Red Supergiants, Yellow Hypergiants, and Post-RSG Evolution
  How massive stars end their lives remains an open question in the field of
star evolution. While the majority of stars above 9 M_sun 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 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.
