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Yellow supergiants generally have spectral types of F and G, although sometimes late A or early K stars are included. [1] [2] [3] These spectral types are characterised by hydrogen lines that are very strong in class A, weakening through F and G until they are very weak or absent in class K. Calcium H and K lines are present in late A spectra, but stronger in class F, and strongest in class G ...
Type I Cepheid variables, more luminous still and mostly supergiants, with even longer periods; Delta Scuti variables, includes subgiant and main-sequence stars. Yellow giants may be moderate-mass stars evolving for the first time towards the red-giant branch, or they may be more evolved stars on the horizontal branch.
The relatively low mass and high luminosity of a post-red supergiant star is a source of instability, pushing it close to the Eddington Limit. However, yellow hypergiants lie in a temperature range where opacity variations in zones of partial ionisation of hydrogen and helium cause pulsations, similar to the cause of Cepheid variable pulsations ...
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.
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.
The primary component of the φ Cassiopeiae system is a very luminous yellow supergiant. Its absolute magnitude is comparable to some yellow hypergiants but it does not show the level of mass loss and instability that would qualify it as a hypergiant itself.
R Coronae Borealis is a low-mass yellow supergiant star in the constellation of Corona Borealis.It is the prototype of the R Coronae Borealis variable of variable stars, which fade by several magnitudes at irregular intervals.
Alpha Leporis has a stellar classification of F0 Ib, [4] with the Ib luminosity class indicating that it is a lower luminosity yellow supergiant star. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified. [ 20 ]