Asymptotic giant branch

H–R diagram for globular cluster M5, with known AGB stars marked in blue, flanked by some of the more luminous red-giant branch stars, shown in orange
  Asymptotic giant branch (AGB)
  Upper red-giant branch (RGB)
  Horizontal branch (HB)
  RR Lyrae variable (RR)
  End of main sequence, subgiant branch, and lower RGB

The asymptotic giant branch (AGB) is a region of the Hertzsprung–Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars (about 0.5 to 8 solar masses[citation needed]) late in their lives.

Observationally, an asymptotic-giant-branch star will appear as a bright red giant with a luminosity ranging up to thousands of times greater than the Sun. Its interior structure is characterized by a central and largely inert core of carbon and oxygen, a shell where helium is undergoing fusion to form carbon (known as helium burning), another shell where hydrogen is undergoing fusion forming helium (known as hydrogen burning), and a very large envelope of material of composition similar to main-sequence stars (except in the case of carbon stars).[1]

  1. ^ Lattanzio, J.; Forestini, M. (1999). "Nucleosynthesis in AGB Stars". In Le Bertre, T.; Lebre, A.; Waelkens, C. (eds.). Asymptotic Giant Branch Stars. IAU Symposium 191. p. 31. Bibcode:1999IAUS..191...31L. ISBN 978-1-886733-90-9.