The Morgan-Keenan system replaced the earlier R-N system as the primary method for classifying them.
Roeland van der Marel et. al. established expressions for the velocity field of the Large Magellanic Cloud by fitting kinematic data from over a thousand of these stars. In 2015, observers of LX Cygni claimed to have witnessed that star evolving into this phase as a result of a third dredge-up event. The Morgan-Keenan system replaced the earlier R-N system as the primary method for classifying them. One of them has the highest flux in the infrared of any known object outside the solar system. The atmospheric composition of these stars leads to a (*) sooty appearance and emission dominated by the Swan bands, giving a ruby-red color. These stars were first recognized from their unique spectra in the 1860's by Angelo Secchi, who called them Class IV. CW Leonis is the most-studied example of, for 10 points, what type of aging stars which are richer in their namesake element than in oxygen?
Roeland van der Marel et. al. established expressions for the velocity field of the Large Magellanic Cloud by fitting kinematic data from over a thousand of these stars.
Carbon stars [generously prompt on red giant]