Rotational mixing in close binaries

TL;DR

This paper investigates rotational mixing in massive close binary stars, predicting nitrogen enhancements and proposing a new evolutionary pathway where stars evolve homogeneously, stay compact, and form close WR binaries.

Contribution

It introduces a method to test rotational mixing efficiency using close binaries and proposes the novel Case M evolutionary scenario for very massive stars.

Findings

Predicted nitrogen surface enhancements in tidally locked binaries.

Demonstrated the feasibility of quasi-chemical homogeneous evolution in massive binaries.

Proposed the formation of very close WR binaries via Case M evolution.

Abstract

Rotational mixing is a very important but uncertain process in the evolution of massive stars. We propose to use close binaries to test its efficiency. Based on rotating single stellar models we predict nitrogen surface enhancements for tidally locked binaries. Furthermore we demonstrate the possibility of a new evolutionary scenario for very massive (M > 40 solar mass) close (P < 3 days) binaries: Case M, in which mixing is so efficient that the stars evolve quasi-chemically homogeneously, stay compact and avoid any Roche-lobe overflow, leading to very close (double) WR binaries.