The Exemplar T8 Subdwarf Companion of Wolf 1130

TL;DR

This paper reports the discovery of a wide-separation T8 subdwarf companion to Wolf 1130, providing a unique benchmark for studying low-metallicity, high-gravity brown dwarfs with implications for atmospheric models.

Contribution

The discovery of WISE J200520.38+542433.9 as the most extreme low-metallicity T dwarf companion to Wolf 1130, offering new insights into subdwarf properties and atmospheric modeling.

Findings

Most extreme inferred metallicity for a T dwarf to date ([Fe/H] = -0.64)

Supports the subdwarf's old age, low metallicity, and small radius

Highlights the need to improve low-metallicity atmospheric models

Abstract

We have discovered a wide separation (188.5") T8 subdwarf companion to the sdM1.5+WD binary Wolf 1130. Companionship of WISE J200520.38+542433.9 is verified through common proper motion over a ~3 year baseline. Wolf 1130 is located 15.83 +/- 0.96 parsecs from the Sun, placing the brown dwarf at a projected separation of ~3000 AU. Near-infrared colors and medium resolution (R~2000-4000) spectroscopy establish the uniqueness of this system as a high-gravity, low-metallicity benchmark. Although there are a number of low-metallicity T dwarfs in the literature, WISE J200520.38+542433.9 has the most extreme inferred metallicity to date with [Fe/H] = -0.64 +/- 0.17 based on Wolf 1130. Model comparisons to this exemplar late-type subdwarf support it having an old age, a low metallicity, and a small radius. However, the spectroscopic peculiarities of WISE J200520.38+542433.9 underscore the importance of developing the low-metallicity parameter space of the most current atmospheric models.