Post-Red Supergiants

TL;DR

This paper reviews the transitional post-Red Supergiant phase of massive star evolution, focusing on yellow hypergiants, their properties, recent observational results, and evidence of their evolutionary history.

Contribution

It provides a comprehensive review of the scarce known post-Red Supergiants, highlighting recent observational techniques and findings that shed light on their evolution.

Findings

Identification of two key post-Red Supergiants with evidence of past mass loss

Recent observational data from interferometry, spectroscopy, and polarimetry

Discussion of real-time evolution of yellow hypergiants

Abstract

The yellow hypergiants are found in a stage between the massive Red Supergiants and the Wolf-Rayet stars. This review addresses current issues concerning the evolution of massive stars, concentrating on the transitional post-Red Supergiant phase. Few yellow hypergiants are known and even fewer show direct evidence for having evolved off the Red Supergiant branch. Indeed, only two such rare objects with clear evidence for having gone through of a previous mass losing phase are known, IRC +10420 and HD 179821. We will review their properties and present recent results employing near-infrared interferometry, integral field spectroscopy and polarimetry. Finally, their real-time evolution is discussed.