Yellow hypergiant

massive star with an extended atmosphere
Intrinsic variable types in the Hertzsprung–Russell diagram showing the Yellow Hypergiants above (i.e. more luminous than) the Cepheid instability strip.

A yellow hypergiant is a huge hypergiant star. It starts off a mass of about 20–60 solar masses, but it soon loses about half that mass (because they are very unstable). It has a spectral class from A to K.

They are amongst the most luminous stars, with absolute magnitude (MV) around −9. They are very rare: only 15 are known in the Milky Way and six of those are in a single cluster.

They are sometimes referred to as 'cool hypergiants' in comparison to O- and B-type stars, and sometimes as 'warm hypergiants' in comparison to red supergiants. Yellow hypergiants have evolved off the main sequence and have little hydrogen left in their centres.