A Spectroscopic Binary at the M/L Transition

TL;DR

This paper reports the discovery of the first small separation spectroscopic binary among M/L transition dwarfs, providing a valuable system for future dynamical mass measurements of ultra cool dwarfs.

Contribution

It presents the first known small separation spectroscopic binary at the M/L transition, with detailed orbital parameters derived from radial velocity measurements.

Findings

Orbital period of approximately 247 days.

Estimated secondary mass of about 0.054 solar masses.

Potential for direct dynamical mass determination with future observations.

Abstract

We report the discovery of a single-lined spectroscopic binary with an Ultra Cool Dwarf (UCD) primary with a spectral type between M8 and L0.5. This system was discovered during the course of an ongoing survey to monitor L dwarfs for radial velocity variations and is the first known small separation (a<1 AU) spectroscopic binary among dwarfs at the M/L transition. Based on radial-velocity measurements with a typical precision of 300 m/s we estimate the orbital parameters of this system to be P=246.73+/-0.49 d, a1 sin(i)=0.159+/-0.003 AU, M2 sin(i)=0.2062 (M1+M2)^(2/3)+/-0.0034 M_{\sun}. Assuming a primary mass of M1=0.08M_{\sun} (based on spectral type), we estimate the secondary minimum mass to be M2 sin(i)=0.054 M_{\sun}. With future photometric, spectroscopic, and interferometric observations it may be possible to determine the dynamical masses of both components directly, making this system one of the best characterized UCD binaries known.