Production and evolution of Li, Be and B isotopes in the Galaxy

TL;DR

This paper introduces a new model for Galactic cosmic ray origins that self-consistently explains the production and evolution of Li, Be, and B isotopes in the Milky Way, aligning with observations and highlighting the roles of various stellar sources.

Contribution

It presents a novel, self-consistent scheme for GCR composition based on stellar wind yields, improving understanding of light element nucleosynthesis in the Galaxy.

Findings

GCRs produce ~70% of solar B11/B10 ratio

GCR and primordial nucleosynthesis account for at most 30% of solar Li

Radial abundance profiles reveal primary and secondary production processes

Abstract

We reassess the problem of the production and evolution of the light elements Li, Be and B and of their isotopes in the Milky Way, in the light of new observational and theoretical developments. The main novelty is the introduction of a new scheme for the origin of Galactic cosmic rays (GCR), which for the first time enables a self-consistent calculation of their composition during galactic evolution. The scheme accounts for key features of the present-day GCR source composition, it is based on the wind yields of the Geneva models of rotating, mass losing stars and it is fully coupled to a detailed galactic chemical evolution code. We find that the adopted GCR source composition accounts naturally for the observations of primary Be and helps understanding why Be follows closer Fe than O. We find that GCR produce ~70% of the solar B11/B10 isotopic ratio; the remaining 30% of B11 presumably result from neutrino-nucleosynthesis in massive star explosions. We find that GCR and primordial nucleosynthesis can make at most 30% of solar Li. At least half of solar Li has to originate in low-mass stellar sources (red giants, asymptotic giant branch stars or novae), but the required average yields of those sources are found to be much larger than obtained in current models of stellar nucleosynthesis. We also present radial profiles of LiBeB elemental and isotopic abundances in the Milky Way disc. We argue that the shape of those profiles - and the late evolution of LiBeB in general - reveals important features of the production of those light elements through primary and secondary processes.