Ultracool Dwarf Binaries

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 forward-modeling method to measure precise radial velocity (RV), I found the first RV-verified T dwarf binaries 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 binary nature 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 coverage from Northwestern, Keck, CNET, EarthSky, Sky & Telescope and Space.com!