The nature of B supergiants: clues from a steep drop in rotation rates at 22000 K. The possibility of Bi-stability braking

TL;DR

This paper investigates the rotation rate drop in B supergiants at 22000 K, exploring whether it marks the end of the main sequence or results from bi-stability braking due to enhanced mass loss, impacting massive star evolution.

Contribution

It introduces the concept of bi-stability braking as a new explanation for the rotation rate drop in B supergiants and discusses its implications for stellar evolution models.

Findings

Steep drop in rotation rates at 22000 K in B supergiants.

Potential link between the drop and bi-stability jump.

Implications for core overshooting and mass loss in models.

Abstract

The location of B supergiants in the Hertzsprung-Russell diagram (HRD) represents a long-standing problem in massive star evolution. Here we propose their nature may be revealed utilising their rotational properties, and we highlight a steep drop in massive star rotation rates at an effective temperature of 22000 K. We discuss two potential explanations for it. On the one hand, the feature might be due to the end of the main sequence, which could potentially constrain the core overshooting parameter. On the other hand, the feature might be the result of enhanced mass loss at the predicted location of the bi-stability jump. We term this effect "bi-stability breaking" and discuss its potential consequences for the evolution of massive stars.