A Small Step on the Long Road to Understanding the R-Stars: CNO Cycling in Candidate R-Star Progenitors

TL;DR

This paper explores the evolution and nucleosynthesis of R-star progenitors resulting from a hypothesized merger between a red-giant and a helium white dwarf, using simulations to assess their properties against observations.

Contribution

It introduces a model simulating the merger-induced ignition and subsequent evolution of R-star progenitors, providing insights into their nucleosynthesis and observable characteristics.

Findings

Model broadly consistent with observed R-star properties

Simulated dredge-up of carbon matches carbon star features

Results depend on merger dynamics details

Abstract

Recent work has proposed that a merger event between a red-giant and a He white dwarf may be responsible for the production of R-stars (Izzard et al, 2007). We investigate the proposed evolution and nucleosynthesis of such a model. We simulate the hypothesized late ignition of the core flash by increasing the neutrino losses until the ignition occurs sufficiently far from the centre that the subsequent evolution produces dredge-up of carbon to the extent that the post-flash object is a carbon star. Detailed nucleosynthesis is performed within this approximation, and we show that the overall properties are broadly consistent with the observations. Details will depend on the dynamics of the merger event.