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Within any giant luminosity class, the cooler stars of spectral class K, M, S, and C, (and sometimes some G-type stars [13]) are called red giants. Red giants include stars in a number of distinct evolutionary phases of their lives: a main red-giant branch (RGB); a red horizontal branch or red clump; the asymptotic giant branch (AGB), although ...
Higher-mass stars never cool sufficiently to become red supergiants. Lower-mass stars develop a degenerate helium core during a red giant phase, undergo a helium flash before fusing helium on the horizontal branch, evolve along the AGB while burning helium in a shell around a degenerate carbon-oxygen core, then rapidly lose their outer layers ...
Many of the well-known bright stars are red giants, because they are luminous and moderately common. The red-giant branch variable star Gamma Crucis is the nearest M-class giant star at 88 light-years. [25] The K1.5 red-giant branch star Arcturus is 36 light-years away. [26]
In these lists are some examples of extremely distant extragalactic stars, which may have slightly different properties and natures than the currently largest known stars in the Milky Way. For example, some red supergiants in the Magellanic Clouds are suspected to have slightly different limiting temperatures and luminosities .
Yellow stars – hydrogen less strong, but evident metallic lines, such as the Sun, Arcturus, and Capella. This includes the modern classes G and K as well as late class F. Secchi class III: Orange to red stars with complex band spectra, such as Betelgeuse and Antares. This corresponds to the modern class M. Secchi class IV
Rare ultramassive stars that exceed this limit – for example in the R136 star cluster – might be explained by the following proposal: Some of the pairs of massive stars in close orbit in young, unstable multiple-star systems must, on rare occasions, collide and merge when certain unusual circumstances hold that make a collision possible. [3]
A K-type main-sequence star, also referred to as a K-type dwarf, or orange dwarf, is a main-sequence (hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence stars ("red dwarfs") and yellow/white G-type main-sequence stars.
The majority of red supergiants were 10-15 M ☉ main sequence stars and now have luminosities below 100,000 L ☉, and there are very few bright supergiant (Ia) M class stars. [22] The least luminous stars classified as red supergiants are some of the brightest AGB and post-AGB stars, highly expanded and unstable low mass stars such as the RV ...