetary-mass T dwarf in a hierarchical quadruple.

Findings

L 122-88 AB is a wide binary with a mildly metal-poor M2 dwarf and a T5 dwarf.

UPM J1040-3551 AB is a hierarchical quadruple system with two M4 dwarfs and a T7+T8 binary.

The T8 component in UPM J1040-3551 has a mass estimate of 9-28 Jupiter masses.

Abstract

Benchmark brown dwarfs in wide binary systems are crucial for characterizing substellar objects and calibrating atmospheric and evolutionary models. However, brown dwarf benchmarks with subsolar metallicity, very cool temperatures, or suitability for dynamical mass measurements are rare, limiting our understanding across the full range of mass, age, and metallicity. We present the discovery of two new multiple systems containing T dwarf companions, identified through a targeted search using CatWISE2020 and Gaia catalogues. L 122-88 AB is a wide binary comprising a mildly metal-poor M2 dwarf and a T5 dwarf, separated by 215.6 arcsec at a distance of 33.106+/-0.014 pc. Atmospheric model fitting to the near infrared spectrum of L 122-88 A suggests a mildly metal-poor composition ([Fe/H] = -0.2). UPM J1040-3551 AB is a candidate hierarchical quadruple system at 25.283+/-0.013 pc, consisting of a likely astrometric binary of two M4 dwarfs and a probable unresolved spectral binary of T7 and T8 dwarfs, separated by 65.48 arcsec from the primary. The H-alpha emission detected in UPM J1040-3551 A indicates an age range of 0.3-2.0 Gyr. This age estimate suggests that the T8 component has a mass between 9 and 28 Jupiter masses, potentially classifying it as a planetary-mass object. These systems augment the sample of benchmark brown dwarfs, particularly in the underexplored regime of cool temperature, providing valuable opportunities for refining our understanding of substellar objects.