Duplicity: its part in the AGB's downfall

TL;DR

This paper explores how binary star interactions, especially mass transfer on the asymptotic giant branch, influence stellar evolution, nucleosynthesis, and observable phenomena like barium stars and planetary nebulae.

Contribution

It reviews recent quantitative research on nucleosynthesis in AGB binary systems and proposes AGB stars as a source of lithium enrichment.

Findings

Mass transfer truncates AGB evolution and nucleosynthesis.

Pollution of companion stars reveals AGB nucleosynthesis.

Binary interactions explain certain stellar phenomena.

Abstract

Half or more of stars more massive than our Sun are orbited by a companion star in a binary system. Many binaries have short enough orbits that the evolution of both stars is greatly altered by an exchange of mass and angular momentum between the stars. Such mass transfer is highly likely on the asymptotic giant branch (AGB) because this is when a star is both very large and has strong wind mass loss. Direct mass transfer truncates the AGB, and its associated nucleosynthesis, prematurely compared to in a single star. In wide binaries we can probe nucleosynthesis in the long-dead AGB primary star by today observing its initially lower-mass companion. The star we see now may be polluted by ejecta from the primary either through a wind or Roche-lobe overflow. We highlight recent quantitative work on nucleosynthesis in (ex-)AGB mass-transfer systems, such as carbon and barium stars, the link between binary stars and planetary nebulae, and suggest AGB stars as a possible source of the enigmatic element, lithium.