Dynamical masses for the nearest brown dwarf binary: Epsilon Indi Ba, Bb

TL;DR

This paper reports preliminary astrometric measurements of the nearest brown dwarf binary, Epsilon Indi Ba, Bb, providing a model-independent total mass estimate and plans for future precise individual mass determinations.

Contribution

It offers the first dynamical total mass measurement of Epsilon Indi Ba, Bb using ongoing astrometric monitoring, improving previous estimates and enabling future individual mass measurements.

Findings

Total mass of 121 MJup for the system

System may be as old as 5 Gyr

Upcoming periastron passage will refine individual masses

Abstract

We present preliminary astrometric results for the closest known brown dwarf binary to the Sun: Epsilon Indi Ba, Bb at a distance of 3.626 pc. Via ongoing monitoring of the relative separation of the two brown dwarfs (spectral types T1 and T6) with the VLT NACO near-IR adaptive optics system since June 2004, we obtain a model-independent dynamical total mass for the system of 121 MJup, some 60% larger than the one obtained by McCaughrean et al. (2004), implying that the system may be as old as 5 Gyr. We have also been monitoring the absolute astrometric motions of the system using the VLT FORS2 optical imager since August 2005 to determine the individual masses. We predict a periastron passage in early 2010, by which time the system mass will be constrained to < 1 MJup and we will be able to determine the individual masses accurately in a dynamical, model-independent manner.