Milli-arcsecond Binaries

TL;DR

This study used VLBA to measure precise parallaxes and high-resolution imaging, revealing a high fraction of tight binaries among young stars, likely due to selection effects.

Contribution

The paper provides the first high-resolution images of young stellar systems and highlights the prevalence of tight binaries, emphasizing the impact of selection biases.

Findings

70% of observed young stars are tight binaries

High-resolution imaging achieved ~1 mas resolution

Selection effects likely influence binary fraction estimates

Abstract

As part of an astrometric program, we have used the Very Long Baseline Array to measure the trigonometric parallax of several young stars in the Taurus and Ophiuchus star-forming regions with great accuracy. Additionally, we have obtained an unprecedented sample of high-resolution (~ 1 mas) images of several young stellar systems. These images revealed that about 70% of the stars in our sample are very tight binary stars (with separations of a few mas). Since it is highly unlikely that 70% of all stars are such tight binaries, we argue that selection effects are at work.