Ultracool Dwarf Binaries

Phase-fold radial velocity curve of the shortest-period ultracool dwarf LP 413-53AB (Hsu et al. 2023).

Binaries are a direct product of star formation. They provide measurements of mass, separation, orbital period and eccentricity which can be used to constrain the star formation models. Using the precise radial velocity (RV) using the forward-modeling method, I found the first RV-verified T dwarfs J1106+2754 and J2126+7617 and the shortest-orbital-period ultracool dwarf binary LP 413-53AB. I also contributed to RV measurements of a young ultracool dwarf (likely) triple system DENIS J0630+1840.
In particular, M9 LP 413-53AB is the shortest-orbital-period (0.71 days = 17 hours) ultracool dwarf binary discovered so far, almost four times shorter than the previously reported short-period binary of 2.9 days. The nature of its binaries is clearly shown within two hours of Keck/NIRSPEC observations. What is interesting is that this system has a nearly circular orbit and an old age compared to other short-period ultracool dwarf binaries. Their separation is just 17-19 stellar radii, implying they have moved to a closer configuration since their birth. We think the system can be formed from a (wider) binary or a triple system in the beginning but their origin is unclear. Identifying more binary/multiple systems would allow us to sample their parameter space, including mass, separation, orbital period, eccentricity, and hopefully ages. Check out the news coverages from Northwestern, Keck, CNET, Earth Sky, Sky and Telescope and space.com!