Gaia Detection Capabilities of Spectroscopic Brown Dwarf Binaries

TL;DR

This paper assesses Gaia's ability to detect brown dwarf binaries through astrometry, supported by precise radial velocity measurements of two systems, predicting detectable signals for these binaries.

Contribution

It provides the first detailed predictions of Gaia's detection capabilities for specific brown dwarf binaries with known RV orbits.

Findings

Gaia can detect astrometric signals of 1.2-1.6 mas for ChaHa8.

Gaia can detect signals of 0.4-0.8 mas for CHXR74.

A relation for astrometric signature considering companion luminosity is presented.

Abstract

The astrometric space mission Gaia is expected to detect a large number of brown dwarf binary systems with close orbits and determine astrometric orbit solutions. This will provide key information for the formation and evolution of brown dwarfs, such as the binary frequency and dynamical masses. Known brown dwarf binaries with orbit constraints from other techniques will play an important role. We are carrying out one of the most precise and long-lasting radial velocity surveys for brown dwarf binaries in the Cha I star-forming region at the VLT. We were able to add two orbit determinations to the small group of a handful of brown dwarf and very low-mass binaries with characterized RV orbits. We show here that the astrometric motion of both systems can be detected with Gaia. We predict an astrometric signal of about 1.2 - 1.6 milliarcseconds (mas) for the brown dwarf binary ChaHa8 and of 0.4 - 0.8 mas for the very low-mass binary CHXR74. We take the luminosity of the companion into account for these estimates and present a relation for the astrometric signature of a companion with non-negligible luminosity.