NLTT 41135: a field M-dwarf + brown dwarf eclipsing binary in a triple system, discovered by the MEarth observatory

TL;DR

This paper reports the discovery of a hierarchical triple system involving an M5 dwarf and a brown dwarf companion, with potential for future observations to refine brown dwarf models.

Contribution

It presents the first detailed characterization of an eclipsing brown dwarf companion in a triple system, discovered by the MEarth observatory.

Findings

Brown dwarf companion has a mass of 31-34 MJup.

The system is a hierarchical triple with an M-dwarf pair and a brown dwarf.

Eclipses are grazing, limiting current radius measurements.

Abstract

We report the discovery of an eclipsing companion to NLTT 41135, a nearby M5 dwarf that was already known to have a wider, slightly more massive common proper motion companion, NLTT 41136, at 2.4 arcsec separation. Analysis of combined-light and radial velocity curves of the system indicates that NLTT 41135B is a 31-34 +/- 3 MJup brown dwarf (where the range depends on the unknown metallicity of the host star) on a circular orbit. The visual M-dwarf pair appears to be physically bound, so the system forms a hierarchical triple, with masses approximately in the ratio 8:6:1. The eclipses are grazing, preventing an unambiguous measurement of the secondary radius, but follow-up observations of the secondary eclipse (e.g. with the James Webb Space Telescope) could permit measurements of the surface brightness ratio between the two objects, and thus place constraints on models of brown dwarfs.