We present the confirmation of SDSS J222551.65+001637.7AB as a closely separated, resolved, white dwarf-brown dwarf binary. We have obtained spectroscopy from GNIRS and seeing-limited $K_s$-band imaging from NIRI on Gemini North. The target is spatially resolved into its constituent components: a 10926$ \pm$ 246 K white dwarf, with log $g = 8.214 \pm 0.168$ and a mass of 0.66$^{ +0.11}_{ -0.06}$ M$_{ \odot}$, and an L4 brown dwarf companion, which are separated by $0.9498 \pm 0.0022$". We derive the fundamental properties of the companion from the Sonora-Bobcat evolutionary models, finding a mass of $25-53$ M$_{ \text{ Jup}}$ and a radius of $0.101-0.128$ R$_{ \odot}$ for the brown dwarf, at a confidence level of 1$\sigma$. We use wdwarfdate to determine the age of the binary as $1.97^{ +4.41}_{ -0.76}$ Gyr. A kinematic analysis shows that this binary is likely a member of the thick disc. The distance to the binary is 218$^{ +14}_{ -13}$ pc, and hence the projected separation of the binary is 207$^{ +13}_{ -12}$ AU. Whilst the white dwarf progenitor was on the main sequence the binary separation would have been $69 \pm 5$ AU. SDSS J222551.65+001637.7AB is the third closest spatially resolved white dwarf-brown dwarf binary after GD 165AB and PHL 5038AB.
Categories: astro-ph.SR astro-ph.EP