B[e] supergiants: What is their evolutionary status?

TL;DR

This paper explores the evolutionary origins of B[e] supergiants, proposing three main scenarios involving critical rotation, recent red supergiant departure, and binary mergers, to explain their circumstellar disks.

Contribution

It introduces and compares three novel hypotheses for the evolutionary status of B[e] supergiants based on stellar evolution theory.

Findings

Three possible evolutionary scenarios for B[e] supergiants are identified.

Different predictions are made for the duration and properties of the B[e] phase.

Observational tests could distinguish between the proposed scenarios.

Abstract

In this paper, we investigate the evolutionary status of B[e]~stars from the point of view of stellar evolution theory. We try to answer to the question of how massive hot supergiants --- i.e. evolved stars --- can be capable of producing a circumstellar disk. We find and discuss three possibilities: very massive evolved main sequence stars close to critical rotation due to their proximity to their Eddington-limit, blue supergiants which have just left the red supergiant branch, and single star merger remnants of a close binary system. While the latter process seems to be required to understand the properties of the spectroscopic binary R4 in the LMC, the other two scenarios may be capable of explaining the distribution of the B[e] stars in the HR~diagram. The three scenarios make different predictions about the duration of the B[e]~phase, the time integrated disk mass and the stellar properties during the B[e]~phase, which may ultimately allow to distinguish them observationally.