J1250+0455AB an ultracool binary in a hierarchical triple system

This is the authors' abstract. We don't add key points for this paper.

We report the discovery of the ultracool dwarf binary system J1250+0455AB, a low-mass (M__tot <$ 0.2 M$_$) system in which the components straddle the M/L dwarf boundary. The binary was resolved through near-infrared adaptive optics imaging with LUCI1-SOUL on the Large Binocular Telescope, revealing a projected angular separation of 0.17 ± 0.015 arcsec, which, combined with a system distance of 71 ± 5.8 pc, corresponds to a physical separation of 12.2 ± 1.5 AU at a position angle of 84.8 ± 0.2∘. We estimated the orbital period of J1250+0455AB to be 156 ± 8 yr, the bolometric luminosities of the primary and secondary luminosities as log (Lbol / L₎ = -3.45 ± 0.04 and -3.58 ± 0.04, respectively, with the spectral types of M9 and L0 determined through binary template fitting and spectrophotometric relations. This binary system is part of a hierarchical triple with a separation of 10.44 arcsec from its primary. We estimated the age of the system from the rotational period of the primary star as 0.56+0.07-0.06 Gyr. Using evolutionary models, for each component we estimate the mass [0.079 ± 0.002 M_ / 0.072 ± 0.003 M_], effective temperature [2350 ± 38 K / 2200 ± 43 K], and radius [0.113 ± 0.003 R_ / 0.108 ± 0.002 R_]. Based on the system’s binding energy, total mass, and separation, J1250+0455AB is predicted to be a highly stable system, remaining bound for $>$10 Gyr. J1250+0455AB extends the growing population of UCD benchmark systems, providing a new system for refining evolutionary theories at the lowest stellar masses into the substellar regime.