On the mass segregation of cores and stars

TL;DR

This paper investigates the apparent contradiction between mass segregation observed in cores and stars in star-forming regions, proposing that stellar dynamical evolution explains the differences.

Contribution

It introduces a fragmentation model that reproduces the initial mass function and suggests dynamical evolution causes the observed differences in mass segregation.

Findings

Fragmentation can reproduce the stellar initial mass function.

Massive cores tend to produce massive stars if few fragments form.

Dynamical evolution likely explains the lack of mass segregation in stars.

Abstract

Observations of pre-/proto-stellar cores in young star-forming regions show them to be mass segregated, i.e. the most massive cores are centrally concentrated, whereas pre-main sequence stars in the same star-forming regions (and older regions) are not. We test whether this apparent contradiction can be explained by the massive cores fragmenting into stars of much lower mass, thereby washing out any signature of mass segregation in pre-main sequence stars. Whilst our fragmentation model can reproduce the stellar initial mass function, we find that the resultant distribution of pre-main sequence stars is mass segregated to an even higher degree than that of the cores, because massive cores still produce massive stars if the number of fragments is reasonably low (between one and five). We therefore suggest that the reason cores are observed to be mass segregated and stars are not is likely due to dynamical evolution of the stars, which can move significant distances in star-forming regions after their formation.