# Hubble Space Telescope astrometry of the closest brown dwarf binary system -- I. Overview and improved orbit

## TL;DR

This paper presents high-precision Hubble Space Telescope astrometry of the nearby brown dwarf binary WISE J104915.57-531906.1, improving orbital estimates and excluding additional companions down to Neptune mass.

## Contribution

It provides the first detailed orbital analysis and improved astrometric measurements of the closest brown dwarf binary system using HST data.

## Key findings

- Improved orbital parameters and mass ratio estimates.
- Exclusion of third bodies with Neptune-like masses and periods over a year.
- Observation of the binary at apparent periastron in 2016.

## Abstract

Located at ~2pc, the L7.5+T0.5 dwarfs system WISE J104915.57-531906.1 (Luhman16AB) is the third closest system known to Earth, making it a key benchmark for detailed investigation of brown dwarf atmospheric properties, thermal evolution, multiplicity, and planet-hosting frequency. In the first study of this series -- based on a multi-cycle Hubble Space Telescope (HST) program -- we provide an overview of the project and present improved estimates of positions, proper motions, annual parallax, mass ratio, and the current best assessment of the orbital parameters of the A-B pair. Our HST observations encompass the apparent periastron of the binary at 220.5+/-0.2 mas at epoch 2016.402. Although our data seem to be inconsistent with recent ground-based astrometric measurements, we also exclude the presence of third bodies down to Neptune masses and periods longer than a year.