Abstract
How massive stars end their lives remains an open question in the field of star evolution. While the majority of stars above ≳9 M ⊙ will become red supergiants (RSGs), the terminal state of these massive stars can be heavily influenced by their mass-loss histories. Periods of enhanced circumstellar wind activity can drive stars off the RSG branch of the HR Diagram. This phase, known as post-RSG evolution, may well be tied to high mass-loss events or eruptions as seen in the Luminous Blue Variables (LBVs) and other massive stars. This article highlights some of the recent observational and modeling studies that seek to characterize this unique class of stars, the post-RSGs and link them to other massive objects on the HR Diagram such as LBVs, Yellow Hypergiants and dusty RSGs.
Highlights
The standard model of massive star evolution follows a rapid progression from the main-sequence, through a blue supergiant (BSG) phase, to the red supergiant (RSG) branch, to terminal supernova (SN) explosion
We summarize some of the literature on the mass-loss histories of evolved supergiant stars and the evidence for post-red supergiant evolution both in observational studies of the circumstellar ejecta and in evolutionary models that predict the effect of various mass-loss mechanisms on massive star evolution
SNe may represent some high-mass RSG population that is as of yet undiscovered, for the moment this does not seem to solve missing high-mass SN progenitors. We focus on another population of transient objects—the yellow supergiants (YSGs) and hypergiants and evidence for post-red supergiant evolution
Summary
The standard model of massive star evolution follows a rapid progression from the main-sequence, through a blue supergiant (BSG) phase, to the red supergiant (RSG) branch, to terminal supernova (SN) explosion. Surveys of the brightest supergiants revealed an empirical upper luminosity limit to stars on the Hertzprung-Russell (HR) diagram [1] This limit suggests that stars above some initial zero-age main-sequence (ZAMS) mass (≈30–40 M ) do not evolve to the RSG branch on the HR. The evolution and terminal state of a massive star is governed not just by its ZAMS mass and by these drastic changes in total stellar mass and outer envelope conditions. We refer to these changes in stellar mass through ejection of CS material as the “mass-loss history.”. We refer to these changes in stellar mass through ejection of CS material as the “mass-loss history.” In this chapter, we summarize some of the literature on the mass-loss histories of evolved supergiant stars and the evidence for post-red supergiant evolution both in observational studies of the circumstellar ejecta and in evolutionary models that predict the effect of various mass-loss mechanisms on massive star evolution
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