The exemplar T8 subdwarf companion of wolf 1130

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 yr baseline. Wolf 1130 is located 15.83 ± 0.96 pc 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. © 2013. The American Astronomical Society. All rights reserved.