Stellar Triples as a Source for Ba Stars

TL;DR

This paper explores the formation of Barium stars through hierarchical triple systems, proposing that Roche Lobe overflow from a tertiary star can lead to surface enrichment and binary mergers, potentially explaining many observed Barium stars.

Contribution

It introduces the hypothesis that hierarchical triples can produce Barium stars via tertiary Roche Lobe overflow, a process not previously emphasized in classical models.

Findings

Hierarchical triples can produce Barium stars through tertiary Roche Lobe overflow.

This formation channel may account for a significant fraction of Barium stars.

Further studies are needed to quantify the contribution of triple systems.

Abstract

Barium stars have been studied extensively over the past few decades, yet our current understanding of how these intriguing objects formed leaves much to be desired. Many trends observed in systems containing barium stars cannot be satisfactorily explained by classical binary evolution models, naturally raising the question of whether triples and other higher-order multiples can give rise to such exotic objects. In this paper, we study the possibility that a Roche Lobe overflow from a tertiary in a hierarchical triple system can potentially lead to surface barium enrichment within the inner binary, while at the same time causing the inner binary to merge, thereby producing a barium star. This possibility has the potential to form a large proportion of Barium stars, as Roche Lobe overflow from a tertiary is typically much more stable for close orbits than that from a binary companion. Various formation channels and mechanisms by which this can be achieved are considered, and constraints on relative formation rates are placed on each scenario. We conclude that a significant, if not dominant, proportion of barium stars are formed from hierarchical triple systems, and that further studies are required in this area before a complete understanding of Barium star populations can be achieved.