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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 (YHG) is a massive star with an extended atmosphere, a spectral class from A to K, and, starting with an initial mass of about 20–60 solar masses, has lost as much as half that mass.
The yellow hypergiants are thought to be generally post-red supergiant stars that have already lost most of their atmospheres and hydrogen. A few more stable high mass yellow supergiants with approximately the same luminosity are known and thought to be evolving towards the red supergiant phase, but these are rare as this is expected to be a ...
Particularly luminous and unstable yellow supergiants are often grouped into a separate class of stars called the yellow hypergiants. These are mostly thought to be post-red supergiant stars, very massive stars that have lost a considerable portion of their outer layers and are now evolving towards becoming blue supergiants and Wolf-Rayet stars ...
The term "hypergiant" was used as early as 1929, but not for the stars currently known as hypergiants. [1] Hypergiants are defined by their '0' luminosity class, and are higher in luminosity than the brightest supergiants of class Ia, [2] although they were not referred to as hypergiants until the late 1970s. [3]
Rho Cassiopeiae (/ ˌ r oʊ k æ s i ə ˈ p iː aɪ,-s i oʊ-,-iː /; ρ Cas, ρ Cassiopeiae) is a yellow hypergiant star in the constellation Cassiopeia.It is about 8,150 light-years (2,500 pc) from Earth, yet can still be seen by the naked eye as it is over 300,000 times brighter than the Sun.
RW Cephei has been classified as a semi-regular variable star of type SRd, meaning that it is a slowly varying yellow giant or supergiant. The General Catalogue of Variable Stars cites a 1952 study giving a period of approximately 346 days, [ 35 ] [ 5 ] while other studies suggest different periods and certainly no strong periodicity.
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In 2012 a study found that the star is more similar to cool LBVs than to yellow hypergiants based on spectral variation, recent circumstellar ejecta and the very high luminosity (which the paper estimated to be 2 million L ☉, significantly above the Humphreys-Davidson limit for stars with temperatures comparable to those of the star. While ...