Exploring the binary origin of B and Be rapid rotators

TL;DR

This paper investigates the binary origin of rapidly rotating B and Be stars, suggesting many are post-mass transfer systems, and compares observations with binary evolution models to understand their formation and implications.

Contribution

It provides evidence that many mid- and late-type rapid rotators are likely post-interaction binaries and compares observed properties with BPASS model predictions.

Findings

A significant fraction of rapid rotators are likely post-mass transfer binaries.

Comparison of observed properties with BPASS models supports binary interaction origins.

Implications for stellar evolution, supernovae, and binary mergers are discussed.

Abstract

Observational evidence has continued to mount that a significant fraction of rapidly rotating early-B type stars are products of binary mass transfer. However, very few mid- and late-type B stars with rapid rotation have been demonstrated to be post-interaction products, despite a growing sample of SB1 binaries among stars within this range of spectral types. By considering the currently available information over the entire range of rapidly rotating B-type binaries, we argue that a significant fraction of the mid- and late-type rapid rotators found in binaries are also likely the result of past mass transfer episodes. The observed properties of this sample are compared to the predictions from the Binary Population and Spectral Synthesis code (BPASS), with attention given to the expected evolutionary pathways of stripped stars and the stellar and binary properties of both components of post-interaction systems across a range of initial conditions. Prospects for directly detecting and characterizing the stripped cores of the previous mass donors in such systems are described, and the implications for the role of binary interaction in causing rapid rotation are discussed. An accurate description of prevalence of binary interaction, the physics of mass transfer, and the post-interaction configuration of systems over a range of initial conditions has far-reaching implications including double-degenerate binaries and their eventual mergers, the output of ionizing UV flux of stellar populations, and the supernova explosions that can arise from stripped or rapidly-rotating progenitors.