Super-AGB star

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evolutionary tracks
for stars in the super-AGB mass range

A super-AGB star is a star with a mass intermediate between those that end their lives as a

core collapse supernova, and properties intermediate between asymptotic giant branch (AGB) stars and red supergiants. They have initial masses of 7.5–9.25 M☉ in stellar-evolutionary
models, but have exhausted their core hydrogen and helium, left the main sequence, and expanded to become large, cool, and luminous.

HR diagram

Super-AGB stars occupy the top-right of the

red supergiant stars (RSG stars).[1] These cool temperatures allow molecules to form in their photospheres and atmospheres.[2]
Super-AGB stars emit most of their light in the infra-red spectrum because of their extremely cool temperatures.

The Chandrasekhar limit and their life

A super-AGB star's core may grow to (or past) the

electron capture supernovae. The error in this determination due to uncertainties in the third dredge-up efficiency and AGB mass-loss rate could lead to about a doubling of the number of electron-capture supernovae, which also supports the theory that these stars make up 66% of the supernovae detected by satellites.[citation needed
]

These stars are at a similar stage in life to red giant stars, such as Aldebaran, Mira, and Chi Cygni, and are at a stage where they start to brighten, and their brightness tends to vary, along with their size and temperature.

These stars represent a transition to the more massive supergiant stars that undergo full fusion of elements heavier than helium. During the triple-alpha process, some elements heavier than carbon are also produced: mostly oxygen, but also some magnesium, neon, and even heavier elements, gaining an oxygen-neon (ONe) core. Super-AGB stars develop partially degenerate carbon–oxygen cores that are large enough to ignite carbon in a flash analogous to the earlier helium flash. The second dredge-up is very strong in this mass range and that keeps the core size below the level required for burning of neon as occurs in higher-mass supergiants.[citation needed]

References

  1. ^
    S2CID 59327105
    .
  2. S2CID 15109583
    .
  3. S2CID 18334243
    .

attribution contains text copied from Asymptotic giant branch available under CC-BY-SA-3.0

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