Limits on the primordial stellar multiplicity

¹ School of Physics & Astronomy, Cardiff University, 5 The Parade, Cardiff CF24 3YB, UK e-mail: Simon.Goodwin@astro.cf.ac.uk
² Sternwarte, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
³ Rhine Stellar Dynamical Network

Received: 7 January 2005
Accepted: 10 May 2005

Abstract

Most stars – especially young stars – are observed to be in multiple systems. Dynamical evolution is unable to pair stars efficiently, which leads to the conclusion that star-forming cores must usually fragment into 2 stars. However, the dynamical decay of systems with 3 or 4 stars would result in a large single-star population that is not seen in the young stellar population. Additionally, ejections would produce a significant population of close binaries that are not observed. This leads to a strong constraint on star formation theories that cores must typically produce only 2 or 3 stars. This conclusion is in sharp disagreement with the results of currently available numerical simulations that follow the fragmentation of molecular cores and typically predict the formation of 5–10 seeds per core. In addition, open cluster remnants may account for the majority of observed highly hierarchical higher-order multiple systems in the field.