A discontinuity in the low-mass initial mass function

TL;DR

This paper demonstrates a clear discontinuity in the initial mass function at the low-mass end, indicating that brown dwarfs and stars are distinct populations with different formation histories.

Contribution

It provides evidence against a continuous IMF in the very-low-mass star and brown dwarf regime, proposing they are separate populations with different origins.

Findings

Discontinuous mass distribution at the VLMS and BD boundary.

Approximately one brown dwarf forms per five stars.

BD-star binary fraction is about 2-3%.

Abstract

The origin of brown dwarfs (BDs) is still an unsolved mystery. While the standard model describes the formation of BDs and stars in a similar way recent data on the multiplicity properties of stars and BDs show them to have different binary distribution functions. Here we show that proper treatment of these uncovers a discontinuity of the multiplicity-corrected mass distribution in the very-low-mass star (VLMS) and BD mass regime. A continuous IMF can be discarded with extremely high confidence. This suggests that VLMSs and BDs on the one hand, and stars on the other, are two correlated but disjoint populations with different dynamical histories. The analysis presented here suggests that about one BD forms per five stars and that the BD-star binary fraction is about 2%-3% among stellar systems.