Super terms and conditions star

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Super AGB stars , also SAGB stars , are massive red giants (seven to about ten  solar masses ) on the asymptotic giant branch (AGB) of the Hertzsprung-Russel diagram , in whose cores there is one or multiple phases of explosive carbon burns similar to helium flashes . But they do not reach the temperature to ignite neon lights, so that their core consists of a degenerate oxygen-neon mixture.

Medium-mass stars are on the main sequence in their core during a phase of stable hydrogen burning . After the hydrogen content has become too low to sustain nucleosynthesis in the nucleus, the hydrogen's shell begins to burn . The star expands with a simultaneous increase in luminosity and becomes a red giant . The ashes of the hydrogen burning, the helium , sinks into the core, and above a certain density the helium burning ignites . As a result, the star contracts and, depending on the metallicity, migrates to the horizontal branch in the HR diagram or remains in the red lump . After the helium in the core has also been exhausted by the nuclear fusions , a bowl-shaped hydrogen and helium burn develops. The star moves asymptotically along the giant red branch on the giant asymptotic branch.

The further evolution depends on the mass of the star:

  • In stars with an initial mass of less than seven solar masses, the carbon in the core does not ignite , and the AGB star evolves into a white dwarf via an OH / IR star .
  • The carbon in the core ignites in the range between seven and about ten solar masses, and the degenerate oxygen-neon core of the super AGB stars is formed. The exact upper limit for the mass of the super AGB stars depends on the metal frequency , the rotation , the mass loss due to stellar winds on the giant branch and the mathematical treatment of the convection .
  • With even more massive stars with more than ten solar masses, the neon would also be converted into a nuclear fusion, and the star would become a red supergiant .

SAGB stars lose large parts of their atmosphere through thermal pulses, the explosive ignition of nuclear fusions combined with an expansion of the star radius .

SAGB stars develop into O-Ne-White Dwarfs or explode as electron capture supernovae . Depending on the mass of the O-Ne core, the star either inflates into a supergiant and the entire atmosphere is shed within a few thousand years. If, on the other hand, a density of 4 * 10 12  kg / m 3 is exceeded in the core of the Super-AGB stars , the degeneracy pressure can no longer prevent the core collapse , and the star ends in an electron capture supernova, from which a neutron star emerges.

Individual evidence

  1. ↑ S. Karaali et al .: Absolute Magnitude Calibration for Red Clump Stars . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1304.2530v1 .
  2. ↑ G. Tautvaisiene et al .: Red clump stars of the Milky Way - laboratories of extra mixing . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1304.4393v1 .
  3. ↑ HJ habing, H. Olofsson: asymptotic giant branch stars . 1st edition. Springer Verlag, Berlin 2003, ISBN 0-387-00880-2 .
  4. ↑ DA Garcia-Hernandez, AI Karakas, M. Lugaro: Nucleosynthesis in massive AGB stars with delayed superwinds: implications for the abundance anomalies in Globular Clusters . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1301.1492v1 .
  5. ↑ Pavel A. Denissenkov et al .: The C-flame Quenching by Convective Boundary Mixing in Super-AGB Stars and the Formation of Hybrid C / O / Ne White Dwarfs and SN Progenitors . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1305.2649v1 .
  6. ↑ Nozomu Tominaga, Sergei I. Blinnikov, Ken'ichi Nomoto: Supernova Explosions of Super-Asymptotic Giant Branch Stars: Multicolor Light Curves of Electron-Capture Supernovae . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1305.6813v1 .